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On the numerical prediction and experimental investigation of reciprocating sliding wear Iyer, Srinivasan

Abstract

This thesis is devoted to the development of an improved wear model for estimating wear-loss in the field of sliding wear. A hard cylinder sliding on a softer disc is adopted for studying the wear system. Four governing sliding wear mechanisms, namely low cycle fatigue, ratchetting, mild wear and crack growth leading to particle detachment are identified. This inference is attained by the investigation of photomicrographs of experimentally obtained sectioned wear specimens. Surface statistical methods are used for quantifying the contacting asperities and finite element methods are used for evaluating the elastic-plastic strains. Equations are developed to predict the wear volume and the number of cycles for failure, from the history of strain-cycles and tangential work equivalence for low cycle fatigue wear and from the history of strain cycles and ratchetting depth for ratchetting wear. Through simulations, it is shown that the low cycle fatigue wear happens during plastic shakedown conditions and that ratchetting wear occurs above the ratchetting threshold. A predictive equation is developed for mild wear, based on tangential work equivalence and Hertzian contact mechanics parameters. It is shown that mild wear occurs during the elastic shakedown state. Applying finite element methods to linear elastic fracture mechanics, a model is developed, simulating crack growth and wear particle detachment, by assuming a surface crack. The range of mixed mode stress intensity factors for cyclic loading is evaluated and related to the crack extension in a prescribed number of cycles using a Paris type equation. The maximum tensile stress criterion is used for determining the crack turn angle during the crack propagation. A wear particle is detached from the parent surface when the crack propagates to the wearing surface. This mechanism occurs below the elastic limit, but under dry sliding and high normal loading levels. Experiments are conducted with specialised test-rig under a variety of loading and friction conditions. The microstructures of sections of the test-worn specimens are analysed for studying the wear characteristics. Experimental values agree well with the predicted values of wear-volume and aspect ratio of wear particles, justifying the validity of the proposed sliding wear model.

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