1.1 本标准涵盖了根据临界裂纹尖端张开角（CTOA）ψ确定金属材料对稳定裂纹扩展的抵抗力 c 和/或裂纹张开位移（COD），δ 5. 阻力曲线 ( 1. ) . 2. 该方法特别适用于疲劳预裂纹试样，这些试样表现出低约束（裂纹尺寸与厚度和未裂纹韧带与厚度之比大于或等于4），并在缓慢增加的远程施加位移下进行测试。试样为致密试样C（T）和中间裂纹拉伸试样M（T）。根据本标准测定的抗断裂强度为ψ c （临界CTOA值）和/或δ 5. （临界COD阻力曲线）作为裂纹扩展的函数。使用单个试样或多个试样程序来表征这两个抗断裂参数。这些断裂量是在加载的开启模式（模式I）下确定的。 本标准不包括环境和快速加载速率的影响，但用户必须意识到加载速率和实验室环境可能对材料断裂行为的影响。 1.2 如果裂纹尺寸与厚度之间存在差异，则根据本标准评估的材料不受强度、厚度或韧性的限制( 一 / B )比率和韧带厚度( b / B )比值大于或等于4，这确保了C（T）和M（T）试样的整体裂纹前缘约束相对较低且相似 ( 2. , 3. ) . 1.3 以国际单位制表示的值应被视为标准值。本标准不包括其他计量单位。 1.4 本标准并不旨在解决与其使用相关的所有安全问题（如果有的话）。本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认的标准化原则制定的。 =====意义和用途====== 5.1 该试验方法根据裂纹尖端张开角（CTOA）、ψ和/或裂纹张开位移（COD）、δ来表征金属材料对稳定裂纹扩展的抵抗力 5. 在感兴趣的实验室或应用环境下。该方法特别适用于疲劳预裂纹试样，这些试样表现出低约束，并在缓慢增加的位移下进行测试。 5.2 在进行断裂试验时，用户必须考虑加载速率和实验室环境对断裂参数的影响。 用户应进行文献综述，以确定之前是否在特定温度和测试环境下观察到材料的加载速率效应。用户应记录每次测试的材料、加载速率、温度和环境（相对湿度）的具体信息。 5.3 该表征的结果包括确定CTOA的临界下限值（ψ c )或δ的电阻曲线 5. ，裂纹张开位移与裂纹扩展的度量，或两者兼而有之。 5.4 试样为致密试样C（T）和中间裂纹拉伸试样M（T）。 5.5 如果裂纹尺寸与厚度之比( 一 / B )韧带与厚度之比( b / B )比率等于或大于4，这确保了相对较低和相似的全局裂纹- C（T）和M（T）试样的前约束 ( 2. , 3. ) . 5.6 CTOA和COD（δ 5. )通过本试验方法确定的值可用于以下目的: 5.6.1 在研发方面，CTOA（ψ c )或COD（δ 5. )或者两者兼而有之，测试可以显示某些参数对金属材料稳定裂纹扩展阻力的影响，这对使用性能至关重要。这些参数包括但不限于材料厚度、材料成分、热机械加工、焊接和热应力释放。 5.6.2 用于基材的验收和制造质量控制规范。 5.6.3 当与断裂力学分析结合使用时，用于检查和缺陷评估标准。需要意识到实验室测试和现场条件之间可能存在的差异，以便进行适当的缺陷评估。 5.6.4 关键CTOA（ψ c )已与弹塑性有限元法一起使用，以准确预测简单和复杂裂纹结构部件的结构响应和承载能力，见 附录X1 . 5.6.5 δ 5. 通过工程处理模型（ETM）将参数与J积分相关联 ( 10 ) 并提供了一种工程方法来预测开裂结构部件的结构响应和承载能力。 5.6.6 K-R曲线法（实践 E561 )与δ相似 5. -阻力曲线，因为该概念已应用于C（T）和M（T）试样（在低约束条件下），K-R曲线概念已成功应用于工业 ( 11 ) 然而，δ 5. 参数与J积分有关，该参数在测量中考虑了材料的非线性效应。还对C（T）、M（T）和结构配置裂纹形态的各种断裂标准进行了比较 ( 12 ) 与临界CTOA相比，K-R曲线概念的应用范围有限 c (ψ c )概念。

1.1 This standard covers the determination of the resistance to stable crack extension in metallic materials in terms of the critical crack-tip-opening angle (CTOA), ψ c and/or the crack-opening displacement (COD), δ 5 resistance curve ( 1 ) . 2 This method applies specifically to fatigue pre-cracked specimens that exhibit low constraint (crack-size-to-thickness and un-cracked ligament-to-thickness ratios greater than or equal to 4) and that are tested under slowly increasing remote applied displacement. The test specimens are the compact, C(T), and middle-crack-tension, M(T), specimens. The fracture resistance determined in accordance with this standard is measured as ψ c (critical CTOA value) and/or δ 5 (critical COD resistance curve) as a function of crack extension. Both fracture resistance parameters are characterized using either a single-specimen or multiple-specimen procedures. These fracture quantities are determined under the opening mode (Mode I) of loading. Influences of environment and rapid loading rates are not covered in this standard, but the user must be aware of the effects that the loading rate and laboratory environment may have on the fracture behavior of the material. 1.2 Materials that are evaluated by this standard are not limited by strength, thickness, or toughness, if the crack-size-to-thickness ( a / B ) ratio and the ligament-to-thickness ( b / B ) ratio are greater than or equal to 4, which ensures relatively low and similar global crack-front constraint for both the C(T) and M(T) specimens ( 2 , 3 ) . 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 This test method characterizes a metallic material’s resistance to stable crack extension in terms of crack-tip-opening angle (CTOA), ψ and/or crack-opening displacement (COD), δ 5 under the laboratory or application environment of interest. This method applies specifically to fatigue pre-cracked specimens that exhibit low constraint and that are tested under slowly increasing displacement. 5.2 When conducting fracture tests, the user must consider the influence that the loading rate and laboratory environment may have on the fracture parameters. The user should perform a literature review to determine if loading rate effects have been observed previously in the material at the specific temperature and environment being tested. The user should document specific information pertaining to their material, loading rates, temperature, and environment (relative humidity) for each test. 5.3 The results of this characterization include the determination of a critical, lower-limiting value, of CTOA (ψ c ) or a resistance curve of δ 5 , a measure of crack-opening displacement against crack extension, or both. 5.4 The test specimens are the compact, C(T), and middle-crack-tension, M(T), specimens. 5.5 Materials that can be evaluated by this standard are not limited by strength, thickness, or toughness, if the crack-size-to-thickness ( a / B ) ratio or ligament-to-thickness ( b / B ) ratio are equal to or greater than 4, which ensures relatively low and similar global crack-front constraint for both the C(T) and M(T) specimens ( 2 , 3 ) . 5.6 The values of CTOA and COD (δ 5 ) determined by this test method may serve the following purposes: 5.6.1 In research and development, CTOA (ψ c ) or COD (δ 5 ), or both, testing can show the effects of certain parameters on the resistance to stable crack extension of metallic materials significant to service performance. These parameters include, but are not limited to, material thickness, material composition, thermo-mechanical processing, welding, and thermal stress relief. 5.6.2 For specifications of acceptance and manufacturing quality control of base materials. 5.6.3 For inspection and flaw assessment criteria, when used in conjunction with fracture mechanics analyses. Awareness of differences that may exist between laboratory test and field conditions is required to make proper flaw assessment. 5.6.4 The critical CTOA (ψ c ) has been used with the elastic-plastic finite-element method to accurately predict structural response and force carrying capacity of simple and complex cracked structural components, see Appendix X1 . 5.6.5 The δ 5 parameter has been related to the J-integral by means of the Engineering Treatment Model (ETM) ( 10 ) and provides an engineering approach to predict the structural response and force carrying capacity of cracked structural components. 5.6.6 The K-R curve method (Practice E561 ) is similar to the δ 5 -resistance curve, in that, the concept has been applied to both C(T) and M(T) specimens (under low-constraint conditions) and the K-R curve concept has been used successfully in industry ( 11 ) . However, the δ 5 parameter has been related to the J-integral and the parameter incorporates the material non-linear effects in its measurement. Comparisons have also been made among various fracture criteria on fracture of C(T), M(T) and a structurally configured crack configuration ( 12 ) that were made of several different materials (two aluminum alloys and a very ductile steel), and the K-R curve concept was found to have limited application, in comparison to the critical CTOA c (ψ c ) concept.