contribute to the energy-absorption characteristics of a material subjected to compression cycling. It can be seen from Fig. 1a which shows the compression-release curves at the first cycle that the knitted fabrics differ from each other with regard to the steepness of both compression and recovery curves indicating their different energy absorbing properties. At the fifth compres- sion cycle the path of both compression and release curves has been modified for all tested knitted fabrics, but the differences in the easiness of compression and recovery speed have remained (Fig. 1b).
It can be noted that determined energy-absorption character- istics of the knitted fabrics (Fig. 2) are the quantitative indication of their repeated compression performance and their different compression behavior as previously demonstrated by compression- release curves. Since the energy dissipation is governed by delayed deformation, the question is which deformation component, irre- versible (plastic) or reversible (viscoelastic) is responsible? To answer this question, the particular procedure was performed. To determine the part of WC parameter coming from the irreversible compression work, the WC parameter for five individual cycles was summed, giving the total nonelastic compression work (WC1-5), or energy dissipated due to nonelastic deformation for all repeated cycles. The area occupied by the compression curve at the first cycle and the release curve at the fifth cycle determines the irreversible five-cycle compression work (WCp). The difference between these two parameters gives the reversible five-cycle compression work (WCve), or the amount of energy dissipated due to viscoelastic deformation of the material. Then, the percentage of both plastic and viscoelastic components can be calculated as shown in Fig. 3. The delayed deformation components seem to be presented almost equally in the cotton knitted fabric. The energy captured in the sample proved to be to a higher extent caused by plastic deforma- tion of the hemp and viscose knitted fabrics (12.8 and 14.6 percentage points, respectively), whereas the plastic deformation is lower than the viscoelastic component (approximately 12 per- centage points) in the PAC knitted fabric.
Starting from the percentage of delayed deformation components, the hysteresis loop of each compression cycle was assessed in terms of the energy lost due to plastic (irreversible) deformation as well as the energy dissipated due to viscoelastic (reversible) deformation. It made possible to determine the share of deformation components in total compression (Table 1). In the next step, the relative deformation components can be calculated. All the calculations can be easily done in Microsoft Excel.
The reduction in total deformation with repeated cycling has already been discussed, but the calculated share of deformation components gives the quantitative indication of deformation character. As can be seen in Table 1, the share of the elastic deformation increases, whereas the share of viscoelastic and plastic deformation components decreases with every successive cycle. This can be explained in terms of irreversible slippage and rearrangement of fibers. Permanent changes in the fibrous system slow down with subsequent cycles on account of the compaction of the structure i.e. an increase in packing density of the fiber assembly.
การดูดซึมพลังงานลักษณะของวัสดุที่อยู่ภายใต้การบีบอัดขี่จักรยาน จะเห็นได้จาก Fig. 1a ซึ่งแสดงเส้นโค้งบีบปล่อยในรอบแรกที่ผ้าถักที่แตกต่างกันตามความสูงชันของการบีบอัดและกู้คืนโค้งแสดงพลังงานของพวกเขาแตกต่างกันที่คุณสมบัติการดูดซับแรงกระแทก ที่ 5 มีการปรับเปลี่ยนเส้นทางของโค้งรวมทั้งรุ่นสำหรับวงจร compres-sion ทดสอบผ้าถัก แต่ความแตกต่างในความสะดวกสบายในการบีบอัดและการกู้คืนความเร็วยังคงมี (Fig. 1b)It can be noted that determined energy-absorption character- istics of the knitted fabrics (Fig. 2) are the quantitative indication of their repeated compression performance and their different compression behavior as previously demonstrated by compression- release curves. Since the energy dissipation is governed by delayed deformation, the question is which deformation component, irre- versible (plastic) or reversible (viscoelastic) is responsible? To answer this question, the particular procedure was performed. To determine the part of WC parameter coming from the irreversible compression work, the WC parameter for five individual cycles was summed, giving the total nonelastic compression work (WC1-5), or energy dissipated due to nonelastic deformation for all repeated cycles. The area occupied by the compression curve at the first cycle and the release curve at the fifth cycle determines the irreversible five-cycle compression work (WCp). The difference between these two parameters gives the reversible five-cycle compression work (WCve), or the amount of energy dissipated due to viscoelastic deformation of the material. Then, the percentage of both plastic and viscoelastic components can be calculated as shown in Fig. 3. The delayed deformation components seem to be presented almost equally in the cotton knitted fabric. The energy captured in the sample proved to be to a higher extent caused by plastic deforma- tion of the hemp and viscose knitted fabrics (12.8 and 14.6 percentage points, respectively), whereas the plastic deformation is lower than the viscoelastic component (approximately 12 per- centage points) in the PAC knitted fabric.Starting from the percentage of delayed deformation components, the hysteresis loop of each compression cycle was assessed in terms of the energy lost due to plastic (irreversible) deformation as well as the energy dissipated due to viscoelastic (reversible) deformation. It made possible to determine the share of deformation components in total compression (Table 1). In the next step, the relative deformation components can be calculated. All the calculations can be easily done in Microsoft Excel.The reduction in total deformation with repeated cycling has already been discussed, but the calculated share of deformation components gives the quantitative indication of deformation character. As can be seen in Table 1, the share of the elastic deformation increases, whereas the share of viscoelastic and plastic deformation components decreases with every successive cycle. This can be explained in terms of irreversible slippage and rearrangement of fibers. Permanent changes in the fibrous system slow down with subsequent cycles on account of the compaction of the structure i.e. an increase in packing density of the fiber assembly.
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