See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/270569329 Dynamic Properties of Air-Jet Yarns Compared to Rotor-Spun Yarns ARTICLE in TEXTILE RESEARCH JOURNAL · FEBRUARY 2015 Impact Factor: 1.33 · DOI: 10.1177/0040517514563726 3 AUTHORS, INCLUDING: Mohamed Eldessouki Ramsis Farag Technical University of Liberec Auburn University 31 PUBLICATIONS 5 CITATIONS 14 PUBLICATIONS 4 CITATIONS SEE PROFILE SEE PROFILE Available from: Mohamed Eldessouki Retrieved on: 24 August 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] Original article Dynamic properties of air-jet yarns compared to rotor spinning Textile Research Journal 0(00) 1–11 ! The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0040517514563726 trj.sagepub.com Mohamed Eldessouki1,2, Sayed Ibrahim3 and Ramsis Farag2,4 Abstract In yarn production, the mechanism of twist insertion is a major factor that affects the structure and ultimately the properties and characteristics of the produced yarn. Moreover, the differences within the same spinning technique may have a similar effect where, for instance, the properties of yarns produced using Murata Vortex Spinning (MVS) and Reiter air-jet spinning (J20) will differ, although both technologies are just varieties of the same twist insertion principle of using a stream of air. In this work, the structure and properties of Murata vortex, Reiter, and rotor-spun yarns are compared with more emphasis on their mechanical behavior under dynamic stresses. Unlike the dynamic mechanical analysis of materials that presumes linear viscoelastic behavior and is only valid under small strains, this work suggests a cyclic loading with larger strains as a means of the dynamic evaluation of the yarns. Results show no significant difference between the technologies in terms of their initial modulus and maximum elongation, while a significant difference between the technologies is observed in the maximum loading and, to some extent, the work of rupture. The dynamic sonic modulus is compared to the results of the standard mechanical and the suggested cyclic loading tests, and a high correlation between the values was observed. Keywords air-jet yarns, dynamic modulus, Rieter jet-spinning, Murata vortex-spinning, viscoelastic properties of yarn Introduction There is a direct relation between the yarn forming process, structure, properties, and performance. Yarn production technology identifies the ‘‘yarn forming process’’ term in this series of relations, where ringspinning, rotor spinning, air-jet spinning, friction spinning, etc., are found to have different effects on the produced yarns. Each production technology has its own advantages and disadvantages, as determined within a certain application window. Air-jet spinning, for instance, was found to be successful in producing yarns with reasonable tenacity (Figure 1(a)) at a relatively much higher speed than the ring spinning and the rotor spinning (Figure 1(b)).1 The Murata Jet Spinner, MJS 801, was first exhibited at ATME-International in 1982 as a modification of the fasciated spinning system introduced by Du Pont in 1956.2 At that stage, the system had some constraints on producing yarns of 100% cotton or cotton-rich blends, which was then solved by introducing the Murata Vortex Spinning (MVS) that allows processing these fibers and producing fine yarn counts. In 2003, the Rieter Group introduced its own J10 air-jet spinning technology that was updated in 2008 with J20, which was commercialized with 200 spinning units and up to 500 m/min delivery speed. The jets used in Murata and Rieter are different in design and construction but produce jet yarns based on the same principle of twist insertion by the stream of air. In both 1 Department of Materials Engineering, Technical University of Liberec, Czech Republic 2 Department of Textile Engineering, Mansoura University, Egypt 3 Department of Textile Technology, Technical University of Liberec, Czech Republic 4 Department of Polymer and Fiber Engineering, Auburn University, USA Corresponding author: Mohamed Eldessouki, Department Materials Engineering, Technical University of Liberec, Studentska´ 2 461 17 Liberec 1 Liberec, Czech Republic. Email:
[email protected] Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] 2 Textile Research Journal 0(00) Figure 1. (a) Relationship between the tenacity and the yarn counts for ring-spun, Murata Vortex Spinning (MVS), and open-end (OE) yarns. (b) Comparative production speeds for different yarn counts produced on ring-spinning, MVS, and OE systems.1 systems (MVS and Reiter), fibers leave the front roller of the drafting device and are drawn into the fiber strand passage by air suction created at the nozzle. The distance between the nozzle tip and the drafting roller is crucial in generating the free fiber ends and this distance should be slightly shorter than the average length of the fibers being processed, because fibers shorter than this distance are usually lost and directed to the waste.3 According to the air pressure, the vortex can revolve at speeds of 1,000,000 rpm, which allows a twist of fibers with a rotation speed of 300,000 rpm where the speed difference is attributed to the mechanical friction.3 The vortex stream focuses the leading ends of the fibers at the yarn center and directs the trailing ends to form the outer layer that wraps the yarn. This action results in a yarn structure with fibers at the core with a very low twist and are almost parallel, while the twist level grows with increasing yarn diameter (yarn build up). Due to the vortex forces and the twist of the surface fibers, a certain torque is generated in the yarn being formed. This torque has the tendency to twist the fiber bundle between the drafting unit and spindle. This kind of twist must be avoided to prevent interference with the generation of the necessary free fiber ends. Therefore, the two systems adopted two solutions for this problem, where Murata used a needle in the nozzle block, as illustrated in Figure 2(a), and Reiter used a curved path of the fibers at the nozzle tip with an arc shape, as shown in Figure 2(b). The fiber path is another difference in the design of the nozzles of the two systems. In the Murata system, the drafting system is located above the spinning nozzle and yarns are delivered at the bottom. For space efficiency reasons, Rieter reversed the setup and the sliver is fed from the bottom and delivered yarn is wound up at the top after passing the air-jet twist insertion. Air-jet yarns were compared with other spinning systems in the literature,5–8 where Soe et al.4 produced cotton yarns spun on the MVS system and compared them with yarns spun on ring and open-end rotor systems. Their work focused on the structure of the yarns and the differences in fiber pitch, arrangement, and angles, as well as some yarn parameters such as the yarn diameter, helix angle, hairiness, evenness, and tenacity. The study found MVS yarns to be the bulkiest among the three yarns, with more parallel fibers at the core (with almost no twist) and wrapped by other fibers. MVS yarns were also found to be stiffer than ring and rotor-spun yarns, while the ring-spun yarn showed the highest tenacity values. Another comparative study for the MVS system with ring and rotor-spun yarns was performed by Erdumlu et al.,6 where the performance of these yarns from different materials and different counts was compared after transforming to knitted finished fabrics. MVS yarns showed the least hairiness and the highest pilling resistance among the three systems. The dimensional stability and the bursting strength of the Vortex knitted fabrics were close to those of the fabrics from ring spinning and outperform the fabrics of rotor spinning. The VORTEX website by Murata-Machinery7 demonstrates some structural and property differences between the Vortex, the ring, and the rotor-spinning systems. Figure 3 shows the twist distribution across the cross-sections of the three yarns where twists are almost constant in ring-spun yarns. The figure also shows the possibility of wrapping fibers to change their twist direction at the surface of rotor yarns, while a monotonic increase in twist intensity is observed in vortex yarns with more parallel fibers at the yarn core. In this work, we are trying to go beyond the comparison of different systems to compare yarns of the same family that are produced using the same production principle with more emphasis on physical properties of the yarns under dynamic loading. This paper tries to investigate the relatively new air-jet system Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] Eldessouki et al. 3 Figure 2. Illustrations for the Murata Vortex Spinning system (a)3 and the Rieter jet spinning (b).4 using Scanning Electron Microscopy (SEM) and proceeds with physical properties of the studied yarns. Mechanical testing of the yarns was performed using the commonly used single-end strength tests at constant rate of extension (CRE) as well as cyclic loading/ unloading. The sonic modulus of the yarns was investigated using the Dynamic Modulus Tester (DMT). Methods Cyclic modulus Figure 3. Twist distribution through the cross-section of yarns produced on different spinning systems (color online only).6 Testing of yarn behavior under dynamic loading/ unloading is required to simulate the actual loading scenarios during the end use of the yarn. This kind of testing is necessary for certain applications, such as tire threads and carpet pile yarns9 (where yarn resilience can be measured before the production of the end product). Warp threads are also subjected to dynamic loading during the weaving process.10 The dynamic loading of yarns is usually studied within the viscoelastic properties of the material, where a sinusoidal strain e (sinusoidal stress is applied in some experiments) with certain amplitude em is applied to the yarn in the form e ¼ em sinð!tÞ developed by Rieter and compares its properties to other systems of the same family (e.g. MVS) as well as other systems (e.g. rotor spinning). The study begins with the structure of the yarns as observed ð1Þ where ! ¼ 2:F is the angular frequency (radian/ second), F is the frequency in Hertz, and t is the time of application. At steady-state conditions, the developed stress f in the fiber’s material will also have a Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] 4 Textile Research Journal 0(00) sinusoidal shape and will be related in phase to the imposed extension as f ¼ fm sinð!t þ Þ ð2Þ where fm is the stress amplitude and d is the angular phase difference between the applied extension and the resulting stress. According to this relation, and using the trigonometric identities, the stress can be rewritten in the form f ¼ fm ½cosðÞ: sinð!tÞ þ sinðÞ: cosð!tÞ ð3Þ Therefore, the stress can be considered as two components: one that is in-phase with the strain and equals fm : cosðÞ, and another that is 90 out-of-phase and equals fm : sinðÞ. These values are used to define the dynamic modulus of the material as E¼ in phase stress amplitude fm : cosðÞ ¼ strain amplitude em ð4Þ dynamic loading cycles.9,12 The calculation of this modulus is slightly modified from the chord modulus by considering the slope of a fitted trend line (instead of the chord line itself) for the loading portion of the cycle. The yarn’s delayed recovery was not considered during the unloading cycle and the calculation of the fitting line excludes the unloading portion of the cycle, because this portion mainly depends on the viscoelastic properties of the fibers, their relaxation time, and the unloading speed. Figure 4 shows a typical dynamic loading of a vortex yarn that goes under 40 loading cycles and the inset of the figure shows an example for the first cycle, where the loading and unloading portions were identified and the modulus of this cycle is calculated as the slope of the demonstrated dotted trend line. The ‘‘resilience’’ (R) of the yarn at each cycle is calculated by the numerical integration of the yarn load (P) as a function of its elongation (x) to calculate the area under the curve (W). This can be expressed mathematically as Z Also, the dissipation or loss factor of the material (w) can be calculated as out of phase stress amplitude ¼ in phase stress amplitude fm sinðÞ sinðÞ ¼ tanðÞ ¼ ¼ fm cosðÞ cosðÞ ð5Þ These parameters are commonly used in evaluating the dynamic behavior of textile materials, but it should be noted that these parameters, according to the above listed equations, are only valid for materials that obey the laws of linear viscoelasticity. Most textile fibers, however, are known for their nonlinear behavior, which means that these parameters can only be applied at very small strains, otherwise they might be considered as approximates to the material behavior.11 Therefore, this study suggests the cyclic loading in a way that simulates the actual loading scenarios by applying higher strains on the yarn. However, the applied strain is limited to have loading cycles within the region around the approximated yarn’s yield point, where the slope modulus of the load–elongation curve changes significantly. The maximum load during loading cycles was about 30–40% from the strength of these yarns, then the yarn was unloaded without reaching a stress value of zero to keep an initial or a static load on the yarn at the beginning of each cycle. Some parameters were extracted from each curve; among them the cyclic modulus and the resilience were examined during the study of these yarns. The ‘‘cyclic modulus’’ can be expressed as the chord modulus of the load–elongation curve at different xmax W¼ pðxÞdx ð6Þ xmin The resilience of the ith cycle (Ri) represents the hysteresis during that cycle and can be calculated as the difference between the loading and the unloading portions of the cycle as follows: Ri ¼ Wloadi Wunloadi ð7Þ Sonic modulus The dynamic (sonic) modulus is based on a principle of the pulse propagation and its speed in the material. To measure the sonic speed, an apparatus with two transducers (transmitter and receiver) that touch the yarn specimen and the time interval for the pulse to travel from one to the other is measured. By knowing the distance between the transducers and the measured time, the sonic speed C through the material can be measured, and this speed can then be used in calculating the sonic modulus of the yarn according to the relation E ¼ :C2 ð8Þ where E is the sonic modulus in GPa, C is the sonic speed in the material in km/s, and is the material density in (g/cm3). This relation can be reformulated to E ¼ k:C2 ð9Þ where E is the sonic modulus in cN/denier, C is the sonic speed in the material in km/s, and k is a constant Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] Eldessouki et al. 5 Figure 4. Load–elongation behavior of vortex yarn under cyclic loading. The inset is an example for the calculation of the modulus in the first cycle (the blue curve represents the unloading, the red curve represents the loading, and the black dotted line represents the fitted trend line for the loading cycle). (Color online only.) conversion factor that accounts for the material volumetric and linear densities, which was found to be 11.3.12 under a pre-tension of 0.5 cN/tex. Thirdly, the DMT by Lawson-Hemphill was used to measure the velocity of the sonic pulses in the yarns at 5 kHz.13 Experimental setup Results and discussion Three yarns of similar counts (20 tex) made from 100% viscose were produced on different systems. MVS and Reiter (J20) yarns were produced at production speed of 375 m/min and an air pressure level of 6 bars. Rotorspun yarn was prepared using a similar sliver as the one used with the other systems. Viscose fibers used in the production were obtained from Lenzing Technik Company with 38 mm average staple length, fineness of 1.52 0.39 dtex and a tenacity of 20.65 3.72 cN/ tex, as measured using the Vibroscope for 50 fiber samples. Yarn samples were analyzed for their structure using a TESCAN VEGA TS 5130 scanning electron microscope (TESCAN s.r.o., Czech Republic). Yarn samples were coated with gold using an SCD 030 auto sputter coating device (Balzers Union FL 9496 Balzers). Yarn mechanical properties were studied using three tests; firstly, the common load/elongation response was performed according to the ASTM standard D 2256 – 0214 on a universal testing machine of the Labortech Tiratest instrument. Secondly, the same instrument was used for applying a cyclic loading– unloading on the yarn. Yarn samples were loaded for 40 cycles at levels between 0.2 and 1 N, followed by a continuous extension until the yarn breakage. All yarn samples were tested at a gauge length of 250 mm and The yarns produced on the three different systems were examined under the scanning electron microscope for their structures. As depicted in Figure 5, air-jet yarns (both Rieter and Murata) show a structure where the strand of the input fibers is divided into two groups of relatively parallel fibers in the core and wrapping fibers at the sheath. The amount of wrapping fibers is affected by the air pressure in the nozzle, the nozzle design parameters, and the delivery speed. Rotor yarns, on the other hand, show wildly entangled wrapping fibers, which do not make a helical shape as the sheath fibers of the air-jet yarns. Yarns produced on Rieter show hairiness and fuzziness that are relatively higher than that for Murata spun yarns, as indicated in Figure 5. Although the twist factor and its measurement are questionable for air-jet yarns, the pitch of the twists and the twist angle are qualitatively higher in the case of Murata yarns compared to Rieter yarns. On the other hand, rotor-spun yarns show the belt fibers that wrap the other twisted fibers in a way that is characteristic for rotor spinning. The mechanical properties of the yarns were evaluated using the stress–strain response of yarns. Graphs are shown in Figure 6 with the individual curves for samples of Rieter yarns in Figure 6(a), Vortex yarns in Figure 6(b), and rotor-spun yarns in Figure 6(c). Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] 6 Textile Research Journal 0(00) Figure 5. Scanning electron microscope pictures for the longitudinal view of Rieter, Murata Vortex Spinning, and rotor yarns, respectively. Figure 6. Force–extension relations for the Rieter, Murata Vortex Spinning, and rotor yarns: (a)–(c) individual curves. The initial modulus, the maximum load, the maximum elongation, and the work of rupture were extracted and analyzed to differentiate between these curves. Identical values for these four parameters with their statistics are shown in Table 1 for the different yarns. Studying these results shows that Rieter yarns have an elastic modulus slightly higher than that of rotor yarns, while Vortex yarns have a lower modulus value. A trend similar to that for the modulus can be observed for the maximum elongation property while the other yarn parameters, such as the maximum load and the work of rupture, have a slightly different trend where Rieter yarns have the highest values followed by Vortex then rotor yarns. It is important to note that this ranking in properties Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] Eldessouki et al. 7 Table 1. Mechanical properties of the different yarns Young’s modulus [g/denier] Maximum force [N] Maximum elongation [mm] Work of rupture [mJ] Sample number Rieter Vortex Rotor Rieter Vortex Rotor Rieter Vortex Rotor Rieter Vortex Rotor 1 2 3 4 5 6 7 8 9 10 Average Stand. dev. 54.7 57.3 55.3 63.7 57.6 82.0 66.5 54.9 64.0 54.9 61.092 8.547 44.0 61.3 70.8 54.5 60.7 90.5 66.1 57.8 69.0 66.3 64.086 12.156 2.932 3.262 2.853 2.730 2.645 2.664 3.214 1.438 1.438 2.549 2.573 0.642 7.420 10.220 14.507 10.696 7.492 14.163 10.239 11.431 11.706 11.353 10.923 2.344 12.256 10.240 6.801 10.441 12.430 7.375 13.575 13.714 14.816 12.500 11.415 2.674 25.473 28.006 21.214 23.421 20.467 20.940 29.689 6.198 6.198 17.267 19.887 8.100 8.462 12.955 24.020 15.997 8.120 25.009 14.874 17.146 19.846 14.469 16.090 5.709 69.8 63.9 64.7 55.5 53.5 54.1 74.0 70.8 70.8 73.4 65.060 8.050 1.688 1.973 2.613 2.316 1.635 2.750 2.276 2.164 2.658 1.995 2.207 0.391 2.020 1.484 1.342 1.745 2.075 2.029 2.070 2.123 2.057 2.084 1.903 0.280 14.154 14.184 11.557 13.644 12.529 12.737 15.206 6.226 6.226 10.774 11.724 3.177 15.337 9.481 5.835 11.633 17.031 9.839 17.910 18.583 18.986 16.488 14.112 4.573 Table 2. Analysis of variance for the mechanical properties of the different yarns Modulus Maximum force Maximum strain Work of rupture Source of variation SS df MS F P-value F crit Between groups Within groups Total Between groups Within groups Total Between groups Within groups Total Between groups Within groups Total 85.5115 2570.6440 2656.1555 2.2482 5.7930 8.0412 3.2639 204.6553 207.9193 172.2703 1072.0674 1244.3377 2 27 29 2 27 29 2 27 29 2 27 29 42.7558 95.2090 0.4491 0.6429 3.3541 1.1241 0.2146 5.2392 0.0120 3.3541 1.6320 7.5798 0.2153 0.8077 3.3541 86.1351 39.7062 2.1693 0.1338 3.3541 does not give absolute superiority to a system over the other where the values of the yarn properties are usually related to the required end product’s performance. The analyses of variance (ANOVAs) for these parameters are indicated in Table 2, which shows no significant difference between the yarn production technologies in terms of their initial modulus and maximum elongation while a significant difference between these technologies in terms of their maximum loading is observed, which is also reflected on the work of rupture with some degree of significance. The significant difference between the maximum load for each yarn can be attributed to the different arrangement of fibers inside the yarn, where more parallel fibers were observed in the Rieter production technology as demonstrated earlier in the SEM pictures. The mechanical behavior of the yarns under cyclic loading is shown in Figure 7 for the different types of yarns. The calculated dynamic moduli as well as the resilience of the yarns at different loading cycles are shown in Figures 8 and 9, respectively. It can be seen from Figure 8 that the yarn modulus increases with the increase in the number of loading cycles. This behavior can be explained by increasing the alignment of fibers to the yarn axis every time the load is applied on the yarn. This alignment increases the helical angle of the fibers and allows more fibers to resist the applied load, which consequently increases the measured modulus. Increasing the orientation of fibers results in increasing their utilization factor in the yarn and allows stiffer behavior of the yarn at higher numbers of loading cycles. The cyclic modulus increased after 40 cycles by Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] 8 Textile Research Journal 0(00) Figure 7. Load–elongation behavior of the Rieter, Murata Vortex Spinning, and rotor yarns under cyclic loading. about 25.7%, 25.9%, and 29.4% from its value at the first cycle for Rieter, Vortex, and rotor yarns, respectively. Also, the rate of change in the cyclic modulus with the number of cycles is almost the same for all yarns produced on different technologies, which might be attributed to the use of the same fiber material in all yarns. On the other hand, the relatively higher increase in the cyclic modulus of the rotor-spun yarn reveals higher rearrangement of the fibers, which is expected, because those yarns are known to be bulkier and have highly random orientation. The resilience of the yarns is demonstrated by their hysteresis, which was found to decrease after the application of the cyclic loading with a tendency of the loading and unloading curves to get closer until being nearly identical after a certain number of cycles. The continuous shift of the hysteresis loops is due to the creep properties of the material and a permanent deformation was found to form in the material after certain number of cycles. The rate of change in yarn resilience (the slope of the curves in Figure 9) is similar in all yarns, which can be attributed to the characteristics of the viscose fibers used in all these yarns. The calculation of the sonic modulus is based on the sonic speed in the yarn material, as indicated earlier. Sonic speed is the relation of the distance between sending and receiving probes to the traveling time of the sonic pulses, as shown in Figure 10 for individual yarn samples. The dynamic sonic moduli, as calculated from sonic speeds in the yarns material, are listed in Table 3 with their ANOVAs shown in Table 4. It can be noticed that the dynamic moduli calculated from the sonic test are correlated to the Young’s moduli obtained from the standard test (as shown in Figure 11) and, therefore, the sonic tester can be preferred as a non-destructive way of measuring the Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] Eldessouki et al. 9 Figure 8. Change in yarn modulus after many cycles of loading. 0.4 0.35 Yarn Resilience [N.mm] 0.3 0.25 0.2 Rieter 0.15 Vortex Rotor 0.1 0.05 0 0 5 10 15 20 25 30 35 40 45 -0.05 No. of loading cycle Figure 9. Change in yarn resilience after many cycles of loading (color online only). Young’s modulus of the material. The sonic tester is also more sensitive to many of the material parameters, especially at the microscopic and molecular levels. Sonic modulus, for instance, is sensitive to the fiber crystallinity, the fiber orientation, and the packing density of fibers inside the yarn (where the effect of porosity and pulse transfer across different media is considered). According to these sensitivity issues, the modulus measured with the sonic test might be lower than that measured with the standard test, as shown in Figure 11. Further investigations might be required to take one or more of these parameters in account to increase the precision of the sonic testing method. Conclusion Staple fiber yarns were produced on different systems of twist insertion mechanisms. All yarns were made of Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] 10 Textile Research Journal 0(00) 22 Reiter 1 Reiter 2 20 Reiter 3 Reiter 4 18 Reiter 5 Distance [cm] Rotor 2 16 Rotor 3 Rotor 4 14 Rotor 5 Rotor 1 12 Vortex 2 Vortex 3 10 Vortex 4 Vortex 5 Vortex 1 8 60 70 80 90 100 Time [microseconds] 110 120 130 Figure 10. Plot of the individual readings of sonic pulse times at different probe distances used to calculate the sonic speed (color online only). Table 3. Sonic (dynamic) modulus [g/denier] Average Stand. dev. Reiter Vortex Rotor 62.09 55.63 68.56 52.75 55.18 58.84 6.44 49.88 52.01 46.05 46.69 53.60 49.65 3.28 66.54 49.12 62.80 53.71 45.89 55.61 8.82 Table 4. Analysis of variance for the sonic modulus Source of variation SS df MS F P-value F crit Between groups Within groups Total 217.762 520.137 737.899 2 12 14 108.881 43.345 2.511974 0.122666 3.885294 viscose fibers. Results show that the tested yarns have no significant difference in terms of their initial modulus and maximum elongation, while a significant difference between the technologies is observed in the maximum loading and, to some extent, the work of rupture. The cyclic modulus of all yarns increased with the same rate by increasing the number of loading cycles due to the better orientation of the fibers inside the yarns, while a slightly higher increase in cyclic modulus was observed with rotor yarns as their initial fiber orientation is more randomized. The dynamic modulus, calculated through the sonic speed in the yarn material, was found to be highly correlated to the Young’s modulus, calculated from the regular yarn breaking test, which gives an indication as to the validity of using such a non-destructive test for evaluating the yarn materials. This work will extend to investigate the physical properties of air-jet yarns with the Downloaded from trj.sagepub.com at Technicka Univerzita on February 27, 2015 XML Template (2014) [20.12.2014–2:39pm] //blrnas3.glyph.com/cenpro/ApplicationFiles/Journals/SAGE/3B2/TRJJ/Vol00000/140210/APPFile/SG-TRJJ140210.3d (TRJ) [1–11] [PREPRINTER stage] Eldessouki et al. 11 70 60 Modulus [g/denier] 50 40 Sonic Standard 30 20 10 0 Reiter Vortex Rotor Figure 11. 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