溶接欠陥を有する溶接接合部の脆性破壊に関する破壊力学的研究

Abstract

If there were cracks in steel material, they could be the rupture starting points and the important factors for the fracture of steel structures. In the beam-to-column of steel structure, it is difficult to weld members completely, so there also be defects. When the earthquake would occur, the existence of cracks would involve a high degree of risk for the fatal fracture of the steel structure frame. Therefore we need to understand the quantitatively of the defects and the mechanical property in column-to-beam joints, or estimate the member's strength for the case that there were cracks. In this article, we proposed the method for evaluating defects in welded joints with J-integral and compared with the method described in WES 2805 at first. Next, We estimate the fracture of welded joints with cleavage fracture stress. Then we presumed the mechanical property of heat-affected zone with the hardness and stress-strain relationship of steel material. To get material's cleavage fracture stress, we conducted tensile and elastic-plastic finite element method. 1) We can evaluate the fracture in beam-to-column joints with the cleavage fracture stress. Then the rupture starting points might be un-welded points and the points with ductile cracks. 2) When we evaluate the fracture at heat-affected zone in beam-to-column joints, we can used the cleavage fracture stress of steel for columns or beams