在含裂纹钢结构的断裂评估中，通常假定断裂韧性试样的断裂抗力等于结构部件的断裂抗力。然而，这种假设通常会导致过度保守的骨折评估。这是由于主要承受拉伸载荷的结构部件失去了塑性约束。相比之下，由于弯曲模式，断裂韧性试样在裂纹尖端附近保持受约束的应力状态。约束损失对于具有高屈服拉伸比（=屈服应力/拉伸强度）的高强度钢来说是非常重要的，近年来，高强度钢已被广泛开发并广泛应用于结构中。 ISO 27306:2016规定了将从实验室试样获得的CTOD（裂纹尖端张开位移）断裂韧性转换为结构部件等效CTOD的方法，并考虑了约束损失。 该方法也适用于使用应力强度因子或J积分概念的断裂评估（见第9条）。 ISO 27306:2016涉及铁素体结构钢中裂纹状缺陷或疲劳裂纹引起的不稳定断裂。伴随大量韧性裂纹扩展的不稳定断裂和韧性断裂不包括在本文范围内。 根据ISO 12135[1]或BS 7448-1规定的试验方法测量结构钢的CTOD断裂韧性。开裂部件的断裂评估是在相关组织中使用FAD（失效评估图）等既定方法进行的，ISO 27306:2016中未提及其细节。 它可以用来消除常规断裂力学方法中经常出现的过度保守，并从结构钢的断裂韧性准确评估结构部件的不稳定断裂起始极限。 这也可用于合理确定材料的断裂韧性，以满足结构部件性能的设计要求。

In fracture assessments of steel structures containing cracks, it has generally been assumed that the fracture resistance of fracture toughness specimens is equal to the fracture resistance of structural components. However, such an assumption often leads to excessively conservative fracture assessments. This is due to a loss of plastic constraint in structural components, which are subjected mainly to tensile loading. By contrast, fracture toughness specimens hold a constrained stress state near the crack-tip due to bending mode. The loss of constraint is significant for high strength steels with high yield-to-tensile ratios (= yield stress/tensile strength) which have been extensively developed and widely applied to structures in recent years. ISO 27306:2016 specifies a method for converting the CTOD (crack-tip opening displacement) fracture toughness obtained from laboratory specimens to an equivalent CTOD for structural components, taking constraint loss into account. This method can also apply to fracture assessment using the stress intensity factor or the J-integral concept (see Clause 9). ISO 27306:2016 deals with the unstable fracture that occurs from a crack-like defect or fatigue crack in ferritic structural steels. Unstable fracture accompanied by a significant amount of ductile crack extension and ductile fractures are not included in the scope hereof. The CTOD fracture toughness of structural steels is measured in accordance with the established test methods, ISO 12135[1] or BS 7448-1. The fracture assessment of a cracked component is done using an established method such as FAD (Failure Assessment Diagram) in the organization concerned, and reference is not made to the details thereof in ISO 27306:2016. It can be used for eliminating the excessive conservatism frequently associated with the conventional fracture mechanics methods and accurately assessing the unstable fracture initiation limit of structural components from the fracture toughness of the structural steel. This is also used for rationally determining the fracture toughness of materials to meet the design requirements of performance of structural components.