Fatigue Performance Of Specimens Repaired By Laser At Crack Tip

In the current industrial production process,fatigue is the main form of failure of machine parts.Especially when the part is cracked during production,transportation and use,it is more likely to cause fatigue damage and cause major economic losses.In this context,finding a way to repair crack in a timely and effective manner is particularly important.Laser repair technology enters people's line of sight with its unique rapid heating,cooling,and small heat-affected zone,providing a new type of crack repair process.In this paper,compact tension(CT)specimens with prefabricated crack were prepared from 304 stainless steel.The crack tip was repaired by laser with addition of different powders.Then,the fatigue properties of these specimens were studied.Firstly,the finite element software ABAQUS was used to analyze the original test piece and the test piece repaired by laser without addition of powder,and the parameters such as residual stress intensity factor and effective stress ratio were obtained.The modified Paris formula was utilized to evaluate the effect of the laser repair without addition of powder process on the fatigue properties of the specimen.At the same time,a model of laser repair with addition of 304 stainless steel powder at the crack tip was established.The numerical analysis results under the two repairing processes were compared to explore the effect of adding powder on the repairing effect.Then,304 stainless steel powder and 5% nano WC and 304 stainless steel composite powder were added at the crack tip of the test piece,respectively,and the CO2 laser equipment was used for melting repair.The fatigue crack growth experiments were carried out with the two sets of test pieces,the test piece repaired by laser only and the original test piece to compare the fatigue life.Scanning electron microscopy was used to observe the microstructure and fracture morphology of the test piece,which can explain the fatigue crack propagation results.The results show that laser repair without addition of powder can cause a large number of shrinkage holes in the melting zone,combined with the residual tensile stress,so that the fatigue properties of the test piece are reduced.Laser repair with addition of 304 stainless steel powder can refine the grain size and reduce the influence of residual tensile stress,thereby suppressing fatigue crack growth and improving fatigue performance.Laser repair with composite powder addition of 5% nano WC and 304 stainless steel will further optimize the grain morphology of the repair zone,but pores and unmelted materials may be generated at the same time,making the fatigue crack growth rate distribution of the specimen uneven.On the surface of the fracture surface,the position of the fatigue crack initiation zone of specimens is found to be different,but the microscopic features of the fatigue failure are observed.Finally,based on the secondary development of finite element software ABAQUS,laser repair at crack tip analysis platform was established.The Origin_Specimen,LaserRepair_Specimen_TEMP,LaserRepair_Specimen_STRESS and LaserRepair_Specimen_Redistribution plug-ins were developed by the RSG dialog constructor to calculate the stress intensity factor of the crack tip of the specimen under different crack lengths and stress loading,analyze the temperature field and stress field of the repaired specimen and simulate the residual stress redistribution after changing the crack length.It can parameterize the problem,reduce the operation flow and improve the efficiency.