Ultra high molecular weight polyethylene deformation and fracture behaviour as a function of high strain rate and triaxial state of stress

The dynamic response and fracture characteristics of Ultra High Molecular Weight Polyethylene (UHMWPE) were investigated both experimentally and numerically. The strain rate sensitivity of the material was studied by carrying out tensile tests on smooth cylindrical specimens over a range of high strain rate conditions using the purpose built 'flying wedge' testing machine at separation velocities up to 9 m/s. The effect of the initial stress triaxiality conditions on the material's ductility at different strain rates was studied using pre-notched cylindrical specimens with different notch radii. The true stress-strain results indicated that the tested material is highly sensitive to strain rate changes. Post-fracture geometric measurements of the fractured specimens indicated that the ductility of UHMWPE is strongly dependent on both the initial stress triaxiality conditions and the strain rate. Numerical simulations of the quasi-static and high strain rate tests were used to predict, for different notch radii, variation of the centre-most element radial strain and stress triaxiality factor with the average radial strain. Based on the combined numerical and experimental results, a simple relation for the ductile fracture of UHMWPE was derived as a function of stress triaxiality and strain rate.