1.1 本试验方法包括使用以下缺口和预裂纹试样中的任何一个，在静态速率下，测定金属材料在模式I载荷下的抗断裂性:中间裂纹张力M（T）试样或致密张力C（T）样本。A. K R 曲线是韧性发展（抗裂纹扩展）的连续记录 K R 当裂纹在增加的应力强度因子下驱动时，相对于试样中的裂纹扩展绘制， K . ( 1. ) 2. 1.2 可测试的材料 K R 曲线的发展不受强度、厚度或韧性的限制，只要试样具有足够的尺寸以保持主要的弹性到感兴趣的有效裂纹扩展值即可。 1.3 需要标准比例的试样，但尺寸是可变的，需要根据材料的屈服强度和韧性进行调整。 1.4 可用于开发的众多可能样本类型中只有两种 K R 这种方法涵盖了曲线。 1.5 该试验适用于材料在不断增加的裂纹驱动力下表现出缓慢、稳定的裂纹扩展的条件，这种裂纹驱动力可能存在于平面应力裂纹尖端条件下相对坚韧的材料中。 1.6 以国际单位制表示的数值应视为标准。国际单位制后括号中给出的值仅供参考，不被视为标准值。 1.7 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的使用者有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 1.8 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 这个 K R 该曲线表征了材料在缓慢、稳定的裂纹扩展过程中的抗断裂能力，是裂纹前塑性区从疲劳预裂纹或尖锐缺口延伸时扩展的结果。它提供了韧性发展的记录，因为裂纹在不断增加的应力强度因子下被稳定驱动 K 对于给定的材料， K R 曲线取决于试样厚度、温度和应变速率。有效金额 K R 试验中产生的数据取决于试样类型、尺寸、加载方法，以及在较小程度上取决于试验机的特性。 5.2 对于未经测试的几何体，K R 曲线可以与应用的-K曲线（裂纹驱动曲线）相匹配，以估计稳定裂纹扩展的程度和导致不稳定裂纹扩展所需的条件 ( 2. ) 在进行该估计时， K R 曲线被认为与初始裂纹尺寸无关 一 哦 以及它们被开发的样本配置。对于给定的材料、材料厚度和测试温度， K R 曲线似乎只是有效裂纹扩展Δ的函数 一 e ( 3. ) . 5.2.1 为了预测构件的裂纹行为和不稳定性，通过计算生成了一组应用的-K曲线 K 作为使用一系列力、位移或组合载荷条件的部件的裂纹尺寸的函数。 这个 K R 曲线可以叠加在应用的-K曲线族上，如 图1 ，与的起源 K R 与假设的初始裂纹尺寸一致的曲线 一 哦 。应用的-K曲线与 K R 曲线显示了每种加载条件下预期的有效稳定裂纹扩展。应用的-K曲线与 K R 曲线定义了临界载荷条件，该临界载荷条件将导致在用于开发应用的-K曲线的载荷条件下发生不稳定断裂。 图1 的示意图 K R 曲线和应用 K 预测不稳定性的曲线； K c , P 3. , 一 c ，对应于初始裂纹尺寸， 一 哦 5.2.2 相反 K R 曲线可以在中向左或向右移动 图1 使其与应用的-K曲线相切，以确定在该载荷条件下会导致裂纹不稳定的初始裂纹尺寸。 5.3 如果 K -选择用于开发 K R 曲线具有负特性（请参见 注释1 )在位移控制的试验条件下，可以驱动裂纹，直到达到最大或平台韧性水平 ( 4. , 5. , 6. ) .当样本呈阳性时 K -梯度特性（参见 注释2 )使用时 K R 当裂纹变得不稳定时，可以发展的曲线终止。 注1: 裂纹线加载试样中的固定位移导致 K 裂纹扩展。 注2: 通过力控制， K 通常随着裂纹扩展而增加，并且在最大力下会发生失稳。

1.1 This test method covers the determination of the resistance to fracture of metallic materials under Mode I loading at static rates using either of the following notched and precracked specimens: the middle-cracked tension M(T) specimen or the compact tension C(T) specimen. A K R curve is a continuous record of toughness development (resistance to crack extension) in terms of K R plotted against crack extension in the specimen as a crack is driven under an increasing stress intensity factor, K . ( 1 ) 2 1.2 Materials that can be tested for K R curve development are not limited by strength, thickness, or toughness, so long as specimens are of sufficient size to remain predominantly elastic to the effective crack extension value of interest. 1.3 Specimens of standard proportions are required, but size is variable, to be adjusted for yield strength and toughness of the materials. 1.4 Only two of the many possible specimen types that could be used to develop K R curves are covered in this method. 1.5 The test is applicable to conditions where a material exhibits slow, stable crack extension under increasing crack driving force, which may exist in relatively tough materials under plane stress crack tip conditions. 1.6 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard. 1.7 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. 1.8 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 The K R curve characterizes the resistance to fracture of materials during slow, stable crack extension and results from the growth of the plastic zone ahead of the crack as it extends from a fatigue precrack or sharp notch. It provides a record of the toughness development as a crack is driven stably under increasing applied stress intensity factor K . For a given material, K R curves are dependent upon specimen thickness, temperature, and strain rate. The amount of valid K R data generated in the test depends on the specimen type, size, method of loading, and, to a lesser extent, testing machine characteristics. 5.2 For an untested geometry, the K R curve can be matched with the applied-K curves (crack driving curves) to estimate the degree of stable crack extension and the conditions necessary to cause unstable crack propagation ( 2 ) . In making this estimate, K R curves are regarded as being independent of initial crack size a o and the specimen configuration in which they are developed. For a given material, material thickness, and test temperature, K R curves appear to be a function of only the effective crack extension Δ a e ( 3 ) . 5.2.1 To predict crack behavior and instability in a component, a family of applied-K curves is generated by calculating K as a function of crack size for the component using a series of force, displacement, or combined loading conditions. The K R curve may be superimposed on the family of applied-K curves as shown in Fig. 1 , with the origin of the K R curve coinciding with the assumed initial crack size a o . The intersection of the applied-K curves with the K R curve shows the expected effective stable crack extension for each loading condition. The applied-K curve that develops tangency with the K R curve defines the critical loading condition that will cause the onset of unstable fracture under the loading conditions used to develop the applied-K curves. FIG. 1 Schematic Representation of K R curve and Applied K Curves to Predict Instability; K c , P 3 , a c , Corresponding to an Initial Crack Size, a o 5.2.2 Conversely, the K R curve can be shifted left or right in Fig. 1 to bring it into tangency with applied-K curve to determine the initial crack size that would cause crack instability under that loading condition. 5.3 If the K -gradient (slope of the applied-K curve) of the specimen chosen to develop the K R curve has negative characteristics (see Note 1 ), as in a displacement-controlled test condition, it may be possible to drive the crack until a maximum or plateau toughness level is reached ( 4 , 5 , 6 ) . When a specimen with positive K -gradient characteristics (see Note 2 ) is used, the extent of the K R curve which can be developed is terminated when the crack becomes unstable. Note 1: Fixed displacement in crack-line-loaded specimens results in a decrease of K with crack extension. Note 2: With force control, K usually increases with crack extension, and instability will occur at maximum force.