Behavior of Fatigue Crack Growth Paths in Peculiar Anisotropic Commercial Pure-Aluminum Sheets (A1100P)

Abstract

Behavior of fatigue crack that grows to the rolling direction about 30 degrees to the loading direction as a mixed mode I + II crack in peculiar anisotropic commercial pure aluminum sheets (A 11110 p) was investigated using CCT specimens. From fatigue tests, it was found that the crack started to change the direction from mode I to the rolling direction when mode I stress intensity factor range was 4.2 MPa·mm1/2 and crack grew continuously to the rolling direction when mode II stress intensity factor range was 4.3 MPa·mm1/2 under small scale yielding state. However, in the case of specimen annealed in 563 k, 30 minutes, the crack did not grow to the rolling direction. The crack that grew on the rolling direction changed direction to mode I direction, due to the nominal stress which was about 80 percent of yield stress. According to the measurement on crystal planes using X ray diffraction, it was found that the slip plane of aluminum. (III) plane dominantly existed on the fracture surface of the crack that grew to the rolling direction. From pole figures, it was also verified that strong textures of (III) planes existed in rolling direction, so that the shear strength on the rolling direction was low as confirmed by shear test. Due to the strong textures of (III) planes that exist around the maximum shear stress region, the mode II crack component becomes easily to occur that makes the mixed mode I+II crack to grow to the rolling direction around 30 degrees towards loading direction.