Probability Fracture Mechanics Based Analysis Of Fatigue Failure Of Structure

Fatigue failure is one of the main failure modes of structures. Since Wohler’s paper on fatigue life and alternating load was published in 1871, people realized the importance of the fatigue life of different materials under different loads and environmental conditions. The safety of the engineering structures can be affected by both the applied loads and the environments. Besides, the fatigue life can be also affected by the grain inhomogeneity, the randomness of internal inclusions and other defects, human-caused direct effect on manufacturing, accidental factors, etc. So we need to analyze the fatigue life of structures based on the theory of probability and the mathematical statistics. This can be helpful to the improvement of the reliability and the service life of mechanical products. The chapters are listed as follows:In chapter 1, importance of the fatigue failure and the development of the fatigue are reviewed. The main content of current work is also outlined.In chapter 2, the basic theory of the Fracture Mechanics is introduced in detail, which includes the classification of the cracks, the propagation of the cracks, the calculation of stress intensity factor and the fatigue crack growth rate. Then the fatigue life prediction methods are introduced. Finally the basic theories of the fatigue applied statistics are described, which are the basis of the subsequent analysis.In chapter 3, Fracture Mechanics model is established. Collapsed element is used to simulate the stress singularity of the crack tip. Monte Carlo method is used to predict the fatigue crack propagation life of the pipeline. The results are compared with the predictive values of deterministic fracture mechanics. Results indicate that the predicted life by the complied program is smaller than the traditional theoretical values and is closer to the real life of the components. Then the effects of the initial crack sizes, fracture toughness and the digital features of random variables on the fatigue crack propagation life are studied, which increases the accuracy and security of the analysis, and has a better engineering performance.In chapter 4, the fatigue crack propagation which corrosion pit in the impeller is simulated. The fatigue crack propagation life of the impeller can be predicted by using of the Monte Carlo method and the Probabilistic Fracture Mechanics with consideration of the uncertainty and the randomness of the parameters. The effects of the aerodynamic load, coefficient of variation, the working speed on the fatigue life of the impeller are studied. The effects of corrosion pit locations, pit sizes, ratio of pit depth and width on the fatigue life in corrosion are further investigated. It provides a basis for the design and maintenance for the relevant structures.