Comparative Study of Crack Initiation Criteria for Flat-Flat Contacts Subjected to Fretting Fatigue of Drive-Train Components

From the literature, we know that the location of failure (in relation to the specimen geometry) in fretting fatigue problems changes significantly depending on the material pairing selected and the prevailing contact parameters. Previous calculation methods were unable to determine the location of failure with sufficient accuracy. A major challenge in the strength assessment of fretting fatigue is to find a criterion that correctly predicts the location of failure. Therefore, experimental tests in the high-cycle-fatigue domain were performed on two different set-ups: a realistic component-connection and its abstraction by fretting pads. The set-ups were then numerically modelled to evaluate the local stresses. For the realistic component-connection tests, the piston rod with shrink-fitted bushing was chosen based on its numerous mentions in the subject-specific literature. The dynamic axial load on the piston rod causes a relative movement between the piston rod and the bushing, which results in fretting fatigue failure. In addition to the piston rod tests, the corresponding contact conditions were then tested using a flat-flat contact in a fretting pad experiment by using a test bench with slip control. The constant slip and pressure conditions determined in the piston-rod tests was applied to the contact between the tensile specimen and the fretting pads. Both tests were performed with the material pairings 34CrNiMo6 + QT/34CrNiMo6 + QT and 34CrNiMo6 + QT/CuSn8 (designation: base-body material/counterbody material) and revealed significantly different locations of failure. Numerical analyses of the experimental tests were then performed. The local coefficients of friction based on the frictional work were considered in the model contacts. Various crack-initiation criteria were then reviewed using the results presented. For the set-ups presented, the McDiarmid criterion gives the smallest error.