Fretting fatigue crack initiation behaviour in heterogeneous materials under out-of-phase loading.

Fretting fatigue commonly exists at the junction of contacting bodies that are subjected to oscillating force. Meanwhile, the presence of fretting will affect the fatigue lifetime dramatically, especially when the material is heterogeneous as cracks initiate at defects such as inclusions, micro-voids and micro-cracks. Fretting fatigue is a multi-axial non-proportional loading problem, in which most components and assemblies undergo asynchronous loads. Thus, investigating the influence of phase angle (Φ) in heterogeneous materials is quite meaningful. In this study, different locations of micro-voids in three different loading phase angles are taken into consideration. The critical plane approach and quadrant method are adopted to predict the crack initiation lifetime and crack orientation. It is found that the existence of micro-voids significantly affects the damage parameter, when Φ equals 180°, and plays a relatively small effect when Φ equals 90°. In addition, the crack initiation lifetime varies with the location of micro-voids since the location of micro-voids has different effects on the damage parameters. [ABSTRACT FROM AUTHOR]