<p><a href="">This work investigates the effect of surface features such as roughness, pits, and cracks on the tribological and fatigue behavior of machine components. It comprises of three main investigations: (i) effect of roughness on non-contacting fatigue, (ii) lubricated contact fluid structure interaction (FSI) behavior in presence of surface cracks, and (iii) the equivalence between non-contacting and contacting fatigue and the effect of roughness.</a></p><p>For the first investigation, a novel microstructure-based approach was developed to model surface roughness. It used a finite element fatigue damage model to predict the effects of roughness on tensile fatigue. AISI 4130 steel specimens with different surface finishes were fabricated and tested in axial fatigue using an MTS machine. The experimental results demonstrated the detrimental effect of roughness on fatigue lives, which was predicted by the model accurately.</p><p>In the second investigation, a partitioned CFD-FEM based FSI solver was developed using Ansys Multiphysics software to model and investigate elastohydrodynamically lubricated contacts typical in gears and cylindrical roller bearings. The FSI model relaxes Reynolds assumptions, and uses Navier-Stokes equations to determine the lubricant flow and utilizes finite element method to model the structural response. The FSI model was evaluated for robustness under various operating conditions. The effect of material plasticity, subsurface features, etc. were also investigated. The model was then extended to investigate the effects of surface cracks in rolling/sliding EHL line contacts. Using CFD based approach enabled the investigation of surface cracks with inclined geometries, overcoming the limitations of standard Reynolds-based solvers. The effects of crack geometry parameters such as crack location, crack length, crack width, crack tip radius and crack orientation on fluid pressure distribution were studied. This investigation identified the crack geometries that affect the contact fatigue behavior by predicting the location and severity of stress concentrations in the material.</p><p>Finally, the relationship between contacting fatigue and non-contacting fatigue was investigated. A test rig was designed and developed to simulate rolling contact fatigue (RCF) surface damage. Experimental investigation revealed that the RCF surface damage stress-life (SN) results can be predicted using torsional fatigue results 10 times faster. A computational contact mechanics model was developed to incorporate the effect of roughness in this prediction, and corroborated against experimental RCF results at different roughness levels.</p>