Rotating bending fatigue fracture from stealth defect

Rotating bending fatigue test was performed to confirm the risk of fatigue failure due to stealth defects which are not visible on X-ray computed tomography. The fatigue test was performed on aluminum die-cast alloy ADC12 specimen that had been previously observed for defects inside specimen by the X-ray CT. After the fatigue fracture, the fracture surface was observed with a scanning electron microscope to identify the defect that became the fracture origin. When the stress intensity factor of the defect that became the fracture origin was predicted from the defect shape of the X-ray CT observation results, all the defects satisfied the crack initiation condition. When a large number of defects exist inside the material, it was found that it is difficult to identify the defect that is the starting point of fracture from CT observation results. On the other hand, it was confirmed that stealth defects cause fatigue failure. In this paper, the risk to the observation result of defects by X-ray CT was mentioned. (author)