Doctor of Philosophy (PhD)
A novel methodology for analysis of damage in contact problems in presented. Two important categories of contact damage are studied, namely crack nucleation and adhesive wear. The proposed methodology is primarily based on the laws of energy and thermodynamics, and as such offers great advantages by unifying the analysis of damage in a variety of contact configurations. Crack nucleation is the first damage type analyzed. For this purpose, the line-contact fretting configuration is chosen. A thermodynamically-based continuum damage mechanics (CDM) approach is employed. Intense stress gradients in the contact region are found to be highly influential in the crack nucleation process. A methodology is proposed that identified the averaging zone as a function of the contact and loading parameters. The predicted crack nucleation lives are verified by comparing against the published experimental data for two different alloys. The utility of the proposed methodology is also investigated for the case of rough surface contact. The deterministic approach is employed to investigate the effect of roughness on the surface tractions and contact stresses. A special averaging technique, proposed for the case of smooth surface, is adopted. The predictions of the crack nucleation life for different roughness values are compared with relevant experimental data in literature, and confirm the validity of the analysis. Adhesive wear is another type of contact damage investigated. The study is carried out for three different contact conditions. These include disk-on-disk unidirectional dry sliding, pin-on-flat reciprocating dry sliding and pin-bushing grease-lubricated oscillatory sliding. It is shown that the wear rate is linearly related to the power dissipation as well as the entropy generation rate. The linear correlations are verified experimentally. Degradation coefficient is obtained and a simple approach is proposed for prediction of wear in dry sliding configuration. The proposed technique can be employed for prediction of wear in circumstances where the direct measurement of power dissipation is encumbered by practical limitations. Also investigated are the relationship between the system’s wear rate, power dissipation and thermal response. The wear-energy dissipation coefficient (WED) is identified as an important property of tribo-systems. The methodology relies on measurement of temperature rise in the sliding system. It is shown that the correlation between the frictional power dissipation and temperature rise can be obtained through thermal analysis of the system. The proposed methodology is shown to be capable of predicting the wear rate under a wide range of loading conditions.
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Babaie Aghdam, Afshin, "Energy and Thermodynamically Based Approaches for Analysis of Damage in Contact Problems" (2014). LSU Doctoral Dissertations. 1438.