材料试验机载荷传感器测试范围小议

this study investigates the mechanical behaviour of polyester fibres over a range of temperatures by the use of a number of experimental techniques including tensile, creep and fatigue tests.the influences of temperature on the different mechanical properties is investigated with particular emphasise on the loss of rigidity and reduction of creep and fatigue lifetimes.A precise description of the stress /strain curves of the fibres highlights the effects with respect to the glass transition temperature. The fatigue failure process is precisely detailed and changes, at high temperatures, to the classical fracture morphology observations made of single fibres and yarns provides valuable information about the interpretation of result obtained with single fibre test to fibre assemblies

We have investigated the dynamic mechanical behavior of two cross-linked polymer networks with very different topologies: one made of backbones randomly linked along their length; the other with fixed-length strands uniformly cross-linked at their ends. The samples were analyzed using oscillatory shear, at very small strains corresponding to the linear regime. This was carried out at a range of frequencies, and at temperatures ranging from the glass plateau, through the glass transition, and well into the rubbery region. Through the glass transition, the data obeyed the time-temperature superposition principle, and could be analyzed using WLF treatment. At higher temperatures, in the rubbery region,the storage modulus was found to deviate from this, taking a value that is independent of frequency.This value increased linearly with temperature, as expected for the entropic rubber elasticity, but with a substantial negative offset inconsistent with straightforward enthalpic effects. Conversely, the loss modulus continued to follow time-temperature superposition, decreasing with increasing temperature, and showing a power-law dependence on frequency.

We study three monodomain single-crystal nematic elastomer materials, all side-chain siloxane polymers with the same mesogenic groups but with different types of cross linking: short flexible siloxane linkage affine to the network backbone, short flexible aliphatic cross links miscible with mesogenic side-chain groups, and long segments of main-chain nematic polymer. The dynamic mechanical response of these three systems shows a characteristically universal decrease of storage modulus and a corresponding increase of loss factor. This effect of dynamic soft elasticity is strongly anisotropic, depending on the nematic director orientation. We examine the important role of the average backbone chain anisotropy , which is affected by the cross-linking geometry and contributes to the magnitude and frequency dependence of the dynamic anomaly, and discuss possible applications in mechanical damping and polarized acoustic technology.

In this work the unsteady-state contact angle at the interface between polymer melt and carbon black (CB) was measured. The transition of contact angle from an unsteady to a steady state can be divided into three stages, the unsteady thermo-stage, the wetting stage, and the reach of equilibrium contact angle. Subsequently, three critical indices, the unsteady heat-transfer period t0, the retardation time τ, and the contact angle at equilibrium state A∞ are defined herein. The decrease in contact angle against time can be simulated by an exponential decay that involves these three critical indices. Molten polypropylene (PP) and polystyrene (PS) have the smallest equilibrium angle A∞, followed by polybutylene terephthalate (PBT), and polymethyl methacrylate (PMMA) has the greatest angle. Interestingly, this order is strongly related to the solubility parameter of each polymer. The CB coated with sulfonated polyester slightly changes the equilibrium angle A∞, but drastically reduces the retardation time τ for PP and PBT. This finding indicates that the CB, whose surface is modified by sulfonated polyester, can effectively reduce the compounding time of PP and polyester. Experimental results also reveal that reduce compact density slightly increases A∞ but barely affects τ. Furthermore, modifying PS with polybutadiene particles yields a high contact angle A∞ and a low τ value.