1.1 该试验方法包括环境辅助开裂阈值应力强度因子参数K的确定 国际原子能机构 和K 出口信用证 ，对于金属材料，来自疲劳预裂纹梁或致密断裂试样的恒定力测试，以及来自疲劳预开裂螺栓载荷致密断裂试样中的恒定位移测试。 1.2 本试验方法适用于水性或其他侵蚀性环境中的环境辅助裂化。 1.3 可以通过该试验方法进行试验的材料不受厚度或强度的限制，只要试样具有足够的厚度和平面尺寸以满足该试验方法的尺寸要求。 1.4 提供了一系列具有成比例平面尺寸的试样尺寸，但尺寸可以是可变的，并根据屈服强度和施加的力进行调整。试样厚度是一个与平面尺寸无关的变量。 1.5 可以使用除本试验方法中包含的试样配置以外的试样配置，前提是- 已建立的应力强度校准是可用的，并且样品尺寸足够大，以满足测试过程中该测试方法的尺寸要求。 1.6 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。 1.7 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 参数K 出口信用证 或K 国际原子能机构 通过该试验方法确定的特征是具有尖锐裂纹的材料在特定环境下，在裂纹产生的载荷条件下对裂纹扩展的抵抗力- 与裂纹深度和未裂纹韧带相比，尖端塑性区较小。K的限制性较小的厚度要求 出口信用证 适用于这样的条件，在这些条件下，结果是试样厚度的强函数，并且应用需要对具有代表应用的厚度的试样进行测试。由于化学和机械影响无法分开，在某些材料/环境组合中，厚度必须视为一个变量。一个K 出口信用证 或K 国际原子能机构 该值被认为代表暴露于持续拉伸载荷下的环境中的预裂纹试样的环境辅助抗裂性的特征测量。一个K 出口信用证 或K 国际原子能机构 该值可用于估计材料在任何使用条件下的失效应力和缺陷尺寸之间的关系，其中预期会出现裂纹状缺陷、持续拉伸载荷和相同特定环境的组合。 （有关该测试方法开发的背景信息，请参阅参考文献 ( 3个- 18 ) 。 5.1.1 表观K 出口信用证 或K 国际原子能机构 材料在给定的一组化学和电化学环境条件下的性能是测试持续时间的函数。很难为门槛的存在提供严格而科学的证据 ( 4. ， 5. ) 因此，K的应用 出口信用证 或K 国际原子能机构 服务部件设计中的数据应考虑到金属材料环境辅助开裂的真实阈值概念中固有的不确定性 ( 6. ， 18 ) .A测量K 出口信用证 或K 国际原子能机构 事实上，材料和环境的特定组合的值可能代表可接受的低裂纹增长率，而不是裂纹稳定性的绝对上限。当服务时间明显长于测试时间时，应格外小心。 5.1.2 与静态拉伸应力的力偏差将影响表观K的程度 出口信用证 或K 国际原子能机构 一种材料的性质在很大程度上是未知的。在某些情况下，观察到小振幅循环载荷，远低于产生疲劳裂纹扩展所需的载荷，叠加在持续拉伸载荷上，显著降低了应力腐蚀裂纹的表观阈值 ( 7. ， 8. ) 。因此，在应用K时应谨慎 出口信用证 或K 国际原子能机构 涉及循环加载的数据到服务情况。此外，由于本标准适用于静态载荷，因此在试验过程中应避免小振幅循环载荷。 5.1.3 在某些材料/环境组合中，试样越小，测得的K值越低 出口信用证 值，而在其他材料/环境组合中，测量的K 国际原子能机构 值将是最低值 ( 5. ， 9 ， 10 ， 11 ， 12 ) .如果对于感兴趣的材料/环境组合，不知道哪种试样尺寸会导致较低的测量值，则建议考虑使用两种试样尺寸； 即具有代表应用厚度的试样和厚度满足要求的试样（参见 7.2.1 )一个K的 国际原子能机构 价值 5.1.3.1 用户可以选择确定并报告K 出口信用证 值或K 国际原子能机构 价值K的样本尺寸有效性要求 出口信用证 值符合为试验方法制定的尺寸要求 电子647 以在试样中实现主要的弹性行为。试验方法 电子647 紧凑试样的尺寸要求应适用于紧凑试样和梁试样。K的样本尺寸有效性要求 国际原子能机构 值符合为试验方法的平面应变条件制定的尺寸要求 1999年3月 。 5.1.4 在不符合有效性要求的条件下环境辅助裂纹扩展的证据 7.2 可以提供对环境开裂易感性的重要指示，但不能用于确定有效的K 出口信用证 价值 ( 14 ) 。 5.1.5 环境辅助开裂受到机械和电化学驱动力的影响。后者可以随着裂纹深度、开口或形状的变化而变化，并且可能不是由断裂力学应力强度因子唯一描述的。作为一个示例，请注意K中报告的大幅下降 ISCC公司 5. 三分之一钢的裂纹尺寸减小到5毫米以下 % NaCl水溶液 ( 15 ) .几何效果 K 应通过实验评估特定材料/环境系统的相似性。基于K的应用程序建模 出口信用证 当试样和构件之间存在裂纹和试样几何形状的显著差异时，应谨慎进行相似性分析。 5.1.6 并非所有材料和环境的组合都会导致环境辅助开裂。一般来说，水性应力腐蚀开裂的易感性随着材料强度水平的降低而降低。 当材料在特定环境中不易受到环境辅助开裂的影响时，将无法测量K 出口信用证 或K 国际原子能机构 .这种方法可以达到以下目的: 5.1.6.1 在研发方面，有效K 出口信用证 或K 国际原子能机构 数据可以定量地确定冶金和环境变量对材料环境辅助抗裂性的影响。 5.1.6.2 在役评估，有效K 出口信用证 或K 国际原子能机构 数据可用于确定材料在特定应力、缺陷尺寸和环境条件下的适用性。 5.1.6.3 在验收和质量控制规范中，有效K 出口信用证 或K 国际原子能机构 数据可用于建立材料加工和部件检查的标准。 5.1.7 在某些材料/环境条件下，恒定位移螺栓加载紧凑试样的力松弛会影响试验结果。 对于强度相对较低的材料、非侵蚀性环境或高测试温度，力松弛可以独立于环境辅助开裂而发生。显著的力松弛会使开裂结果难以解释。如果怀疑力松弛会影响数据，建议进行以下试件试验。在所有感兴趣的测试条件下测试试件，但不使用任何环境的情况除外。使用带有电子称重传感器的螺栓监测样品上的力。这种类型的仪表螺栓可在市场上买到。大于5的力松弛 % 24小时后表明恒定位移试验方法可能不适用于这些试验条件，应考虑进行恒定力试验。 5.1.8 残余应力会对环境辅助开裂产生影响。当试样从无法完全消除应力的材料（如焊接件）上移除时，其影响可能非常显著- 热处理材料、复杂的锻造零件以及有意产生残余应力的零件。叠加在施加应力上的残余应力会导致局部裂纹尖端应力强度因子与根据外部施加的力或位移计算的因子不同。预裂纹过程中的不规则裂纹扩展，如裂纹前缘曲率过大或平面外裂纹扩展，通常表明残余应力将影响随后的环境辅助裂纹扩展行为。预裂纹扩展导致的裂纹口张开位移的零力值的变化是残余应力将影响随后的环境辅助裂纹扩展的另一个迹象。 5.1.9 对于螺栓加载的试样，用户应该意识到，在非环境温度下测试的材料可能具有与环境温度下不同的位移与力比，而且螺栓材料可能具有不同于被测试材料的热膨胀系数。 应注意尽量减少这些影响。

1.1 This test method covers the determination of the environment-assisted cracking threshold stress intensity factor parameters, K IEAC and K EAC , for metallic materials from constant-force testing of fatigue precracked beam or compact fracture specimens and from constant-displacement testing of fatigue precracked bolt-load compact fracture specimens. 1.2 This test method is applicable to environment-assisted cracking in aqueous or other aggressive environments. 1.3 Materials that can be tested by this test method are not limited by thickness or by strength as long as specimens are of sufficient thickness and planar size to meet the size requirements of this test method. 1.4 A range of specimen sizes with proportional planar dimensions is provided, but size may be variable and adjusted for yield strength and applied force. Specimen thickness is a variable independent of planar size. 1.5 Specimen configurations other than those contained in this test method may be used, provided that well-established stress intensity calibrations are available and that specimen dimensions are of sufficient size to meet the size requirements of this test method during testing. 1.6 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. 1.7 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 parameters K EAC or K IEAC determined by this test method characterize the resistance to crack growth of a material with a sharp crack in specific environments under loading conditions in which the crack-tip plastic region is small compared with the crack depth and the uncracked ligament. The less restrictive thickness requirements of K EAC are intended for those conditions in which the results are a strong function of the thickness of the specimen and the application requires the testing of specimens with thickness representative of the application. Since the chemical and mechanical influences cannot be separated, in some material/environment combinations, the thickness must be treated as a variable. A K EAC or K IEAC value is believed to represent a characteristic measurement of environment-assisted cracking resistance in a precracked specimen exposed to an environment under sustained tensile loading. A K EAC or K IEAC value may be used to estimate the relationship between failure stress and defect size for a material under any service condition, where the combination of crack-like defects, sustained tensile loading and the same specific environment would be expected to occur. (Background information concerning the development of this test method can be found in Refs ( 3- 18 ) . 5.1.1 The apparent K EAC or K IEAC of a material under a given set of chemical and electrochemical environmental conditions is a function of the test duration. It is difficult to furnish a rigorous and scientific proof for the existence of a threshold ( 4 , 5 ) . Therefore, application of K EAC or K IEAC data in the design of service components should be made with awareness of the uncertainty inherent in the concept of a true threshold for environment-assisted cracking in metallic materials ( 6 , 18 ) . A measured K EAC or K IEAC value for a particular combination of material and environment may, in fact, represent an acceptably low rate of crack growth rather than an absolute upper limit for crack stability. Care should be exercised when service times are substantially longer than test times. 5.1.2 The degree to which force deviations from static tensile stress will influence the apparent K EAC or K IEAC of a material is largely unknown. Small-amplitude cyclic loading, well below that needed to produce fatigue crack growth, superimposed on sustained tensile loading was observed to significantly lower the apparent threshold for stress corrosion cracking in certain instances ( 7 , 8 ) . Therefore, caution should be used in applying K EAC or K IEAC data to service situations involving cyclic loading. In addition, since this standard is for static loading, small-amplitude cyclic loading should be avoided during testing. 5.1.3 In some material/environment combinations, the smaller the specimen, the lower the measured K EAC value, while in other material/environment combinations the measured K IEAC value will be the lowest value ( 5 , 9 , 10 , 11 , 12 ) . If, for the material/environment combination of interest, it is not known which specimen size will result in the lower measured value, then it is suggested that the use of both specimen sizes should be considered; that is, specimens with thicknesses representative of the application and specimens in which the thickness meets the requirements (see 7.2.1 ) of a K IEAC value. 5.1.3.1 The user may optionally determine and report a K EAC value or a K IEAC value. The specimen size validity requirements for a K EAC value meet the size requirements developed for Test Method E647 to achieve predominately elastic behavior in the specimen. Test Method E647 size requirements for compact specimens should be applied to both the compact specimen and the beam specimen. The specimen size validity requirements for a K IEAC value meet the size requirements developed for plane strain conditions for Test Method E399 . 5.1.4 Evidence of environment-assisted crack growth under conditions that do not meet the validity requirements of 7.2 may provide an important indication of susceptibility to environmental cracking but cannot be used to determine a valid K EAC value ( 14 ) . 5.1.5 Environment-assisted cracking is influenced by both mechanical and electrochemical driving forces. The latter can vary with crack depth, opening, or shape and may not be uniquely described by the fracture mechanics stress intensity factor. As an illustrative example, note the strong decrease reported in K ISCC 5 with decreasing crack size below 5 mm for steels in 3 % NaCl in water solution ( 15 ) . Geometry effects on K similitude should be experimentally assessed for specific material/environment systems. Application modeling based on K EAC similitude should be conducted with caution when substantial differences in crack and specimen geometry exist between the specimen and the component. 5.1.6 Not all combinations of material and environment will result in environment-assisted cracking. In general, susceptibility to aqueous stress-corrosion cracking decreases with decreasing material strength level. When a material in a certain environment is not susceptible to environment-assisted cracking, it will not be possible to measure K EAC or K IEAC . This method can serve the following purposes: 5.1.6.1 In research and development, valid K EAC or K IEAC data can quantitatively establish the effects of metallurgical and environmental variables on the environment-assisted cracking resistance of materials. 5.1.6.2 In service evaluation, valid K EAC or K IEAC data can be utilized to establish the suitability of a material for an application with specific stress, flaw size, and environmental conditions. 5.1.6.3 In acceptance and quality control specifications, valid K EAC or K IEAC data can be used to establish criteria for material processing and component inspection. 5.1.7 Test results will be affected by force relaxation in constant displacement bolt-loaded compact specimens for some material/environment conditions. For relatively low strength material, non-agressive environments, or high test temperatures, force relaxation can occur independently from environment-assisted cracking. Significant force relaxation would make cracking results difficult to interpret. If force relaxation is suspected of influencing the data, the following trial specimen test is recommended. Test a trial specimen with all the test conditions of interest, except with no environment applied. Monitor the force on the sample using a bolt with an electronic load cell attached. Instrumented bolts of this type are commercially available. A force relaxation of more than 5 % after 24 h indicates that the constant displacement test method may not be suitable for these test conditions, and a constant force test should be considered. 5.1.8 Residual stresses can have an influence on environment-assisted cracking. The effect can be significant when test specimens are removed from material in which complete stress relief is impractical, such as weldments, as-heat-treated materials, complex wrought parts, and parts with intentionally produced residual stresses. Residual stresses superimposed on the applied stress can cause the local crack-tip stress-intensity factor to be different from that calculated from externally applied forces or displacements. Irregular crack growth during precracking, such as excessive crack front curvature or out-of-plane crack growth, often indicates that residual stresses will affect the subsequent environment-assisted crack growth behavior. Changes in the zero-force value of crack-mouth-opening displacement as a result of precrack growth is another indication that residual stresses will affect the subsequent environment-assisted crack growth. 5.1.9 For bolt loaded specimens, the user should realize that material being tested at an non-ambient temperature may have a different displacement-to-force ratio from that at ambient temperature, and also the bolt material may have a different coefficient of thermal expansion from that of the material being tested. Care should be taken to minimize these effects.