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Single-yarn impact results have been reported by multiple authors in the past, providing insight on the fundamental physics involved in fabric impact. This insight allowed developing full fabric models that were able to reproduce properly wave propagation, deflection, and ballistic limits. This paper proposes a similar experimental methodology but for a specific composite material made of ultra-high molecular weight polyethylene. The presence of the polyurethane matrix in the composite is expected to slow down wave propagation. But the high-speed photographic tests reported in this paper indicate that wave propagation in strips and single-layer material is similar to that expected for dry fiber. An explanation is proposed for this unexpected result. This paper also reports the critical velocities (i.e., impact velocities that fail the fibers immediately) measured for the composite material and compares them to the velocities expected from the theory. The velocity is accurately predicted when taking into account wave interactions in front of the projectile. Finally, tests on multilayer composites are presented. In particular, a flash produced under the projectile during the first few microseconds was recorded with high-speed video cameras. A simplified study of the temperature increment upon impact indicates that the material may be reaching the autoignition point. This mechanism is speculated to be the origin of the flash systematically observed.

SUMMARYWe demonstrate the locking-free properties of the displacement formulation of p-finite elements when applied to nearly incompressible Neo-Hookean material under finite deformations. For an axisymmetric model problem we provide semi-analytical solutions for a nearly incompressible Neo-Hookean material exploited to investigate the robustness of p-FEM with respect to volumetric locking. An analytical solution for the incompressible case is also derived to demonstrate the convergence of the compressible numerical solution towards the incompressible case when the compression modulus is increased.

A finite element methodology to predict the behaviour of Dyneema® HB26 fibre composites at quasistatic rates of deformation, under low velocity drop weight impact, and high velocity ballistic impact has been developed. A homogenised sub-laminate approach separated by cohesive tied contacts was employed. The modelling approach uses readily available material models within LS-DYNA, and is validated against experimental observations in literature. Plane-strain beam models provide accurate mechanisms of deformation, largely controlled through Mode II cohesive interface properties and kink band formation. Low velocity drop weight impact models of HB26 give force-deflection within 10% of new experimental observations, with in-plane shear strain contour plots from models directly compared with experimental Digital Image Correlation (DIC). Ballistic impact models utilising rate effects and damage showed similar modes of deformation and failure to that observed in literature, and provide a good approximation for ballistic limit under 600 m/s impact speed.

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