Sliding-induced subsurface deformation in metal matrix composites.

摘要

A coupled finite element - computerized image analysis (FEM/CIA) method for predicting dry sliding subsurface strains in metal matrix composite (MMC) has been implemented. This method includes an algorithm designed to detect phase boundaries from digitized image of multi-phase materials for subsequent meshing of real microstructures, large strain and displacement formulation, multiscale finite element technique, sequentially coupled thermal-mechanical analysis, and dynamic contact modeling. The dynamic contact model permits simulation of topography evolution using random number generation, dynamic conditional stick/slip at discrete asperity of real area of contact using Lagrange Multiplier technique, and nonlocal/nonlinear friction formulation.; Applicability evaluation of this FEM/CIA method has been performed through assessing the tribological behavior of 2124 Al-SiC{dollar}rmsb{lcub}w{rcub}{dollar} as a function of variation of normal load, sliding velocity, sliding distance, and MMC reinforcement volume fraction. Direct comparison between quantitative computational and experimental assessment of global damage accumulation has revealed excellent agreement for experimental conditions in which subsurface plastic deformation controlled wear. Decreased agreement occurred when delamination became the predominant wear mechanism. This was attributed to physical phenomena that are not accounted for by the developed FEM/CIA model, i.e., reinforcement cracking, reinforcement/matrix interface failure and high plastic strain induced void nucleation within the matrix.; FEM/CIA simulations have revealed four principal sources of strain concentration in sliding-induced subsurface deformation of discontinuously reinforced composite, these strain concentrations sources being located at whisker ends, at reinforcement clusters, within shear bands between two whisker ends, and at near-surface whisker ends. In addition computational results of the net hydrostatic stress component, the latter controlling, in concurrence with strain accumulation, void formation at second phase particle or inclusion, have revealed that two sources of hydrostatic stress state are superimposed in sliding wear, i.e., a locally developed hydrostatic pressure or tensile stress due to constrained deformation associated with the presence of hard particles, and superimposed pressure originating from high pressure contact at discrete asperities. Finally these predictions have showed that the net hydrostatic stress component features a local and dynamic character, as opposed to the global and static character considered by previous investigators.