Effect of Crack Interval on Multiple Crack Propagation Behavior

Abstract

In the authors' previous study, fatigue crack propagation tests were performed using four-point bending specimens with multiple parallel edge notches at regular intervals of 10 mm. In this study, similar tests were carried out using the specimens with crack intervals of 5 mm or 2.5 mm. It was found that multiple crack propagation behavior was affected by the crack interval. A small number of cracks grew selectively in the specimen with narrow crack intervals while many cracks grew to long lengths in the specimen with broad crack intervals. Experimental results were first simulated by a previously proposed method using stress intensity factor solution for multiple cracks with alternately different lengths. Simulation results showed a good agreement with experimental results in case of specimens with broad crack intervals but showed different tendency from test results in case of specimens with narrow crack intervals. To simulate the experimental results a new method was proposed, in which the stress intensity factor solution was modified to include an effect of cracks outside the neighboring two cracks. The method gave a good simulation result for the specimens with narrow crack intervals but gave higher propagation rate than experiment for the specimens with broad crack intervals, resulting in a conservative evaluation.