综合考虑微观力学和宏观力学特征，研究了钢解理断裂的脆韧性转变。断裂安全设计中过渡温度方法的演变基于这样一个概念，即在较高的过渡温度范围内，金属延性系数应优先于机械约束系数。通过动态断裂试验确定的转变温度范围为改进钢的开发提供了必要的指导。断裂力学的概念强调宏观断裂韧性由机械约束和缺陷严重度因素控制。 虽然这是事实，但在一定范围内，这些原则得到了不必要的延伸，表明转变温度对断裂过程没有基本意义。与流行的观点相反，这些概念并不是对立的:冶金因素决定了金属固有的延展性，而机械参数用于描述金属对特定应力状态的响应。最近对大截面尺寸效应的研究表明，如断裂力学理论所预测的，增加的机械约束会导致转变温度的变化。 然而，这些位移的幅度相对较小，更重要的是，不会消除转变温度特性。 断裂韧性在狭窄温度范围内迅速变化，这表明断裂力学的实际工程应用必须基于简单类型的转变温度试验。由于KIc和KId定义的断裂韧度试验的尺寸大、费用高，以及非常陡峭的斜率温度依赖性，常规断裂力学试验不适用于转变温度定义。 对于这种用途，测试必须能够根据KIc和KId参数进行索引。动态撕裂（DT）测试代表了最先进的工程测试，它提供了真实转变温度范围和断裂力学适用于该范围的特定间隔的准确索引。还定义了断裂力学性能范围之外的高断裂韧性的温度区间。尺寸效应可以解释，并与预期的转变温度变化有关。 所有这些因素都已整合到简单的参考图中，该图显示了缺陷的大小- 在过渡范围内断裂萌生的应力关系。断裂分析图（FAD）程序现在扩展到覆盖整个厚度范围。这些额外的研究证实了它的有效性，不再完全基于经验因素。相反，经验因素有助于验证断裂力学理论的预测，并继续为分析方法的可靠性提供工程保证。

The brittle-to-ductile transition for cleavage fracture of steels has been examined with integrated considerations of micromechanical and macromechanical features. The evolution of transition temperature approaches to fracture-safe design has been based on concepts that metal ductility factors should override mechanical constraint factors, in the higher temperature range of the transition. The transition temperature range, determined by dynamic fracture tests, has provided the necessary guidance for the development of improved steels. Fracture mechanics concepts emphasize that macroscopic fracture toughness is controlled by mechanical constraint and flaw severity factors. While true, within limits, there has been an unwarranted extension of these principles to signify that the transition temperature does not have a basic significance to fracture processes. Contrary to popular beliefs, these concepts are not in opposition: metallurgical factors determine the intrinsic metal ductility, and mechanical parameters serve to describe the response of the metal to specific stress states. Recent investigations of the effects of large section size have demonstrated that increased mechanical constraint results in shifts of the transition temperature, as predicted by fracture mechanics theory. However, these shifts are of relatively small magnitude and, more importantly, do not eliminate transition temperature characteristics. The rapid changes in fracture toughness which develop over a narrow temperature range indicate that practical engineering use of fracture mechanics must be based on transition temperature tests of simple types. Conventional fracture mechanics test are not practical for transition temperature definitions because of large size, prohibitive expense, and the very steep-slope temperature dependence of KIc and KId defined fracture toughness tests. For such use, the tests must be indexable to KIc and KId parameters. The Dynamic Tear (DT) test represents the most advanced engineering test which provides accurate indexing of the true transition temperature range and the specific interval in this range for which fracture mechanics applies. The temperature interval of high fracture toughness which is outside the range of fracture mechanics capabilities is also defined. Size effect can be interpreted and related to expected transition temperature shifts. All of these factors have been integrated into simple reference diagrams which index flaw size-stress relationships for fracture initiation in the transition range. The Fracture Analysis Diagram (FAD) procedure is now extended to cover the full range of thickness. Its validity is confirmed by these additional studies and is no longer based entirely on experience factors. Conversely, the experience factors serve to validate the predictions of fracture mechanics theory and continue to provide engineering assurance that the analytical methods can be relied on.