Failure Analysis of Bulb Pin

After endurance testing of a vehicle, a bulk pin was found to have cracked. In this paper, macro and micro observation on the bulk pin were carried out. Hardness and chemical composition were tested. The results indicate that the crack of the bulk pin is bi-directional bending fatigue crack. The neck position of the pin did not have hardened layers, resulting in lower fatigue resistance. Another cause for the failure is that the pin couldn't rotate smoothly, which increased the applied force around the neck of the pin.