Incremental Impact Loading of Plastically Prestressed Aluminum by Combined Tension-Torsion Load

Abstract

Based on Clifton's theory we obtained the stress and strain paths for combined longitudinal and torsional impact loading of a semi-infinite tube initially pre-stressed to the plastic range by combined static longitudinal and torsional loads. We found that there were three types of stress paths according to the value of combined step loading, and that paticularly there was a region which can not be reached without unloading in spite of the loading side. Meanwhile, in order to compare the theoretical results with experimental ones, we designed an apparatus which can prestress the tube to arbitary values of tensile and shear stresses and can give incremental impact loading. Using this apparatus a tube is statically pre-stressed in the plastic range, and then sujected to an incremental longitudinal or torsional impact loading. Measurements are made of strain-time profiles at some stations along the tube. In the case of longitudinal impact, the strain response at the gages qualitatively corresponds to the arrival of a fast wave for which torsional strain decreases while longitudinal strain increases followed by a slow simple wave for which both torsional and longitudinal strains increase. But in the case of torsional impact, the strain response does not correspond to the theoretical results. In all cases the velocity of propagation of wave front was found to be that of the elastic one.