An experimental study and fatigue damage model for fretting fatigue

Fretting is associated with the small amplitude relative oscillatory motion between two solid surfaces in contact. Fretting fatigue is a damage mechanism observed in a machine components subjected to fretting in tandem with fluctuating bulk stresses. This paper presents the results of an experimental investigation of the fretting fatigue behavior of AISI 4140 vs. Ti-6-4 in a cylinder-on-flat contact configuration, and a computational fatigue damage model of the same configuration. In the experimental investigation, a fretting test fixture was designed and developed which was coupled with an MTS machine to impose the fretting fatigue damage. Fretting fatigue experiments were conducted under completely (R=−1) reversed axial stress amplitudes, a constant maximum Hertzian Pressure (Ph) of 3 GPa and at a frequency of 5 Hz. The test rig was also used in a fretting wear configuration under gross slip conditions to determine coefficient of friction for the same contacting pair of materials. In the computational modeling, damage mechanics constitutive relations were incorporated in a finite element model to analytically investigate the fretting fatigue. Voronoi tessellation was used to account for the randomness of the material microstructure and its effects on the fatigue behavior. Material properties needed for the damage model were determined using the analytical solution for maximum fretting stress (σfretting) at the trailing edge of the contact which is assumed to drive the fretting fatigue failure. The critical damage value for AISI 4140 was extracted using the method of variation of elasticity modulus. Fretting fatigue lives predicted from the analytical model show good agreement with the measured experimental results.