Abstract
The essence of rolling contact fatigue is so-called “Mode II fatigue crack propagation.” However, its understanding has not progressed as much as that of Mode I. When cyclic Mode II loading is applied, plastic strain localizes in a region depending on the crystal structure ahead of the crack tip, crack initiates repeatedly and crack propagates by its coalescence. This will be termed “damage accumulation mode fatigue crack propagation.” In this study, localization and progress of plastic strain were successively observed during damage accumulation type fatigue crack propagation, and the relationship between plastic strain and microstructure was observed under cyclic Mode II loading by using digital image correlation (DIC) method. We used perlite steel as a test material. As a result of the DIC analysis, plastic strain localization was observed ahead of the crack tip by cyclic Mode II loading. The plastic strain was localized at the interface of the microstructure. Crack propagation was observed from the location where plastic strain is localized. In pearlite steel, when cyclic Mode II loading is applied, strain concentrates due to the discontinuity of deformation at the interface of the microstructures, and crack initiation and coalescence along the interface causes damage accumulation mode fatigue crack propagation.
