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This paper presents a comparative study on the mechanical properties of seven monofilaments of 0.12 mm diameter made with different polymeric materials including PET, PBT, PE, PP, and PA6 in order to assess their suitability for being spacer yarns for developing high-quality spacer fabrics. Their support capability and elasticity corresponding to fabric compression resistance and resilience, respectively, were evaluated by analyzing the tensile stress–strain relationships and residual strains of monofilaments subjected to cyclic tensile loading. Slack and taut heat setting on the monofilaments were also considered to select a proper heat setting method for their spacer fabrics. The mechanical properties of the monofilaments were explained by using the supramolecular structure information from X-ray diffraction and sonic orientation tests. The results showed that PET monofilaments have much higher moduli than the other monofilaments and possess better support capability as spacer yarns for spacer fabrics. PET monofilaments also have better elasticity under small deformation below 5% strain than the other monofilaments, but their elasticity is inferior under large deformation above 5% strain. PET monofilaments are suitable for being spacer yarns to achieve high compression resistance and resilience for spacer fabrics. The PET monofilament with higher molecular weight possessed the lower Young's modulus which is good for the knitting process. PET monofilaments with high molecular weight and taut heat setting are recommended for producing spacer fabrics with high compression resistance and resilience, especially for small fabric deformation. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study of the compressive mechanics of warp-knitted spacer fabrics. The first part, as presented in the current paper, focuses on the establishment of a constitutive model that can give accurate compressive stress–strain relationships of warp-knitted spacer fabrics. Based on the analysis of three existing models for polymeric or metallic foams, a constitutive model consisting of seven parameters was firstly proposed for spacer fabrics. The effect of each parameter on the regressive stress–strain curves was then parametrically studied. Experimental validation was finally conducted by using 12 warp-knitted spacer fabrics produced with different spacer monofilament diameters and inclination angles, fabric thicknesses, and outer layer structures to identify the physical sense of the parameters. The analysis has showed that an excellent agreement exists between the regressive and experimental results, and all seven parameters have a quantitative effect on a particular phase of the resultant compressive stress–strain curves of warp-knitted spacer fabrics. The change of each parameter makes a clear physical sense on the stress–strain curve. Therefore, the proposed constitutive model can be used as a useful tool to engineer the cushioning properties of warp-knitted spacer fabrics. The adoption of the constitutive model to develop a dynamic model for predicting the impact compressive responses of warp-knitted spacer fabrics under various loading conditions will be presented in Part II. [ABSTRACT FROM AUTHOR]

This paper aims to identify the creep mechanisms of high tenacity (HT) polyester industrial fiber under different loads. In-situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) tests were conducted on a 1000 D HT fiber during the creep and creep recovery process with a low load (15 N) and a medium load (50 N) as well as creep rupture process with a high load (60 N). The measured creep strain-time curves comprised tensile zone (I), creep deformation zone (II) and creep recovery/rupture zone (III). The SAXS indicated that the macroscopic initial creep strain in zone I and creep deformations in zone II were attributed to conformation transition from gauche to trans in amorphous region, increasing the amorphous orientation and long period. Irreversible portion of conformation changes accounts for the small unrecoverable plastic creep strain after removing 15 N load in zone III. The initial creep strain in zone I and creep deformations in zone II of the 50 N creep process were bigger than the microscopic long period strain, because amorphous layers had conformational transformation and microfibril slippage which also produced a higher unrecoverable plastic creep strain in zone III. The long period increased significantly at the beginning of rupture zone with 60 N due to fragmentation of amorphous tie molecular. The disappearance of lamellar peaks at the end of rupture zone implied destruction of periodic lamellar structures, for the entire breakage of amorphous chains. The WAXS suggested that the crystal structure was stable under the creep loads. [ABSTRACT FROM AUTHOR]

The influence of strain rate on the deformation induced crystal transition from forms II to I of Polybutene-1 is investigated by in situ Wide Angle X-ray Diffraction at different temperatures. The structural evolution during the subsequent stress relaxation is further monitored. As strain rate increases, the phase transition rate decreases apparently, while the dependence on stress and strain also becomes weak. The phase transition during deformation with three strain rates shows consistent dependence on external work. The transition rate in terms of form I content drops instantly when stretching stops. Further analysis on the evolution of crystallinity and orientations of both forms II and I shows that a small amount of recrystallization occurs in form II during stress relaxation at 80 °C, accompanied by a continuous increase in the content of form I, which further confirms occurrence of deformation induced melting and recrystallization. Structural evolution of Polybutene-1 during the deformation induced phase transition from forms II to I and the following stress relaxation process is investigated by in situ Synchrotron Radiation Wide Angle X-ray Diffraction (SR-WAXD). During the tensile with different strain rate, the phase transition rates show consistent dependence on external work. After deformation at 80 oC, crystallinity of unstable form II increase inversely, while the phase transition from forms II to I continues at a slower rate. The full cycle consideration provides a more comprehensive basis for the use of materials. [Display omitted] • The structural evolution of Polybutene-1 during stress relaxation is first considered. • The phase transition rates during deformation with three strain rates show consistent dependence on external work. • Recrystallization of unstable form II is found during stress relaxation after deformation at high temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • This work develops a strain sensor that is insensitive to humidity and temperature changes. • The sensor shows a linear sensing feature throughout the whole sensing range. • It provides a new route for enhancing the sensing reliability of wearable sensors. Wearable and stretchable strain sensors have attracted much attention for their unique applications in monitoring human motion and health. However, state-of-the-art sensors lack sensing reliability on temperature and humidity changes at the wearable microinterface, leading to suboptimal sensing accuracy in body area sensing networks. For that, we design and fabricate a strain sensor using silk/polyurethane composite yarns with a core-sheath structure. The silk is modified using graphene with the assistance of 3-glycidyloxypropyl trimethoxy silane as coupling agent. The sensor exhibits fast response speed (i.e., 80 ms), high durability (>1500 cycles), remarkable linear sensing feature (R2 = 99.8 %) throughout the whole working range, and negative resistance response towards strain deformation. More importantly, the sensor performance will not be affected by temperature and humidity changes in typical use conditions. Testing is conducted and sensor responses in various body motions are also reported. In addition, a demonstration for the real-time body area sensing network using the fabricated sensor is provided. Experimental results from this study show that the fabricated strain sensor will have huge potentials for future personalized healthcare and public health management. [ABSTRACT FROM AUTHOR]