ビード熔接による薄板の挫屈変形に関する研究

Abstract

Distortion due to welding is one of the most troublesome problems especially in welding of thin plate. The authors pointed out in the previous paper (M. Watanabe and K. Satoh; J. of J.W.S. Vol. 26 399/405) distortion in welding of thin plate is produced by buckling due to compressive thermal stress during welding. In this paper we studied on two fundamental problems for buckling of bead-on plate, that is to say, minimum half-wave length, below which a plate does not buckle, and maximum radius of curveture after buckling.Specimens used are rectangular steel plate of 700 mm long and 1.6 mm thick. In order to obtain time of buckling, deflections during cooling are measured by the apparatus as shown in Fig. 1, and the results are shown in Fig. 2. Deflection abruptly changes during cooling in moderately wide plate. It seems that plate buckles at this time, but in narrow plate abrupt change of deflection does not occur. For this case, the time of buckling was assumed as shown in Fig. 3. In order to obtain compressive thermal stress at the time of buckling longitudinal strain and temperature rise during cooling were measured. The results are shown in Figs. 5 and 6. Fig. 7 is an example of calculation of thermal stress at the time of buckling. Critical thermal stress σcr for each specimen is shown in Table 1.By considering the analogy betwcen buckling of an angle due to compression (Fig. 9) and buckling of bead-on plate, the critical inherent shrinkage is given by equation (4), in which k is a numerical factor dependent on aspect ratio L/B of the plate. k is represented by a linear function of (B/L)2 as shown in Fig. 10.Inherent shrinkage ξ1 due to welding, an example of which is shown in eq. (6), becomes to a critical value ξ1cr, then the plate buckles. If welding condition, and therefore inherent shrinkage, is constant, there is a minimum half-wave length or minimum weld length below which the plate does not buckle. In the case of panel specimen in Fig. 11, the minimum half-wave length is estimated about 190mm as shown in Figs. 12 and 13. Fig. 14 is minimum half-wave length of 1.6 mm thick plate for various breadth of plate and welding conditions.It has been already known that maximum deflection of buckled plate is linear to square of half-wave length. It implies that maximum radius of curveture is independent to half-wave length. Maximam radius of curveture for varius breadth of plate is shown in Fig. 15.