Random Fatigue Crack Growth Analysis And Life Prediction Of Structures With Defects

With the development of science and technology industry,the structure and function of major equipment become more diversified and complicated,which puts forward higher requirements for durability and reliability of mechanical structure.Fatigue performance analysis and fracture failure prediction of crucial structural parts can effectively save a lot of economic costs and reduce the risk of damage accidents.However,due to the complexity of processing,transportation and abrasion,there are inevitably cracks and defect-like structures in the mechanical mechanism,which lead to crack initiation and propagation.The main cause of failure is the decrease of structural strength and even fracture,which makes fatigue crack growth analysis very important in fatigue design and life prediction.Under the action of cyclic loading,the processes of initiation and propagation of cracks from defects of components are stochastic and are related to many uncertain factors such as crack location,initial crack length,crack growth rate and applied load.Therefore,it is necessary to predict the fatigue crack growth life of components by considering the uncertainty from the perspective of statistics and probability analysis.According to these issues,the following work are carried out in this thesis:(1)Failure probability prediction of stochastic fatigue crack growth.In order to comprehensively consider the uncertainty of failure of structural with cracks,the statistical probability method is used to analyze the dispersion of crack propagation based on the fatigue experimental data.By combining the randomness of initial crack length with the randomness of crack growth rate,a new model is proposed to predict the crack exceedance probability,which provides a method for predicting the failure probability of fatigue crack growth.(2)Surface crack coalescence failure probability prediction.In the process of multiple crack propagation,the process of crack interaction and coalescence are common.Considering the practical engineering significance,the randomness of crack propagation is introduced into the crack coalescence probability model to calculate the failure probability.Due to the influence of size effect,specimens in different size often have different failure life.Based on high stress volume method,a failure life prediction model combining size effect and failure probability of crack coalescence is proposed.(3)Remaining life prediction and reliability analysis of structures with defects.Considering the influence of parameter distribution in Paris law on the residual life of the structure with single crack propagation,the influences of statistical distribution of the parameter randomness on the residual life and on the reliability are quantified.The relationship between the uncertainty of damaged surface area and initial crack length and the reliability of the structure multiple surface crack is analyzed.