Fatigue crack growth under stationary Gaussian random loading is considered. A specially 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).

The objective of this paper is to develop a computational model and a software for predicting the fatigue propagation of collinear multiple surface cracks under constant-amplitude and variable-amplitude loading. After examining fatigue crack growth rate data for compact tension (CT) specimens and single surface crack specimens, an empirical equation is proposed for the prediction of fatigue life in a multiple surface crack geometry. The accuracy of the proposed model is verified using a life prediction computer program. The predictions are compared with the results from several case studies to check the accuracy of the proposed model and to verify the usefulness of the developed program. Good agreement is observed between the numerical results based on the proposed model and the published experimental data.

The validity of using constant amplitude crack growth rate data for the prediction of fatigue crack growth behavior and lives of center-cracked tension (CCT) specimens under random spectrum loadings was assessed. Analytical predictions obtained from the EFFGRO computer program were the results from two different approaches. One approach did not account for the load interaction effects to the fatigue crack growth, while the other approach considered both the tensile overload retardation and the compressive load acceleration effects as well as the reduction of overload retardation effect caused by the compressive load immediately following the tensile overload. This paper describes the fatigue crack growth rate equation, the load interaction model, the numerical procedure, and the cycle counting technique used in the EFFGRO program. Results from other studies, including the sensitivity of the overload shut-off ratio, the crack growth rate constants determination procedure, and the range-pair counting effects to the prediction accuracies, are also presented.

The proceedings of the 23rd National Symposium on Fracture Mechanics, held in College Station, Texas, June 1991, present a broad overview of the current state of the art in fracture mechanics research. Following the Swerdlow Lecture (Structural Problems in Search of Fracture Mechanics Solutions by