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In order to reveal the failure mechanism of the weld structure of the new generation launch vehicle in ultralow temperature environment and to provide scientific basis for improving the welding quality and the carrying capacity of the tank, in this project, this paper studied full-field mechanical parameters inversion and failure mechanism of non uniform joints at ultralow temperature environment. Firstly, the test method of ultralow temperature mechanical properties of aluminum alloy welded specimens based on DIC is described, and an open system for simulating the ultralow temperature environment was established. Secondly, two specimens based on the welding and friction stir welding were studied. In this paper, the relationship between load and stress strain curve, strain distribution along the direction of the load and the strain concentration factor of the welded specimen were analyzed. Results show that the friction stir welding specimen was better than the fusion welding specimen in mechanical properties. Finally, this paper also compared the influence of test area effect on, and it show that the measurement error was not more than 8.8% when heat affected zone size was between 2～8mm. The three tensile specimens were all broken in the gauge length and the fracture location was consistent. There was obvious plastic deformation near the fracture. The microstructure was observed. The tensile specimens were all broken in the gauge length and the fracture location was consistent. There was obvious plastic deformation near the fracture. The microscopic morphology observation showed that the whole section showed shear dimple morphology, and no material defects were observed. The fracture mode of the tensile fracture is plastic fracture.This project would provide a scientific basis for the welding process optimization and improvement of the ultra temperature tank of the new generation launch vehicle in China.
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