Research On Multi-Axial Fatigue Prediction Of Steel Wheel Considering Forming Effects

Dynamic bending fatigue life is one of the most important performance indexes for automotive wheel. At present, the fatigue life prediction methods are still based on nominal stress approach or local stress-strain approach. However, these methods have not considered the effects of forming process, and mostly ignored the multi-axial stress state at the surface, which make the analysis result inconsistent with the actual and difficult to be applied in engineering practice. Therefore, Research on the multi-axial fatigue life prediction of automotive wheel considering the forming effects is one kind of new way.Adopting incremental forming numerical simulation and grid mapping technology, combined with multi-axial fatigue damage model and FEA method, the multi-axial fatigue life prediction method is discussed in this paper, accurately predicting fatigue life for the automotive wheel. This method aims to pre-analyze the residual stress and thickness variation caused by forming process before wheel structure analysis, and introduces the pre-analysis results to structure analysis and fatigue life prediction to obtain more reliable analysis and prediction results. Mainly includes the following aspects work:1,The multi-step forming process of the wheel was numerically simulated adopting incremental approach, and the drawing process was improved to solve the crack problem during the inverse-drawing process, reducing the thickness thinning rate, improving the formability and providing reliable guidance for the making of forming process and designing of mould.2> One key problem in structure analysis considering the forming effects is how to introduce the forming results into structure analysis. In this paper, the mapping method and ANSYS Parametric Design Language (APDL) were adopted to solve the data exchange problem between DYNAFORM and ANSYS, realizing the organic combination of structural FEA and forming numerical simulation. The structure FEA model was established according to the bend fatigue test, and the effects of forming residual stress and thickness variation on the wheel strength and stiffness were researched.3,About the problem of fatigue life prediction, the multi-axial stress state is determined at one key point. Based on the concept of multi-axial fatigue damage plane, the direction of the critical plane was determined and the shear strain and normal strain history on the plane was obtained, the multi-axial fatigue model of Brown-Miller was adopted to predict the fatigue life and the effects of forming process on multi-axial fatigue was discussed.4,Through dynamic bending fatigue test of N1 type wheel, verifying the effectiveness of predicting multi-axial fatigue life considering forming effects.