Theoretical Study and Experimental Verification for Fatigue Crack Initiation and Propagation on Rubber Suspension Under Multi‐Axial State Using S‐N Methodology

ABSTRACT The S‐N curve developed by Wöhler has been utilized in fatigue crack initiation for over 160 years, but has not been applied to crack propagation in rubber materials. This study employed the S‐N methodology to predict rubber crack propagation. A general S‐N function, incorporating the elastic constant ratio and the effective tensile stress containing the effect of R ratios (the ratio between minimum and maximum stress), was integrated to predict rubber crack initiation and propagation. This approach was validated on an industrial product, a rail vehicle suspension without preexisting cracks, subjected to block fatigue testing with three loading sets over 125k cycles. The predicted crack initiation occurred at 81k cycles, compared to the experimental observation of 82k cycles. The predicted crack length was 93–95 mm, while the actual length after the fatigue test was 97 mm. This newly developed approach could be easily integrated into engineering design and applications once more cases validate the methodology, as S‐N curves are typically available in industries. However, if the requisite S‐N curve is unavailable, the S‐N function presented in this investigation may serve as a reference, providing significant reductions in costs and time.