Study On Fatigue Fracture Resistance Method Of Non-penetrating Laser Welding Joint

The paper was based on the study of the 301L cold-rolled stainless steel passenger car body,car body's outer plate with outer plate and outer plate with stiffener laser welding was studied.The paper was based on the two defects of existing laser welding:(1)Lapped penetration laser welding structure has low plasticity and fracture displacement is small.(2)Lapped penetration laser welding structure's fatigue fracture occurred mainly in the key service components,namely the penetration outer plate,fatigue strength needs to be strengthened.We designed two kinds of welding forms,such as positive tilt laser welding and reverse tilt laser welding.Each welding form has three sheets in combination,through the six plates combination's tensile test,fatigue test and finite element simulation analysis,we studied penetration tilt laser welding structure's tensile properties and fracture plasticity,fatigue property and fracture mode.In order to optimize the stainless steel laser welding structure,through improving the service performance,safety and reliability to provide theoretical and experimental basis.Tensile test study demonstrates:1.5mm+1.5mm and 2.0mm+2.0mm plate combination of positive tilt,reverse tilt laser welding structure's tensile fracture patterns were along the weld interface shear crack,tensile properties and plastic fracture were enhanced,among them,reverse tilt structure's tensile property was the most optimum.In the form of 0.8mm+2.0mm plate combination,they were all plate cracked,it did not make full use of the advantage of the welding form change,tensile properties did not improve.Fatigue test study demonstrates:1.5mm+1.5mm and 2.0 mm+2.0mm plate combination of positive tilt,reverse tilt laser welding structure's fatigue fracture patterns are along outer plate loading end crack.Fatigue strength is greater than the vertical structure's laser welding,the fatigue performance enhancements of positive tilt is the most obvious,it can be applied in engineering.In the form of 0.8mm+2.0 mm plate combination,fracture mode were along the plate loading end,positive tilt welding structure fatigue perform was very well,the fatigue performance of reverse tilt laser welding structure was the same as vertical laser welding,project feasibility needs to further research.The finite element analysis demonstrates:Dangerous areas concentrated on the outer plate loading end near the weld seam and the weld near inter plate loading right end,fatigue crack initiation from the two places,X axis direction of shear stress is less than the stress of the Y direction,initial crack continuously extended in the direction of thickness.The stress intensity factor analysis showed,in the process of crack propagate,positive tilt seam structure stress intensity factor was the smallest,crack extension speed is the slowest,the vertical structure of weld crack expanding is the fastest,so tilt seam structure fatigue life is longer,the fatigue strength is higher,the structure is better.