No abstract

In order to predict the distortion generated by welding with high accuracy, distortion with fillet welding was measured by three-dimensional photographic measurement. Then, the experiment was simulated by three-dimensional thermal elastic-plastic analysis by FEM. The important matters that should be noted on predicting the distortion with high accuracy were shown by comparing with the results of the experiment and those of the analysis. The results of measuring temperature could be accurately simulated by non-steady state thermal conduction analysis based on FEM. In carrying out the elastic-plastic analysis, four conditions (equilibrium equation, constitutive equation, condition of compatibility and yield condition) should be satisfied. In welding, the temperature largely changed from a melting temperature to a room temperature. So, yield stress of materials largely changed, too. In particular, yield stress becomes about zero above 700℃. The analysis should be carried out under the yield condition that equivalent stress generated in temperature increment ∆T did not exceed yield stress of materials at high temperature above 700℃. It should be sufficiently recognized that the obtained results were not reliable if the yield condition was not satisfied. Angular distortion generated in fillet welding could be accurately predicted by regarding the weld metal as a deposited metal not assuming that a deposited metal zone was a simple triangle. Specifying an influence factor on longitudinal bending distortion was difficult because the absolute value was small. However, it was indicated that the reasonable result could be obtained by regarding the weld metal as a deposited metal because the absolute value of longitudinal bending distortion at pass ② (the second pass) of which restraint was severer became smaller than that at pass ① (the first pass).

The aim of this paper is to develop the high efficiency and high quality fillet welding technique using the combination of hot wire system and Laser welding. The melting of filler wire depends on wire current and there is an adequate vale of the current in each wire feeding speed. The leg length increases by the addition of filler wire compared with the non filler welding. The length is also larger than the laser irradiated area. This must be caused by the laser beam reflection on the molten pool surface. The results reveal that the parameter optimization leads to the stationary welding phenomenon. Besides, obtained welds have attractive properties, namely low heat input and low dilution.

No abstract

The enlargement of containership requires the higher tensile strength steel and thicker plate around the hatch coaming more than the prescribed classification rules. These call the concerns about the safety of brittle crack initiation and arrestability of hull structure. It is known that increasing of stress and thickness of plates will reduce the toughness of base metal and welding joints. Therefore, the authors conducted to assure the toughness of base metal and welding joint for new higher tensile strength steel of 460MPa yield strength (YP460) and 60mm thickness. It has been considered that weld assembled steel plate structure has some arrestability at intersections of plates, though there are no prescription on the rules. And it was reported that very thicker mother plate has not enough toughness to arrest brittle crack recently. The authors investigated the structural arrestability by model testing and FE analysis and established it. Furthermore, structural details for intersections were also established. Both preventing the brittle crack initiation and arresting the brittle crack of weld structure were described, focusing on developing higher yield strength and heavier thickness of YP460 for containership in this paper.