Characterization and Failure of an Automotive Ball Joint

Burcham, M. N., Escobar, R., Jr., Yenusah, C. O., Stone, T.W., Berry, G. N., Schemmel, A. L., Watson, B. M., & Verzywyvelt, C. U. (2017). Characterization and Failure of an Automotive Ball Joint. Journal of Failure Analysis and Prevention. 17(2), 262-274. DOI:10.1007/s11668-017-0240-4.

Abstract

This case study describes the failure analysis of an automotive lower ball joint that fractured under normal driving conditions. Through spectroscopy, the material was determined to be SAE-AISI 5135H steel. The metallographic examination revealed a tempered martensitic structure, and hardness measurements radially across the surface of the cut ball stud suggested that the stud was through hardened. Scanning electron microscopy of the fracture surfaces indicated fatigue as the main failure mechanism. Finite element analysis was used to analyze the performance of the part under a normal loading condition. A detailed fatigue analysis to determine the effect of various loads on the life of the ball joint was completed using three methods: S-N curve approximation using hardness values, S-N approach using Basquin’s equation, and a linear elastic crack-growth model. The cause of failure was determined to be from surface cracks forming in the high stress concentration neck region where the ball and stud are joined. The presence of a small surface flaw in this region was shown to significantly reduce the fatigue life of the ball joint.