Kichinosuke Tanaka

Dynamic Strength of Ti-Alloys and Al-Alloys

Continuous compression tests and incremental strain rate change tests of four kinds of titanium alloys and four kinds of aluminium alloys are carried out within the strain rate range of 10–4 ∿103/s and the temperature range of -195°∿50°C. The experimental results reveal the effects of the strain rate and the temperature on the flow stress at 5% strain. The strain rate sensitivity obtained by the continuous tests or the incremental tests is also revealed. The thermal and the athermal components of stress are presumed and the relation between the activation volume and the thermal component of stress is discussed.

Plastic Stress Wave Propagation in a Circular Bar Induced by a Longitudinal Impact

This paper mainly deals with the axisymmetric elastic-plastic wave propagation for the collision of an elastic-plastic bar with an elastic bar. The problem is analysed numerically by finite difference method. In this analysis, different types of both rate independent and rate dependent stress-strain relations are assumed for the elastic-plastic material. The calculated strain histories on the surface of the elastic bar are compared with the experimental results obtained from aluminium 1050 bar (elastic-plastic bar) and steel bar(elastic bar). The experimental results show good agreement with the calculated ones if the high strain-rate sensitivity at high strain rate \((\mathop \varepsilon \limits^{\cdot} \ge_{\!\!\!\!\!-}10^{2}-10^{3}1/{\rm{s}})\) is taken into consideration. The cases of the elastic bars collision and of the elastic-plastic bars collision are also described.

Stress rise at the impact end of a circular bar induced by its radial inertia.

Stress wave induced by the longitudinal collision of an elasto-plastic bar with either a rigid wall or an elastic bar was analysed numerically. The constitutive equation of the elasto-plastic bar was assumed to be rate-independent.A steep rise in axial stress at the impact end occurred immediately after collision and the peak value of the average axial stress within the cross section of the impact end was found to be equal to the predicted value as calculated using the stress-strain relationship in a uni-axial strain state. This is because, during a short period after impact, the immediate area of the impact end is in a state of uni-axial strain caused by its radial inertia.This high stress level dropped and relaxed as the dilatational wave propagated from the cylindrical surface to the central axis. This stress rise was apparent only in the space equivalent to one measurement of the bars diameter. Beyond that point there was no particular rise in stress.The stress level oscillated and asymptotically approached to a constant value, which is calculated by Karmans theory in a uni-axial stress state.