Fretting fatigue of AISI 9310 case-hardened steel

This document details the fretting fatigue of AISI 9310 case-hardened steel. The research involved two main parts: experiments were performed in order to determine the fretting fatigue life of the material under certain operating conditions, and semi-analytical methods were used to determine contact stresses and crack growth during the experiments. Fractographic analyses were performed in support of this research to observe characteristics of the fretting process. The results from the experiments and subsequent analysis were compared with failure characteristics observed in gears made of the same material in an effort to identify similarities present. Twelve fretting fatigue experiments were performed at room temperature with case hardened steel specimens and pads. These twelve experiments are divided into two sets, one in which a re-cast layer was present on the pads and one in which there was no re-cast layer. Post-experimental fractography of the specimen and pad allowed for study of the contacting surfaces and resultant crack formation. Of the twelve experiments, four interrupted tests were performed to determine crack growth behavior, five tests to failure were performed to determine life, and three tests were performed to determine the coefficient of friction due to the contact during the other nine experiments. Of the tests to failure, the tests with re-cast layer removed from the pads failed in fewer cycles than the tests with the re-cast layer present. The contact tractions and stresses for the experiments were obtained using computer code that utilizes Singular Integral Equations and FFT, which is well suited for the problem provided certain assumptions. The results from the SIE calculations compare well with FEM analyses. The Paris model was used to predict crack growth and experiment life, and the results were compared with the experiments. The modeled remaining life compared well when the experiment was stopped after the fretting cracks had formed into one crack, but the model underestimated the expected life when the experiment was stopped while multiple separate fretting cracks were present