Validation of a path-dependent constitutive model for FCC and BCC metals using "symmetric" Taylor impact

Abstract
In this study, the rod-on-rod impact geometry was used at impact speeds of ca. 200 m s^-1. This is widely believed to be equivalent to the impact of a single rod on an infinitely rigid target and hence an ideal form of the Taylor test as no real target is infinitely rigid. However, our modelling studies showed that the two rods do not behave symmetrically. Two metals were studied : AQ85 iron and XM copper. These were machined into cylinders 15mm long and 5.35mm in diameter. High-speed photographic sequences of the impacts were taken with an interframe time of 5 µs. These pictures were then digitised to obtain profiles as a function of time. The bcc material (iron) exhibited the classic "mushroom" shaped profile which was relatively easy to model as a function of time using existing constitutive models. However, the fcc material (copper) exhibited an additional bulge a few millimetres from the impact face. This behaviour proved impossible to simulate using path-independent models. It proved, however, possible to simulate the behaviour of fcc copper in the "symmetric" Taylor impact configuration using a newly-developed path-dependent constitutive model. The paper contains the results of this comparison between experiment, theory and modelling.