| The series of cold-rolled301L stainless steel plates are the main material in manufacture of lignt-weight vehicle body. This kind of steel has the characteristics of cold-rolled hardened and non-hardening,the fatigue fracture behavior and mechanism of spot welding structure are very different from steady-state alloy. At present, research on fatigue behavior of cold-rolled301L welding structural is few, which forms a great contrast to urgent engineering needs. This paper, based on the stress intensity factor and the finite element notch stress, in order to achieve the welding spot specimen fatigue life prediction assessment, has conducted a systematic analysis of the fatigue life of301L spot welding joints and its multi-spot welding structure, studied relationships and patterns of stress intensity factors and notch stress with fatigue life. With analysis of fatigue fracture and fatigue crack propagation path of Spot welding fatigue fracture in the301L specimen, this paper studied fatigue fracture mechanism of spot welding joints and multi-spot welding specimen and the law of fatigue crack expansion in the plate, as well as the influence of welding defects on the fatigue fracture behavior.The study results show that, the equivalent stress intensity factors and notch stress can be used as the basis of stress parameters of different forms of301L plate spot welding joint fatigue life analysis, and the analysis values reflects a good correlation with the experimental data. With the stress intensity factor of301L stainless steel welding decreases, the average fatigue life of welding spot test pieces showing the increasing trend in the same pattern. With the application of two stress intensity factor analysis method proposed by Pook and S.Zhang, the average fatigue life of301L board structure welding spot joint assessment and prediction can be accomplished. Through coarse grid finite element analysis, maximum notch stress of301L single and multi-spot welding specimen fatigue fracture under the average fatigue limit loads are230-270Mpa. With the thickness of plate or the nugget diameter increases, stress value in the welding spot joint between the plate decreasess、the fatigue load increases, and due to the interaction between the solder in multi-spot structure, the notch stress of the solder joint forefront will increase, fatigue loads will reduce.301L spot welding joints produced the two-sided and single-sided fatigue fracture. The crack began in the HAZ near the nugget where has the maximum notch stress,grow with semi-ellipsoid shape in the direction of thickness and width, and the fracture has no typical fatigue striations; fatigue fracture is made up of the center smooth area and the ridge stripe stairs district, the steps of the ridge and the fatigue crack is vertical, there are fatigue striations on narrow arc; the irregular plate will lead to the heat-affected zone folding defects, increasing the notch stress. The stress between different joints will change expansion path of cracks in the plate,the specimens with smaller stress in the loading direction has a higher fatigue loads. |
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