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The fretting problem is one of the main factors that cause the failure of mechanical connection structures. Most studies are currently conducted under constant normal contact load conditions. However, in many practical engineering problems, the multi-axis loading conditions with variable normal load and axial load widely exist and lead to the fact that the current research results on the fretting motion operation mechanism can not well explain the fretting behavior under multi-axis loading conditions. Therefore, firstly based on the traditional fretting fatigue model, the micro-oscillation behavior and dynamic characteristics under the combined action of cyclic alternating normal load and axial load were analyzed, and a Q-P curve analysis method was proposed. Secondly, the functional expression between the biaxial alternating load parameters and the micro-motion operating state was derived. Finally, the effects of different loading parameters (mean value of normal load Pm, amplitude of normal load Pa, mean value of bulk load FB,m, amplitude of bulk load FB,a , phase difference φ of biaxial loading and stiffness ratio Rsti) on the shape and position of Q-P curves were discussed separately. The research results show that the Q-P curve is a linear function under proportional loading and an elliptical function under non-proportional loading. The loading parameters affect the shape and position of the Q-P curve. The Q-P curve analysis method provides an effective characterization method for micro-motion failure analysis under complex alternating loads. [ABSTRACT FROM AUTHOR]

Fretting wear is one of the main forms of failure of mechanically connected structures. Most of the current studies are based on constant normal contact loading conditions. However, in actual engineering, there are widely existing multiaxial loading conditions with variable normal load and axial load, which leads to the fact that the results of the current research on fretting wear under constant normal load cannot explain the fretting wear behavior under multiaxial alternating loading conditions. Therefore, taking the fretting wear of titanium alloy as an example, simulation analysis and experimental test study of fretting wear under variable biaxial loading was carried out. Firstly, a fretting wear model subjected to cyclic alternating biaxial loading was established. Then, the fretting wear behaviors were simulated under different normal load amplitudes, displacement load amplitudes, and phase differences of biaxial loading. Based on the Q-P curve analysis method, the fretting wear mechanisms under these complex micromotion cases were discussed. Finally, the biaxial fretting wear test was carried out on a biaxial fretting wear tester, which verified the rationality of the wear morphology of the finite element model. The research results show that the wear scar of the variable normal load is different from that of the constant normal load, the mean value of the normal load under the variable load remains the same as the value of the constant normal load, the wear depth and width under the variable normal load are larger than those under the constant normal load. For a certain displacement amplitude and phase difference, the wear width and depth increase with the increase of normal load amplitude, and the wear scar changes from " W" to " W + V" . For a certain normal load amplitude and phase difference, the wear width and depth increase with the increase of displacement amplitude. For a certain normal load amplitude and displacement amplitude, when the biaxial loading phase difference changes, the maximum wear depth of 0 ° phase difference occurs in the contact trailing edge, the maximum wear depth of 180 ° phase difference occurs in the contact leading edge, and the wear depth of the leading and trailing edges of the 90 ° and 270 ° phase difference are close to each other in the extreme value. [ABSTRACT FROM AUTHOR]