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.
EXPERIMENTAL STUDY AND NUMERICAL SIMULATION ON COALESCENCE AND INTERFERENCE OF SHORT CRACKS FOR LOW CYCLE FATIGUE AT HIGHT TEMPERATURE
High temperature low cycle fatigue at short crack stage was experimentally studied by using the material 16MnR under multiaxial stress.A model of stochastic distribution evolution of collective short fatigue cracks is established basic on the experiment analysis results.The model refers to the effect of material microstructure and interference influence between cracks.The whole process of short fatigue crack initiation,propagation,coalescence and interference on the surface of the material is numerically simulated,and the result agrees well with the experiment data.The model can be used to simulate the short cracks effectively.
Short Crack Growth and Fatigue Life Evaluation
The experimental observations of the short crack growth in several metallic materials show two contributions to the total crack growth rate. Until the critical length is achieved the crack growth rate is independent oft the crack length and above it follows Paris law. A simplified crack growth equation was derived using these experimental data. This equation was integrated yielding the fatigue life curve, equivalent to Manson-Coffin law. The parameters of the Manson-Coff in equation and those of the crack growth equation can be correlated. The crack growth equation can be used for life prediction and residual life evaluation.