Probabilistic Fatigue Analysis Of Structures Considering Corrosion Pits

In engineering practice,crack is the direct factor for determination of failure of material.The analyses on crack propagation and fatigue life are very important.The influential factors of crack include load,fatigue parameters of material,crack morphology after initiation,etc.These factors can lead to uncertainties of fatigue fracture properties.So,the traditional fracture mechanics cannot be directly used to predict the fatigue life of structures with uncertainties.It is found that these uncertain parameters are random variables that conform to a certain type of statistical distribution.The effect of uncertain parameters on crack initiation and crack growth can be considered by probability analysis.Firstly,the fatigue strength analysis of martensitic stainless steel with corrosion defects is carried out by multi axis gradient criterion and Crossland criterion.The comparison of results shows the validity and superiority of the multiaxial gradient criterion.The computational results show that the multi axial gradient criterion with consideration of hydrostatic pressure gradient shows higher accuracy for the materials with corrosion pits.The effects of the defect sizes and the geometries on the fatigue strength are further studied.This paper further considers the variability of fatigue strength parameters and load,and then proposes a fatigue reliability prediction method based on the multiaxial gradient criterion.Secondly,the probabilistic local stress strain method is used to research LY12-CZ aluminum alloy plate under cyclic fatigue load.The results show that the randomness of the fatigue property parameters and nominal stress have a significant influence on the fatigue life,which should not be ignored in practical engineering.The statistical eigenvalues of cyclic stress-strain and fatigue life can be obtained by probabilistic local stress strain method,thus fatigue reliability analysis can be carried out conveniently.Finally,based on the experimental data of fatigue crack propagation,the probability model of fatigue crack propagation rate are studied by randomizing deterministic equations.The results show that the probability curve coincides with the experimental data.The randomization method of quantitative equation can easily predict the fatigue crack growth rate and residual life of the structure under the given reliability and confidence level.It provides an economical and simple method for the reliability analysis of fatigue life.