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This investigation studies a two-dimensional model of a layered medium subjected to the frictional excitation of a high-speed asperity traversing over the surface of the medium. The general analytical solutions of the mechanical stress state, the temperature field and the thermal stress state are obtained and expressed in the Fourier transform expressions. Numerical solutions are carried out for cases of uniform and parabolic pressure distributions. The resulting stress state yields the conditions for the asperity to initiate cracks in the layered medium. This paper studies further the thickness effect of the surface layer, the effect of relative stiffness of the surface layer and the substrate, and the effect of an insulating layer versus a conductive layer.

This paper deals with the problem of an asperity-excited thermo-mechanical field in a medium with a thin surface layer and a near surface void defect. The solutions for the temperature distribution and stress state in the vicinity of the void are obtained. Numerical results are obtained using the material properties of Stellite III for both the coating and the substrate. The parametric effects of material properties in the coating and the substrate are considered by varying the corresponding property in the coating or the substrate. The stress field solutions of the coated medium with a cavity are compared with the solutions for a single material with a cavity. In the case of the single material with a cavity, while the thermal stress is much larger than the thermal stress of the no cavity case, the principal directions of the thermal stress are not significantly changed. However, for the case of a coated medium with a cavity, not only is the thermal stress much larger than that of the no cavity case, but also the principal directions of the thermal stress are changed. The principal directions of the thermal stress field depend on both the material properties and the ligament thickness (thickness between the wear surface and the top edge of the cavity). When the angle of the principal directions becomes larger, shear delamination will initiate at the coating/substrate interface.

This paper discusses the temperature distribution and the stress state in the vicinity of a near-surface rectangular cavity. They occur when the solid is subjected to the Coulomb frictional loading of an asperity moving at moderately high speed. The finite difference method is employed to calculate both the temperature and stress fields. The energy balance method is applied at the corners of the rectangular cavity to resolve the problem of singularities in the temperature field there. The stress singularity at each corner is represented by a special element that is introduced representing the behavior of the known stress singularity at the corner and its surrounding vicinity. Results show that the thermal stress effect dominates the stress field and eventually leads to failure. When a defect, such as a cavity, exists, the stress state that determines the failure phenomenon is more severe and can be quantified depending on the location of the cavity. These results were determined through a numerical computation based on the material properties of Stellite III. However, the parametric effect of material variations including changes in both thermal and mechanical properties were also considered. The study of the cavity location also established the existence of a critical cavity location. This location is defined by the critical ligament thickness (thickness between the wear surface and the top edge of the cavity), at which the cavity-influenced thermal tensile stress reaches a maximum. This thickness is important to designers when cavities at coating/substrate interface are either unavoidable or are too expensive to control in fabrication.