The stress distributions in a infinitely large circular plate welded at its centre are discussed in this paper. When plastic deformations take place in a portion of the plate, adequate corrections are to be made upon elastically determined stress values, the amounts of which can be graphically estimated considering the equilibrium and boundary conditions. The stress variations are calculated by each small time intervals and superposed on the previous stress distiibutions. Fig. 9 and table 3 are the required residual stresses and plastic ranges when a line heat source, strength of 5000 (cm2-°C), appeared at the centre.
If a construction is made of steel by welding, some contraction of length occurs generally. When base metal plates are restrained externaly and the free contraction is prevented, extrcardinary large welding-stresses arise in comparison with the case in which base metal plates are hold freely. Undoubtedly, the stress induced by welding becomes large in accordance with the large restraint-degree, in the extreme, weldments do crack. In this research, the author prepared many rectangular special specimens made of an alloy steel. The form of such special specimens was deviced by the author. Next, he arcwelded the V-groove in the center of the specimen and investigated the relation between the probability for the occurrence of longitudinal cracks in the weld metal or in the heat-affected zone and the length of the parallel part of the base metal which is perpendicular to the bead line and parallel to the plate surface. And the following results were obtained. Namely, these cracks are apt to occur in the welded construction of which parallel part is shorter. In other words, longitudinal cracks, which are parallel to the bead line and exist in the weld metal or in the heat-affected zone, are apt to occur in the case which the lateral restraint-degree, that is, the restraint-degree in the direction perpendicular to the bead line, is larger. Further, in this research, using θ-form specimens which professor Y. Tanaka proposed, the author made an experiment, and confirmed the following facts. The larger the cross section of the grcove welded is, the larger the amount of the lateral contraction by welding becomes. In the case in which the area of crcss section of the groove is constant, the lateral contraction by welding changes according to the electrode or the condition of the weld-deposition. Owing to these results, the following supposition may readily be made. Namely, if sections of the groove to be welded and weldingelectrodes, which result in large lateral deformations, are applied to the welding of the part of construction which is under large restraint, longitudinal cracks in the weld metal or in the heat-affected zone may be apt to occur.