Study on non-linear fracture mechanics of welding connections of steel structure

研究钢结构焊接节点在几十年一遇的大震作用下的力学性能和受力性能具有重要意义。本文研究了焊接接头或母材在大变形下的力学性能，并探讨了它们所要求的性能。然后，研究了焊接区缺口长度与所需性能的关系，以获得确定极限允许流动长度的基础数据，结果表明：1）高应变速率下的断裂韧性转变温度明显高于低应变速率下的断裂韧性转变温度;结果表明，焊缝区的断裂韧性比垫板的焊接缺陷或缺口对断裂的影响更大。在低于转变温度的情况下，当应变速率较高时，变形量明显减小。3）为了处理断裂力学中的三维裂纹问题，对三维裂纹的计算公式进行了规范化，并对公式的准确性进行了检验。在弹性范围内，K（应力强度因子）等于J值，在单调加载下，J值几乎等于j^^值。因此，可以将j^^值应用于三维问题。

It is important to investigate the mechanical properties or the behaviors of welded connections in steel structures under large earthquakes which occur once in several decades. We have studied mechanical properties of welded connections or base metals under large deformation, and investigate the required properties of them. Then, the relationship between notch length in welded zone and the required properties was investigated in order to obtain the basic data for deciding limits allowed flow length, and obtained some results as follows.1) It was confirmed that the transition temperature of fracture toughness under high strain velocity was fairly higher than it under low strain velocity.2) It became clear that the fracture toughness of welded zone is more important factor than welding flaws or notches of backing strips for the fracture. It was also confirmed that the deformation became remarkably small when high strain velocity was given in case of lower temperature than the transition temperature.3) In order to deal with three dimensional cracks in fracture mechanics, three dimensional formula was standardized and accuracy of it was examined. Then, It was confirmed that K (stress intensity factor) is equal to J value during elastic range, and J value is almost equal to j^^ value under monotonic loading. Therefore, it became possible to apply j^^ value on three dimensional problems.