INFLUENCE OF THICKNESS/DIAMETER RATIO ON STRAIN HARDENING BEHAVIOR OF HIGH MOLECULAR WEIGHT POLYETHYLENE AFTER DYNAMICAL COMPRESSIVE TESTS USING HOPKINSON PRESSURE BAR

摘要

Ultra-high molecular weight polyethylene samples were submitted to dynamical compressive test in a split Hopkinson Pressure Bar. Three thickness/diameter ratio (0.11, 0.44 and 0.64) and two strain rates (3250 s-1 and 6500 s-1) were used to understand how the test set-up influences the stress equilibrium and the constancy of strain rate during the impact. Concepts of stress equilibrium, constancy of strain rate, dynamical stressstrain curves and dynamical mechanical properties of the material were evaluated. All studied samples achieved stress equilibrium, but the samples with smaller ratio achieved it more easily. Nevertheless, samples with the smallest ratio were not able to achieve strain rate constancy. Additionally, dynamical stress-strain curves were plotted to investigate the mechanical properties of this material at high strain rates. T-tests pointed out that the properties are controlled by the strain rate rather than by the specimen’s thickness/diameter ratio.