| A contact mechanics analysis of elastic-plastic layered media was performed to study contact between rough surfaces, thermal-mechanical sliding contact, sliding on layered media with surface layers under residual stress, and valid hardness measurement of layered media. The work included both analytical and finite element studies.; Using a finite element model of a rigid sphere in normal contact with a semi-infinite elastic-plastic homogeneous medium, constitutive relations were obtained for the mean contact pressure and real contact area in terms of representative strain. This contact model was extended to layered media by modifying the constitutive equation of the homogeneous medium to include the effects of the mechanical properties of the layer and substrate materials and the layer thickness. Insight was obtained about the evolution of elastic, elastic-plastic, and fully-plastic deformation at the rough contact interface in terms of the maximum local surface interference, and the dependence of the contact load and real contact area of rough surfaces on fractal parameters and the layer thickness.; An elastic-plastic contact analysis, based on a finite element model and real surface topographies, was performed to elucidate deformation at the head-disk interface. The study illustrated the significance of the thickness, mechanical properties, and residual stress of the layer on the development of plasticity and likelihood of cracking in the layer and the substrate media.; The coupled effects of surface mechanical and thermal (frictional) loadings on the deformation of layered media were examined using a three-dimensional finite model of an elastic sphere sliding over an elastic-plastic layered medium. Friction traction and thermal loading were shown to enhance stress intensification and plasticity, especially in the case of relatively thin layers of low thermal conductivity.; Moreover, a three-dimensional finite element model was developed to simulate a rigid spherical asperity indenting and sliding on an elastic-plastic layered medium exhibiting varying magnitudes of residual stress in the top layer for two different coefficients of friction. The optimal residual stress to minimize the possibility of yielding and cracking was shown to be between zero and −0.5 times the peak contact pressure, the exact value depending on the type of contact (normal or sliding), coefficient of friction, and deformation mode of the layer.; Hardness of elastic-plastic layered media was evaluated in the context of finite element simulation results. The critical interference distance, below which substrate effects can be neglected, was determined by considering the variation of the equivalent hardness with the interference distance. The minimum interference distance, above which the occurrence of sufficient plasticity leads to the determination of the real hardness of the material, was determined from the contact constitutive model mentioned earlier and a relation between hardness, yield strength, and elastic modulus for a homogeneous half-space. A new scheme of hardness measurement for thin-film media was proposed and validated by finite element simulation results for an elastic-perfectly plastic layered medium.; The findings of this dissertation provide new information about the effect of surface topography, thermal loading, friction traction, and thickness, mechanical properties, and residual stress of the top layer on the deformation behavior of layered media. The results are of particular relevance to thin-film media and interface topographies used in computer hard disk drives. However, most of the analytical and finite element models can be extended to other type of contact interfaces with slight modifications. |
