A Statistical Study on Evaluation for Defect and Deformation Capacity of Welded Connection

本计画的目的是定量评估高应变区有缺陷结构连接构件的断裂临界值。为了评价裂纹扩展后断裂的缺陷构件的变形能力，采用缺口板试件测量裂纹扩展后的COD和总应变量。当试件完全塑性后，COD和COD之间的关系几乎变为线性。但随着裂纹扩展，COD增量逐渐增大，直至线性关系消失。假设此时的COD值为裂纹扩展的临界值delta_c。可以看出，对于特定类型的钢，delta_c值几乎是恒定的，与试样的尺寸无关。因此，delta_c是钢构件断裂行为的有效临界值。其次，本文通过数值分析，对缺口板的变形能力和断裂行为进行了评估。考虑裂纹扩展和板厚的影响，采用有限元法进行了二维弹塑性分析。基于非线性断裂力学理论计算了COD和J积分，研究了COD、J积分与总应变ε的关系，确定了缺陷构件裂纹扩展后的断裂临界值，从而定量测量了梁柱节点在循环荷载作用下的断裂变形能力。根据非线性断裂力学中的COD概念，将缺陷连接的试验结果与缺口板试件的试验结果进行了比较，得到了缺陷长度、挠度幅值和断裂滞后能的关系式。

The purposes of this project are to evaluate quantitatively the critical value of fracture of defective structural connection members on high strain region. In order to evaluate the deformation capacity of defective structure members which fracture after crack propagation in according with the COD criterion, the COD and the overall strain epsilon were measured using notched plate specimens. The relationship between COD and epsilon becomes almost linear after the specimens turn fully plastic. However, as the crack propagates, the increment of COD increases until the linear relationship disappears. The value of COD at this point is assumed as the critical value of crack propagation delta_c. It can be seen that the delta_c value for a particular type of steel is almost constant regardless of the size of specimens. Therefore, it is thought that delta_c is an effective critical value for fracture behavior of steel members.Next, we evaluate the deformation capacity and the fracture behavior of notched plates by numerical analysis. The two-dimensional elasto-plastic analysis using the finite element method considering the effects of crack growth and plate thickness is devised. The COD and the J-integral based on the non-linear fracture mechanics are calculated, and further the relationships between the COD, the J-integral and the overall strain epsilon are investigated.Next, we determine the critical value of fracture of defective structural members after crack propagation and thereby to measure quantitatively the fracture deformability of beam-column connections under cyclic loading. The results of experiments on defective connections are compared with those on notched plate specimens to obtain a relational expression of defect length, deflection amplitude, and hysteresis energy to fracture based on the COD concept in non-linear fracture mechanics.