Kevlar® KM2 fiber is a transversely isotropic material. Its tensile stress-strain response in the axial direction is linear and elastic until failure. However, the overall deformation in the transverse directions is nonlinear and nonelastic, although it can be treated linearly and elastically in infinitesimal strain range. For a linear, elastic, and transversely isotropic material, five material constants are needed to describe its stress-strain response. In this paper, stress-strain behavior obtained from experiments on a single Kevlar KM2 fiber are presented and discussed. The effects of loading rate and the influence of axial loading on transverse and transverse loading on axial stress-strain responses are also discussed.

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A pulse-shaped split Hopkinson pressure bar (SHPB) was employed to determine the dynamic compressive mechanical responses and failure behaviors of a S-2 glass/SC15 composite along two perpendicular directions under valid dynamic testing conditions. The loading pulses in SHPB experiments were precisely controlled to ensure that the composite specimen deforms at a nearly constant strain rate under dynamically equilibrated stress during dynamic compression. Quasi-static experiments were conducted with an MTS and an Instron to study material rate sensitivity over a wider range. The compressive stress-strain behaviors along both directions were found to be strain-rate sensitive, but with different strain-rate sensitivities. A compressive constitutive model with strain-rate and damage effects was modified to accurately describe both quasi-static and dynamic compressive stress-strain behaviors of the composite material along the two perpendicular directions.

a b s t r a c tUniaxial tensile experiments were performed on pig skin to investigate the tensile stressestrain response at both quasi-static and dynamic rates of deformation. A Kolsky tension bar, also called a split Hopkinson tension bar (SHTB), was modified to conduct the dynamic experiments. Semiconductor strain gages were used to measure the low levels of the transmitted signal from pig skin. A pulse shaper technique was used for generating a suitable incident pulse to ensure stress equilibrium and approximate constant strain rate in the specimen of a thin skin sheet wrapped around the ends of the bars for minimizing radial inertia. In order to investigate the strain-rate effect over a wide range of strain rates, quasi-static tests were also performed. The experimental results show that pig skin exhibits rate-sensitive, orthotropic, and non-linear behavior. The response along the spine direction is stiffer at lower rate but is less rate sensitive than the perpendicular direction. An Ogden model with two material constants is adopted to describe the rate-sensitive tensile behavior of the pig skin.