Effect of strain rate change during uniaxial dynamic tensile tests on instability strain

Abstract
In order to investigate the effect of strain rate change during dynamic tests on the stress-strain curves, an analytical study using the maximum load condition and a simple constitutive equation, [MATH], was carried out. Three kinds of typical loading pulse, i.e. a usual constant incident pulse, an acceleration pulse and a deceleration pulse, were chosen. When the incident pulse is assumed to be [MATH], these pulses correspond, respectively, to the cases with β=0,β>0 and β<0. From the analysis, an instability strain or a strain at maximum load point, ε^*, was derived to be [MATH]. It was found that the instability strain increases with the increase of acceleration parameter, β, of loading pulses. To check this analytical result, a series of dynamic tensile tests for 0.45%C steel using SHPB apparatus was performed with the three types of loading pulse. A tapered striker tube was used for acceleration and deceleration dynamic tests. The experimental result agreed well with that predicted by the analysis.