Influence Of Pre-torsion Processing On Fatigue Properties Of The Torsion Bar

Torsion bars are the main components in vehicle suspension systems. They are subjected to random torsion loads, and absorb deformation energy to maintain stability of vehicles. The main failure mode of the torsion bars is torsion fatigue fracture due to the repeated torsion loads during the service of torsion bars. Thus, the investigation of the new processing is very important in enhancing the service reliability of the torsion bars. The load-bearing capacity and the fatigue life of the torsion bars can be improved significantly after the pre-torsion processing. However, investigations on effects of the pre-torsion processing on torsion fatigue properties are still rare.In this study,45CrMoVA alloy steel, which is a typical material for torsion bars, is selected. Microstructures, mechanical properties under static loading and torsion fatigue properties of the steel subjected to different pre-torsion treatments were investigated systematically. The influence of the pre-torsion processing on torsion fatigue properties was also investigated. Conclusions can be drawn as follows,Residual stresses were generated in the45CrMoVA alloy steel after pre-torsion treatment, and exhibit a gradient distribution along the radial direction of the sample, varying from residual tensile stress in the center region to residual compressive stress on the surface region. The residual stress increases with increasing pre-torsion angle.As shear strain amplitude is less than0.0125,torsion fatigue strength of the steel pre-torsion treated is evidently higher than that of the steel without pre-torsion treatment. Torsion fatigue strength increases with increasing pre-torsion angle. As the pre-torsion angle is more than8.65°, the ability in enhancing torsion fatigue properties via increasing pre-torsion angle approaches saturation. Torsion fatigue fracture modes of the45CrMoVA steel were changed by the pre-torsion treatment from the shearing mode under higher shear strain amplitude to the mixed mode of the normal and shear fractures under lower shear strain amplitude, leading to a positive influence on torsion fatigue strength and lifetime.