突合せ十字継手の塑性変形を伴う脆性破断に関する研究 １ 単調荷重下における溶接十字継手の脆性破断発生と伸び能力

Abstract

In The Great Hanshin-Awaji Earthquake Disaster, brittle fractures with plastic strain were observed in beam-column connections of steel building frames. It is considered that the mechanical properties of weld metal, especially the ductility of weld metal, have a substantial effect on the fracture.In this paper we describe bi-axial loading test results using cruciform butt specimens under monotonic loading. The specimens are modeled on a cruciform joint by taking out the part of the beam-flange to column-flange connection and welded by two types of welding consumable. So we use two series of specimen that have different ductility. The purpose of this paper is to examine the effect of the ductility of weld metal on fractures under monotonic loading at room temperature and -40°C The high strain rates during the earthquake are substituted for static tests at -40°C.The main results under monotonic loading are summarized as follows. 1) The fracture-surface appearance mainly depends on the specimen temperature and hardly depends on the ductility of the weld metal. 2) In the case of the ductile weld metal specimen, it presented a brittle fracture-surface at -40°C, but the elongation is almost equal to that at room temperature which presented a ductile fracture-surface. 3) In the case of the brittle weld metal specimen, the elongation at -40°C fell to less than 1/2 of that at room temperature, mainly because the brittle fracture occurred after the plastic deformation. 4) In the case of the brittle weld metal specimen, the elongation in the bi-axial tests tends to become large with specimen temperature rising. 5) In the range of this experiment, only the absolute values of reduction of area in tensile test correspond to the elongation capacity in the bi-axial loading test using cruciform butt specimens.