Fretting fatigue crack initiation behavior using process volume approach and finite element analysis

This study investigates crack initiation behavior by incorporating fretting fatigue process volume. Three critical plane based fretting fatigue crack initiation parameters are characterized by computing their averaged values over the process volume and then comparing with their counterparts obtained from the localized approach. Two approaches are used: first one involves the computation of parameter at several points over a rectangular region and then its average, and second approach computes the average state of stress/strain over a radial region from which the averaged parameter is calculated. Both approaches require pre-determination of a critical location at or around which the process volume needs to be placed. Effects of size and location of process volume on the averaged value of parameters are studied in detail. Two radii of cylindrical pad are analyzed to investigate the effect of severity of stress gradient on process volume approach. Effects of finite element mesh refinement are also investigated. Averaged value of parameter decreases with the increase of process volume size. This decrease is higher when the process volume is located in the region that is away from the contact zone. Further, a parameter based on normal stress on the critical plane shows more dependence on the size of process volume than that based on shear stress or on a combination of both shear and normal stresses. Orientation of crack initiation changes within a range that is well within the scatter band of experimental observations as the process volume size increases. Averaged value of parameter for a pad with higher stress gradient has a larger reduction with the increase of process volume size than that with a lower stress gradient. Process volume size has less effect on the averaged value of parameter with coarser finite element mesh. Finally, the localized approach provides a conservative value of fretting fatigue crack initiation parameter compared to its counterpart based on the process volume.