“EXPERIMENTAL DETERMINATION AND ANALYSIS OF FRACTURE TOUGHNESS OF MMC”

VISVESVARAYA TECHNOLOGICAL UNIVERSITY“Jnana Sangama”, Belgaum-590018 A PROJECT REPORT ON “EXPERIMENTAL DETERMINATION AND ANALYSIS OF FRACTURE TOUGHNESS OF MMC” Submitted in partial fulfillment of the requirement for the award of degree of MASTER OF TECHNOLOGY IN DESIGN ENGINEERING By: SHIVARAJA.H.B USN: 1DB12MDE12 Under the guidance of Mr. B.S. PRAVEEN KUMAR Associate professor Department of Mechanical Engineering Don Bosco Institute of Technology Department of Mechanical Engineering DON BOSCO INSTITUTE OF TECHNOLOGY Kumbalagodu, Mysore Road, Bangalore - 560074 TABLE OF CONTENTS CHAPTER 1 INTRODUTION Page No 1.1 Preamble 1 1.2 Statement of the Problem 1 1.3 Aim and Objective of the Project 2 1.4 Methodology 3 CHAPTER 2 LITERATURE REVIEW 4-10 CHAPTER 3 INTRODUCTION TO COMPOSITE 3.1 Background 11 3.2 Composites 12 3.2.1 Composite Definition 13 3.2.2 Need for Developing Composite materials 14 3.2.3 Characteristics of composites 14 3.3 Classification of Composite 16 3.3.1 The Matrix Material 16 3.3.2 The Reinforcing Material 16 3.3.3 Classification (According to the Type of Reinforcement) 17 3.3.3.1 Particulate Composites 18 A. Non-Metallic in Metallic Composites 18 B. Metallic in Non-Metallic Composites 18 C. Non-Metallic in Metallic Composites 19 3.3.3.2 Fibrous Composites 19 3.3.3.3Laminated Composites 19 3.4 Applications of Composites 19 3.5 Fabrication techniques of MMC’s 3.5.1 Solid Phase Fabrication Method 20 20 3.5.2 Diffusion Bonding 21 3.5.3 Powder Metallurgy Technique 21 3.5.4 Liquid Phase Fabrication Techniques 21 3.5.5 Liquid Metal Infiltration 22 3.5.6 Squeeze Casting 22 3.5.7 Spray Co-deposition Method 23 3.5.8 Stir Casting 23 3.5.9 Compo Casting 23 3.6 Metal matrix composites 24 3.7 Examples 27 3.7.1 Advantages and Disadvantages of MMC’s 3.8 Scope of Present Investigation 27 28 CHAPTER 4 SELECTION OF MATERIALS 4.1 Matrix Material: Al 356 29 3 Composition of matrix and reinforcement 37 39 6.2.1 Fracture Toughness 40 6.4 Tensile test 43 6.2 Reinforcement Material (silicon carbide) 29 30 4.3 Reinforcement Material (Zirconium Silicate) 32 4.2 Applications of SiC 32 4.1 Stir Casting 35 5.9 Optical metallurgical microscope 50 6.4.5 Hardness test 46 6.7 Microstructure 48 6.3.1 Properties of Zirconium silicate 33 4.8 Etching 49 6.2 Applications of ZrSiO4 33 5.1 Chemical Composition and Mechanical Properties of Matrix Material Al356 4.10 Finite element analysis 51 .6 Compression test 48 6.3.1.2 Steps Involved in Stir Casting Method 5.3 Test for Fracture toughness 41 6.1 Physical Properties of SiC 31 4.2 Specimen dimensions as per ASTM standards 41 6.2. 3 Tensile test results 55 7.7.6 Microstructure 60 CHAPTER 8 CONCLUSION CHAPTER 9 6 6 5 63 .4 Hardness test results 57 7.2 Comparison of the experimental and FEA results 54 7.5 Compression test results 59 7.1 Fracture toughness results 53 7. 1 ASTM codes for mechanical test and sample dimensions 41 7.2 Classification of composites (based upon the reinforcing materials) 16 3.1 Variation of Fracture toughness with different wt% reinforcements 53 7.1 Chemical composition of Al356 30 4.1 Project Methodology 3 3.5 Compression strength for different wt% reinforcement 59 LIST OF FIGURES Fig No Description Page No 1.3 Tensile properties of the MMC 55 7.2 Comparison of the experimental and FEA results 54 7.1 Flow chart of fabrication of Composite 34 5.1 Ingot Structure of Al 356 29 4.4 Electric furnace 37 .1 Different wt% ratios of matrix metal and reinforcement 39 6.1 Classification of composites (based upon the matrix materials) 16 3.3 Pre heating the mould box 36 5.2 Split type mould box 36 5.4 Variation of hardness with different wt% reinforcement 57 7.3 Schematic Presentation of Three Shapes of Metal Matrix Composite Materials 18 4.3 Properties of Zircon sand 33 5.2 Reinforcement Material (SiC) 31 4.2 Mechanical properties of matrix material Al356 30 4.LIST OF TABLES Table No Description Page No 4.3 Reinforcement material (ZrSiO4) 32 5. 5 Molten Metal in Furnace 38 .5. 3 Hardness value for different wt% reinforcement 58 7.2 Variation of tensile strength and yield strength with different wt% Reinforcement 56 7.9 Polishing machine 49 6.5 Microstructure of Al356+0%SiC+8%ZrSiO4 60 7.10 Optical Metallurgical microscope 50 6.4 Specimens for Tensile test 45 6.6 Formation of Vortex 38 5.8 Microstructure of Al356+4%SiC+4%ZrSiO4 61 7.8 Compression test specimens 48 6.2 Fracture toughness specimens 42 6.6 Microstructure of Al356+6%SiC+2%ZrSiO4 60 7.11 SENB specimen model 51 6.1 Variation of Fracture toughness with different wt% reinforcement 54 7.6 Hardness test specimens 47 6.9 Microstructure of Al356+8%SiC+0%ZrSiO4 62 .4 Compression strength for different wt% reinforcement 59 7.9 Cast Aluminium Composites 38 6.3 Dimension of Tensile Specimen 43 6.5 Universal testing machine 45 6.7 Brinell hardness testing machine 47 6.7 Microstructure of Al356+2%SiC+6%ZrSiO4 61 7.12 FE mesh model 51 6.13 Stress distribution from finite element simulations 52 7.5.7 Pre heating of reinforcement 38 5.8 Poured molten metal in mould box 38 5.1 SENB specimen 41 6. stiff and yet light-weight materials in fields such as aerospace. In general. when compared to the unreinforced matrix material. Since then there has been an everincreasing demand for new. these materials exhibit higher strength and stiffness. and low thermal expansion. MDE. automobile and construction sectors. This contribution leads to an excellent balance between cost and mechanical properties. thermal conductivity. in addition to isotropic behavior at a lower density. M-Tech.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 1 INTRODUTION 1. These materials have low specific gravity that makes their properties particularly superior in strength and modulus to many traditional engineering materials such as metals. it has become possible to develop new composite materials with improved physical and mechanical properties. was responsible for this growth in the technology of reinforcements. Dept of Mech Engg. strong. and in other structural applications.1 Preamble New and high performance particle reinforced metal matrix composites (PRMMC) are expected to satisfy many requirements for a wide range of performance-driven. The recognition of the potential weight savings that can be achieved by using the advanced composites. If the first two decades saw the improvements in the fabrication method. and price sensitive.. better high temperature properties (in comparison with its monolithic alloy). applications in aerospace. systematic study of properties and fracture mechanics was at the focal point in the 60’s. which in turn means reduced cost and greater efficiency. and the high toughness of the metal matrix. transportation. PRMMC benefits from the ceramic’s ability to withstand high velocity impacts. This is primarily due to the broad spectrum of unique properties it offers at relatively low processing cost. automobiles. DBIT. bicycles. Some of the attractive property combinations of Al based matrix composites are: high specific stiffness and strength. which helps in preventing total shattering. 1.2 Statement of the Problem Aluminium and its alloys have continued to maintain their mark as the matrix material most in demand for the development of Metal Matrix Composites (MMCs). Bangalore Page 1 . golf clubs. matrices and fabrication of composites. As a result of intensive studies into the fundamental nature of materials and better understanding of their structure property relationship. which are appealing for many applications. e. Here we have used the Aluminium alloy of grade 356 with addition of varying weight percentage composition of Zirconium Silicate and Silicon Carbide particles by stir casting technique. 3. Bangalore Page 2 . The objectives of the project are listed below. The change in physical and mechanical properties was taken in to consideration. 1.Experimental Determination and Analysis of Fracture Toughness of MMC The project is associated with the study of Fracture Toughness and mechanical properties of Aluminium. Dept of Mech Engg.3 Aim and Objective of the Project The aim of the project is to synthesize and characterize hybrid metal matrix composite by stir casting technique and to experimentally evaluate the fracture toughness and mechanical properties of the composite.. hardness and compression. 4. The micro structural observations to evaluate the quality of the castings i.. 1. 2. The mechanical properties were tested under laboratory conditions. DBIT. 5. an experimental set up was prepared to facilitate the preparation of the required specimen. M-Tech. base alloy with Silicon Carbide and Zirconium Silicate (Al356+Sic+ZrSio4). Tests are conducted to evaluate the Fracture toughness and mechanical properties such as tensile. Finite element (FE) simulation to validate the results. Preparation of specimen to required dimensions for the various tests. Preparation of composite casting by liquid metallurgy route. The experiments were carried out to study the effect of variation of the percentage composition to predict the mechanical properties as well as to measure the micro hardness. Zirconium Silicate and Silicon Carbide Metal Matrix Composite (MMC). For the achievement of the above. Then finite element analysis is carried out to validate the obtained results. MDE. Finite element (FE) simulations for the proposed SENB geometry was carried out using ANSYS software package (v12) to investigate stress distribution around the notch and to validate the experimental results. Experimental Determination and Analysis of Fracture Toughness of MMC 1.4 Methodology The methodology of the project in presented in figure 1. MDE.. Dept of Mech Engg. Bangalore Page 3 . DBIT.1 Literature review Identification of the problem Development of Metal matrix composites Casting and curing Tensile Fracture Toughness Testing Compression Hardness Microstructure FE analysis Results and discussions Conclusion Fig 1.1 Project Methodology M-Tech. Halesh Koti. V. SiCp composites having 3. and sample representatives of each composition were subjected to age-hardening treatment at 1800 °C for 3 hours. K. MDE. and 12 volume percent of SiC were produced. Bangalore Page 4 . and structural components. From the experimental studies.O.K.Daniel Jebin[1] The present study deals with the investigation of the mechanical behaviour of Aluminium6063 alloy composites reinforced by Zircon sand(ZrSiO4) and Alumina(Al2O3) particles were taken in to account for investigating the properties such as density tensile strength and hardness of the composites synthesized by Stir casting technique. resulting in savings of material and energy. 6.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 2 LITERATURE REVIEW J. was investigated. automotive (pistons. Experimental results show that the ageing treatment resulted in little improvement in the tensile strength of the composites. Al (6063). silicon carbide particulate composites produced. bearings). mechanical properties.. increased fatigue resistance and superior dimensional stability at elevated temperatures etc. 9.D. cylinder liners. The properties and behavior of various Al alloys and their composites are much explored in terms of microstructure. the tensile properties and fracture toughness of the composites. Dr. Alaneme. respectively. Aluko [2] The tensile and fracture behavior of as-cast and age-hardened aluminium (6063). high specific stiffness. controlled co-efficient of thermal expansion. Tensile and Circumferential Notched Tensile (CNT) specimens were utilized for tension testing to evaluate. using borax additive and a two step stir casting method. DBIT. high specific strength. loading conditions and applications.Jenix Rino. The mechanical properties evaluation reveals variations in hardness and the tensile strength values with the composite combinations. Discontinuous reinforced aluminum metal matrix composites (DRAMMCs) are a class of composite materials having desirable properties like low density. The unique tailor ability of the composite materials for the specific requirements makes these materials more popular in a variety of applications such as aerospace. Dept of Mech Engg. The tensile strength and yield strength increased to almost the same magnitude with an increase in SiC volume percent M-Tech.Sivalingappa. the optimum volume fraction of hybrid reinforcement in Al 6063 alloy on the basis of microstructure and mechanical properties it is found that the (4+4) wt% combination. A. among others. A. Gonzalez Oliver[4] Metal matrix composites (MMC) are materials made from the dispersion of a ceramic phase. R. Hardness and tensile properties of the composite showed an improvement as compared to the alloy without silicon carbide additions. thermal conductivity. automobile and general engineering industries owing to their favourable microstructure and improved mechanical behavior. however. both pure Al and alloys are employed. better high temperature properties (in comparison with its monolithic alloy). In the particular situation of Aluminum MMCs. Bangalore Page 5 . Perez Ipina. Yawny. Silicon carbide content in the alloy was fixed at 5 Weight % and 10 weight % during the casting.The present paper highlights the salient features of casting technique and characterization of aluminum alloy A356 and silicon carbide metal matrix composite. Continuous fibers (Continuous metal matrix composites CMMC) as well as short fibers and particles (Discontinuous Aluminum reinforced DAR) are employed. SA Kori. The strain to fracture was less sensitive to volume percent SiC reinforcement and ageing treatment. The multifunctional nature of Al matrix composites has seen its application in aerospace technology. Aluminium and its alloys have continued to maintain their mark as the matrix material most in demand for the development of Metal Matrix Composites (MMCs). This is primarily due to the broad spectrum of unique properties it offers at relatively low processing cost. typically SiC or Al203 fibers or particles. The increase was. automotive drive shaft fins. Stukeb. C. Mohan Vanarotti. electronic heat sinks. in order to improve the mechanical and physical properties of the matrix.A.E. Shrishail B. solar panelsubstrates and antenna reflectors. Aluminium alloy A356 and silicon carbide composites were obtained by stir casting technique. with values less than 12% strain to fracture observed in all cases. BR Sridhar. more significant for the 9 and 12 volume percent SiC reinforcement. MDE. and low thermal expansion. Some of the attractive property combinations of Al based matrix composites are: high specific stiffness and strength. J. Dept of Mech Engg. DBIT.Experimental Determination and Analysis of Fracture Toughness of MMC for both as-cast and age-hardened conditions. and explosion engine components. Microstructure revealed a uniform distribution of the silicon carbide throughout the matrix. The production and use of composite materials is under intensive development because of the interesting physical and mechanical properties that these materials present and also due to the possibility to manipulate them by means of the variation of the type and proportion of M-Tech.Padasalgi [3] Aluminum alloy and silicon carbide metal matrix composites are finding applications in aerospace.. crankshafts. From the result of the investigation in this research work it could be concluded that addition of ZrSiO4 particles using Al-4. Dept of Mech Engg. varying the percentage ZrSiO4 in the range of 5-25wt%. However. Al4.Aigbodion [5] The as-cast microstructure and properties of Al-4. elastic modulus. the yield and ultimate tensile strength increased by 156.65 and 34.5Cu matrix alloy improved properties. thermal conductivity. the results are not very consistent. resistivity. 25 and 30%) in aluminum matrix using stir casting technique. E.5Cu/ZrSiO4 particulate composite synthesized via squeezed casting route was studied. bicycle frames and base ball shaft) and in construction company (truss structure). These results had shown that. As the weight percent of ZrSiO4 increases in the matrix alloy. Okafor .G..23% respectively and decrease impact energy by 43. 15. recreational products (golf club shaft and head.5Cu/ZrSiO4 particulate composite synthesis via squeeze casting should not exceed 15% in order to develop balance in the necessary properties.Experimental Determination and Analysis of Fracture Toughness of MMC the reinforcement employed as well as the type of the metallic matrix. maximum service performance of the Al.5%Cu alloy increased both the strength and hardness and an overall reduction in toughness and density. values and suspension arms). skating shoe.5Cu/15%ZrSiO4 particulate composite could be appreciable in automobile industries (brake drum. The result obtained revealed that addition of ZrSiO4 reinforcements.S. beyond a level of 25-30 percent SiC. DBIT. etc) properties can be produced in this way. increased the hardness value and apparent porosity by 107. little increase in the apparent porosity of the composite with percentage increase in ZrSiO4 addition was observed. The distribution of the brittle ZrSiO4 phase in the ductile matrix alloy led to increase strength and hardness values.16 %.52 and 155. Bangalore Page 6 . Also. From the result. additions of ZrSiO4 particles to Al-4.81% up to a maximum of 15% ZrSiO4 addition respectively. Khalid Mahmood Ghauri1. V. Materials with designed mechanical (yield stress.4. Pronounce increase in hardness value was observed by reinforcing the matrix alloy with 5-25% zircon sand. Liaqat Ali [6] The present work was mainly carried out to characterize the SiC/Al composite which was produced by reinforcing the various proportions of SiC (5. etc) and physical (thermal expansion coefficient. and depend largely on the uniformity of distribution of SiC in the aluminum matrix It was observed that as the volume fraction of SiC in the composite is gradually M-Tech. 10. MDE. Mechanical properties of test specimens made from stir-casted Aluminum-Silicon Carbide composites have been studied using metallographic and mechanical testing techniques. 5. Al-SiC composites fabricated using induction melting exhibited better mechanical properties than the composites processed in open furnace. Bangalore Page 7 . Grinding and fine polishing was done using diamond paste to prepare different samples for microscopic study. % of SiC were successfully fabricated by casting process. The Al-SiCp composites were fabricated using induction melting show higher compressive strength values than those fabricated using open furnace melting. which were formed in inter-dendritic aluminum silicon eutectic composition. These guides possess very good surface finish. % of SiC. Hemath Kumar. The tensile strength decreases when the amount of reinforcement content exceed to 30 wt. Dept of Mech Engg. 25 and 30 wt. The SiC particulates were observed to be in irregular shape. The induction furnace gives the advantage of self stirring action on the introduction of SiC particles. In the current research work it is evident that as we increase the amount of silicon carbide in aluminum matrix.Experimental Determination and Analysis of Fracture Toughness of MMC increased. DBIT. alloying and making composite in such a way that the newly reinforcing phase acts like a barrier against movement of these dislocations. 20. 15.. % of SiC) were fabricated through casting process. there is improvement in hardness and the impact properties. these are sufficiently high in the vicinity of mechanical mixture of 25% silicon carbide and 75% aluminum. The compressive strength. density and hardness of AlSiC composites increase with increase in wt. 10. M. percent of SiC particulates for all the composites tested. sufficiently increases. The experimental results showed that the composition of the composite for the optimized properties ranges between 70 to 80 percent aluminum and 20 to 30 percent silicon carbide. The induction furnace and open furnace were used for melting of Al-SiC particulate composites. MDE. M-Tech. Al-SiC composite poppet valve guides with 5 to 30 wt. There are numerous ways to block these dislocations like increasing the dislocation density. Al-SiC composite specimens with different weight % of SiC (viz. the hardness and toughness increase. Sreenivasan [7] The present work reports on mechanical properties and microstructure analysis of Al-SiC particulate composites with different wt. These SEM micrographs clearly indicate that the SiC particulates are dispersed uniformly in the Al matrix even at higher percentage such as 20 weight % SiC. G. % of SiC. The microstructure examination of the polished and carefully etched Al-SiC composite specimens showed that the structure consists of a network of silicon particles. It is quite evident that deformation in metals is because of the movement of dislocations and if we block these dislocations by some means the strength which is resistance against the applied force of the material. (KIC) values for particulate reinforced metal matrix composites is an important step in the process of developing useful products from these materials and increasing confidence in their properties and performance. Void initiation is more pronounced in the matrix near the interface. Bangalore Page 8 . Consequently. It is found that the matrix alloy controls both flow properties and fracture in the materials investigated. The fracture in this composite is studied experimentally. in terms of fracture toughness testing. These differentials degrade the matrix alloy near the interface by its strain hardening capacity and by stress intensification introduced by the SiC particle geometry. This study shows that this material must have adequate wettability with both Al and SiC to achieve good bonding. Ranjbaran [8] This experimental investigation was initiated to study the lowtoughness fracture in Al 356-SiCp (silicon carbide particles) with respect to the role of the various elements of the microstructure and their probable contribution. the matrix near the interface is subjected to high localized damage leading to premature fracture. The low-toughness fracture is believed to be an inherent property of this composite and is caused mainly by the differential elastic and thermal properties of the two constituents. Crack propagation occurs by linking these micro cracks locating the crack path preferentially in the matrix adjacent to the interface. The measurement of valid plane strain fracture toughness. The micro cracks can grow from these micro voids to absorb available strain energy. MDE. Guoding Zhang [9] A structure-toughened SiC particle reinforced 6061 aluminum alloy matrix composite (SiCp-6061Al/6061Al) was designed and fabricated by vacuum infiltration processing. the proposed material must have high value of tensile ductility and a low yield stress in order to accommodate the plastic strain developed during processing and relax stress concentrations introduced by particle geometry.Experimental Determination and Analysis of Fracture Toughness of MMC Mohammad M. The value of the KIC characterizes the fracture resistance of a material in the presence of a sharp crack under tensile loading. Moreover. Its fracture toughness KQ was tested by three-point bending method and compared with a conventionally stirring-cast SiCp/6061Al composite's in case of same particle size and volume fraction. It is concluded that a higher toughness composite requires a proper choice of constituent properties which dominate the stress state at the interface. Shuyi Qin.. Dept of Mech Engg. This study shows that the failure is initiated by micro void nucleation at the different initiation sites. The fractography of the SiCp-6061Al/6061Al composite was observed on a Cambridge Instrument S360 Scanning Electron Microscopy (SEM). The results showed that SiCp-6061Al/6061Al M-Tech. DBIT. The optimal cutting conditions are arrived as feed rate 0.Experimental Determination and Analysis of Fracture Toughness of MMC composite has higher fracture toughness KQ but lower yield strength and a comparative elastic modulus. The S-N plot is drawn to show the characteristics of each parameter with respect to surface roughness. have been investigated using Taguchi’s orthogonal array (L9). Sanjeev.5mm. Vignesh. The deformation of the unreinforced 6061Al matrix and the SiCp-6061Al/6061Al interface debonding toughen this composite cooperatively.. turning experiments on machining of particle reinforced Hybrid Metal Matrix composite (MMC) have been carried out. the machining of these metal matrix composites become significantly more difficult than those of conventional materials. Hybrid metal matrix composites are economically cheaper in both raw materials and method of fabrication. The surface quality obtained in turning aluminium (Al 356) metal matrix composites with reinforcements of ceramic particles with 10% by weight of SiC and 5% by weight of B4C under different cutting conditions with a PCD tool of 1600 grade. Bangalore Page 9 . DBIT. feed rate and depth of cut. S. This kind of composite can avoid abrupt failure occurring in most other conventional composite. Dept of Mech Engg. Stir casting method is followed to prepare cylindrical rods of specific length and diameter. M-Tech. The results are validated by analysis of variance method (ANOVA) and the percentage of contribution of feed. the effect of machining parameters on the surface quality (Ra) has been evaluated and optimal machining conditions would be arrived to minimize the surface roughness. C [10] In this paper. Poly Crystalline Diamond (PCD) insert of grade 1600 is used for turning operations. The crack opening displacement (COD) vs load curve of the designed composite showed that the fracture procedure of SiCp-6061Al/6061Al composite is by three stages and the maximum load on it can maintain for a long time. The following conclusions are drawn based on the experimental and analytical results: 1. cutting speed as 70 m/min and depth of cut as 0.1 mm/rev. The reinforcement particles selected are Silicon-Carbide of 10% by weight and BoronCarbide of 5% by weight respectively. The complete fracture procedure of the designed composite was schemed by a model. Taguchi’s method of design of experiment is followed by using orthogonal array L9. Due to the reinforcement of ceramic materials. The influence of these parameters on machined surface quality is determined by measuring the surface roughness of the workpiece by surface roughness tester. Three level machining parameters selected are cutting speed. MDE. By using Taguchi method. Tool wear study also performed for a duration of 20 minutes. speed and depth of cut are determined. The hardness of the SZ shows higher value than that of the BM because some defects are remarkably reduced and the eutectic Si and SiC particles are dispersed over the SZ. which yields improved mechanical properties. Constant tool rotation speed of 1800 r/min and travel speed of 127 mm/min were used in this study. high wear resistance. the homogeneous distribution of SiC particles as well as the spherodization of Si needles and their spreading through the matrix are the dominant reasons for improvement of properties in the SZ. The composite material of A356 with SiC particles was produced successfully by FSP. at lower cost. Yong-Hwan KIM [12] Friction stir processing (FSP) was used to incorporate SiC particles into the matrix of A356 Al alloy to form composite material. light weight. DBIT. were improved by the dispersed Si. 2) In the SZ. Nearly 92% increase in the hardness and 57% increase in the tensile strength were obtained in the nano-composites as compared to the commercially pure aluminium. In addition. MDE. SiC particles and the homogeneous microstructure. low coefficient of thermal expansion and light weight. Dept of Mech Engg. possibly as a result of bimodal and tri-modal microstructures. compared to the BM and SZ without SiC.Experimental Determination and Analysis of Fracture Toughness of MMC Dinesh Kumar Koli.Al2O3 composites. Bangalore Page 10 . Geeta Agnihotri [11] This paper reviews the characterization of mechanical properties with production routes of powder metallurgy and castings for aluminium matrix. submicron or nano-sized range is one of the key factors in producing highperformance composites. Ultrasonic assisted casting and powder metallurgy methods are becoming more common for the production of Al-Al2O3 composites. and with improved ductility. 3) The mechanical properties of the SZ with SiC particles. Agglomeration of the reinforcing particles along with the increasing volume percentage is still a challenging task in composites materials manufacturing. M-Tech. wear resistant metal matrix composites with acceptable ductility by solidification processing and powder metallurgy. processing methods must be developed to synthesize these materials in bulk. The eutectic Si and SiC particles are dispersed homogeneously in primary Al solid solution. The microstructure of the stir zone (SZ) is very different from that of the BM. Don-Hyun CHOI. Metal matrix nanocomposites can lead to significant savings in materials and energy and reduce pollution through the use of ultra-strong materials that exhibit low friction coefficients. The base metal (BM) shows the hypoeutectic Al−Si dendrite structure. Reinforcing aluminium matrix with much smaller particles. There are exciting opportunities for producing exceptionally strong. with little or no voids or defects.. it has become possible to develop new composite materials with improved physical and mechanical properties. Testing of a National Aerospace Plane (NASP) prototype is scheduled for the early to mid 1990s.. it may be possible to incorporate MMCs in the structure or engines of the production vehicle. In general. applications in aerospace. bicycles. Based on information now in the public domain. As a result of intensive studies into the fundamental nature of materials and better understanding of their structure property relationship. these materials exhibit higher strength and stiffness. which in turn means reduced cost and greater efficiency. which might be too early to include MMCs. which helps in preventing total shattering. matrices and fabrication of composites. was responsible for this growth in the technology of reinforcements. MDE. the following military applications for MMCs appear attractive: high-temperature fighter aircraft engines and structures. These materials have low specific gravity that makes their properties particularly superior in strength and modulus to many traditional engineering materials such as metals. The recognition of the potential weight savings that can be achieved by using the advanced composites. Dept of Mech Engg.1 Background New and high performance particle reinforced metal matrix composites (PRMMC) are expected to satisfy many requirements for a wide range of performance-driven. automobile and construction sectors. strong. and spacecraft structures. If the first two decades saw the improvements in the fabrication method. PRMMC benefits from the ceramic’s ability to withstand high velocity impacts. Bangalore Page 11 . golf clubs. systematic study of properties and fracture mechanics was at the focal point in the 60’s. and the high toughness of the metal matrix. transportation. high-temperature missile structures. This contribution leads to an excellent balance between cost and mechanical properties. A PRMMC consists of a uniform distribution of strengthening ceramic particles embedded within a metal matrix. and in other structural applications. in addition to isotropic behavior at a lower density. Since then there has been an everincreasing demand for new. Composite materials are emerging chiefly in response to unprecedented demands from technology due to rapidly advancing activities in aircrafts. and price sensitive. automobiles. which are appealing for many applications.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 3 INTRODUCTION TO COMPOSITE 3. stiff and yet light-weight materials in fields such as aerospace. DBIT. M-Tech. when compared to the un-reinforced matrix material. aerospace and automotive industries. However. Bangalore Page 12 . the penetration of these advanced materials has witnessed a steady expansion in uses and volume.. High performance FRP can now be found in such diverse applications as composite armoring designed to resist explosive impacts. While composites have already proven their worth as weight-saving materials. Thus the shift of composite applications from aircraft to other commercial uses has become prominent in recent years. DBIT. The successes of these various researches have stimulated application of composite in the design of many engineering and non engineering component. manufacturing. the use of composites rather than metals has in fact resulted in savings of both cost and weight. The increased volume has resulted in an expected reduction in costs. especially for composites. the need of composite for lighter construction materials and more seismic resistant structures has placed high emphasis on the use of new and advanced materials that not only decreases dead weight but also absorbs the shock & vibration through tailored microstructures.Experimental Determination and Analysis of Fracture Toughness of MMC 3. that the improvement in manufacturing technology alone is not enough to overcome the cost hurdle. It is obvious. support beams of highway bridges and even paper making rollers. The composites industry has begun to recognize that the commercial applications of composites promise to offer much larger business opportunities than the aerospace sector due to the sheer size of transportation industry. the current challenge is to make them cost effective. Some examples are cascades for engines. Composites are now extensively being used for rehabilitation/ strengthening of pre-existing structures that have to be retrofitted to make them seismic resistant. or to repair damage caused by seismic activity. windmill blades. process. industrial drive shafts. material. carbon and aramid. Further. The efforts to produce economically attractive composite components have resulted in several innovative manufacturing techniques currently being used in the composites industry. It is essential that there be an integrated effort in design. curved fairing M-Tech. Dept of Mech Engg. quality assurance. MDE. tooling. fuel cylinders for natural gas vehicles. and even program management for composites to become competitive with metals. For certain applications. Increasingly enabled by the introduction of newer polymer resin matrix materials and high performance reinforcement fibers of glass.2 Composites Three decades of intensive research have provided wealth of new scientific knowledge on the intrinsic and extrinsic effects of ceramic reinforcement to metals and their alloys. particles. As defined by Jartiz. Materials with designed mechanical (yield stress. M-Tech. One constituent is called as Matrix phase and the other is called Reinforcing phase. and/or fillers) embedded in a matrix (polymers. Reinforcing phase is embedded in the matrix to give the desired characteristics. blade containment bands etc. Composites are multifunctional material systems that provide characteristics not obtainable from any discrete material. DBIT. or ceramics). thermal expansion etc. cylinders. the new combined material exhibits better strength than would each individual material. The production and use of composite materials is under intensive development because of the interesting physical and mechanical properties that these materials present and also due to the possibility to manipulate them by means of the variation of the type and proportion of the reinforcement employed as well as the type of the metallic matrix. different in composition and characteristics and sometimes in form.g. thermal conductivity.1 Composite Definition A Composite material is defined as a structural material created synthetically or artificially by combining two or more materials having dissimilar characteristics.. flakes. 3. replacements for welded metallic parts. Unlike conventional materials (e. steel). MDE. Bangalore Page 13 .g.Experimental Determination and Analysis of Fracture Toughness of MMC and fillets. Generally. The matrix holds the reinforcement to form the desired shape while the reinforcement improves the overall mechanical properties of the matrix. Dept of Mech Engg. When designed properly. stiffness. tubes.) can be varied continuously over a broad range of values under the control of the designer. etc) properties can be produced in this way.2. Composite properties (e. the properties of the composite material can be designed considering the structural aspects. elastic modulus. The constituents are combined at macroscopic level and are not soluble in each other. etc) and physical (thermal expansion coefficient. ducts. Careful selection of reinforcement type enables finished product characteristics to be tailored to almost any specific engineering requirement. a composite material is composed of reinforcement (fibers. metals. They are cohesive structures made by physically combining two or more compatible materials. The design of a structural component using composites involves both material and structural design.. resistivity. precipitation strengthening. along with high specific strength. also favors MMC use in automotive engine and brake parts. the combination has its own distinctive properties. Good wear resistance. Dislocations are critically important as they drastically reduce shear stress required to the slip process and hence make the metals to deform plastically. The increasing demand for lightweight. Metals can be strengthened by a number of strengthening mechanisms namely. stiff and strong materials in aircraft. defense and automotive applications have stimulated steadily growing efforts to develop composite materials.2 Need for Developing Composite Materials Composites with high specific stiffness and strength could be used in applications in which saving weight is an important factor. precision machinery. high-speed machinery. Automobile weight reduction can directly translate into reduced fuel consumption. In the broader significance. the current level of development effort appears to be inadequate to bring about commercialization of any of these in the next 5 years.2..2.3 Characteristics of the Composite Metal matrix composites are strong and tough and can be plastically deformed easily. with the possible exception of diesel engine pistons. MDE. Dept of Mech Engg. and electronic packaging. In terms of strength or resistance to heat or some other desirable quality. Reduction in the weight of aircraft and marine vessels can lead to increased loading capacity. Included in this category are robots. high malleability and ductility. 3. strengthening due to phase transformation and dispersoid strengthening. space. The crystalline structures make the metals posses excellent properties like thermal and electrical conductivity. Lightweight composites are attracting a great deal of attention due to the possibility of weight saving in industrial applications. and high-speed rotating shafts for ships or land vehicles. By intentional addition of hard M-Tech. grain boundary strengthening. energy saving. strain hardening. Tailorable coefficient of thermal expansion and thermal conductivity make them good candidates for lasers. inexpensive. it is better than either of the components alone or radically different from either of them. However.Experimental Determination and Analysis of Fracture Toughness of MMC Kelly very clearly stresses that the composites should not be regarded simple as a combination of two materials. 3. Bangalore Page 14 . DBIT. DBIT. The composite properties may be the volume fraction sum of the properties of the constituents or the constituents may interact in a synergistic way resulting in improved or better properties. usually measured as volume or weight fraction.Experimental Determination and Analysis of Fracture Toughness of MMC dispersoid particles in the matrix it is possible to increase the strength as these particles retard the motion of the dislocation. MDE. M-Tech. which plays an important role in determining the extent of the interaction between the reinforcement and the matrix. their distribution and the interaction among them. the size and size distribution (which controls the texture of the material) and volume fraction determine the interfacial area. determines the contribution of a single constituent to the overall properties of the composites. Bangalore Page 15 . size and size distribution) influences the properties of the composite to a great extent. The shape of the discontinuous phase (which may by spherical. or rectangular cross-sanctioned prisms or platelets). cylindrical. Apart from the nature of the constituent materials. the geometry of the reinforcement (shape. but also an easily controllable manufacturing variable used to alter its properties. The orientation of the reinforcement affects the isotropy of the system. It is not only the single most important parameter influencing the properties of the composites. Properties of composites are strongly dependent on the properties of their constituent materials. Concentration. Dept of Mech Engg.. The concentration distribution and orientation of the reinforcement also affect the properties. 1. Li & Ti) Refractory metals Ceramic Matrix Ceramics Carbon Glass Fig 3. Mg..1 The Matrix Material Matrix Material Polymer Matrix Metal Matrix Thermoplastics Thermo sets Light metals & alloys(Al. MDE. Dept of Mech Engg.2 M-Tech.2 The Reinforcing Material Reinforcing Material Particulate reinforced Large particles Dispersoids Fiber reinforced Continuous fibers Discontinues (short) Aligned or random Structural composites Laminates Sandwich panels Fig 3.1 Classification of composites (based upon the matrix materials) 3.3. DBIT.2 Classification of composites (based upon the reinforcing materials) The classification of composites based upon the Reinforcing materials is as shown in figure. Bangalore Page 16 .3.3 CLASSIFICATION OF COMPOSITE 3.Experimental Determination and Analysis of Fracture Toughness of MMC 3. or particles in an alloy matrix that solidifies the restricted spaces between the reinforcing phases to form the bulk of the bulk of matrix. Furthermore. conventional monolithic materials have limitations in terms of achievable combinations of strength. Particulate Composites (Compose of Particle in a Composite) 2. the solidification microstructure of the matrix is refined and particles. including foundry techniques. electrical conductivity. coefficient of expansion.3. In addition. have recently become available. The potential advantage of preparing these composite materials by foundry technique is near-neat shape fabrication in a simple and cost-effective manner. 3.Experimental Determination and Analysis of Fracture Toughness of MMC Systematic combinations of different constituents. which is required by automotive and other consumer oriented industries. Laminated Composites (Consists of Layers of Various Materials) M-Tech. and grain size in the matrix. damping properties. fatigue strength. DBIT. MDE. Dept of Mech Engg. Structurally. thermal conductivity. systematic design and syntheses procedures can be developed to achieve unique combination of engineering properties such as high elevated-temperature strengths. Fibrous Composites (Consists of Fibers in Matrix) 3. A variety of methods for producing MMCs.3 Classification (According to the Type of Reinforcement) 1. MMCs can be imparted a tailoring set of use full engineering properties that cannot be realized with conventional monolithic materials.. This represents an opportunity to develop new matrix alloys. Bangalore Page 17 . coefficient of thermal expansion. In addition. and density engineered MMCs consisting of continuous or is continuous fiber. Whiskers or particle in a metal results in combination of very high specific strength and specific modulus. foundry processes lend themselves to the manufacture of large number of complexly shaped components at higher production rates. By carefully controlling the relative amounts and distributions of the ingredients constituting a composite and by controlling the solidification conditions. as cast MMCs consist of continuous or discontinuous fibers. whiskers. indicating the possibility of controlling macro segregation. stiffness. M-Tech.3. A. Aluminium paint is actually Aluminum flakes suspended in paint. Metallic in Non-Metallic Composites The most common example is rocket propellants. Upon application the flakes orient themselves parallel to the surface giving good coverage. whisker composite materials as shown in figure.3 Schematic Presentation of Three Shapes of Metal Matrix Composite Materials B. Bangalore Page 18 . Inclusion of copper in an epoxy resin increases the conductivity immensely. Mica in glass composite is used in electrical application because of good insulating and machining qualities. The composite is strong.and monofilament) and short fibers or. The particle can be metallic or non-metallic. which consists of inorganic particles such as Al powder and per chlorate oxidizer in a flexible organic binder such as polyurethane or Polysulphide rubber. DBIT. as can the matrix following are the types.. 1. Fiber composite materials can be further classified into continuous fiber composite materials (multi. Cold solder is metal powder suspended in thermosetting resin. MDE. ` Figure 3. Dept of Mech Engg.3. hard and conducts heat and electricity. Flakes of non-metallic materials such as mica or glass can form an effective composite material when suspended in a glass or plastic respectively.Experimental Determination and Analysis of Fracture Toughness of MMC 3.1 Particulate Composites This consists of particulates of one or more material suspended in a matrix of another material. Similarly. rather. similar flakes can be applied to give good electrical conductivity. Metal flakes in a suspension are also common.3. Non-Metallic in Metallic Composites The most common example in this case is concrete. oxide based and carbide based composites. The resulting component is called cermets. but generally very short and stubby. A more common is laminated fiber reinforced composite.3. Carbide Cement has particles of carbide of tungsten.versa. Cermets are also used as nuclear reactor fuel element and control rods. generally cobalt matrix. Here layers of fiber-reinforced materials are built up with the fiber direction of each layer typically oriented in different direction to give stiffness and strength to fiber. DBIT. MDE. They are of following types: Bimetals Clad metals Laminated glass These are hybrid class of composite involving both fibrous composite and laminate technique.2 Fibrous Composites A fiber is defined with respect to its length to diameter ratio and it’s near crystal diameter. although the length to diameter ratio can be in hundreds. 3.3. A whisker has essentially the same near crystal size diameter as a fiber. which can take loads. Non-Metallic in Metallic Composites Non-metallic particles such as ceramic can be suspended in metallic matrix. These are used in dies. These basically used in tool and high temperature application where erosion resistance is required. Automotive M-Tech. 3. 3. Two common classes of cermets are. Dept of Mech Engg. turbine parts. Fibers and whiskers are of little use unless they are bounded together to take the form of a structural element. 2.4 Applications of Composites a.Experimental Determination and Analysis of Fracture Toughness of MMC C. b. and titanium in metal matrix.3 Laminated Composites Laminated composites consist of layers of at least two different materials that are bonded together. 3. 1.3.. valves. Oxide Based Cermets can be either oxide particles in a metal matrix or vice.3. chromium. Bangalore Page 19 . Aerospace and Space-craft applications. etc. squeeze casting. hot rolling. stir casting and compo casting. Bangalore Page 20 . and a liquid matrix is used in liquid-metal infiltration. rolling. Liquid-phase fabrication methods: liquid-metal infiltration. spray co-deposition. Solid-phase fabrication methods: diffusion bonding. Generally powder is used in pneumatic impaction and the powder metallurgy technique.1 Solid Phase Fabrication Method There are several ways to fabricate MMC using solid-phase materials but among them diffusion bonding and the powder metallurgy route are used widely. extrusion. stir casting. plasma spray. Defense d. stir casting etc. compo casting. A molecular form of the matrix is used in electroforming. DBIT. squeeze casting. MDE. pneumatic impaction. Normally the liquid-phase fabrication method is more efficient than the solid-phase fabrication method because solid-phase processing requires a longer time. 3. pressure casting. squeeze casting. Due to the choice of material and reinforcement and of the types of reinforcement. investment casting. PM route. extrusion. Space hardware e.. gravity casting. explosive welding. Two phase (solid/liquid) processes: Which include Rheocasting and Spray atomization. etc. vapor deposition and metal foils are used in diffusion bonding. the powder metallurgy route. 2. spray co deposition. liquid-metal infiltration. Brief Description of these processes is given below. There are certain main manufacturing processes which are used presently in laboratories as well as in industries are diffusion bonding. Electrical and electronic devices 3. Dept of Mech Engg. drawing. M-Tech. the fabrication techniques can vary considerably.5 Fabrication techniques of MMCs There are several fabrication techniques available to manufacture the MMC materials: there is no unique route in this respect. spray casting. The processing methods used to manufacture particulate reinforced MMCs can be grouped as follows. pressure casting.Experimental Determination and Analysis of Fracture Toughness of MMC c. The matrix metal is used in various forms in different fabrication methods.5. etc. Marine application f. 3. 1. Dept of Mech Engg. the compact is then heated to a temperature that is below the melting point but sufficiently high to develop significant solid-state diffusion (sintering).2 Diffusion Bonding This method is normally used to manufacture fiber reinforced MMC with sheets or foils of matrix material. The applied pressure and temperature as well as their durations for diffusion bonding to develop.5. 3. otherwise inclusions will be incorporated into the product with a deleterious effect on fracture toughness. MDE.3 Powder Metallurgy Technique The PM technique is the most commonly used method for the preparation of discontinuous reinforced MMCs. 3. expensive and potentially dangerous operation. the solid line shows this. it is difficult to achieve an even distribution of particulate throughout the product and the use of powders requires a high level of cleanliness. After bonding.5. vary with the composite systems.Experimental Determination and Analysis of Fracture Toughness of MMC 3. secondary machining work is carried out. In this technique. The blending step is a time consuming. Pressure is then applied to further compact the powder (cold pressing). etc. However sometimes the fibers are coated by plasma spraying or ion plating for enhancing the bonding strength before diffusion bonding. In addition. The liquid composite M-Tech. The consolidated product is then used as a MMC material after some secondary operation. In order to facilitate the bonding between the powder particles. fatigue life. this is the most expensive method of fabricating MMC materials. Then fibers are placed on the metal foil in pre-determined orientation and bonding takes place by press forming directly. This method is popular because it is reliable compared with other alternative methods.4 Liquid Phase Fabrication Techniques Most of the MMCs are produced by this technique.. DBIT. as shown by the dotted line. This technique is used to manufacture MMCs using either particulates or whiskers as the reinforcement materials. the ceramic particles are incorporated into liquid metal using various processes. However. In general process the powders of matrix materials and reinforcement are first blended and fed into a mould of the desired shape. but it has also some demerits. Bangalore Page 21 . Here primarily the metal or metal alloys in the form of sheets and the reinforcement material in the form of fiber are chemically surface treated for the effectiveness of interdiffusion.5. The process has major advantage that the production costs of MMCs are very low. Once the infiltrated wires are produced. magnesium. The major difficulty in such processes is the non-wettability of the particles by liquid aluminium and the consequent rejection of the particles from the melt.5.Experimental Determination and Analysis of Fracture Toughness of MMC slurry is subsequently cast into various shapes by conventional casting techniques or cast into ingots for secondary processing.5. and shape. silver and copper have been used as the matrix materials in this liquid infiltration process because of their relatively lower melting points.. non-uniform distribution of particles due to their preferential segregation and extensive interfacial reaction. Metals such as Aluminium. they must be assembled into a preform and given a secondary consolidation process to produce a component. Secondary consolidation is generally accomplished through diffusion bonding or hot molding in the two-phase liquid and solid region. FP yarn is made into a handle able FP tape with a fugitive organic binder in a manner similar to producing a resin matrix composite preparation. and the mold is infiltrated with molten metal and allowed to solidify. The fabrication process of MMC by squeeze casting. This method is desirable in producing relatively small-size composite specimens having unidirectional properties. Bangalore Page 22 . Usually the fibers must be coated in line to promote wetting.5 Liquid Metal Infiltration This process can also be called fiber-tow infiltration. the preform of the ceramic fiber is pre-heated to several hundred degrees centigrade below the melting temperature of the matrix and then set into a metal die.6 Squeeze Casting Squeeze casting is a one-step metal forming process in which a metered quantity of liquid metal in a reusable die is subjected to a rapid solidification under high pressures (50 to 100 MPa) to produce close-tolerance. and are then inserted into a casting mold of steel or other suitable material. In this technique. Dept of Mech Engg. DBIT. 3. high-integrity finished shapes. The Al or Mg alloy is heated to just above its melting temperature and is then squeezed into the fiber preform by a hydraulic press to form a mixture of fiber and molten metal. MDE. M-Tech. The fugitive organic binder is burned away. Fibers tows can be infiltrated by passing through a bath of molten metal. fiber volume loading. as the first step. 3. Fibre FP tapes are then laid-up in the desired orientation. this is the most economical method of fabricating a composite with discontinuous fibers M-Tech. DBIT. the crucial thing is to create good wetting between the particulate reinforcement and the molten metal. when cold. the pressure levels and duration and the plunger speed.8 Stir Casting This approach involves mechanical mixing of the reinforcement particulate into a molten metal bath and transferred the mixture directly to a shaped mould prior to complete solidification. fiber degradation. In homogeneity in reinforcement distribution in these cast composites could also be a problem as a result of interaction between suspended ceramic particles and moving solid-liquid interface during solidification. at the same time. The shape of the final product depends on the atomizing condition and the shape and the motion of the collector. Imperfect control of these process variables results in various defects. thermal spraying.5. Bangalore Page 23 . particles (reinforcement) are injected into the atomized metal and deposited on a preheated substrate placed in the line of flight. squeeze casting is the most effective method of constructing a machine parts with a complex shape in a short time. the melt quality. 3. is moved from the substrate for subsequent rolling. A solid deposit is built up on the collector. the metal alloying elements. in practical use. 3. the tooling temperature.Experimental Determination and Analysis of Fracture Toughness of MMC This process can be used for large scale manufacturing but it requires careful control of the process variables. including the fiber and liquid metal preheat temperature. The deposited strip. external cooling.5.5.9 Compo Casting Other than PM. including freeze chocking. The crucible is pressurized and the metal is ejected through a nozzle into an atomizer where. oxide inclusions and other common casting defects. 3. However. In this process.. diffusion bonding and high-pressure squeeze casting. the time lag between die closure and pressurization. Micro structural in homogeneties can cause notably particle agglomeration and sedimentation in the melt and subsequently during solidification. MDE. The alloy to be sprayed is melted in a crucible by induction heating. Dept of Mech Engg.7 Spray Co-deposition Method Spray co-deposition method is an economical method of producing a particulate composite. preform deformation. This process has major advantage that the production costs of MMCs are very low. 6 Metal matrix composites Metal matrix composites are materials with metals as the base and distinct. typically ceramic phases added as reinforcements to improve the properties.Experimental Determination and Analysis of Fracture Toughness of MMC (chopped fiber. a water-cooled vacuum chamber with its associated mechanical and diffusion pumps and a crucible and mixing assembly for agitation of the composites. at which point the nonmetallic particles are added to the slurry. 3000 Hz). Stirring is continued until interface interactions between the particulates and the matrix promote wetting. They offer superior combination of properties in such a manner that today no existing monolithic material can rival and hence are increasingly being used in the aerospace and automobile industries.or stir-casting. The melt is then superheated to above its liquid temperature and bottom poured into the graphite mould by raising the blade assembly. However. The reinforcements can be in the form of fibers. whiskers and particulates. DBIT. This is using to make the composite of the highest values of volume fractions of reinforcement. Properties of the metal matrix composites can be tailored by varying the nature of constituents and their volume fraction. whisker and particulate). M-Tech. The induction power is lowered gradually until the alloy is 40 to 50% solid. This process is the improved process of slush. useful combinations of mechanical and physical properties can be obtained 3. MDE. The principal advantage MMCs enjoy over other materials lies in the improved strength and hardness on a unit weight basis. Then the chamber is evacuated and the alloy is superheated above its melting temperature and stirring is initiated by the DC motor to homogenize the temperature. which consists of fibers and solid globules of the slurry. First. The apparatus consists of an induction power supply (50 kW. The melt containing the nonmetallic particles is then transferred into the lower die-half of the press and the top die is brought down to shape and solidify the Composite by applying the pressure. suggests that MMCs will be less forgiving in terms of processing practice than unreinforced alloys. Dept of Mech Engg.. Literature in general. the temperature is raised during adding in such a way that the total amount of solid. but if the appropriate practice is employed. does not exceed 50%. a metal alloy is placed in the system with the blade assembly in place. Bangalore Page 24 . Metals are reinforced either to increase certain properties like elastic modulus and tensile strength or decrease certain properties like coefficient of thermal expansion and thermal conductivities. fabrication process. alumina. crankshafts.. MDE. gear parts brake drum cylinder block and suspension arms. the development of metal matrix composite (MMCs) has been receiving worldwide attention on account of their superior strength and stiffness in addition to high wear resistance and creep resistance comparison to their corresponding wrought alloys. air craft firms. Boron nitride or metallic system like tungsten. This will severely affect the safety and reliability of components fabricated from Al matrix composites (AMCs). ground vehicles brake rotors. M-Tech. Aluminium matrix composite (AMCs) have shown high mechanical properties such as high strength. wear resistance and good elevated temperature properties when compared to the unreinforced matrix alloy. However. which can be categorized based on their matrix composition. Dept of Mech Engg. at the same time. high stiffness. carbon. electronic heat sinks. the plasticity and ductility can substantially reduced. Silicon carbide. graphite. Mg or Ti) or a super alloy (Ni based or Co based super alloy). or reinforcement type. The ductile matrix permits the blunting of cracks and stress concentrations by plastic deformation and provides a material with improved fracture toughness. It has been proved that particle reinforced aluminum matrix composites can improve considerably the strength and hardness of aluminum and its alloys. Stirring casting route has been used successfully to synthesis metal matrix composite. Boron carbide. In recent years. The family of metal-matrix composites is made up of many varieties of materials. electronic instrument racks. beryllium or steel. jet fighters. automotive drive shaft. the development and use of MMC’s are still in their infancy when compared to monolithic materials or even polymer resin-matrix composite systems. satellite struts. which has lead to the use of aluminium matrix composite in the following. The reinforcement materials include Boron. DBIT. The form of reinforcement material can be either fiber or whisker or particulate. New researches on metal matrix composite have focus on particle reinforcement due to low cost of the ceramic reinforcement and less complex fabrication technique. However.Experimental Determination and Analysis of Fracture Toughness of MMC The family of materials classified as metal-matrix composites (MMC’s) comprises a very broad range of advanced composites of great importance to both automobile. Metal matrix composites have a metal matrix usually of lighter metal such as (Al. Bangalore Page 25 . aerospace & defense applications. which is usually non-metallic and commonly ceramic such as SiC and Al2O3. which forms percolating network and is termed as matrix phase. nonstructural and functional applications in different engineering sectors. PRAMCs benefits from the ceramic's ability to withstand high velocity impacts. economic and environmental benefits. and price sensitive. which are appealing for much application. growth. Mono filament-reinforced AMCs (MFAMCs) New and high performance particle reinforced AMCs (PRAMCs) are expected to satisfy many requirements for a wide range of performance-driven. The main contribution to the strengthening of PRAMCs is particle addition. which is caused by the nucleation. and in other structural applications. which affects most of the mechanical properties of PRAMCs. golf clubs. applications in aerospace. Properties of AMCs can be tailored by varying the nature of constituents and their volume fraction. Bangalore Page 26 . Continuous fiber reinforced AMCs (CFAMCs) 4. The other constituent is embedded in this aluminum/ aluminum alloy matrix and serves as reinforcement. Whiskers or short fiber reinforced AMCs (SFAMCs) 3. bicycles. one of the constituent is aluminum/ aluminum alloy. and coalescence of voids created by the ceramic reinforcement. Particle reinforced AMCs (PRAMCs) 2. automobiles. which are M-Tech. Dept of Mech Engg. Aluminum matrix composites system (AMCs) offer superior combination of properties in such manner that today no existing monolithic material can rival. DBIT. AMCs have been tried and used in numerous structural. A PRAMCs consists of a uniform distribution of strengthening ceramic particles embedded within aluminum matrix. AMCs can be classified into four types depending on the type of reinforcement 1.Experimental Determination and Analysis of Fracture Toughness of MMC In aluminum matrix composites system (AMCs). the main drawback of these materials is their low ductility. these materials exhibit higher strength and stiffness.. in addition to isotropic behavior at a lower density. Over the years. when compared to the unreinforced aluminum matrix. which helps in preventing total shattering. and the high toughness of the metal matrix. Driving force for the utilization of AMCs in these sectors include performance. This contribution leads to an excellent balance between cost and mechanical properties. In general. The key benefits of AMCs in transportation sectors are lower fuel consumption. MDE. less noise and lower airborne emissions. Several particle parameters. Bangalore Page 27 . SiC continuous fiber reinforced Al alloy has been used vertical section of advanced fighter aircrafts.7 Examples Continuous carbon fiber reinforced Al alloy likewise has been used in most structures (vertical support structures) in the Hubble telescope. piston rods etc.Experimental Determination and Analysis of Fracture Toughness of MMC critical in determining the mechanical properties of PRAMCs. With 20% SiC whiskers. Discontinuous SiC fibers 1 to 3mm in diameter and 50 to 200mm long are mixed with Al powders consolidated by hot pressing and then extruded or forged to the desired shape. include the volume fraction (vf).. shape. SiC coated on inter-metallic compound Ti3Al fibers in Ti alloy matrix have been found to be very effective for high temperatures resistance. MDE.1 Advantages and Disadvantages of MMC’s Advantages Very high specific strength and specific modulus. Retention of properties at higher temperatures.e. Precision components of missile guidance system demand very high dimensional stability i. Al alloy with 20% SiC continuous fiber satisfy this requirement. 3. Dept of Mech Engg. for automobiles. which helps in reducing weight of automobile and enhanced engine life. Hybrid composites of 12% by volume fraction of alumina particles (for high strength) and 9% volume fraction of graphite fibers (for self lubrication) in alloys have been developed by Honda for Engine blocks. SiC continuous fiber reinforced Ti alloy has been used for hypersonic aircraft. size. Low thermal coefficient of thermal expansion. and distribution of reinforced particles within the metal matrix. A relatively new technique called rapid solidification rate processing has been developed to obtain metallic glass ribbons which can be effective reinforcing material in MMC’s. geometries should not change with temperature excursions during use. 3. the tensile strength increased from 310Mpa to 480Mpa and the tensile modulus can be increased from 69 to 115 Gpa. DBIT. These composites find applications in compressor discs and blades in aero-engines..7. connecting rods. M-Tech. Insensitivity to moisture. the composites have emerged as the single most material. composite materials are gaining wide acceptance due to their unusual characteristics of behavior with their high strength to weight ratios. Non-flammability. hardness. microstructure and Fracture Toughness of Al356 with Silicon Carbide (SiC) and Zirconium silicate (ZrSio4) composite castings. during which these materials is expected to behave as expected and provide a long life under different environments. DBIT. 3. Bangalore Page 28 . Processing methods are expensive. Disadvantages Higher densities as compared to PMC’s. The most widely used material in these industries is aluminum and their alloys because of their light weight property. a study had been conducted to evaluate the various mechanical properties such as tensile. compression. which can provide a better service and better quality.Experimental Determination and Analysis of Fracture Toughness of MMC Higher operating temperatures. MDE.. Therefore in the present investigation.8 Scope of Present Investigation Due to the advancement in the material technology to produce desired materials from various industrial applications and fast changing scenario in the production of lighter and stronger materials. MMC’s are expensive as compared to PMC’s. Dept of Mech Engg. M-Tech. Better capability to withstand compression and shear loading. MMC’s demand higher processing temperatures. To make these alloys of aluminum further versatile and flexible for varieties of application. Dept of Mech Engg.1 Ingot Structure of Al 356 4. MDE. DBIT. eutectic silicon particles and heat treatments. However.. Aluminium Metal matrix composites (AMMC).1 and 4.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 4 SELECTION OF MATERIALS Cast Al356 is one of the most widely used commercial Al-Si-Mg alloys in the aircraft and automotive industries due to its good castability and the fact that it can be strengthened by artificial aging.1 Matrix Material: Al 356 Fig 4. 4. intermetallics.1 Chemical Composition and Mechanical Properties of Matrix Material Al356 Chemical composition and mechanical properties of matrix material Al356 is as shown in Table 4. the mechanical properties of Al356 are significantly affected by micro structural features such as microporosity. where hard ceramic particles are distributed in a relatively ductile matrix. have widespread applications in aerospace.1. Bangalore Page 29 . mechanical and tribological properties.2. automobiles and other engineering industries because of their excellent physical. M-Tech. It is also highly inert chemically. Ultimate (MPa) 228 Tensile Strength. also known as carborundum..45% 0. and good resistance to creep. It was originally produced by a high temperature electro-chemical reaction of sand and carbon. is a compound of silicon and carbon with chemical formula SiC. and o where load-bearing components are required to operate at temperatures up to 1500 C. Dept of Mech Engg. Silicon M-Tech. low density.1% Rem Table 4. Silicon Carbide is the only chemical compound of carbon and silicon.25% 0. Bangalore Page 30 . Silicon carbide.2 Mechanical properties of matrix material Al356 4. Silicon carbide does not melt at any known pressure.2 Reinforcement Material (silicon carbide) Silicon carbide (SiC). Grains of silicon carbide can be bonded together by sintering to form very hard ceramics which are widely used in applications requiring high endurance. is a high-temperature structural material.Experimental Determination and Analysis of Fracture Toughness of MMC Element Wt% Si Fe Cu Mn Mg Ni Zn Ti Pb Aluminium 7. DBIT. It occurs in nature as the extremely rare mineral moissanite.5% 0. MDE.2% 0.2% 0. offering many advantages such as high melting temperatures.685 Poisson’s ratio 0. piston engines and heat exchangers. such as car brakes and ceramic plates in bulletproof vests.1% 0. high elastic modulus and strength.35% 0. oxidation and wear.5% Shear Strength (MPa) 180 Thermal Conductivity (W/m-K) 151 Melting Temperature 5550C Fatigue Strength(MPa) 60 Table 4. These properties make SiC suitable for use in applications such as gas turbines. Yield (MPa) 165 Elongation (%) 3.33 Tensile Strength.35% 0.1 Chemical composition of Al356 Density(*1000 Kg/m3 ) 2. ceramics. Bangalore Page 31 .. The reinforcement material (SiC) is as shown in figure. Today the material has been developed into a high quality technical grade ceramic with very good mechanical properties. flame igniters and electronic components. DBIT.2 Reinforcement Material (SiC) 4. MDE.Experimental Determination and Analysis of Fracture Toughness of MMC carbide is an excellent abrasive and has been produced and made into grinding wheels and other abrasive products for over one hundred years.2. Dept of Mech Engg. The material can also be made an electrical conductor and has applications in resistance heating. and numerous high-performance applications. Structural and wear applications are constantly developing. refractories.2.1 Physical Properties of Sic Low density High strength Low thermal expansion High thermal conductivity High hardness High elastic modulus Excellent thermal shock resistance M-Tech. Fig 4. 4. It is used in abrasives. 4. MDE.3 Reinforcement Material (Zirconium Silicate) Zircon silicate is naturally occurring sand. Chemical inertness.2. This has made it a good reinforce for the production of MMCs for engineering applications. DBIT. It possesses properties such as high temperatures up to 2400°C. Dept of Mech Engg. 4.. bearings Ball valve parts Hot gas flow liners Heat exchanger Semiconductor process equipment. gold and calcium oxide.Experimental Determination and Analysis of Fracture Toughness of MMC Superior chemical resistance. Ionic electrical conduction. High density. Zirconium silicate contains mainly zirconium oxide and silicon oxide with a minor amount of potassium. Bangalore Page 32 . Low thermal conductivity (20% that of alumina). High fracture toughness and High hardness. Resistance to molten metals.3 Reinforcement material (ZrSiO4) M-Tech.2 Application of SiC Fixed and moving turbine components Suction box covers Seals. Fig 4. Wear resistance. Super conductive magnets..2 Applications of ZrSiO4 Nuclear reactors.Experimental Determination and Analysis of Fracture Toughness of MMC 4.70 0 Linear coefficient of expansion (μm/m C) 4.3.5 Fracture toughness (MPa-m1/2) 5 Crystal structure Tetragonal Table 4. Zirconium is used in optical glasses and for glass toughening. Dept of Mech Engg.1 Properties of Zirconium Silicate Good strength Corrosion resistant Low thermal conductivity Good thermal shock resistance Excellent Thermal resistance High flexural strength High hardness 4. MDE. Zirconium with Aluminium. Bangalore Page 33 . Foundry/investment casting Properties Zircon Sand M. Zirconium is used in satellites as reflective surface agent.5-4.5 Density (g/cm3) 4.3 Properties of Zircon sand M-Tech.3. DBIT. (0C) 2500 Limit of application (0C) 1870 Hardness 7. iron and titanium are used in vacuum tubes.P. MDE.1 Aluminium matirx (Al356) Metal matrix composite Al356-Sic-ZrSio4 Reinforcement (Silicon Carbide+ Zirconium Silicate) Matrix Furnace Degassing+ Scum powder Stir Reinforce Pouring Casting Fig 5. Bangalore Page 34 .1 Flow chart of fabrication of Composite M-Tech.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 5 FABRICATION OF COMPOSITES Flow chart of composite fabrication is as shown in figure 5.. Dept of Mech Engg. DBIT. This process was followed to modify reinforcement particles distribution through the molten aluminum. Molten aluminum was stirred for (1. and before mixing the SiC and ZrSio 4 particles were preheated for 1 to 3 hours to make their surfaces oxidized. Cut pieces of alloy A356 were heated at 840 °C for 3 to 4 hours before melting.Experimental Determination and Analysis of Fracture Toughness of MMC 5. A preheated permanent cast iron mould with diameters in the range of 10 mm to 25 mm was used to prepare cast bars. Composites were produced by Stir casting process. the composite slurry was re-heated to a fully liquid state and then automatic mechanical mixing was carried out for about 5 minutes at an average stirring rate of 300 rpm.) until the molten aluminum becomes slurry.. which is preheated at 350°C to prevent sudden cooling for molten aluminum.1 Stir Casting The large ingots of matrix material were cut into small pieces for accommodating into the crucible. Later molten aluminum was poured into suitable cast iron mould. Due to difficulties of mixing in semi solid state. M-Tech. Later reinforcement particles were added to molten metal.) to get suitable vortex. reinforcement particles were pulled inside the molten metal and uniformly distributed. initially manual mixing was used for the synthesis of A356 and SiC and ZrSio 4. the furnace temperature was controlled to be within 840±10 °C. Degassing was carried out with hexachloroethane tablets and Scum powder .5 min. electrical stirrer was inserted into the crucible. In the final mixing processes. The preheating temperature 350 °C for Cast Iron moulds was maintained for slower cooling. After this. MDE.m. DBIT.p. Dept of Mech Engg. The pouring temperature was controlled to be around 820 ° C. To ensure the homogeneity of the added reinforcement particles through molten aluminum. Melting was carried out in a cast iron crucible in a resistance furnace. Finally the super heated melt was poured into the cast iron mould. At this stage the preheated SiC and ZrSio4 particles were added and mixed manually according to the required proportions. Furnace temperature was first raised above the liquidus to melt the alloy scraps completely and was then cooled down just below the liquidus to keep the slurry in a semi-solid state. Due to the vortex effect. Molten aluminum was stirred at (300 r. Bangalore Page 35 . The mould is then heated to a temperature of about 300-3500c to prevent the sudden cooling of the molten aluminium. The mould cavity holds the liquid material and essential acts as a negative of the desired product. Dept of Mech Engg.3.3 Pre heating the mould box M-Tech. Bangalore Page 36 . Pre heating of the mould box is shown in figure 5. MDE.. DBIT.Experimental Determination and Analysis of Fracture Toughness of MMC 5.2. Fig 5. The mould box is tightened with the help of screws and is checked for any gaps in the mould box. Permanent split type mould box is used for casting the composites in the present study as shown in the figure 5.2 Split type mould box Fig 5.2 Pre-heating of Mould Box A mould is an assembly of two or more metal blocks. A permanent mould box which is prepared according to required dimensions of the casting is used. Reinforcement material Sic and ZrSiO4 powder was added according to the required proportions to molten metal in steps while stirring. After 10 mins titanium dioxide was added to remove the entrapped gases (degasification) and Stirrer was introduced. Fig 5. Dept of Mech Engg.Experimental Determination and Analysis of Fracture Toughness of MMC 5. DBIT. Addition of scum powder. The mould box is opened and cast components are obtained. MDE. Stirrer was rotated at a speed of 0 to 300 rpm to create a vortex in the liquid metal. After 15 mins molten metal is poured to the pre-heated mould and left for solidification. Slag removal. Bangalore Page 37 .4 Electric furnace M-Tech.4. Formation of slag.2 Steps Involved in Stir Casting Method Aluminum (Al356) 3kg was melted in the furnace to a temperature of 850 degree centigrade as shown in figure 5.. Dept of Mech Engg.5 Molten Metal in Furnace Fig 5.Experimental Determination and Analysis of Fracture Toughness of MMC Fig 5. Bangalore Page 38 . MDE.9 Cast Aluminium Composites M-Tech. DBIT..6 Formation of Vortex Fig 5.8 Poured molten metal in mould box Fig 5.7 Pre heating of reinforcement Fig 5. Dept of Mech Engg. Bangalore Page 39 . DBIT. Casting 1: Al356+0%SiC+8%ZrSiO4 Casting 2: Al356+6%SiC+2%ZrSiO4 Casting 3: Al356+2%SiC+6%ZrSiO4 Casting 4: Al356+4%SiC+4%ZrSiO4 Casting 5: Al356+8%SiC+0%ZrSiO4 M-Tech.1 Different wt% ratios of matrix metal and reinforcement The composition of the matrix metal and the reinforcement in different wt% ratios is shown in the above table.Experimental Determination and Analysis of Fracture Toughness of MMC 5.3 Composition of matrix and reinforcement Samples 1 Al356 (kg) 3 Sic (%) - ZrSio4 (%) 8 2 3 6 2 3 3 2 6 4 3 4 4 5 3 8 - Table 5.. MDE. The casting samples with different wt% reinforcements were prepared respectively as shown below. If a material has much fracture toughness it will probably undergo ductile fracture. Experimental methods for characterizing fracture toughness play a critical role in applying fracture mechanics to integrity assessment. nuclear reactor components.e. and quality assurance for critical structures such as high-pressure gas and liquid transmission pipelines.. Dept of Mech Engg. The Single-Edge-Notched Beam (SENB) method was developed as a simple and inexpensive alternative. Brittle fracture is very characteristic of materials with less fracture toughness. Fracture toughness properties are frequently used as a basis for material selection. In more precise terms.. was broadly based on the work of A. Fracture toughness is a material property that characterizes the material’s resistance to crack propagation when under load or stress. and crack depth.. In the case of ideally brittle materials. measurement of the load at failure stress respectively. the fracture toughness is independent of the crack extension. The measurement procedure of fracture toughness is based on the principle of linearelastic fracture mechanics (LEFM) and contains three main steps: generation of cracks in the test specimen. fitness-for-service evaluation. Some structural ceramics show an increase of fracture resistance with crack extension under stable crack growth.e. MDE. material qualification programs. Fracture toughness is a quantitative way of expressing a material's resistance to brittle fracture when a crack is present. M-Tech. petrochemical processing vessels. A. pressure vessels. Fracture mechanics. which leads to the concept of fracture toughness. Griffith who. DBIT. ductile fracture).1 Fracture Toughness The measurement of valid plane strain fracture toughness. among other things. brittle fracture) or by stable tearing means (i. Bangalore Page 40 . and aircraft.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 6 EXPERIMENTAL DETAILS 6. The crack growth resistance increases with the increasing crack extension. studied the behavior of cracks in brittle materials. and limit state analyses for a wide variety of engineering structures. it refers to the resistance of a preexisting crack to extend either under unstable (i. (KIC) values for particulate reinforced metal matrix composites is an important step in the process of developing useful products from these materials and increasing confidence in their properties and performance. but the results can be influenced by the tip radius of the sawed notch. 1. Fig 6. The specimens (127 X 13 X 6 mm) were tested with a span length of 65mm using three point bend setup with 10 ton capacity high precision computer controlled UTM. Dept of Mech Engg.1 SENB specimen M-Tech.Experimental Determination and Analysis of Fracture Toughness of MMC 6. ASTM standards are given in Table. as shown in Fig 6. Sl. DBIT.5 N at a loading rate of 1 mm/min.1 ASTM codes for mechanical test and sample dimensions 6.2 Specimen dimensions as per ASTM standards The samples were cut to the dimensions as per ASTM standards ASTM C39362 for Testing.. No ASTM Code Mechanical Test Sample Dimensions Span length (mm) (mm) 1 ASTM-D790 Flexural 127 x 13 x 6 65 Table 6. Bangalore Page 41 . The tests were performed with a load resolution of 0. The single edge notch bend (SENB) specimens were used to determine the fracture behaviour by K IC. The rate of loading was maintained at 1mm/min. which satisfied the requirements of ASTM D5045-99. MDE.3 Test for Fracture toughness The Fracture toughness of the specimens were determined as per ASTM-D790. The total span (length) of the specimens was 65 mm. .2 Fracture toughness specimens M-Tech.Experimental Determination and Analysis of Fracture Toughness of MMC The following equation is used to calculate the fracture toughness. DBIT. Fig 6. MDE.(2) The KIC parameter denotes mode I fracture in which crack formation occurs in tensile mode due to bending.(1) Where --------------. KIC. Bangalore Page 42 . Dept of Mech Engg. of MMC: --------------. 3. In a stress. Fig 6. The results from the test are commonly used to select a material for an application. The applied tensile load and extension are recorded during the test for the calculation of stress and strain. The tensile testing is carried out by applying longitudinal or axial load at a specific extension rate to a standard tensile specimen with known dimensions (gauge length and cross sectional area perpendicular to the load direction) till failure. As the load is increased beyond which the stress is no longer proportional to strain. Properties that are directly measured via a tensile test are ultimate tensile strength. maximum elongation and reduction in area. The test specimen is in a direction parallel to the applied load. for quality control. % elongation. yield strength. These important parameters obtained from the standard tensile testing are useful for the selection of engineering materials for any applications required. and to predict how a material will react under other types of forces. 6. Elastic limit is the maximum stress that can be applied to the material without producing a permanent plastic deformation when the load is removed.3 Dimension of Tensile Specimen The ultimate tensile strength was measured using 10 ton capacity servo hydraulic universal testing machine as shown in Fig.Experimental Determination and Analysis of Fracture Toughness of MMC 6. % area of reduction and Young's modulus.4 Tensile test Uniaxial tensile test is known as a basic and universal engineering test to achieve material parameters such as ultimate strength.strain graph the initial portion of the curve is a straight line and represents the proportionality of stress to strain according to Hooke's law. Yield point is the maximum stress at which the specimen is deformed without a noticeable . MDE.. Dept of Mech Engg. M-Tech. DBIT. Bangalore Page 43 . UTS is the maximum stress that a test specimen can bear before fracture and is based on original area.increase in load. the specimen is strain hardened or work hardened. The yield stress.Experimental Determination and Analysis of Fracture Toughness of MMC Yield stress By considering the stress-strain curve beyond the elastic portion. At this stage. yielding occurs at the beginning of plastic deformation. the stress-strain curve will reach the maximum point. If the load is continuously applied. Ultimate Tensile Strength Beyond yielding.. The degree of strain hardening depends on the nature of the deformed materials. the specimen can withstand the highest stress before necking takes place. which affects the dislocation motion. which is the ultimate tensile strength (UTS). if the tensile loading continues. Bangalore Page 44 . Ductility Ductility can be expressed either in terms of percent elongation or percent reduction in area as expressed in the equations below M-Tech. crystal structure and chemical composition. This can be observed by a local reduction in the cross sectional area of the specimen generally observed in the centre of the gauge length. continuous loading leads to an increase in the stress required to permanently deform the specimen. MDE. DBIT. Dept of Mech Engg. can be obtained by dividing the load at yielding (Py) by the original cross-sectional area of the specimen (Ao) as shown in equation below. At this point. The computer controlled testing machine was adjusted to read zero. 6. 2.5 Universal Testing Machine The procedure is as follows: 1. The tensile specimens of diameter 8.4 Specimens for Tensile test Fig 6. Five specimens were tested and the average values of the ultimate tensile strength (UTS) and ductility (in terms of percentage elongation) were measured. 5. Remove the broken specimen from testing machine and observe for the failure characteristics. Strain rate was selected as per standard 2mm/ min. and diameters.9 mm and gauge length 76 mm were machined from the cast composites with the gauge length of the specimen parallel to the longitudinal axis of the castings. the parts were held together and measure gauge length and length between the shoulders. 3. .Experimental Determination and Analysis of Fracture Toughness of MMC All tests were conducted in accordance with ASTM standards. The dimension of smallest section was measured. 4. Tensile tests were conducted at room temperature using UTM in accordance with ASTM E8-82. The average cross section of the specimen was determined using the micrometer. Applied load until the specimen was broken. Fig 6. Firmly grip the upper end of the specimen in the fixed head of universal testing machine using fixing shackles. . Bangalore Page 45 . Dept of Mech Engg.M-Tech. MDE. DBIT. This test uses the depth of indentation to determine the hardness number. The tip first overcomes the resistance of the metal to elastic deformation and then a small amount of plastic deformation upon deeper indentation of the tip. DBIT. should be used. However. loaded on a material test-piece. It is one of several definitions of hardness in materials science. Brinell hardness test is also known as indentation hardness test where indentation hardness is defined as the resistant to permanent or plastic deformation under static or dynamic loads. A minor load is applied to hold the sample in place then a major load is applied to indent the sample.d2) The hardness of the specimens was measured using a standard Brinell hardness testing machine (shown in Fig. should be smooth. Brinell hardness number (BHN) is expressed as the ratio of applied load to surface area of the spherical indentation mode. The hardness tests were conducted in accordance with the ASTM E10 standards as shown in Fig. The static indentation test was the type of test used in the present study to examine the hardness of the specimens in which a ball indenter was forced into the specimens being tested.5.(D2 . Bangalore Page 46 . It overcomes large deformation. The Brinell and Rockwell Tests are the most common experiments to determine the hardness of metals. we find hardness tests useful for estimating the tensile strength of materials.5 Hardness test Hardness is the property of a material that enables it to resist plastic deformation. As engineers. Dept of Mech Engg.14 X D)/2 (D. The relationship of the total test force to the area or depth of indentation provides the measure of hardness. abrasion or cutting. usually by penetration. clear. dry and free from oxides and scales to permit accurate measurement. 5. For ferrous metals the load ranges P = 30 d should be used. Both Tests measure the resistance to indentation of a metal under a static load. BHN= Load/ Spherical area of indentation = P/ (3. The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter. A ball indenter of diameter 5 mm was used and a load of 250 Kgs was applied over the specimens of diameter 20 mm and thickness 6 M-Tech.6).Experimental Determination and Analysis of Fracture Toughness of MMC 6. 2 for non-ferrous metals like brass and aluminium load range P= 5 D . the surface of the specimen on which the impression is to be made. the term hardness may also refer to resistance to bending. 5. scratching. In this process of hardness determination when the metal is indented by a spherical tip.. MDE. For the Brinell hardness test. Experimental Determination and Analysis of Fracture Toughness of MMC mm for a period of 30 seconds. MDE. 6. 3. 2. For each composition 6 indentation diameters are noted and average BHN is calculated.7 Brinell hardness testing machine M-Tech. Fig 6. Select the load by selector button for various metals and for non-ferrous metals. Wait till handle on left side comes to rest and allow the load to act for 30 seconds. DBIT. The diameter of indentation was measured by built in microscope of the machine. 5.6 Hardness test specimens Fig 6. The procedure for measuring hardness is described below: 1. 4. The fine polished specimen was placed on platform and 5mm diameter ball indenter was fixed. Dept of Mech Engg. Platform was raised till it was focused on the screen.. six readings were taken two each at the periphery. Handle was pressed to release the load and to bring objective back in to position. Bangalore Page 47 . In order to minimize the error due to segregation effect of the particles. 7. middle and centre. The specimens were held firmly in hand and rubbed smoothly against the SiC papers. 800 and 1200 grit silicon carbide papers.Experimental Determination and Analysis of Fracture Toughness of MMC 6.8 Compression test specimens 6. Excessive heat formation during polishing was avoided as Al alloys contain many metastable phases. Grinding and polishing after usual grinding and machining. The compression test specimens are shown in fig 6. Bangalore Page 48 . Fig 6.21 mm diameter and 40 mm length machined from the cast composites. exercising sufficient care to avoid any deep scratches since the Al alloys are comparatively soft. The specimens for optical microscopy were prepared according to ASTM E3 standards. The samples were first subjected to grinding and polishing followed by etching.6 Compression test Compression test was carried out using a standard 10-ton capacity universal testing machine. MDE..3. DBIT. Fine polishing was performed using magnesium oxide paste followed by diamond paste using polishing machine shown in Fig. Dept of Mech Engg.5. 600. 200. The tests were conducted according to ASTM E9 at room temperature. by gradually applied loads and corresponding strains were measured until failure of the specimen. the specimens were rough polished using 100. 400. The Universal testing machine used for the compression test is shown in Fig.4. 4. The platform was covered with billiard cloth. These papers are less susceptible to loading than emery papers. Separate platforms were used for magnesium oxide and diamond polishing. 5.7 Microstructure The optical metallurgical microscope (model: NIKON Epiphot 200) was used for microstructure characterization of the Al356 matrix alloy reinforced with SiC and ZrSio4 to study the effect of reinforcement on the matrix. Compression tests were conducted on specimens of 20. During fine polishing M-Tech. . the specimens were finally polished with 1 m thin diamond paste after changing the platform. Fig 6.Experimental Determination and Analysis of Fracture Toughness of MMC with magnesium oxide paste. Etching duration was 4 to 5 sec. After polishing with magnesium oxide. The specimens were then cleaned with alcohol and dried in air. The samples were dipped in alcohol and dried in a stream of clean warm air. then in running water and etched while wet. Dept of Mech Engg. Bangalore Page 49 . MDE.8 Etching The most useful etchant for microscopic examination of Al and Al alloys is the aqueous solutions of chromic acid to which sodium sulphate has been added. followed by rinsing in water. The specimen surface was first cleaned in alcohol. DBIT. hands as well as the specimens were washed with water in between to prevent carryover of coarser grit from previous steps. Etchant composition is as follows: 200gm chromic acid. M-Tech. To avoid staining after etching. 15gm sodium sulphate and 1000 ml water.9 Polishing machine 6. it was immediately rinsed in a solution of 200 gm chromic acid in 1000 ml of water. the final magnification is the product of: the objective lens magnification. This is independent of whether it is on a print from a film negative or displayed digitally on a computer screen. although there are many complex designs which aim to improve resolution and sample contrast. Bangalore Page 50 .10 Optical metallurgical microscope M-Tech. Fig 6. MDE. the camera optics magnification and the enlargement factor of the film print relative to the negative. often referred to as the "light microscope".Experimental Determination and Analysis of Fracture Toughness of MMC 6.9 Optical Metallurgical Microscope The optical microscope. As with a film camera the final magnification is the product of: the objective lens magnification.. Dept of Mech Engg. the camera optics magnification and the enlargement factor. is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. A typical value of the enlargement factor is around 5× (for the case of 35mm film and a 15x10 cm (6×4 inch) print). The enlargement factor from the detector to the pixels on screen can then be calculated. When using a camera to capture a micrograph the effective magnification of the image must take into account the size of the image. DBIT. In the case of digital cameras the size of the pixels in the CMOS or CCD detector and the size of the pixels on the screen have to be known. In the case of photographic film cameras the calculation is simple. Basic optical microscopes can be very simple. 12 FE mesh model M-Tech. DBIT.10 Finite element analysis The study is performed on common specimen with nominal dimensions equal to 127×13×6 mm with and span S = 65 mm.. Dept of Mech Engg. Bangalore Page 51 . Fig 6.11. In this study the three point bending test is performed experimentally and then repeated with FE technique. MDE. In the mid span of the specimen a notch is created with length 6mm and width 1mm.11 SENB specimen model Fig 6. The geometry of the SENB specimen was modeled in catia and is shown in figure 6.Experimental Determination and Analysis of Fracture Toughness of MMC 6. (1) is used to calculate the fracture toughness of the specimen. (1) gives us the Fracture Toughness for all the composition of the composite. By putting the stress values obtained by the FEA technique in Eq.Experimental Determination and Analysis of Fracture Toughness of MMC Fig 6. by analyzing the SENB specimen under different loading conditions. The stress in Eq. The values of fracture toughness calculated in this study are near to the general range of fracture toughness values obtained experimentally. (2) by the known dimensions of the specimen.13. Eq.13 Stress distribution from finite element simulations The above figure shows the results from finite element simulations. The stress value obtained from FEA is shown in the figure 6. . (1) is determined using FE technique. The values of the maximum load at which the specimen breaks are taken by the experimental results. The geometric factor of the specimen is calculated using Eq. DBIT..M-Tech. MDE. Dept of Mech Engg. Bangalore Page 52 . Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 7 RESULTS AND DISCUSSIONS 7. DBIT. MDE. There is a considerable increase in the fracture toughness for the combination of 6% SiC+2% ZrSiO4 and 4% SiC+4% ZrSiO4. A reduction in particle size is observed to increase the proportional limit. It is well established that large particles are detrimental to fracture toughness due to their tendency towards fracture. The deformation and fracture behavior of the composite reveals the importance of particle size. Bangalore Page 53 .67 18. The fracture toughness (which is a measure of the resistance to crack propagation) was observed to improve significantly with the increase in the addition of the reinforcement particles.1 Fracture toughness results Peak load Al356+ Al356+ Al356+ Al356+ Al356+ 0%Sic+ 6%Sic+ 2%Sic+ 4%Sic+ 8%Sic+ 8%Zrsio4 2%Zrsio4 6%Zrsio4 4%Zrsio4 0%Zrsio4 660 720 780 780 660 15.. yield stress and the ultimate tensile stress. Dept of Mech Engg.27 (N) Fracture toughness (MPa m1/2) Table7. M-Tech. The improvement might be due to the presence and distribution of fine SiC and ZrSiO 4 particles in the Al matrix.05 15.05 18.1 Variation of Fracture toughness with different wt% reinforcements The values of the fracture toughness for the different composition of the reinforcement and the matrix are shown in the above table.27 16. Experimental Determination and Analysis of Fracture Toughness of MMC Variation of the fracture toughness with varying weight percentage of the reinforcements is shown in Fig 18.5 Fracture toughness (MPa m1/2) 18 17.5 17 16.5 16 15.5 15 14.5 14 13.5 1 2 3 4 5 Reinforcement in wt% Fig7.1 Variation of Fracture toughness with different wt% reinforcement 1. Al356+0%Sic+8%ZrSio4 2. Al356+6%Sic+2%ZrSio4 3. Al356+2%Sic+6%ZrSio4 4. Al356+4%Sic+4%ZrSio4 5. Al356+8%Sic+0%ZrSio4 7.2 Comparison of the Experimental and FEA results Fracture toughness (experimental) Fracture toughness (FEA) Al356+ Al356+ Al356+ Al356+ Al356+ 0%Sic+ 0%Sic+ 0%Sic+ 0%Sic+ 0%Sic+ 8%Zrsio4 15.27 8%Zrsio4 16.67 8%Zrsio4 18.05 8%Zrsio4 18.05 8%Zrsio4 15.27 14.13 15.28 16.89 16.89 14.13 Table 7.2 Comparison of experimental and FEA results M-Tech, MDE, Dept of Mech Engg., DBIT, Bangalore Page 54 Experimental Determination and Analysis of Fracture Toughness of MMC 7.3 Tensile test results Al356+ Al356+ Al356+ Al356+ Al356+ 0%Sic+ 6%Sic+ 2%Sic+ 4%Sic+ 8%Sic+ 8%Zrsio4 2%Zrsio4 6%Zrsio4 4%Zrsio4 0%Zrsio4 Peak load (KN) 14.60 18.30 17.70 17.80 17 Displacement at 10 13 12.6 12.2 13.1 12 15.50 14.90 15.70 14.50 97.93 126.49 125.18 127.92 119.28 149.34 148.70 145.03 139.85 4.60 5.78 4.40 3.32 peak (mm) Load at yield (KN) Yield Stress N/mm2) Tensile strength 119.15 2 (N/mm ) % Elongation 2.90 Table 7.3 Tensile properties of the MMC The average values of the ultimate tensile strength, yield strength, and % elongation obtained from the tensile test are summarized in table 7.2. It is observed that the tensile strength and yield strength are increased with an increase weight percent of both SiC and ZrSiO4. The increase was more significant for the Al cast with 6%SiC+2%ZrSiO 4 and 2%SiC+6%ZrSiO4. The increase in tensile strength is due to the presence of the hard and higher modulus SiC and ZrSiO 4 particles embedded in the Al (356) matrix, which act as a barrier to resist plastic flow when the composite is subjected to strain from an applied load. Also, the decreased interparticle spacing, due to the increasing weight percent of SiC and ZrSiO 4 reinforcement, creates increased resistance to dislocation motion, which contributes to the enhanced strength of the composites. M-Tech, MDE, Dept of Mech Engg., DBIT, Bangalore Page 55 Experimental Determination and Analysis of Fracture Toughness of MMC Variations of ultimate tensile strength and yield strength with the varying weight Strength (N/mm2) percentage of the reinforcement particles is shown in Fig 160 140 120 100 80 UT S 60 YS 40 20 0 1 2 3 4 Reinforcement ratios 5 . The zircon sand addition to the matrix alloy results to elastic and plastic incompatibility due to differences in the coefficient of thermal expansion in the hard reinforcing and soft matrix alloy. This is also due to high proportion of the hard and brittle phase of the zircon sand in the alloy.Experimental Determination and Analysis of Fracture Toughness of MMC 7. This is due to the high hardness values of silicon carbide particles and the good bonding between the reinforcement particles and matrix phases. MDE.4 Hardness test results The hardness values of composite specimen for different weight percentage of reinforcements is shown in table 7. which causes high dislocation density. The presence of reinforcement particles in the matrix could impede the movement of dislocations since these particles are stronger than the matrix in which they are embedded.6 Al356+8%SiC+0%ZrSiO4 55. DBIT.6 Al356+2%SiC+6%ZrSiO4 56. Bangalore Page 57 . From the above table it can be observed that the hardness values are high for the matrix with weight percent reinforcement of 2%SiC+6%ZrSiO 4 and 4%SiC+4%ZrSiO4.6 Al356+4%SiC+4%ZrSiO4 56. The high dislocation density also contributed to high hardness value. Dept of Mech Engg.3.3 Variation of hardness with different wt% reinforcement The values in above table show that.. Aluminium composition Hardness (BHN) Al356+0%SiC+8%ZrSiO4 52 Al356+6%SiC+2%ZrSiO4 52. hardness is increasing with increase in reinforcement weight fractions. M-Tech.6 Table 7. Al356+6%Sic+2%ZrSio4 3.Experimental Determination and Analysis of Fracture Toughness of MMC Variations of hardness with the varying weight percentage of the reinforcement particles is shown in Fig 57 56 Hardness (BHN) 55 54 53 52 51 50 49 1 2 3 4 5 Reinforcement in wt% Fig 7. Al356+4%Sic+4%ZrSio4 5. Dept of Mech Engg.. Al356+8%Sic+0%ZrSio4 M-Tech. Al356+2%Sic+6%ZrSio4 4. MDE.3 Hardness value for different wt% reinforcement 1. Al356+0%Sic+8%ZrSio4 2. Bangalore Page 58 . DBIT. 43 56.6 56.17 22656.63 14 16.5 Peak (mm) Compression 56. 57.5 55 54.91 Displacement at 11. MDE.5 54 53. Peak load (Kg) Al356+ Al356+ Al356+ Al356+ Al356+ 0%Sic+ 6%Sic+ 2%Sic+ 4%Sic+ 8%Sic+ 8%Zrsio4 2%Zrsio4 6%Zrsio4 4%Zrsio4 0%Zrsio4 22093.75 22313.4 Variation of compression strength with different wt% reinforcement The compression strength of the matrix alloy reinforced with SiC and ZrSiO 4 is shown in Fig 7..12 54.8 13.43 20306. Bangalore Page 59 .Experimental Determination and Analysis of Fracture Toughness of MMC 7.5 12.23 56.5 1 2 3 4 5 Reinforcement in wt% Fig7. Dept of Mech Engg.5 Compression strength (Kg/mm2) 57 56.4 Compression strength for different wt% reinforcement M-Tech.5 56 55.97 2 Strength(Kg/mm ) Table 7.05 22019.4. It can be observed from the fig below that the composition with 0%SiC+8%ZrSiO4 and 2%SiC+6%ZrSiO4 have high compression strength. DBIT.5 Compression test results The compression test results are shown in table below. 6 Microstructure The optical metallurgical microscope (model: NIKON Epiphot 200) was used for analyzing the distribution of the reinforcement in the matrix alloy.6 Microstructure of Al356+6%SiC+2%ZrSiO 4 M-Tech. Dept of Mech Engg. DBIT. Bangalore Page 60 .. 100X 500X Fig7.Experimental Determination and Analysis of Fracture Toughness of MMC 7. MDE.5 Microstructure of Al356+0%SiC+8%ZrSiO 4 100X 500X Fig7. 8 Microstructure of Al356+6%SiC+2%ZrSiO 4 M-Tech.7 Microstructure of Al356+2%SiC+6%ZrSiO 4 100X 500X Fig 7. MDE.Experimental Determination and Analysis of Fracture Toughness of MMC 100X 500X Fig 7. Bangalore Page 61 . DBIT. Dept of Mech Engg.. agglomerates of the reinforcement particles are clearly visible as shown in figures above.. From the above figures it can be observed that there is a reasonably homogenous distribution of the reinforcement particles in the cast composite. In the microstructure of the composite. Once the particles are transferred into the liquid.Experimental Determination and Analysis of Fracture Toughness of MMC 100X 500X Fig 7. During the distributive mixing. the distribution is strongly affected by certain flow transitions.9 Microstructure of Al356+8%SiC+0%ZrSiO 4 The specimens for microscopic observations were prepared by the standard technique of grinding with SiC abrasive papers and polishing with a diamond suspension solution. the rotation of the stirrer generates a vortex through which the reinforcement particles are drawn into the melt. Dept of Mech Engg. MDE. M-Tech. DBIT. The axial flow causes lifting of particles due to momentum transfer and radial flow prevents particle settling. It was found that the particles showed a strong tendency to accumulate in the colonies which froze in the last stage of solidification. Bangalore Page 62 . The result shows the increasing hardness with the increase in the reinforcement weight fractions. M-Tech.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 8 CONCLUSION Aluminum based metal matrix composites are the most promising materials for the future automotive. Microstructure reveals a reasonably homogeneous distribution of SiC and ZrSiO 4 particles in the cast composite. 1. DBIT. 4. Dept of Mech Engg. Al 356 alloy matrix hybrid composites reinforced with Zirconium Silicate and Silicon Carbide particles has been successfully synthesized by the stir casting method.. 2. MDE. The matrix alloy with 2%SiC and 6%ZrSiO 4 reinforcement has shown high toughness for fracture. 3. aerospace and other applications. The ultimate tensile strength and the yield strength of the composite are more in presence of both the reinforcement than compared to the alloy in presence of single reinforcement. Bangalore Page 63 . The presence of hard reinforcement particles in the matrix could impede the movement of dislocations since these particles are stronger than the matrix in which they are embedded. The increase in the strength can be attributed to homogenity of the reinforcement particles in the matrix alloy. It was found that the particles showed a strong tendency to accumulate in the colonies which froze in the last stage of solidification. The results from the study reveal that there is considerable increase in the fracture toughness in the presence of both silicon carbide and zirconium silicate reinforcement in the matrix alloy. The microstructure was analyzed by metallurgical microscope. The mechanical properties can also be evaluated after the heat treatment of the composite. Similar studies can be carried out using the compact tension specimen. M-Tech. MDE. The amount of reinforcement in metal matrix composite used in the present study is limited to 8 weight percentage. 3. DBIT.Experimental Determination and Analysis of Fracture Toughness of MMC CHAPTER 9 SCOPE FOR FUTURE WORK 1. corrosion and wear test can be evaluated. 5. Dept of Mech Engg. To analyze the microstructure SEM and EDAX can be used. Further tribological properties like friction. 4. Bangalore Page 64 . Single Edge Notch Bend specimen is used in the present study to evaluate the Fracture Toughness.. Further studies can be carried out by varying the weight percentage of the reinforcement. In the present study mechanical properties have been evaluated. 2. D. 2. Dept of Mech Engg. 5. Singapore. Akure. Sreenivasan.. PMB 704. Hughes. T. Lavizan. Hosur. Philipp Grohmann and Bogna Stawarczyk.M. MDE. E. GB-Oxon OX16 7SP. J. SA Kori. 8.Sivalingappa. DBIT. 7. K.Jordan.O.5Cu Matrix Particulate Composites Synthesized via Squeeze Cast Route”.Padasalgi. 9. No. 16788. 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