Uniaxial Load Specification for Vehicle Knuckle Part Using Maximum Stress Similarity in Triaxial Load Case

Knuckle parts have a complex relationship with adjacent vehicle parts, making it difficult to determine the proper fatigue evaluation specification when considering vehicle operation. An accelerated triaxial load case for the knuckle part was derived using a combination of four event modules from the test code developed by the Korea Automotive Technology Institute. The fatigue damage analysis of the front and rear knuckle models was conducted with respect to the accelerated triaxial load case, and the maximum stress was measured at hotspots for the magnitude and orientation of the critical plane. The sensitivity analysis of the knuckle models was conducted for six directions of the unit force, and the proper uniaxial force orientations of the two knuckle models were determined for the maximum stress similarity in the triaxial load case in terms of the magnitude and orientation of the critical plane. The final uniaxial load specification was derived by adjusting the magnitude of the candidate uniaxial load and the error analysis showed reliable results through inverse safety factors with 0.02, 0.04 error, and critical plane angles with 10.8, 0.8 degrees error for front and rear knuckles, respectively, verified by comparing the maximum stress similarity between the triaxial and uniaxial load cases.