Shock Response and Dynamic Failure of High Density-(HDPE) and Ultra-High Molecular Weight Polyethylene (UHMWPE)

Two different polyethylene materials—high density polyethylene and ultrahigh molecular weight polyethylene—were chosen for investigation of the influence of a high percentage of crystallinity (> 60%) on the shock response and dynamic tensile failure (spall). We have applied in situ electromagnetic gauging techniques to measure the evolution of particle velocity wave profiles with wave propagation distance to elucidate the nature of the previously reported discontinuous Hugoniot at low pressures. The first evidence of a three-wave structure in highly crystalline polyethylene was measured above a shock stress of 0.4 GPa. Above this region of discontinuity in the principal Hugoniot, the transition is overdriven, and a single shock wave is observed to shock stresses exceeding 10 GPa. Further, a series of dynamic tensile experiments were performed on polyethylene to assess the dynamic tensile (spall) strength as a function of shock stress. Experiments were performed over a range of shock input stresses, and with two different types of impactors to vary the dynamic tensile condition, and the results for polyethylene were compared with earlier results for polymers such as polytetrafluoroethylene and polychlorotrifluoroethylene. The dynamic failure experiments were modeled using a failure criterion in the glassy amorphous polymer model, which captures the volumetric and deviatoric responses of polymers at low shock stresses.