A novel approach to predict fretting fatigue crack initiation
Résumé
This approach consists of representing the movement in the vicinity of a contact front by using a set of degrees of freedom and reference spatial fields. These new variables can be used to set up a crack initiation criterion.The reference fields are built, once and for all, by a principal component analysis of the velocity field (Karhunen-Loeve transform) and are tailored to provide the best possible approximation of the velocity field close to the contact front. The intensity factors of these reference spatial fields are hence a set of non-local variables which constitute the degrees of freedom of the problem. It is shown that a very small number of them is required to accurately describe the mechanical problem. The so-called "linear intensity factors characterize the elastic part of the field while the "complementary intensity factors" characterize partial slip within the contact area. 3D finite element analyses were conducted, first to build the framework of this approximation, second to qualify its accuracy and finally to determine the non-linear response of a contact in multiaxial fretting-fatigue conditions. An incremental constitutive model was developed to predict this non-linear response and was compared to the results of the finite elements analyses. Finally, life prediction was made using a criterion built with intensity factors to estimate crack initiation for variable number of cycles. Results were compared to experimental data.This non-local representation has the advantage of being independent of the geometry of the contacting bodies. Moreover, the incremental constitutive model allows the use of this description even with coarse mesh. So, intensity factors can be used to predict the behavior of real-scale industrial assembly using data obtained on laboratory test geometry.