Doctor of Philosophy (PhD)
Civil and Environmental Engineering
Severe contact stress problems generate high temperature and create thermomechanical gouging and wear due to high velocity sliding between contacting materials. The major consideration is to develop an experimental and theoretical model for the material constitutive behavior in order to better characterize and predict the internal failure surroundings the gouging and wear events and understand the physical behavior of high speed contact environment. An enhancement of an existing tribometer device developed by Philippon et al.  is made up of a dynamometer ring and a load sensor that allows to apply an apparent normal force on specimens and measure frictional forces, respectively. The setup has been adapted on a hydraulic testing machine and pressure gas gun to carry out Steel 1080 on Steel VascoMax experiments. The recordings of the normal and tangential forces allows the determination of the friction coefficient. The effects of the sliding velocity on the surface roughness and the dry fiction coefficient are investigated. Performed scans (SEM) show the roughness decrease and reveal the occurrence of the wear. The second part is devoted to the theoretical approach capturing the phenomena of the wear with extension to incorporate gauging problems. The principle of virtual power is used by introducing the contributions from damage and its corresponding gradients. In addition two internal state variables are introduced on the frictional contact interface measuring the tangential slip and the wear. The constitutive model is formulated with state laws based on the free energies and the complimentary laws based on the dissipation potentials. The proposed model is implemented as user defined subroutine VUMAT in ABAQUS Explicite to analyze the structural response of the high speed sliding experiment from the first part. This model provides a potential feature to relate the non-local continuum plasticity and damage of the bulk material to friction and wear at the contact interfaces. This research is invaluable in providing a multiscale material model and numerical procedure that will be used within a hydrocode to better facilitate the design components of the severe contact stress applications.
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Lodygowski, Adam, "Friction and Wear at Elevated Velocities" (2010). LSU Doctoral Dissertations. 3271.
Voyiadjis, George Z.