Natural Frequency Change Characteristics Of Stainless Steel Laser Welding Joint In The Process Of Fatigue Damage

Since the1990s, the research and development of stainless steel railway vehicles hasbeen investigated in China. Resistance spot welding technology had been used in productionof the body of stainless steel railway vehicle all time, but the body structure of resistance spotwelding exists defects of side penal deformation, discontinuity and no beautiful. In view ofindustrial developed countries of Europe, the US and Japan have adopted laser weldingtechnology to produce stainless steel railway vehicle which fast, high-grade and lightweight,in recent years, China also began to research and develop the laser welding technology whichapplied to between stainless steel outer panel and framework, and the research of stainlesssteel body with laser welding in service life and security in using, is a step toward to achievethe goal of instead of resistance spot welding with laser welding.In this paper, it is researched that fatigue damage and life prediction of laser lap jointsand spot welding joint, with natural frequency for damage variables, surveys laser weldingand spot welding joints samples different stage fatigue damage through the fatigue test anddynamic response test, and put forward the method of fatigue life of laser welding and spotwelding joints. At the same time, it is simulated the natural frequency of the crackpropagation variation characteristics of laser welding and spot welding joints withdimensional Finite Element, compared with the experimental results proved, dimensionalFinite Element can simulate the crack propagation variation characteristics of laser weldingand spot welding joints very well.Main conclusions are reached as follows:1. In the fatigue process, the natural frequencies of laser welding and resistance spotwelded joint specimens have different rate of decline with the increase of fatigue cycles,decline rate of the eleventh-order natural frequency is the largest and mostregular.2. In finite element analysis, with the crack expand of laser welding model its naturalfrequency dropped uniformly,that is sample of laser welding cracks, uniform degree of injurya substantial increase in the specimen quickly destroyed; resistance spot welding after themodel of the crack length reaches3mm, the only obvious change of the natural frequency andthe degree of injury smaller decline increases as the crack to continue to expand, when thecrack is large enough, the degree of injury, it has rapidly increased.3. Laser welded joints in the60%life when cracks began to initiation, to80%of thelife of a macroscopic crack, the damage extent of50%, with the fatigue process to continuethe rapid crack propagation to the specimen is destroyed. Resistance spot welding joints in thelife expectancy of about30%when the crack initiation, about60%life, a macroscopic crack, the degree of injury was50%, reaching about90%life, crack rapid expansion until the spotwelded joint is completely destroyed.4. It can be build a life prediction model through the relationship of natural frequencyrange and the damage, through proven，the calculate results are same to the test results.