Experimental study of brittle fracture with plastic strain at cruciform butt joints. Report 3: Effect of bi-axial loading condition

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, affected the fractures. In the first report, monotonic loading test results are described using cruciform butt specimens welded by three types of welding consumable. The effects of mechanical properties of weld metal are examined on fractures under monotonic loading. And in the second report, test results are described on the effects of cyclic loading like the earthquake. In this third report, monotonic bi-axial loading tests are described for the results under two types of of bi-axial loading condition using the cruciform butt specimens. The purpose of this paper is to examine the effect of bi-axial loading condition on fractures. The main results are summarized as follows. (1) The effects of the bi-axial loading condition on the elongation capacity and the fracture-surface appearance are small compared to the ductility of the material and temperature of the specimen. And by this experiment, the following considerations about the elongation capacity and the fracture-surface appearance becomes more reliable. (2) The ductility of weld metal greatly affects the elongation capacity regardless of other conditions. In the case of the cruciform butt joints with brittle weld metal, the temperature of the specimen also greatly affects the elongation capacity. (3) The fracture-surface appearance of the specimen is mainly affected by the temperature of the specimen that substituted for high strain rates.

阪神・淡路大地震において、鋼製建造物フレームの梁-柱結合部に塑性歪を伴った脆性破壊を観察した。溶接金属の機械的性質とくに延性が破壊に影響すると考えた。第1報において、3タイプの消耗溶接で溶接した十字型突合せ継手を使用した単調負荷試験の結果を報告した。単調負荷の下で、溶接金属が破壊に及ぼす機械的特性の影響を調べた。第2報において、地震のような繰返し負荷の効果を調べた結果を報告した。第3報である本報告で、十字型突合せ継手を使用した2タイプの2軸負荷条件下における、単調な2軸負荷試験結果を報告した。2軸負荷条件が破壊におよぼす影響を研究することを目的とした。以下、得た結果を総括した。(1)材料の靱性および試験片の温度と比較して、伸びおよび破壊表面の外観に及ぼす効果が2軸負荷条件では小さかった。(2)他の条件と比較して、溶接金属の靱性が伸張許容度の大きく影響した。なお、十字型突合せ継手については、試験片温度もまた伸張許容度に大きく影響した。および(3)試験片の破断面の外観は高速歪の代替えである試験片温度に主として影響を受けた。