Stress Intensity Factor And Fatigue Crack Propagation On 14mnnbq Welded Plates

Fatigue and fracture is the main reason to failures of engineering structures and component. It is agreed that the life of welded steel bridge members relates to fatigue crack life. Crack Inevitably exists in the welded steel bridge members .So it is very important to study mayor material facture's parameters-stress intensity factor (SIF)and the crack propagation.Based on existing fatigue experiment results of the steeling 14MnNbq with initial crack and the fatigue experimental data of the steeling 14MnNbq under constant stress cycles.Firstly,SIF of center crack tension(CCT) is studied. two-dimensional finite element model are established by using 1/4 singular element method simulation of cracktip singularity, Numerical examples of specimens are calculated and the results are coincident with the results obtained by formula. It shows that two-dimensional finite element model is efficient for SIF solution of center through-thickness crack in plates under tensile,and then the propagation of the center through-thickness crack is studied by methods of this article, The predicted results are compared with the experimental data of the center through-thickness crack, The comparison shows that two-dimensional finite element model predict the propagation of the center through-thickness crack agrees with experimental predictions.Secondly, SIF of surface crack of the steeling 14MnNbq is studied. the crack is assumed to be semi-elliptical shape during the crack propagation. Two types of finite element model are established, one model is three-dimensional finite element mode obtained by the mesh generating program , another is two-dimensional line spring mode. Numerical examples of specimens are calculated. Firstly the Finite element results are compared with the data of Newman formula.Then, the modification to Newman formula for SIFs calculation of surface crack is brought forward according to three-dimensional finite element analysis(FEA) result.Finally the propagation of surface crack is studied by methods of this article, the predicted results are compared with the experimental data of surface crack.The comparison shows line spring model predict the propagation of surface crack is more conservative than three-dimensional finite element mode.