2006 Volume 55 Issue 4 Pages 402-408
Effects of rolling ratios, microstructures and crystal orientations on the fatigue cracks that grow on the rolling direction as mixed mode I + II cracks in pure aluminum sheets were investigated by conducting fatigue tests. The CCT specimens were used and made from cold-rolled pure aluminum sheets with rolling ratio of 50%, 75%, and 90%. It was found that the cracks grow to the rolling direction as mixed mode I + II cracks in the specimens with rolling ratio above 75%. It was also confirmed that microstructures in the high rolling ratio specimens are smaller and more elongated to the rolling direction than those with lower rolling ratio. However, there was no effect of microstructure size on the fatigue crack path. The crystal planes on the fracture surfaces and the slip plane of aluminum, (111) planes in the sheets were measured using X-ray diffraction. It was found that (111) planes mainly existed on the fracture surface of the crack that grew on the rolling direction. In addition, there were strong textures of (111) planes on the rolling direction of specimens with rolling ratio higher than 75%. It was clarified that the fatigue cracks, which grow to the rolling direction as mixed mode I + II cracks, are caused by strong textures of (111) planes on the rolling direction that exist in the maximum shear-stress region.
