Biaxial Stress Measurement Using the Grain Growth Direction in Electrodeposited Copper Foil

A method that uses grain growth direction in copper foil to measure cyclic biaxial stress is examined in this paper. The grain growth direction is measured by image processing software after a cyclic bending-torsion test for various biaxial stress ratios is carried out. Peaks of the relative frequency distribution of the grain growth direction correspond well with the direction of maximum shearing stress, and the interval from one peak to another peak is almost 90°. These results mean that the grain growth direction is controlled by the maximum shearing stress. The principal stress is obtained with Mohr's stress circle and the peak of the curve obtained by approximating the relative frequency distribution. The number of grains necessary to measure the biaxial stress is estimated by a statistical approach. From this result, it is cleared that the area necessary for the principal stress measurement was only 9mm^2. This area is almost half of the area necessary for conventional method.