Prediction of Fatigue Crack Growth under Constant Amplitude and Random Loadingusing Specimens with Multiple Cracks

摘要

Fatigue crack growth under stationary Gaussian random loading is considered. Aspecially developed computerized testing system and software are used for generation of the random loading and investigation of crack growth. The sliding summation numerical method was used for generation of a random loading history characterized by a given autocorrelation function. As far as the loading history of a sufficient length is generated a sequence of maxima and minima is extracted and arranged with the predetermined frequency. The next Operation is elimination of the small amplitude cycles in accordance with the predetermined threshold value and. determination of the minima and maxima two-dimensional distribution of the edited process. A specially built transition matrix derived from this distribution was used for the real-time generation of the random loading during the test. Experimental investigation of the developed random loading generation procedure and crack growth process was performed using aluminium alloy multicrack panel type specimens providing possibility of observation of an array of simultaneously growing cracks. Dependence of fatigue crack life time on random loading parameters as well as stochastic characteristics of crack growth were studied. (MM).