FATIGUE CRACK INITIATION IN METALLIC MATRIX

This paper will provide a study on the behaviors of fatigue crack initiation in metal matrix in five metallic materials using very high cycle fatigue testing and electron microscopy with electron backscatter diffraction and electron channeling contrast technique. The damage and crack initiation mechanisms in metal matrix have been focused. It shows that straining in these materials during the fatigue process was highly localized. This strain localization has led to the damage or fatigue crack initiation at grain boundaries or twin boundaries by impingement cracking. High strain localization causes dislocation accumulation during each cyclic straining and consequently the formation of local "fine grain zone" that increases the local damage by plasticity exhaustion. This can cause the formation of fatigue crack origin in the matrix. Strain localization and local plasticity exhaustion can be used to explain this phenomenon.