An Experiment on the Effect of Induction Hardening on Fatigue Strength : Report 5,An Experiment in Relation to Fatigue Crack Propagation (the Journal and the Transactions of the Japan Society of Mechanical Engineers)

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An experimental investigation was undertaken to study the fatigue crack propagation in an induction hardened V-notched specimen (d=10mm, ρ=0.35mm) of C=0.16% steel. The experimental results may be summarised as follows : (1) Fatigue cracks were detected in extremely early stages of stress repetitions. For example, at the higher stress level of 70 kg/mm^2 the first crack was detected at 150 repetitions. (2) It was observed that the rate of crack propagation was max. at the early time and decreased as the crack grew. This phenomena can be interpreted by using the concept of the stress σ' at the crack-tip under the presence of the residual compressive stress. (3) It was found that there was a simple relation between the calculated stress σ' and the rate of crack propagation dλ/dN. (4) Furthermore, the rate of crack propagation in the specimen subjected to the varying stress amplitude in two or three stages was studied. It appears that the rate of crack propagation depends upon its stress history and is accelerated by varying the stress amplitude.
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