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.

In this study, the mechanical response of a single yarn pull-out from single layers of Kevlar Õ and Twaron Õ fabric under out-of-plane loading at both quasi-static and dynamic rates was experimentally investigated. In order to perform the dynamic experiments, a pendulum impact setup was designed and constructed to pull out a single yarn dynamically. The pull-out load was measured directly by a load cell and the movement of the fabric was measured to portray the loaddisplacement history. The effects of transverse pressure, different weave direction, and loading rates were also investigated.Woven fabrics with aramid fibers have gained great attention as protective systems from damage under ballistic impact for several decades. Aramid fibers are composed of long molecular chains produced from p-phenylene terephthalamides (PPTA), and popular examples of these materials include Kevlar Õ developed by DuPont, and Twaron Õ and Technora Õ produced by Teijin. These PPTA fibers provide unique characteristics of high strength, low density, and high flexibility in the woven structure, and are therefore in popular demand for body armor and aircraft turbine engine fragment barriers. The impact resistance of the fabrics under ballistic loading is known to be determined by various factors, such as single fiber properties, the fabric structure or weave type, geometry of the impacting projectile, projectile impact velocity, multiple ply interaction between the fabric layers, far-field boundary conditions away from the zone of impact, and interyarn friction. 1 It has been shown that this yarn-yarn friction increases the energy dissipated via frictional sliding, as well as yarn strain energy and yarn kinetic energy. 2 The ballistic limit (defined as the projectile velocity required to penetrate the fabric at least 50% of the time) of these fabrics was also shown to increase by approximately 10%, as demonstrated by computational results from Rao et al. 3 comparing baseline plain-woven Kevlar Õ KM2 fabrics with and without inter-yarn friction. The effects of inter-yarn friction and yarn pull-out can be correlated to pull-out force and total pull-out energy. The results obtained using the force-displacement history can be used to develop friction models for yarn pull-out at different rates such that the models can be implemented in numerical simulations of fabrics under impact. Kirkwood et al. 4 have demonstrated the usefulness of yarn pull-out analysis in predicting the ballistic performance of these bulletproof fabrics.The relation between yarn pull-out and friction suggests that yarn pull-out is an important behavior to study the effect of inter-yarn friction in the woven structure. According to Dong et al. 5 and Kirkwood et al.,4 yarn pull-out force in fabric has a correlation with the fabric's performance of ballistic resistance, as fabrics with higher yarn pull-out force displayed better capabilities in resisting ballistic impact. The main factors

In this study, the mechanical response of a single yarn pull-out from single layers of Kevlar Õ and Twaron Õ fabric under out-of-plane loading at dynamic rates was experimentally investigated, as ballistic applications typically occur at higher velocities and out-of-plane directions compared to previous literature. In order to perform the dynamic experiments, a pendulum impact setup was designed and constructed to pull out a single yarn dynamically. The pull-out load was measured directly by a load cell and the movement of the fabric was measured to portray the load-displacement history. The effects of fabric length, out-of-plane versus in-plane yarn pull-out, and constraining boundary conditions were compared.

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