Towards a faster determination of high cycle fatigue properties taking into account the influence of a plastic pre-strain from selfheating measurements

Abstract

The high cycle fatigue (HCF) is a major element for a great design of automotive parts. A wide part of the steel sheets for the automotive industry are stamped, sometimes deeply. During this operation, the steel is plastically strained in different directions, so that a good prediction of the fatigue behaviour requires the determination of the fatigue properties of the pre-strained material. Nowadays, the evolution of HCF properties is often neglected. There are two major reasons for this lack. On the one hand, a good finite element simulation of the forming operation to predict pre-strain field is still a difficult task. On the other hand the time dedicated to traditional fatigue test campaigns (e.g. staircase method) to quantitatively identify this influence is prohibitive. To determine faster this influence, it is proposed to use self heating measurements under cyclic loadings. To illustrate this approach, different pre-strain paths are studied: shear and tension. Finally, a model taking into account the influence of pre-strain on high cycle fatigue properties is proposed and identified from self-heating measurements. The validation of the proposed approach is obtained by predicting S/N curves for pre-strain to 20% of a dual phase steel.