Microstructure evaluation and crack initiation crack for AZ31 sheet under biaxial stress

Abstract

In this study, a biaxial tensile test of cruciform specimens containing centre notch was conducted with a miniature biaxial tensile test system in order to clarify the deformation behavior near the crack tip at the early stages of crack initiation when objected to a biaxial stress state. Stress distributions were determined by X-ray diffraction stress measurement, and the crack initiation angle was predicted by modified Dugdale model. The microstructure evolutions were investigated by the electron backscatter diffraction technique. The deformation twins were formed at the biaxial tensile test due to the creation of a large stress field near the crack-tip region. The formation region of deformation twins became small with the equiaxial tension due to the lower stress concentration. Observation of the microstructure reveals that the deformation is dominated by basal slip under equal biaxial tensile loading. The asymmetrical biaxial tensile loading generates deformation twins near the crack tip. These results indicate that deformation twinning in the vicinity of crack tip is more significant in predicting the initial crack growth.