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

研究钢结构焊接连接在几十年一遇的大地震作用下的力学性能或行为具有重要意义。研究了焊接接头或贱金属在大变形条件下的力学性能，并对其性能要求进行了探讨。然后，研究了焊接区缺口长度与所需性能之间的关系，为确定极限允许流动长度提供了基础数据，得到了以下结果：1)高应变速度下断裂韧性的转变温度明显高于低应变速度下的转变温度。2)焊接区断裂韧性是导致断裂的重要因素，而不是焊接缺陷或垫片的缺口。在温度低于转变温度的情况下，给予高应变速度时，变形显著减小。3)为了处理断裂力学中的三维裂纹，对三维公式进行了标准化，并对其精度进行了检验。然后，确定了弹性范围内K（应力强度因子）等于J值，单调加载下J值几乎等于J ^^值。因此，将j^^值应用于三维问题成为可能。

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.