Strain rate sensitivity of the in-plane mechanical properties of two UHMWPE thin ply composites

The mechanical characterisation of two recent grades of Ultra High Molecular Weight PolyEthylene (UHMWPE) fibres composite is proposed. Used in bulletproof vests, they share the same type of fibres, while composed of different matrices (respectively polyurethane and rubber). The in-plane characterisation is performed through tensile tests on thin layer samples at 0 degrees of the fibres and in-plane shear, in both quasi-static and dynamic conditions. Digital Image Correlation is used for each test to accurately measure strains and evaluate its homogeneity. To study the strain rate effect, various experimental methods were adapted: universal press, drop tower, Split Hopkinson Tensile Bars (SHTB). A significant increase of stiffness with strain rate was observed for both materials At 0 degrees, it transcribed into an increase of 60% for the Young's modulus, and 40% on failure stress. The in-plane shear modulus was multiplied by two and even eight depending on the considered grade.