Abstract
Fatigue damage analysis was performed in order to predict the fatigue life of an automotive drag link, which is very critical for vehicle safety. Uniaxial specimens taken from the drag link tube were used for the monotonic tensile test and strain-controlled low-cycle fatigue test, which resulted in the monotonic and cyclic properties of the drag link steel. Finite element method was employed to determine local stress and strain distributions of the drag link. The experimental stress analysis was performed using strain-gages in order to verify the accuracy of the finite element analysis results. Calculated local strains at the curved region of the link were close to the experimental strains within 8 percent difference. STKM12C steel used for the drag link exhibited cyclic softening behavior. Cyclic yield strength was about 25 percent lower than the monotonic yield strength. As expected by the finite element stress analysis, cracking occurred at the curved region of the tubular steering drag link rod and propagated circumferentially to the opposite side of the link rod, resulting in the final fracture. Based on the fatigue life curves and the finite element stress analysis results, the fatigue life of the drag link was predicted and compared with the experimentally determined fatigue life. Predicted fatigue life of the drag link correlated fairly well to the experimental life within a factor of three.
