Fracture Analysis on Screw of Brake Drag Link

A screw of the brake drag link of a car was found to have broken after repeated dismounting. The failure cause of the screw was analyzed by macroscopic and microscopic examination of fracture surface, metallographic examination, microhardness testing, and thermal simulation testing. The results show that the failure mode of the crew is over-loading fracture. Without modified treatment, the strength of the material and the toughness was poor. Besides, the screw might have experienced the coeffect of abnormal impact load and flexural load during service. As a result, the screw fractured at the joint of nut and screw. Strict heat treatment processing should be carried out to improve the strength and toughness of the material.