Investigation of the Failure of an Automobile Torsion Bar
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This paper presents the failure analysis of a steel torsion bar of the automobile suspension system. The bar fractures in service and the fracture surface was 45° to the axis of the bar, with radial marks and shear lips, characteristic of the brittle fracture of a mechanical element under torsion. Scanning electron microscope was used to characterize the fracture surface that did not present evidence of extensive plastic deformation. The torsion bar fracture initiated at a weld point which had produced a fatigue crack and a martensite transformation in the heat-affected zone. The instrumented indentation technique was used for the mechanical characterization (microhardness and elastic modulus) of the microscopic and macroscopic regions near failure. The heat-affected zone was approximately 400–600 μm in thickness and the weld was a “point” approximately 4 mm diameter. The results obtained allowed differentiating the tempered martensite from the martensite (without tempering) in the heat-affected zone, the latter being 47% harder.
KeywordsTorsion bar Weld Failure analysis Instrumented indentation
The authors thank CNPq, the Surface Phenomena Laboratory (LFS) at the University of Sao Paulo and the reviewers for contributing to improvement of the paper.
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