Application of the local strain approach on a rolling point contact model

Abstract

A newly developed cold forming process, the linear flow splitting process, allows the bifurcation of thin metal sheets by severe plastic deformation (SPD). This process produces flanges with an ultra-fine grained (UFG) microstructure, which is characterized by an increased hardness and lower surface roughness in comparison to the material in as-received state. The technology is researched within the Collaborative Research Centre 666 (CRC 666) “Integral Sheet Metal Design with Higher Order Bifurcations”. The increased hardness and reduced surface roughness of the flanges make this technology suitable for manufacturing linear guide rails. In order to achieve the required reliability and fatigue strength, the assessment of the performance of the linear flow-split profiles with gradient microstructure is of great importance. When considering rolling contact fatigue, the examination of the mechanical behavior of the side of the flange with higher hardness due to the UFG microstructure is required. In order to reduce time and costs, a numerical method to determine the rolling contact fatigue behavior would be useful minimizing the normally applied experimental effort. The present work aims to check the applicability of the local strain approach for the evaluation of the rolling contact fatigue behavior of linear flow split components by a Finite Element (FE) analysis. The Hertzian theory is only valid for homogeneous materials and cannot be directly applied to the flanges with gradient microstructure. Therefore an accurate modeling of the material in order to take into account the gradient in the mechanical properties is required. In this paper the characterization of the material behavior under axial cyclic loading will be presented. These results will be used for the Bergmann damage parameter to analyze the rolling contact fatigue behavior. Some parameters required for the application of the Bergmann approach are determined by a numerical simulation of the rolling contact. Results are compared to rolling contact fatigue tests performed on a recently developed test rig under the assumption of rolling without sliding and neglecting the effect of surface roughness and residual stresses.