Failure Analysis of Torsion Bar in Automotive Suspension Application

摘要

Torsion bars are commonly used in pickup trucks and sports utility vehicles as the weight bearing springs. A number of torsion bars fractured during or soon after the installation in a customer's assembly plants. Investigations from several sources concluded that hydrogen embitterment was the culprit. Extensive efforts were directed to avoid hydrogen pickup in the manufacturing processes. However, a few more bars still fractured in the same manner afterwards. A review of the application mechanics indicated that the bars had a high tensile residual stress in the unyielded core after pre-setting. When loaded, the high resultant stresses at the core and the discontinuities, which had propagated into torsional shear crack during presetting caused the fractures. Thus the solution to the fractures would be to control the discontinuities in the steel, especially in the range that is yielded or close to be yielded during pre-setting.