Fretting contact of dissimilar isotropic /anisotropic materials
Abstract
A better understanding of the damage caused by the surface tribological phenomenon of fretting contact is achieved by a study of the local contact stresses. Many real life instances of fretting contact can be approximated as two elastic half spaces in contact with an appropriate gap function. This work presents a numerical method, based on the solution to coupled Cauchy Singular Integral Equations (SIEs), to obtain the contact tractions when two half-spaces made from dissimilar isotropic/anisotropic materials are in partial slip contact. If one of the half-spaces is anisotropic, Coulomb's law of friction is modified by assuming that the out-of-plane shear traction is identically zero. The numerical method is extensively verified by comparing its results to those found in the literature and to results obtained using FEM. A numerical method, based on the FFT technique, to obtain the sub-surface stresses in an anisotropic half-space is also presented. Well characterized fretting fatigue experiments were conducted with dissimilar isotropic materials (Ti-6Al-4V & Inco718 alloys) to study the effect of the contact loads on component life. Experiments were also conducted to measure the average coefficient of friction as a function of the number of fretting cycles. It was found that, similar to other fretting fatigue experiments, the average coefficient of friction stabilizes after a certain number of fretting cycles. A numerical method is developed to obtain the slip zone coefficient of friction from the measured average value. The calculations showed that the slip zone coefficient of friction is considerably higher than the average value. The SIE method is used to obtain the contact stresses in the experimental specimens by taking into account the slip zone coefficient of friction and the small deviations, caused by machining, in the fretting pad profiles. The contact stresses are then used in conjunction with a crack nucleation approach to predict life to fretting crack nucleation in the experimental specimens. The effect of residual stresses in the specimens was also included in this analysis. The trend of the predicted fretting crack nucleation lives was quite encouraging. Finally, the ability of the SIE method to calculate the contact stress evolution due to “fretting missions”, with changing normal load, shear load, and moment, is demonstrated.
Degree
Ph.D.
Advisors
Farris, Purdue University.
Subject Area
Aerospace materials
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