Numerical Simulation Of Fatigue Crack Growth Of Surface Crack

The phenomenon of brittle rupture in low stress of parts often occurs underalternating load due to fatigue failure.The process of fatigue failure comprise crackinitation,crack growth and fracture. Cracks usually initiate on surface of part.Surfacecrack growing under alternating load lead to failure of part,which causes big loss andbrings security menace.So it is of great significance and value to research surfacecrack growth.Fatigue crack growth of surface cracks in structures have been simulatedand residual life have been predicted in AxDPFlow procedure by finite elementmethod on the basis of linear fracture mechanics in this paper. The main contents ofthis paper are as follows:1)The basic theory of numerical simulation of fatigue crack growth isexpatiated.Then the process of numerical simulation is confirmed.The key problemthat the theory and computing method of stress intesity factor is discussed.2)Plate is taken as the subject and partitioned in cracked and uncracked block viapre-processing software HyperMesh.The finite element model of cracked block isestablished by AxDPFlow procedure and mapped as standard iso-parametric elementin ABAQUS library.The uncracked block remain unchanged and is applied loads andboundary conditions.Multi-point constrain(MPC) is used to connect cracked anduncracked block.3)The flow of numerical simulation of fatigue crack growth is established byAxDPFlow procedure.Finite element analysis(FEA) is worked on ABAQUS.Stressintesity factor(SIF) caculated by two numerical methods in this paper is comparedwith the Newman and Raju empirical value.The distribution of SIF in crack front isinvestigated.The effect of mesh orthogonality and MPC for SIF are considered. Crackgrowth increment is calculated according to Paris law and crack front is described bycubic spline curve.4)Fatigue crack growth of surface crack in plates and round bar under remotetension, bending or combined load is modeled. The relationship between a/c amd a/t of different initial crack shape in the process of crack growth is examined under theenvironment of AxDPFlow procedure step by step. The law of crack shape change inthe process of fatigue crack growth is analyzed. The results indicate that load form hasgreat effect on crack shape in growth and surface cracks of different initial shape havesame growth law under same load.5)The methods and influencing factors of prediction of structure fatigue life arereviewed. Fatigue crack growth life of plate is estimated according to Paris law withconsideration of crack growth increment and stress ratio. The results show that crackgrowth increment used in this paper can predict the fatigue life exactly;the effects ofmean stress and residual stress for fatigue life can be reflected by stress ratio. Fatiguecrack growth of surface crack in crankshaft is simulated.The residual life ofcrankshaft with surface crack is predicted in this paper and suggestions can besupplied to damage tolerance design.