| At present an important subject is researched on prediction methods of the initiation life of rolling/sliding contact fatigue of surface hardening layer based on shakedown theories under cycle contact loading for the strategies of applications of contact element, such as gears, bearings, and railroad rails. In this thesis, the strain-hardening model of contact surface layer, the numerical theories and computational methods for shakedown analyses of contact body are systematically studied and applied to the aero-gear. The mentality is that the effects of the surface hardening and contact fatigue on contact surface layer under cycle contact loading are investigated by using shakedown analysis methods considering in a quantitative way the details of stress-inelastic strain responses, residual stress and residual strain computations. The experiment on the conclusion of shakedown analysis with the direct analysis method was conducted for proving residual stress of contact surface layer of the rolled specimen.The paper concerns itself on the following specific aspects:1. Studying on the shakedown theories and plastic deformation of contact surface layerThe shakedown of contact surface layer is related to the strain-hardening models of materials, such as isotropic hardening, kinematic-hardening, and mixed-hardening. The existing results based on experiments and theory show that the shearing strain behavior of contact surface layer caused by friction can be comparatively described with kinematic-hardening. The shakedown conditions of contact surface layer based on kinematic-hardening model was given. In this thesis, the research result was shown, kinematic-hardening contact surface layer could not involve incremental collapse, but could only cause alternating plasticity. And it also have been shown that the back stresses have effect on the shakedown limit of contact surface layer, however, there are some difficulties on the definition of back stress as the "center" of the yield surface in the Cauchy space. So, the back stress tensor is taked usually in the Lagrangian stress space.2. Studying on the shakedown analysis methods of contact surface layerA series of efficient computational approaches, for example, a direct analysis method and a line programming, for the shakedown analysis and limit is proposed, which is used to investigate the effect of strain hardening and residual stress on the shakedown limit of contact element. The direct analysis method has more efficientthan the line programming for the shakedown analysis of contact surface layer, therefore, the mentality of shakedown analysis of contact surface layer was introduced based on the direct analysis method as follows:First, the direct method for shakedown analysis was presented and its application to a two-dimensional rolling/sliding contact problem was demonstrated. The direct method consists of operator split technique, which transforms the elastic-plastic problem into a purely elastic problem and a residual problem with prescribed eigenstrains, and an incremental projection method to determine the eigenstrain. Second, the direct analysis method was applied to determine the residual stress of rolling/sliding contact between cylinder and plane. More over the limit of shakedown load of contact surface layer was computed with different friction affection. Finals, rolling and sliding contact between cylinder and plane was analyzed with ANSYS? Four contact state depending on rate of rolling/sliding between the couple of contact element were studied based on Hertz contact model, and the results was shown that the rate of slide would affect the distribution of pressure in contact area and stress in the half plane.3. Studying on prediction methods of the initiation life of aero-gear using shakedown analysis methodsIn order to directly consider in a quantitative way the details of stress-inelastic strain responses, residual stress and residual strain computations, fatigue crack initiation life was evaluated in aero-gear by using th... |
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