Crack Growth Rate: Its Measurement and a Controlling Factor in Rolling Contact Fatigue

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Abstract
An optical method has been developed for measuring the extent if cracking in test specimens which have failed by fatigue under rolling contact conditions. The data from these measurements are expressed in terms of an over-all crack growth rate, and it is found that an excellent correlation exists between fatigue life and the rate at which cracks branch and propagate. The correlation appears to be independent of stress, lubricant chemistry, and probably metallurgy; this shows that crack branching rate controls fatigue life. The results do show that lubricant chemical factors affect fatigue life through the crack branching rate.