Application of Copper Electroplating Method to an Element that Changes the Principal Axes of Strain (Superposing Static Torsion on Rotating Bending)

Abstract

A copper electroplating stress measurement method is applied to an element that changes the biaxial stress ratio in stress cycle over time. First, we originally produced a fatigue testing machine that was able to produce the combined stress state of rotating bending and static torsion. Since static torsion makes the biaxial stress ratio change over time, we examined the effect of static torsion on the grain growth by comparing the plane bending tests that do not change the biaxial stress ratio. The critical shearing stress at which grain growth occurs for a prescribed number of cycles and the grain growth rate almost the same values in the plane bending test and the rotating bending-static torsion test. These results mean that the static stress that is superposed on cyclic stress has no effect on grain nucleation and grain growth. The main reason for this result is that the magnitude and direction of the maximum shearing stress amplitude are equal in both cases.