Service Load and Fatigue Strength : Report 14, Crack Propagation under Repeated Varying Load

Abstract

Using V-notched specimens of medium carbon steel, three kinds of fatigue tests under sinusoidally varying load are performed and following results are obtained. The rates of crack propagations are accelerated and the superposition law of crack propagation is not applicable to these test results. The reduced lives of the final fracture are about 30 or 40% of the expected ones which are estimated using the superposition law of crack propagation. Then, simple calculation method, namely multiplication law, is proposed to estimate the lives of final fracture under these varying load fatigue tests, whose method is based on the calculation using the fatigue lives under stepwise varying load and simple sinusoidally varying load fatigue tests. From these test results, authors reaffirm that some kinds of loading pattern perhaps make the fatigue lives of specimens shorter to the same degree as those of practically fatigued members, such as car axles, driving shafts and so on.