Formation mechanism of two different crack surfaces in a median crack formed by scribing wheel

Abstract Two types of crack appearances may be observed in a median crack formed by scribing wheels. A cracked surface with a striped pattern and smooth cracked surface are formed, and a distinct crack-arrest line is formed at the boundary between them. This study explored the mechanisms that control changes in crack surfaces. The median crack caused by wheel scribing propagated within a symmetric stress field composed of axial and shear stresses. Numerical analysis revealed that the direction of the shear stress changed in regions that formed cracks with stripe patterns and smooth cracks. Depending on the combination of the crack propagation direction and symmetry shear stress direction, the crack propagated toward or deviated from the symmetry plane. These crack-propagation characteristics caused differences in the appearance of the crack surface. The existence of an area behind the scribing wheel where the crack temporarily stopped was predicted by estimating the crack behavior based on the stress intensity factors. This temporary crack stop was the cause of the distinct crack arrest lines. This study suggests that crack propagation behavior and surface appearance of cracks can be controlled by generating a symmetrical shear stress field in an appropriate direction.