On the use of thin wafers to study dynamic properties of metals

Abstract

Many different impact test arrangements have been utilized to investigate the dynamic properties of metals. This paper discusses the applications and limitations of a one-dimensional theory of bar impact, particularly as it relates to a specific experimental configuration known as the ‘thin wafer’ or ‘split Hopkinson pressure-bar’ technique. An analysis of this experiment, which utilized a bilinear approximation for the stress-strain curve of the aluminium being tested, led previous investigators to demand the incorporation of strain rate effects in the constitutive relation of metals. However, the present nonlinear analysis of the same test demonstrates that the experimental data for this particular metal can be predicted from a strain rate independent theory. This new analysis indicates the influence of assumptions which neglect certain stress wave propagation phenomena. These mechanical effects are shown to be an important contribution to dynamic observations which had been attributed only to intrinsic material properties, such as strain rate dependence.