After the experience of Hanshin-Awaji Earthquake, demands for full penetration welding joint with large plate thickness have been increased to improve the performance of bridges under severe earthquake. At the same time, the full penetrated T-joints without significant defects are required from the fatigue strength point of view. In case of conventional methods, removable backing material or back gouging are employed. When the removable backing material is used, root openings are required and assembly process becomes complicated. The gouging produces large noise and fume which are not welcome for good working environment. To achieve defect free full penetration T-joint without environmental problem, high current pulsed MAG welding is introduced as an alternative method. By using this welding method, the plate with thickness from 15 to 30 mm can be welded without back gouging. It is reported that no welding defect occurs when the plate thickness is less than 17mm1). However, when the plate thickness is over 25 mm, the pear-shaped bead cracking were sometimes generated if appropriate welding conditions are not selected. Therefore, in order to apply this welding method for the construction of bridges, it is necessary to clarify the welding conditions which can prevent the formation of pear-shaped bead cracking.
In this study, the influence of the welding conditions on the formation of pear-shaped bead cracking is examined through the experiments of the full penetration welding of T-joints. And the same problems are analyzed using Finite Element Method. The formation and growth of pear-shaped bead crack in T-joints welded by full penetration high current pulsed MAG welding can be simulated using temperature dependent interface element which is introduced in the thermal-elastic-plastic FEM analysis.
Results of experiments show that the pear-shaped bead cracking is not formed when the heat input is greater than 2,500 J/mm or when the penetration bead is formed. However, both large heat input and large penetration bead (deep penetration compared to the penetration width) have negative influence on hot crack formation according to the commonly accepted knowledge. To understand these experimental results, FEM simulations are conducted and influences of heat inputs and size of penetration bead are investigated.
