1.1 本试验方法包括测定平面应变（V形缺口）断裂韧性， K 四、 或 K IvM公司 ，由金属材料制成。该方法的断裂韧性与在人字形缺口处开始并在人字形韧带中扩展的缓慢推进稳态裂纹有关( 图1 ). 当用这种方法测试时，一些金属材料表现出偶发的裂纹扩展，其中裂纹前缘几乎保持静止，直到达到临界载荷。然后，裂纹变得不稳定，并突然高速前进到下一个止裂点。对于这些材料，本试验方法包括测定平面应变断裂韧性， K Ivj公司 或 K IvM公司 ，相对于不稳定点处的裂纹。 （A） 看见 图6 . （A） 看见 图6 . （B） 看见 注1 . （A） 根据参考文献编译 ( 1. ) , ( 2. ) , ( 3. ) 和 ( 4. ) ，并使用 表5 . （B） 最小值 Y *. （A） 根据参考文献编译 ( 1. ) , ( 2. ) , ( 3. ) 和 ( 4. ) . （B） Y * = 经验[ C 0 + C 1. r + C 2. r 2. + C 3. r 3. + C 4. r 4. ]，精度±0.5 %. （C） 根据有限元分析估算 ( 3. ) ，并根据参考文献外推公式 ( 4. ) . 精度为0.3 ≤ r ≤ 0.85为±0.5 %. （D） 根据参考文献中的等式外推 ( 4. ) . 精度估计为±0.5 % 对于0.2 ≤ r ≤ 0.85. （E） 参考公式 ( 4. ) . 精度估计为±0.5 % 对于0.15 ≤ r ≤ 0.6. ====意义和用途====== 5.1 通过本试验方法确定的断裂韧性表征了材料通过缓慢前进的稳态裂纹断裂的阻力（见 3.2.5 )在严重拉伸约束下的中性环境中。裂纹前缘附近的应力状态接近平面应变，裂纹- 与约束方向上的裂纹尺寸和试样尺寸相比，尖端塑性区域较小。A. K 四、 或 K Ivj公司 当预期出现上述条件时，该值可用于估计失效应力和缺陷尺寸之间的关系，尽管该关系可能不同于从 K 集成电路 值（参见 注1 ). 关于在线弹性断裂力学方面开发本试验方法的基础的背景信息，可在参考文献中找到 ( 6- 15 ) . 5.1.1 这个 K 四、 , K Ivj公司 或 K IvM公司 给定材料的值可以是测试速度（应变率）和温度的函数。此外，循环力可导致裂纹扩展 K 我 值小于 K 四、 腐蚀性环境的存在会增加裂纹扩展。因此，应用 K 四、 在设计服务部件时，应意识到实验室测试和现场条件之间可能存在的差异。 5.1.2 平面应变断裂韧性测试是不寻常的，因为无法预先保证有效的 K 四、 , K Ivj公司 或 K IvM公司 将在特定测试中确定。因此，如本文所述，仔细考虑与结果有效性有关的所有标准至关重要。 5.2 本试验方法可用于以下目的: 5.2.1 确定冶金变量（如成分或热处理）或制造操作（如焊接或成型）对新材料或现有材料断裂韧性的影响。 5.2.2 用于验收规范和制造质量控制，但只有在有可靠的基础来规范最低 K 四、 , K Ivj公司 或 K IvM公司 仅当产品尺寸足以提供有效尺寸所需的样品时 K 四、 决心 ( 9 ) . 规范 K 四、 与特定应用相关的值应表示已对部件进行了与预期载荷历史和环境相关的断裂控制研究，以及与使用前和预期寿命内后续应用的裂纹检测程序的灵敏度和可靠性相关的断裂控制研究。 5.2.3 在测量母件材料的平面应变断裂韧性变化时提供高空间分辨率 ( 14 ) . 注2: 高空间分辨率是可能的，因为允许的样本尺寸标准很小， B ≥ 1.25 ( K 四、 /σ YS公司 ) 2. ( 9 ) ，并且由于韧性是在试样的大约中线处测量的，并且仅在裂纹横向范围覆盖的材料中测量，该范围约为试样横向尺寸的三分之一， B .

1.1 This test method covers the determination of plane-strain (chevron-notch) fracture toughnesses, K Iv or K IvM , of metallic materials. Fracture toughness by this method is relative to a slowly advancing steady state crack initiated at a chevron-shaped notch, and propagating in a chevron-shaped ligament ( Fig. 1 ). Some metallic materials, when tested by this method, exhibit a sporadic crack growth in which the crack front remains nearly stationary until a critical load is reached. The crack then becomes unstable and suddenly advances at high speed to the next arrest point. For these materials, this test method covers the determination of the plane-strain fracture toughness, K Ivj or K IvM , relative to the crack at the points of instability. (A) See Fig. 6 . (A) See Fig. 6 . (B) See Note 1 . (A) Compiled from Refs ( 1 ) , ( 2 ) , ( 3 ) , and ( 4 ) , and using the polynomials in Table 5 . (B) Minimum value of Y *. (A) Compiled from Refs ( 1 ) , ( 2 ) , ( 3 ) , and ( 4 ) . (B) Y * = exp[ C 0 + C 1 r + C 2 r 2 + C 3 r 3 + C 4 r 4 ], accuracy ±0.5 %. (C) Estimated from finite element analysis ( 3 ) , and extrapolated equation from Ref ( 4 ) . Accuracy for 0.3 ≤ r ≤ 0.85 is ±0.5 %. (D) Extrapolated from equations in Ref ( 4 ) . Accuracy estimated to be ±0.5 % for 0.2 ≤ r ≤ 0.85. (E) Equation from Ref ( 4 ) . Accuracy estimated to be± 0.5 % for 0.15 ≤ r ≤ 0.6. ====== Significance And Use ====== 5.1 The fracture toughness determined by this test method characterizes the resistance of a material to fracture by a slowly advancing steady-state crack (see 3.2.5 ) in a neutral environment under severe tensile constraint. The state of stress near the crack front approaches plane strain, and the crack-tip plastic region is small compared with the crack size and specimen dimensions in the constraint direction. A K Iv or K Ivj value may be used to estimate the relation between failure stress and defect size when the conditions described above would be expected, although the relationship may differ from that obtained from a K Ic value (see Note 1 ). Background information concerning the basis for development of this test method in terms of linear elastic fracture mechanics may be found in Refs ( 6- 15 ) . 5.1.1 The K Iv , K Ivj , or K IvM value of a given material can be a function of testing speed (strain rate) and temperature. Furthermore, cyclic forces can cause crack extension at K I values less than K Iv , and crack extension can be increased by the presence of an aggressive environment. Therefore, application of K Iv in the design of service components should be made with an awareness of differences that may exist between the laboratory tests and field conditions. 5.1.2 Plane-strain fracture toughness testing is unusual in that there can be no advance assurance that a valid K Iv , K Ivj , or K IvM will be determined in a particular test. Therefore, it is essential that all the criteria concerning the validity of results be carefully considered as described herein. 5.2 This test method can serve the following purposes: 5.2.1 To establish the effects of metallurgical variables such as composition or heat treatment, or of fabricating operations such as welding or forming, on the fracture toughness of new or existing materials. 5.2.2 For specifications of acceptance and manufacturing quality control, but only when there is a sound basis for specification of minimum K Iv , K Ivj , or K IvM values, and then only if the dimensions of the product are sufficient to provide specimens of the size required for valid K Iv determination ( 9 ) . The specification of K Iv values in relation to a particular application should signify that a fracture control study has been conducted on the component in relation to the expected history of loading and environment, and in relation to the sensitivity and reliability of the crack detection procedures that are to be applied prior to service and subsequently during the anticipated life. 5.2.3 To provide high spatial resolution in measuring plane strain fracture toughness variations in parent pieces of material ( 14 ) . Note 2: The high spatial resolution is possible because of the small allowable specimen size criterion, B ≥ 1.25 ( K Iv /σ YS ) 2 ( 9 ) , and because the toughness is measured at approximately the midline of the specimen, and only in the material covered by the crack's lateral extent, which is about one third of the specimen's lateral dimension, B .