Abstract In this work, the unified constraint-based FAD (failure assessment diagram) assessment methodology has been investigated and developed for ductile fracture in cracked pipes. Two unified constraint parameters Ap and Ad are utilized to incorporate both in-plane and out-of-plane constraints. The results show that the FAD approaches based on two-parameter K-Ap and K-Ad can predict similar fracture initiation loads. With decreasing crack length and depth, the constraint level decreases and fracture toughness increases, thus the predicted fracture load increases. For some shallow and short pipe cracks with lower constraints, the unified constraint-based FAD assessment can reduce conservatism degree of the conventional FAD assessment. For some deep and long cracks, their constraint levels may be higher than the standard plane strain specimen, and the application of the unified constraint-based FAD assessment approaches may eliminate non-conservative assessment in the conventional FAD approach. The unified constraint-based FAD approaches and CDF (crack driving farce) approaches using parameters Ap and Ad can produce similar fracture prediction results, thus they are basically equivalent.

中文翻译：

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裂纹管道韧性断裂的基于统一约束的 FAD 评估

摘要 在这项工作中，研究和开发了基于统一约束的 FAD（失效评估图）评估方法，用于裂纹管道的延性断裂。两个统一的约束参数 Ap 和 Ad 用于合并平面内和平面外约束。结果表明，基于双参数 K-Ap 和 K-Ad 的 FAD 方法可以预测类似的断裂起始载荷。随着裂纹长度和深度的减少，约束水平降低，断裂韧性增加，因此预测的断裂载荷增加。对于一些约束较低的浅管和短管裂纹，基于统一约束的FAD评估可以降低传统FAD评估的保守程度。对于一些深长裂纹，其约束水平可能高于标准平面应变试件，统一基于约束的FAD评估方法的应用可以消除传统FAD方法中的非保守评估。基于统一约束的FAD方法和使用参数Ap和Ad的CDF（crack drive farce）方法可以产生相似的裂缝预测结果，因此它们基本等效。