Study on the Law of Short Fatigue Crack Using Genetic Algorithm-BP Neural Networks
The initiation and propagation of short crack is a complex process of nonlinear dynamics. The material field has been concerning of the law of short crack and put forward a number of models and predictive equations. But most of them have to meet the problems which are unclear physical parameters meaning, narrow range of applications etc. That is the reason why there is not yet widely recognized quantitative model of crack evolution so far. The introduction of genetic algorithm-BP neural networks could solve those problems by avoiding building the explicit model equation and directly extracting the potential rules from the data. In this paper, the short crack for low cycle is studied under complex stress at high temperature. The material adopted in the experiment is Q245R steel. The initiation, propagation and coalescence of short crack are observed. The comparisons between experiment results and neural network simulation results show that genetic algorithm-BP neural networks simulation method can predict the law of short crack with higher prediction accuracy.
Computation Method of Processing Time Based on BP Neural Network and Genetic Algorithm
Looking-up standard processing time table is a commonly used and important determination method of processing time. However, the large error in nonstandard nodes brings adverse effect on its accuracy. In view of the problem, a computation method of processing time based on back propagation neural network (BPNN) and genetic algorithm (GA) is proposed. Several key technologies of BPNN based on Matlab, including computation of the number of neurons in hidden layer, determination of training algorithm, and affecting factors of generalization ability, are researched in depth. In order to improve the training efficiency of BPNN, GA is used to optimize its connection weights and thresholds. The encoding method, selection operation, crossover, and mutation operation of GA are discussed in detail. The higher computation precision and faster operation speed of the proposed method is demonstrated through application cases.
Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components
The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation.This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.RésuméOn a analysé en application de la mécanique de rupture la vie en service de composants de structures aéronautiques soumis à une sollicitation cyclique aléatoire. A l'aide d'essais à la charge d'épreuve, on a établi les dimensions initiales d'une fissure aux points critiques de sollicitation, pour analyser sa croissance par fatigue.Les vitesses de croissance d'une fissure de fatigue dans le cas des charges aléatoires ont été calculées par la méthode des demi-cycles. On a mis au point une nouvelle expression pour calculer le nombre d'heures de vol résiduelles pour des éléments de structure. S'il résulte de cette nouvelle expression, ce nombre est beaucoup plus faible que celui prédit par les équations de vie résiduelle conventionnelles.