Research On The Reliability Life Of Component Fatigue Crack Based On Continuum Damage Theory

With the global development of modern mechanical industry,component fatigue failure has become an important topic of concern in the engineering field.For general engineering components,the fatigue failure process can be divided into two stages,crack formation and crack propagation.In the frame of the current fatigue analysis,although the crack formation and crack extension stage belongs to a continuous fatigue failure process,but they are treated as two independent process to research respectively.Therefore,changing their status to be processed independently and in a combination of both unified theory of damage mechanics,and study of fatigue crack life has important theoretical and realistic significance.Based on the continuum damage theory,this paper introduces the engineering component without considering the initial damage,and forecast the closed-form solution of fatigue crack initiation life about tension and compressive rods and pure bending of curved beam by alternating loads.On the basis of results using the virtual work principle further derived the closed-form solution of fatigue crack initiation life in engineering common deformation of tension and compression and bending combination.By analyzing the results,it can be seen that the closed solution formula with the results of the pure bending are similar in form.Applying ANSYS finite element simulation analysis to validate the correctness of the calculation results.Then it gave two methods to determine material P-S-N curve.First,by using the method of damage mechanics,establishing the initial any relationship with the reliability,and according to the acquired median fatigue curve data of high strength aluminum alloy-LC4 material,to determine P-S-N curve of the material;Second,by using the method of statistics,doing hypothesis testing of fatigue life distribution for aluminum alloy-LY12CZ material,under a given stress level obtained the survival rate(i.e.,reliability)relationship with life and draw P-S-N curve of the material.The P-S-N fitted curve is used,to give a method for calculating the fatigue reliability life when the working stress and life are given to obey a certain distribution.This paper derived the closed-form solution of fatigue crack initiation life in engineering common deformation of tension and compression and bending combination,for solving the problem of practical engineering provides the theoretical basis.Applying the method of damage mechanics to determine P-S-N curve of the material,which not only saves the cost of test,but also can choose a proper fatigue curve according to the reliability requirement.On the basis of P-S-N curve of the material obtained in statistics,this paper presents a simple and errors smaller method for calculating the fatigue reliability life.