Abstract
Structures are often subjected to various types of random loading in service. Hence fatigue crack propagation under random loading is one of practically interesting topics. This study aims at finding empirically a practical relation for predicting the fatigue crack propagation rate under different types of random loading from constant amplitude loading tests.
The specimen used was CCT (center crack tension) one with 3.2mm thick, made of JIS SPCC mild steel. Several patterns of power spectrum with different band widths in frequency were used, and the mean stress level was changed from compression to tension to identify the crack closure effect. Cycle counting was made using “hysterisis loop method”. The constant amplitude loading test was carried out to compare with the random loading test. The stress range ΔSr of random loading was converted into the fixed value ΔSeq (equivalent stress range). By using this ΔSeq and considering the crack closure effect, a possibility has been shown that the fatigue behavior under random loading may be predicted from the constant amplitude loading test.
