High strain rate testing of metals

Abstract

Tensile and compressive tests were carried out on a selection of metals of interest in engineering applications. These metals were tested at a range of strain rates and temperatures with the aim of calibrating material constitutive models for the simulation of full scale structures in industry. In order to validate these models for use under conditions of strain rates exceeding those imposed by the tests which were used for calibration of the models, both tensile and compressive ballistic tests were carried out. A ball on plate experiment was used to compare the deformation predicted under the tensile conditions, including high speed speckle DIC for out of plane displacement measurement. A bespoke gas gun for the purpose of carrying out Taylor impact tests on samples of the same materials was designed and installed at Imperial College. The gas gun was used to carry out Taylor tests which were also lmed at high speed for comparison with tests simulated under compressive loading. Furthermore, post-impact samples were sectioned so that a hardness survey could be carried out across the internal section of a sample. These data were combined to produce a map indicative of plastic strain within the sample and used as another validation tool for the model using the Taylor test. It was found that the Johnson-Cook model was not su cient to represent the materials at the conditions under study. Both the ball on plate and Taylor test comparisons revealed the discrepancy between the model and the actual material response. Furthermore, the hardness map of the post test Taylor cylinders revealed that a volume within the cylinder at the base of the bulge experienced less hardening than the volume around it, consistent with predictions made from the nite element analysis.