In the present work, a systematic and detailed investigation on the plastic collapse load of 90° structurally defected pipe bends under in-plane opening bending was performed using three-dimensional finite element (FE) analyses. The analysis considers the material behavior as elastic-perfectly plastic (EPP) with a large strain formulation option. The structural defects in the pipe bend models included were ovality at mid-portion and throughwall axial crack (TAC) at the crown portion. Ovality varied from 0 to 20 % with 5 % increment at each step while the normalized throughwall axial crack (TAC) parameter length a/D from 0 to 1 with an increment of 0.2 in each step. As per the recommendation of clause NB-3213.25 in Section III of ASME B&PV code, Twice-elastic slope (TES) technique was extensively used to determine the plastic collapse moment (PCM) for all simulated pipe bend models from their corresponding reaction moment versus angular rotation curve. The analysis illustrated that both ovality and throughwall axial crack (TAC) significantly affected PCM load of pipe bends and when combined, the effect was almost double. In pipe bend models with thin walls and short bend radius, both ovality and TAC were found to be more vulnerable and the effect decreased with an increase in bend radius and thickness. The experimental results for pipe bend's plastic collapse moment available in open literature were used to validate the present finite element (FE) procedure and a new improved structural assessment correlation proposed for pipe bends with ovality and TAC defects.

在目前的工作中，使用三维有限元 (FE) 分析对平面内开口弯曲下 90° 结构缺陷弯管的塑性坍塌载荷进行了系统和详细的研究。该分析将材料行为视为具有大应变公式选项的完美弹塑性 (EPP)。包括的弯管模型中的结构缺陷是中间部分的椭圆度和冠部的穿壁轴向裂纹 (TAC)。椭圆度从 0 到 20% 变化，每步增加 5%，而标准化的穿墙轴向裂纹 (TAC) 参数长度 a/D 从 0 到 1，每步增加 0.2。根据 ASME B&PV 规范第 III 部分 NB-3213.25 条的建议，二次弹性斜率 (TES) 技术被广泛用于根据所有模拟弯管模型的相应反作用力矩与角旋转曲线确定塑性坍塌力矩 (PCM)。分析表明，椭圆度和穿壁轴向裂纹 (TAC) 都显着影响了弯管的 PCM 载荷，当两者结合时，影响几乎是两倍。在具有薄壁和短弯曲半径的弯管模型中，发现椭圆度和 TAC 都更容易受到影响，并且影响随着弯曲半径和厚度的增加而降低。公开文献中可用的弯管塑性坍塌力矩的实验结果用于验证当前的有限元 (FE) 程序和为具有椭圆度和 TAC 缺陷的弯管提出的新的改进结构评估相关性。