On the Measurement of Shear-Strength in Quasi-isentropic Loading

Abstract

It has been a subject of discussion that the rate of loading of a material determines the strength it appears to exhibit. This observation has implications for understanding and modelling the deformation mechanisms involved in high-strain rate and shock-loading. Discussion has focussed upon the response of various metals. The loading has ranged from prompt shock to pillow loads (graded density impactors) which give uniformly rising pulses over varying times. One variant upon such loading is to allow the stress to rise in steps to a final Hugoniot level which averages to a lower rate. Clearly, while the applied strain-rate during the rise in the steps is still of the same order as that in shocks, the loading is more quasi-isentropic in nature. As a means of observing the strength of a material, the lateral stress in the sample may be monitored along with the longitudinal stress therefore allowing a direct measurement (in uniaxial strain) of the difference between these two values. Potential mechanisms explaining the experimental results and comments on the interpretation of the experimental diagnostics and design is given.

Strength behavior of materials at high pressures

“…Much higher strengths are surprising, and appear to be in error [49]. In part to address the validity of the Bat'kov et al results, Rosenberg et al [63] loaded copper, iron, and mild steel using a ''ring-up'' technique. Though the error bars were rather large, they found that the shear stress of copper was essentially the same for shock and isentropic loading to nearly 12 GPa.…”

The effect of shape and mounting on the piezo-resistive response of embedded manganin conductors

“…The rise time of the trace obtained from the grid and T gauges were ∼1.3 µs and ∼0.1 µs, respectively. In order to take advantage of the superior rise time of the T gauges, dynamic strength measurements have been made using grid gauges to measure the longitudinal stress and T gauges to measure the lateral stress (see, for example, Rosenberg et al [5]). However, a possible disadvantage with this scheme is that the construction of the two gauges are significantly different and therefore the processes controlling the resistance changes of the gauges may be different.…”