A new drop weight tester system was developed to obtain compression stress-strain curves of the aluminum alloy A2024 (JIS) and PMMA (polymethyl methacrylate) at a medium strain rate of approximately 100 s-1. To evaluate the strain rate or the strain of the specimen it has been necessary to measure the motion parameters, i.e., velocity or displacement, of the tup and anvil. In this new method, the velocity and displacement of the tup and anvil, which were in contact with both end surfaces of the specimen were computed on the basis of the equations of motion of the tup and anvil, respectively. The differential equation, in which the measured dynamic force versus time characteristics were contained, was integrated by the Runge-Kutta method using Microsoft Excel. For the aluminum alloy A2024, stress was not markedly affected by strain rate. On the other hand for PMMA the stress was affected significantly by strain rate.
FeMnSi-based shape memory alloy (SMA) is expected to be utilized for pipe installations and large structural members. Since the shape recovery action in these applications must evolve under a stress, it is important to grasp the shape recovery behavior under a controlled stress. In this study, the shape recovery behavior of FeMnSi-based SMA under a constant stress is investigated in detail, and the interpretation based on the mechanism of stress-induced martensitic transformation, which controls the shape recovery action of FeMnSi based SMA, is conducted. The stress applied to oppose the reverse transformation decreases the degree of shape recovery and increases shape recovery temperature. On the other hands the stress applied to assist the reverse transformation increases the degree of shape recovery and decreases recovery temperature. The effect of the type and amount of prestrain on the shape recovery force is also studied. The degree of shape recovery and shape recovery force shown for FeMnSi-based SMA should be useful in designing pipe joints as well as structural members with knowledge of the results and the interpretation presented in this study.
Pressure and frictional stress distributions on the contacting surface between a billet and a container have been investigated during the hot extrusion of aluminum alloy 6063 using sensors that have been developed by the authors. Frictional stress increases with the distance from the die and is markedly high in the front part of the dummy block. The distribution of friction is caused by the shearing deformation between the boundary material fixed on the container surface and the central part moving to the die exit. The relations with the internal deformation and stress state have been investigated by FEM analysis. Furthermore, the influences of several parameters in the extrusion on the pressure and frictional stress distributions have been observed. Knowledge of the friction between the billet and the container surface is useful for setting the proper extrusion conditions to achieve extruded material of constant quality.