機械的性質の不連続部をふくむ材の静的引張強度に関する基礎的研究

抄録

In the welded joints, chemical composition and metallurgical structures of weld metal and heat-affected zone are different from those of base metal and change continuously in them. Mechanical properties in them will be also different from those in base metal. Mechanical behaviors of weldments will be different from those of homogeneous and isotropic materials. It will be important, therefore, to investigate the effect of the heterogeneity in mechanical properties on the mechanical behaviors of weldments.
In the present report, the welded joints are idealized as a model consisting solely of base metal and a soft interlayer as shown in Fig. 1. Such model specimens are made by flash butt-welding or narrowgap manual welding. Static tension tests of model specimens were made for several combinations of interlayer thickness and specimen diameter and several combinations in strength of base metal and soft interlayer. The quantitative evaluation of tensile strength is also made theoretically.
The results obtained are as follows.
(1) Static strength of welded joints including a soft interlayer depends upon the relative size of a soft interlayer, or the relative thickness X of interlayer thickness to specimen diameter for round bar specimens, and the relative thickness Xt of a soft interlayer to the plate thickness and the plate thickness to width ratio t₀/W₀ for plate specimens.
(2) The strength is elevated from that of a soft interlayer as the relative thickness (Xor Xt) decreases. When the ratio t₀/W₀ decreases from unity under a constant Xt-value, the strength rises to a certain definite value depending upon the Xt-value. The plate width W_∞ above which the strength becomes almost the same as that of an infinite plate is roughly given by W_∞=5t₀(Xt≤1).
(3) The elevation of tensile strength is influenced by strength of the base metal as well as the value of X. Strength of welded joints increases predominantly for small values of X as the strength of the base metal is large. The tensile strength of welded joints is evaluated quantitatively by the authors' theoretical analysis and the experimental equations.
(4) Ductility of the welded joints depends upon the value of X and the ratio κ of tensile strength of base metal to that of soft metal. The ductility decreases with decrease of X up to a certain minimum value, after which it increases in the opposite direction. The minimum value becomes smaller as the κ-value increases.