High Strain Rate Sensitivity of Ultra-High Molecular Weight Polyethylene and its Consequence on Cold-Spray Deposition Behavior

The yield and flow in Ultra-High Molecular Weight Polyethylene (UHMWPE) are complex and sophisticated compared to metals due to their dependency on time, temperature, strain, strain-rate and the history of the polymer processing. Hence, uncovering cold spray deposition mechanism requires a detailed understanding of strain rate sensitivity of UHMWPE. In this research work, powder sintered UHMWPE of 10.5 Mg/mol was subjected to various strain-rates ranging from 10^-2s^-1 to 10³s^-1 via low compression strain-rate testing and Split Hopkinson Pressure Bar testing (SHPB). The experimental true stress-strain curves in compression of a sintered UHMWPE at pre-yield, yield point and post yield were analyzed. The pre-yield and yield point region, 10.5 Mg/mol UHMWPE exhibited an increase in the tangent modulus and the yield stress with an increase in strain rate. Further, the post yield phenomenon in UHMWPE shows no apparent post yield softening and shows an increase in the strain-hardening with increase in the strain-rate. The curves at increasingly higher strain rates showed an increasingly pronounced bi-linearity to its flow behavior with the rate of hardening increasing above 10~15% strain. Under the domain tested, the strain rate dependence for UHMWPE can be depicted by a logarithmic fit.