In-plane shrinkage strains and their effects on welding distortion in thin-wall structures

It is difficult to predict welding distortion in large welded structures and even more difficult to achieve both fast and accurate distortion predictions in such structures. Distortion modeling of large welded structures is always associated with enormous computational cost in terms of computer memory requirement and CPU time. This research work was conducted to obtain better understanding and characterization of the plastic deformation that leads to in-plane shrinkage in thin-wall structures. It also aimed to develop a fast and accurate approach for predicting the welding distortion in large thin-wall structures. Some examples of this type of structures are vehicle underbody frame and motor compartment frame.; The engineering approach was developed based upon the principle that plastic deformation is the root source of welding distortion. A hypothesis was proposed regarding such development and it is stated as the following: welding distortion can be accurately predicted if the plastic deformation the same as or similar to that induced by welding is introduced into the finite element analysis (FEA) model. On one hand, the research was intended to validate the hypothesis; on the other hand, the hypothesis served as a guideline to the research. Specifically, there were two important aspects of the research work as implied in the hypothesis: (1) characterizing the plastic deformation produced by welding, and (2) generating the plastic deformation equivalent to the actual one in the FEA model without resorting to detailed transient analysis.; After being verified by the experimental results, the FEA model was utilized to perform the welding simulations of three types of simple joints including butt-welded plates, Tee joint, and plate with slot weld. These weld joints had the same structural and process characteristics as those of large thinwall automotive body structures. The analysis results were extracted and analyzed to study the in-plane shrinkage and plastic behaviors. The plastic strain distributions were examined in combination with the peak temperatures experienced during welding and the material softening at elevated temperatures. The in-plane shrinkage was correlated to the distribution characteristics of plastic strains, and furthermore the relationships between the plastic strains and their influencing factors were established. It was concluded from this study that the in-plane shrinkage plastic strains are determined by the peak temperature and material's softening temperature range, and that peak temperature is the thermal parameter that controls the plastic strains. (Abstract shortened by UMI.)...