OS1610 ECCI法による疲労き裂近傍の転位構造観察(OS16-2 微視的な視点からの変形と強度,OS-16 ナノ・マイクロの視点からの変形と破壊の力学)

Abstract

Dislocation structures formed around a fatigue crack in copper were observed with electron channelling contrast imaging (ECCI) technique. The ECCI technique enables us to observe dislocations lying near surface using a scanning electron microscope (SEM). For a cyclically-deformed copper, self-organized dislocation structures such as vein structure were successfully observed with the ECCI technique. To investigate relationship between dislocation structure around a fatigue crack and stress concentration, a fatigue crack growth test was conducted on a center-cracked tensile (CCT) copper specimen. The ECCI observation along the fracture surface revealed that cell structures were generated at the close vicinity of the fracture surface and the vein structure existed around outer edge of the cell structure. The formation of the cell structure was affected by the degree of stress concentration: measured size of the cell-structured area l_c was a power function of stress intensity factor range ΔK_I. To estimate distribution of ΔK_I value along a fracture surface, a lot of ECCI observations of the subsurface microstructure were performed on a smooth-shape copper specimen which was fractured under push-pull fatigue. The distribution of ΔK_I value, which was calculated from the above l_c-ΔK_I relation, was consistent with crack growth direction that was predicted from striation.