Estimating Method for Fatigue Crack Growth under Narrow Band Random Loading

It is essential for the structural engineer to be able to estimate fatigue strength of structural members under the effect of randomness in service loading on the basis of the conventional fatigue test data. In the previous paper, fatigue crack propagation tests under narrow band random loading were carried out and the relationship between fatigue behaviors under random loading and constant amplitude loading was discussed. It was concluded that consideration of crack closure was indispensable for examination of fatigue behavior under random loading.In this study, additional fatigue tests are conducted in order to obtain the data under different stress conditions. Crack closure phenomena of the specimens are automatically recorded over a long period of fatigue cycles using strain gage method aided by microcomputer system.The significance of crack closure for understanding crack growth under variable-amplitude loading is emphasized and an estimating method for fatigue crack behavior under random loading is proposed.