Fretting occurs when two bodies in contact are subjected to small-amplitude oscillations. It involves two complex structural damage mechanisms: wear and fatigue crack initiation, both of which are driven by steep stress gradients in the contact region. In this thesis, a phenomenological macroscopic wear law is formulated based on microscopic information, such as the dynamic evolution of the debris layer and contact surface properties. To predict the fatigue life of Ti-6Al-4V alloy, a continuum damage mechanics (CDM) approach combined with the critical plane concept is implemented. A damage law based on CDM is proposed to accurately describe the crack initiation process under proportional and non-proportional cyclic loading conditions. The evolution of debris layer and wear profiles are proposed by the evolving debris layer and local ejection, which is defined by the volume fraction of ejected debris related to the accumulated debris thickness. The numerical algorithms of the proposed wear model are developed and implemented via the user subroutine UMESHMOTION in the commercial finite element software ABAQUS. The proposed fretting wear model with debris layer and local ejection effects are able to provide a more accurate estimation of the wear profiles in different wear configurations compared to the wear model without debris effect. To investigate the fretting fatigue mechanism of Ti-6Al-4V alloy in a cylinder–plane contact system, a series of fretting configurations were constructed with varying relative slip ranges under in-phase loading. A critical relative slip range can be identified by the significant change in the hysteresis loop between tangential force and relative slip, distinguishing the transition from partial slip to gross sliding. The lowest fretting fatigue life occurs at the critical relative slip range. Fretting fatigue life declines with increasing relative slip ranges under partial slip conditions. However, fretting fatigue life increases with the relative slip range increasing under gross sliding conditions, while wear becomes the dominant mechanism in the fretting process. Fretting fatigue initial crack under out-of-phase loading is also investigated in the present work, considering three types of phase differences in the loading conditions applied to the specimen: (1) a phase difference between the normal force and the axial stress, while the axial stress and the fretting slip displacement remain in phase; (2) a phase difference between the axial stress and the fretting slip displacement with a stress ratio of Rₛ = 0. 03 ; and (3) a stress ratio of Rₛ = -1. No obvious differences in fretting hysteresis loops and wear profiles are observed under phase differences between the normal force and the axial stress (or the relative slip range). However, phase differences between the axial stress and the relative slip range can significantly affect fretting life, failure locations (hot spots), and the orientation of initial crack plane. Therefore, to accurately predict fretting fatigue life, not only the magnitude and combination of the applied loads, but also the effects of out-of-phase loading must be considered.
Le Zhang (Thu,) studied this question.