Study On Numerical Prediction Method For Fillet Weld's Angular Distortion

Bridge and ship manufactures have always been troubled by welding distortion which results in. the rising of operating cost and the delaying of production. With the rapid improvement of computer calculating ability and the advances of numerical calculation technique, numerical simulation with finite element analysis has become the most important means for welding distortion predictions. To enhance product's quality and improve production efficiency, it is of great engineering significance to seek simple and available numerical method to predict welding distortion.Thermal elastic-plastic finite element method is the most basic numerical method which tracks the instantaneous temperature fields and stress fields throughout the whole welding thermal cycle and can achieve high precision. But when it comes to the actual large-scale structure, this method occupies not only computer resources but also lengthy computing time. So it only adapts to analyze small weld joints to study the forming mechanism of welding phenomenon. When it comes to large-scale structure's welding distortion, simplified linear elastic or elastic plastic finite methods are adopted. However, the existing simplified methods' prediction effect is not so good for fillet weld's angle distortion. This paper introduces the simplified methods' characteristics and points out that only when we understand weld distortions' mechanisms rightly can we make the best use of simplified methods to predict welding distortion.This paper takes nonlinear finite element analysis as worktable, with a welded T-joint as the object to study the forming mechanism of fillet weld's angle distortion. The research shows that the transverse inherent normal strain component makes the right angle a little smaller, while both of the other two inherent normal strain components make the right angle a little bigger. The actual distortion, that the right angle becomes smaller, mainly comes from the inherent shear strain component which is vertical to the weld line and exists in the plane paralleling to weld line, but not comes from the traditional thought uneven transverse inherent component. The other two shear strain components' effect on the angle distortion can be ignored.By handling and analyzing the results of thermal elasto-plastic numerical analysis, this paper presents double paraboloid distribution model of the inherent shear strain, and deduced the experiential formulas for the undermined parameters in the model function expression those varying along with weld length, heat input density, weldment thickness and so on basing on a series of numerical experiments. Basing on double paraboloid distribution model of the inherent shear strain, an approach named inherent shear strain method is ulteriorly put forward to forecasting fillet weld's angular distortions. For this method, the corrected approximation of inherent shear strain is exerted to the fillet weld zone as initial strain of the welded structure and angle distortion is predicted by elastic analysis. The welding angle distortions of a T-joint and a stiffened plate are predicted by inherent shear strain method and corresponding welding experiments are carried out. The prediction results agree well with the experiment ones.Inherent shear strain method rectifies the direction mistake of traditional simplified methods those predict angle distortion by transverse normal inherent strain, and expands the applicable distortion styles for simplified methods. It can rapidly, economically and comparatively exactly analyze the compositive distortion effect of large welded structures where the fillet welds and surrounding elastic structures work mutually.