The effect of dehumidified silicone and paraffin oils with viscosities from 5 to 60, 000 cS, on fatigue crack propagation in a low alloy steel is examined at both near-threshold (~ 10-6 mm/cycle) and higher (~ 10-6 to 10-3 mm/cycle) growth rates. Results show that at low load ratios crack growth rates in oil exceed those in moist air at near-threshold levels, whereas at higher growth rates crack propagation in moist air is considerably faster than in oil. Such observations are discussed in terms of three mechanisms specific to dry oil environments: suppression of moisture-induced hydrogen embrittlement and/or metal dissolution, minimization of oxide-induced crack closure and hydrodynamic wedging effects of the viscous fluid within the crack.
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