In the analysis of welding mechanics, it is difficult to analyze large-scale structures because of welding-specific moving local nonlinearity. In this research, the authors proposed a new numerical method for welding mechanics based on the Dynamic Explicit FEM. In the proposed method, the temperature step is divided into hundreds of time steps as implicit FEM and the displacements are computed for each time step based on dynamic explicit FEM until the whole system reaches the static equilibrium state. And, to achieve the static equilibrium state faster, modified mass and damping matrix are introduced. The modified mass and damping matrix are based on the Courant condition and the vibration theory, respectively. The proposed method and static implicit FEM are compared at the final path of multilayer welding of thick bead-on-plate to verify validity and accuracy. The transient and residual deformation and stress distribution of the proposed method show good agreement with those of static implicit FEM. In addition, the computing time and memory consumption of the proposed method are 1/12 and 1/40 times shorter than those of static implicit FEM, respectively, in 243,243 degree of freedom model. It is found that the proposed method has an advantage in large-scale analysis whose nodal points are more than tens of thousands.
The technique which can measure the transient welding deformation directly is very important to investigate the mechanism of welding deformation. In this study, in-situ displacement measurement method using digital camera is self-developed. This system is non-contact type and it doesn't need any complicated optical systems but it can measure the in-situ displacement over the full-field in high accuracy by using digital image correlation technique. Therefore, it is considered to be useful and easy to apply to practical problems. The number of measuring points that can be obtained at a time is more than 10 million. It is the same as the available pixels of the digital camera. Furthermore, since the active light source is not necessary in this system, the influence of the fluctuation of the atmosphere caused by the high temperature area is small.In this study, the detail of the proposed system is performed and it is applied to the transient in-plane deformation problem under very high brightness lightened by welding arc. Through the comparison between the experiment and Thermal-elastic-plastic FE analysis, the validity of the transient transverse shrinkage distribution which is measured by proposed system is verified. The residual deformation is also investigated to check the accuracy and usefulness of the proposed system.
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