Cumulative Fatigue Damage And Life Analysis Of Tensile-Shear Spot-welded Joint

Resistance spot-welded is an important method for connecting of metal sheet, due to its advantages of easy to operate, cost effective, high efficiency, suitable for automatic control, very adapt large-scale production, so it is widely applied in many fields in modern society. Due to the complexity of spot-welded structure loaded in a multiaxial stress and load condition, the mechanics analysis is difficult. It is of great significance to study the fatigue damage and life of spot-welded structure. This paper intends to study the fatigue of tenson shear spot-welded joint, contents of this study is as followed:First, ST12car sheet metal spot-welded joint are loaded in the the constant amplitude cyclic loading in the MTS fatigue test machine. The fatigue life is analyzed with load, maximum load and the load ratio, the change rule of spot-welded joint under the nominal stress S-N curve which are used to predict fatigue life under constant amplitude loading. Through the fatigue destruction of spot-welded joint metallographic observation, its fracture mechanism and failure form can be drawn.Secondly, a finite element model of the combined action of tensile and shear specimens spot-welded plastic finite element simulation. According to the loading direction impose constraints and loads, set the loading process. Finite element results showed that:the stress concentration zones are in the vicinity of the weld nugget, nugget roots are not in this spot specimens with tensile shear test results similar to the situation observed in the fracture.Then, spot-welded joint were tested under the four different load levels of high-low and low-high of two-stage loading situation, by analyzing the two levels of load under the load order and load level’s influence on the fatigue cumulative damage and fatigue life, fatigue life and cumulative fatigue damage is analyzed and the value changing with the first-level load cycle number. Through the variable amplitude loading fatigue experiment, this paper analyzes the effect of load sequence, stress ratio, overload etc effect on life of welded joint. The damage accumulation in high-low loading levels is more than1which results in higher delayed cracking tendency, and in low-high loading levels is less than1which results in expending of tht crack.