Experimental and numerical investigation of fretting failure in lug-bush members under cyclic loading

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Ozen_MScThesis_160721.pdf

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2021-7

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Özen, Emine Burçin

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In this study, experimental and numerical work to investigate the mechanisms occurring at the contact region of the lug-bush members under cyclic loading are presented. Post-mortem macroscopic and microscopic investigations of the mating lug and bush surfaces are conducted using digital microscope and scanning electron microscope. The black-brown residues observed at the mating surfaces are shown to be tribolayer regions using energy dispersive spectroscopy analysis. Locations of sliding regions at the contact surfaces are identified by considering the locations of tribolayer regions which indicate the existence of relative sliding. Crack initiation locations are observed to be in the vicinity of the boundary between the sticking and sliding regions. In order to investigate the mechanisms occurring at the contact surfaces during cyclic loading, a 3-dimensional finite element model is created and cyclic loads are applied. It is observed that the steady state response is reached during the 2nd cycle when sliding region areas and relative sliding distances are compared. This result verifies that the application of the cyclic loading is crucial in order to evaluate the behavior using the steady state response. For each material combination, type and sequence of contact mechanisms are observed to be different. A parametric study on the effect of friction coefficient is presented. Increase in the value of friction coefficient leads to decrease in the size of sliding regions. Fatemi-Socie and SmithWatson-Topper multiaxial fatigue damage parameters are applied in order to predict the crack initiation locations. It is shown that these parameters are not able to predict the crack locations of the specimens. In fact, boundaries of the sticking-sliding regions obtained from the simulations are able to predict the crack initiation locations. Good correlation is obtained between the sliding regions observed in the experiments and simulations when the experimental disturbances are taken into consideration in the simulations.

Subject Keywords

Fretting fatigue, Sticking-sliding regions, Slip-front velocity, Fatigue damage parameters

URI

https://hdl.handle.net/11511/91562

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

E. B. Özen, “Experimental and numerical investigation of fretting failure in lug-bush members under cyclic loading,” M.S. - Master of Science, Middle East Technical University, 2021.