13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- 4. FEM computation of the Stress Intensity Factor's (SIF) evolution below the fretting contact 4.1. Contact modeling A 2D-plain strain FEM modeling of the studied plain fretting test was developed. All the elastic and friction properties previously defined during experiment tests were implemented in the FEM-model. The fretting model is composed of a fixed plane and a moving cylindrical pad (Fig. 5). The mesh is composed of triangular (CPE3) and quadratic (CPE4R) linear elements. Quadratic elements were used to define the crack tip zone in a round domain of a radius of 5µm. Outside the crack tip zone, triangular elements were considered in order to reduce time costs. The mesh size in the contact zone was refined down to 20 µm in order to provide a more accurate estimation of the contact stress fields. The contact and the crack were described by a master-slave algorithm, and the tangential loading was determined by Lagrange multipliers through a constant friction coefficient (µt=0.85). During a computation, a fretting cycle were reproduced through the introduction of a normal load P=436.5 N/mm and through the application of a cyclic tangential cycle with a Q*=200 N/mm. Figure 5. FEM description of the plain fretting cracking experiments a) FEM model - b) Loads applied As elastic loads were imposed, the cracking computation was restricted to a single loading cycle. Results and interpretations were made for a single crack located at the trailing contact border (x=-aH) at the loading stage (Q=Q*) which infers an open crack condition (Fig. 5).
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