Fatigue Crack Propagation of Steel in Oil

概要

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Numerical analysis of a simplified crack model has been conducted on the wedge action of the viscous fluid in the cracks subjected to the bending moment, and rotating bending fatigue tests have been carried out on carbon steel specimens in paraffin oils of high and low viscosity. The crack rate decreases when the product of the viscosity and the cycle frequency, ηf, is increased in agreement with the analysis. However, the crack rate increases when ηf is greater than about 10^5 owing to the poor penetration of oil into the fissures. The protective effect of oil, which limits the access of oxygen to freshly created surfaces, is hardly found. Neither the effect of the viscosity nor that of the cycle frequency is observed in silicone oil. This may be due to the small pressure index and to the weaker adhesion to the crack wall of silicone oil, which is improved by activation with stearic acid.
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