Failure analysis of the fifth wheel couplings utilized in heavy semi-trailer tractors

Abstract

Fifth wheel coupling is a key component of heavy duty semi-trailer tractor, providing the link between the semi-trailer and the towing tractor. In the present work, the failure of fifth wheel coupling utilized in heavy duty semi-trailer tractors was analyzed. Firstly, the chemical composition and metallographic microstructure of the material of the fifth wheel coupling were characterized using scanning electron microscopy with an energy dispersive spectrometer. Secondly, the mechanical properties of the material was investigated by tensile tests on specimens manufactured out from the failed fifth wheel couplings. Thirdly, the stress distributions of the fifth wheel coupling under typical loading conditions were obtained via multibody dynamics analysis and finite element analysis. Finally, crack morphology and fracture surface were examined. Results showed that the chemical composition, metallographic microstructure and mechanical properties of the matrix material were in accordance with standard requirements, which rules out the possibility that the failures were caused by casting defects in the matrix material. Stresses in the crack regions were in tensile stress state under different loading cases and were much smaller than both the mechanical strength and fatigue strength of the material. Therefore, the failure of the fifth wheel couplings was attributed to stress corrosion cracking induced by tensile stress and damp environment. Measures to prevent such failures were discussed in details as well.