Dynamic contact and friction study of homogeneous and layered media

The principal objective of this dissertation was to develop both analytical and finite element models of contact and friction phenomena encountered over a broad range of length scales, from the atomic level to the macroscopic level. This was accomplished by developing continuum and discrete material models of the deforming media (homogeneous or layered) and the use of scale-invariant (fractal) parameters for the description of the interface topography to preserve self-affinity throughout the range of lengths where a probabilistic (fractal) approach was employed. The specific accomplishments of this work are the following.; Dynamic contact and friction analyses of homogeneous and/or layered media were performed using numerical and analytical methods. The dynamic response of homogeneous and layered media subjected to contact loads and the dependence of the coefficient of friction on load, contact geometry, and material parameters were examined. Most studies were based on continuum mechanics models, while atomic-scale friction was studied by molecular dynamics simulations, suitable for atomic-/nano-scale mechanics analysis.; Static friction between rough surfaces was studied based on an analytical approach. The surface profiles were characterized by fractal geometry, and a theoretical treatment was developed using a piece-wise power-law size distribution and a normal slope distribution of the asperity contacts. Normal and friction forces were obtained for constant interfacial shear strength and negligible interaction between neighboring contact spots. The variation of the static coefficient of friction with normal load is interpreted in the context of analytical results. The dependence of the friction coefficient on interfacial shear strength and surface topography parameters is discussed, and the regime where the friction coefficient assumes a minimum is determined from simulation results.; The findings of this dissertation provide new insight into the tribological behavior of homogeneous and multi-layered media. In particular, the dynamic response of homogeneous and multi-layered media subjected to contact loads, the dependence of the friction coefficient on surface topography and material properties, and the tip size and shape effects on atomic-scale friction anisotropy were examined in light of finite element, analytical, and molecular dynamics results. Most results are relevant to general engineering components, especially those for multi-layered media are of particular significance to thin-film media used in hard disk drives. (Abstract shortened by UMI.)...