Study On The Constitutive Relation And Fracture Properties Of Materials Repaired By Laser Based On Finite Element Method

In actual production and manufacturing,various metallurgical or machining defects will inevitably exist in materials or components.These cracks like defects will grow into cracks during service.The existence of cracks not only reduces the load capacity of the workpiece,but even triggers a major disaster during the service of the workpiece,causing serious loss of life and property.The timely and effective repair of defective parts can not only save resources and increase the service life of components,but also avoid major life and property losses.Laser repair technology uses the high energy density of the laser to melt the specimen to be repaired and the repair powder to form a metallurgical combination.The characteristics of rapid solidification are used to refine the metal grains,so as to repair damaged parts and increase the service life.Studying the influence of laser process parameters on the material properties of the repair area and the fracture properties of the specimens is of guiding significance for the actual repair process.In this paper,the cracked 304 stainless steel Compact tension specimen and nano repair powder are used as research objects.The finite element analysis software ABAQUS has been used to establish the temperature field analysis model during the laser repair process and the stress field analysis model after the repair is completed.The temperature field analysis model was used to study the temperature field distribution near the laser repair area of the crack under the action of specific laser process parameters,and then to obtain the temperature gradient,solidification rate and cooling rate of the crack tip of the specimen along the thickness direction after repair.According to the solidification theory,when the laser power is2000 W and the diameter is 2 mm,the distribution of the grain morphology in the thickness direction of the repaired area after heating for 1 s;the laser power and the spot diameter affect the size of the repaired area by affecting the cooling rate Potential impact.Using the plane stress model of the repair specimen to explore the influence of the mechanical parameters of the repair area on J integral of faraway,J integral of interface and J integral of crack tip of the repair specimen.The relationship between the dilution rate and laser process parameters were calculated through the temperature field analysis results.Then the repair zone materialcomposition were obtained from the substrate material composition,repair powder material composition and dilution rate.The image processing software IPP and material performance simulation software JMatPro were used to calculate the mechanical properties of the material.Finally,the plane stress model was used to simulate the effect of laser power and spot diameter on the J integral of crack tip.The results show that the temperature gradient and the solidification rate decrease with increasing depth in the thickness direction.The ratio of the temperature gradient and the solidification rate increases with increasing depth.Grain morphology changes from equixed grain to dendrite in the thickness direction.The cooling rate increases with the increase of the laser power and decreases and with the increase of the spot diameter.The dilution rate increases with the increase of the laser power and the decrease of the spot diameter.The grain size of the repair area decreases first and then increases with the increase of the laser power and spot diameter.The greater the Young's modulus,the yield strength,the hardening index,and the smaller the hardening coefficient of the repaired material in the repair specimen,the smaller the J integral of the crack tip after repaired and the better the fracture performance.