Experimental Investigation of Crack Propagation and Strain Fields Evolution around a Crack Tip in 5A05 Aluminum Alloy

In situ scanning electron microscopy three-point bending test was employed in this study to investigate the crack initiation and propagation in 5A05 aluminum alloy. The microscale strain fields around the crack tip were measured by using the geometric phase analysis method. Results show that prior to the crack initiation, the normal strain εyy (y direction is perpendicular to the load direction) was tensile around the notch, whereas the normal strain εxx (x direction is parallel to the load direction) was compressive around the notch. The shear strain εxy was nearly zero. With the increase in load, the normal strains εyy and εxx gradually increased, but the change in shear strain εxy was not evident. When the stresses at several sharp points at the notch root reached the breaking strengths, a few microcracks initiated at these points. At this moment, the normal strains εyy and εxx were much greater than the shear εxy, and dominated the strain fields around the crack tip. In the crack propagation process, the normal strains εyy and εxx, and the shear strain εxy dominated the strain fields around the crack tip, thereby leading to a Z-form of crack propagation path in the specimen.