Fatigue Crack Growth under Random Loading (4th Report)

Abstract

Fatigue crack growth under random loading has been extensively studied since nearly a decade in relation with the design of offshore structures, ship hulls, pressure vessels and so on.For the sake of simplicity, random loads in service conditions are often simulated by block programmed loads in laboratory fatigue tests. However, very few studies have been conducted on the difference of fatigue crack growth behaviour between random loads and block programmed loads.The authors previously presented an experimental study on fatigue crack growth under block programmed loads, and discussed on the effect of block size on fatigue crack growth life. A proposed model gave a good prediction of fatigue crack growth life in block programmed loading tests. In the present paper, fatigue crack growth tests were performed under three different types of block or random loads. Experimental results show that fatigue crack growth behaviour under random loads is very similar to that under block programmed loads with short periods. Miner's rule gave a non-conservative estimation for crack growth life under both random and short block loads. Life estimation by the model previously proposed agreed well to the experimental results.