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.
Short fatigue crack behaviour in 316L stainless steel
Abstract Short crack growth mechanism and kinetics were studied under symmetrical push–pull straining in austenitic stainless 316L steel. Fatigue cracks initiated along strain localized areas and crack linking was the main mechanism of the early crack growth. Two different regimes in short crack growth rate were identified. Based on the experimental data, the quantitative description of crack propagation rates was obtained for short and long cracks. The integration of this equation can be used to predict the fatigue life or residual life and to evaluate the number of cycles necessary to reach a given crack length.
FATIGUE DAMAGE IN TWO STEP LOADING OF 316L STEEL I. EVOLUTION OF PERSISTENT SLIP BANDS
An experimental study of the surface evolution during controlled plastic strain amplitude single-step and two-step loading tests reveals the important damage mechanisms for 316L stainless steel. In the first stage, the cyclic plastic strain is concentrated into persistent slip bands (PSBs) and a surface relief is formed consisting of extrusions and intrusions. The frequency of occurrence and the total density of PSBs has been assessed using systematic observations in a scanning electron microscope. The relative volume occupied by PSBs determines the fatigue damage in this stage. Two-step loading has only a small effect on the PSB damage evolution and nearly equal saturated values (corresponding to the applied plastic strain amplitude) were achieved in the single-step and the two-step loading investigations.