Effect of elevated strain rates on the mechanical performance of polyethylene structures
The theme of this research was the development of an integrated approach to establish how the stiffness of a thermoplastic material could be measured and modelled for use in impact simulations. By undertaking this an understanding was obtained of how thermoplastic materials behave and the structures that are made from them perform when subjected to mechanical impact loads. A series of tensile tests was undertaken using three control methods to establish a tensile test control method suitable for a wide range of strain rates. The effect of applied strain rate on the mechanical performance of High Density Polyethylene (HDPE), as illustrated by the tensile stress-strain curve, was investigated. Tests were performed at various elongation rates and temperatures to simulate different practical operating conditions. Extensive use of the finite element method was made in simulating the mechanical impact performance of various beam, disc and automotive fuel tank structures with the predictions of these analyses being correlated with experimental test data. The research is novel and of direct practical relevance as indicated by the prediction and correlation with experimental data, of the impact performance of a HDPE fuel tank, which to the author's knowledge has not been previously done. The demonstrated methodology thus provides a significant advance in the prediction of the impact performance of components made from polymers, whose mechanical performance is strain rate sensitive.