This report delineates the rate sensitivity of three commodity thermoplastics and assesses the appropriateness of assuming simple rate dependence in finite element analysis. Polycarbonate does indeed show simple rate dependence in the plastic region with very rapid adjustment from one rate to the next; thus, a rate dependent model is an accurate representation. Acrylonitrile/Butadiene/Styrene (ABS) does not exhibit such large plastic strains and is a bit more complex with a process of craze formation leading to more variable necking and failure. It also shows a rapid transition from one rate to another, but superimposed failure processes impart considerable variability. Assuming simple rate dependence is a reasonable approximation and directionally correct. An impact-modified polypropylene exhibits craze formation, a very low Poisson's ratio to large extensions and simple rate dependent behavior before failing. At elevated temperature, it draws and forms a stable neck and again shows simple rate dependence. However, the processes of failure and transition to necking are not simply rate dependent and this will keep this assumption from being generally valid.
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