1.1 本标准试验方法包括通过恒定应力弯曲试验测定高级陶瓷的缓慢裂纹扩展（SCG）参数，其中弯曲试样的失效时间在 四点 弯曲是环境温度下给定环境中恒定施加应力的函数。此外，还介绍了试样制造方法、试验应力水平、数据收集和分析以及报告程序。在特定环境中，随着施加应力的增加，失效时间的减少是该试验方法的基础，该方法能够评估材料的缓慢裂纹扩展参数。 本方法中的首选分析基于裂纹速度和外加应力强度之间的幂律关系；对于幂律关系不适用的情况，还讨论了替代分析方法。 注1: 本标准中的试验方法通常称为“静态” 疲劳 “或应力断裂测试 ( 1- 3. ) 2. 其中术语“ 疲劳 与术语“缓慢裂纹扩展”互换使用以避免与“ 疲劳 “术语中定义的仅在循环载荷下发生的材料现象 E1823 ，该测试方法使用术语“恒定应力测试”而不是“静态测试” 疲劳 “测试。 1.2 本试验方法主要适用于宏观均匀和各向同性的整体高级陶瓷。该试验方法也适用于某些晶须或颗粒增强陶瓷以及某些表现出宏观均匀行为的不连续纤维增强复合陶瓷。 通常，连续纤维陶瓷复合材料不表现出宏观各向同性、均匀、连续的行为，不建议将本试验方法应用于这些材料。 1.3 本试验方法适用于各种试验环境，如空气、其他气体环境和液体。 1.4 以国际单位制表示的数值应视为标准，并符合IEEE/ASTM SI 10标准。 1.5 本试验方法可能涉及危险材料、操作和设备。 本标准并非旨在解决与其使用相关的所有安全问题。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 ====意义和用途====== 4.1 许多结构陶瓷部件的使用寿命通常受到裂纹亚临界扩展的限制。本试验方法提供了一种评估陶瓷材料在环境温度下特定环境下相对缓慢裂纹扩展敏感性的方法。 此外，该试验方法可以确定加工变量和成分对新开发或现有材料的缓慢裂纹扩展以及强度行为的影响，从而允许裁剪和优化材料加工以进行进一步修改。总之，该试验方法可用于材料开发、质量控制、表征、设计代码或模型验证，以及有限的设计数据生成目的。 注4: 本试验方法产生的数据不一定对应于在使用条件下可能遇到的裂纹速度。 根据所用施加应力的范围和大小，将本试验方法生成的数据用于设计目的可能需要外推和不确定性。 4.2 本试验方法与试验方法有关 C1368 （“恒定应力速率弯曲试验”），然而， C1368 使用恒定应力速率来确定相应的弯曲强度，而本试验方法使用恒定应力来确定相应的失效时间。通常，与恒定应力相比，该试验方法生成的数据可能更能代表实际使用条件- 速率测试。然而，就测试时间而言，恒定应力测试固有且明显比恒定应力速率测试更耗时。 4.3 本试验方法中的弯曲应力计算基于简单弹性梁理论，假设材料各向同性且均匀，拉伸和压缩弹性模量相同，且材料具有线性弹性。晶粒度不应大于五十分之一( 1. / 50 )通过平均线性截距法（试验方法）测量的波束深度 E112 ). 在材料晶粒尺寸为双峰或晶粒尺寸分布较宽的情况下，该限制应适用于较大的晶粒。 4.4 根据试验方法选择了试样尺寸和试验夹具 C1161 和 C1368 ，它在实际配置和由此产生的错误之间提供了平衡，如参考 ( 4. , 5. ) . 4.5 通过将施加的对数应力与失效时间对数回归到实验数据来评估数据。建议通过应用幂律裂纹速度函数来确定缓慢裂纹扩展参数。 关于这一点的推导以及替代裂纹速度函数，请参见 附录X1 . 注5: 文献中存在多种裂纹速度函数。从短期动态疲劳数据预测长期静态疲劳数据的功能比较 ( 6. ) 表明指数形式比幂律形式更好地预测数据。此外，指数形式具有理论基础 ( 7- 10 ) 然而，幂律形式在数学上更简单。两者都被证明是短小的- 术语测试数据良好。 4.6 该方法中使用的方法假设材料没有表现出上升的R曲线行为，即，随着裂纹长度的增加，断裂阻力（或裂纹扩展阻力）没有增加。根据该测试方法无法确定是否存在此类行为。分析进一步假设，相同的缺陷类型控制所有故障时间。 4.7 陶瓷材料的缓慢裂纹扩展行为随机械、材料、热和环境变量的变化而变化。 因此，测试结果准确反映研究中特定变量的影响至关重要。只有这样，才能在有效的基础上将一项调查的数据与另一项调查的数据进行比较，或作为表征材料和评估结构行为的有效基础。 4.8 与强度一样，承受缓慢裂纹扩展的高级陶瓷的失效时间本质上也是概率的。因此，在给定恒定外加应力下，从时间到失效的缓慢裂纹扩展也是一种概率现象。 恒定应力测试中的失效时间分散远大于恒定应力速率（或任何强度）测试中的强度分散 ( 1. , 11- 13 ) 看见 附录X2 . 因此，为了统计再现性和可靠的设计数据生成，需要适当的恒定施加应力范围和数量，以及适当数量的试样 ( 1- 3. ) . 本标准提供了这方面的指导。 4.9 给定试样和测试夹具配置的陶瓷材料的失效时间取决于其固有的抗断裂能力、缺陷的存在、外加应力和环境影响。 在分析SCG数据以验证相同缺陷类型在整个试验范围内占主导地位时，验证失效机制的断口分析已被证明是一种有价值的工具 ( 14 , 15 ) ，并将在本标准中使用（参考实践 C1322 ).

1.1 This standard test method covers the determination of slow crack growth (SCG) parameters of advanced ceramics by using constant stress flexural testing in which time to failure of flexure test specimens is determined in four-point flexure as a function of constant applied stress in a given environment at ambient temperature. In addition, test specimen fabrication methods, test stress levels, data collection and analysis, and reporting procedures are addressed. The decrease in time to failure with increasing applied stress in a specified environment is the basis of this test method that enables the evaluation of slow crack growth parameters of a material. The preferred analysis in the present method is based on a power law relationship between crack velocity and applied stress intensity; alternative analysis approaches are also discussed for situations where the power law relationship is not applicable. Note 1: The test method in this standard is frequently referred to as “static fatigue ” or stress-rupture testing ( 1- 3 ) 2 in which the term “ fatigue ” is used interchangeably with the term “slow crack growth.” To avoid possible confusion with the “ fatigue ” phenomenon of a material that occurs exclusively under cyclic loading, as defined in Terminology E1823 , this test method uses the term “constant stress testing” rather than “static fatigue ” testing. 1.2 This test method applies primarily to monolithic advanced ceramics that are macroscopically homogeneous and isotropic. This test method may also be applied to certain whisker- or particle-reinforced ceramics as well as certain discontinuous fiber-reinforced composite ceramics that exhibit macroscopically homogeneous behavior. Generally, continuous fiber ceramic composites do not exhibit macroscopically isotropic, homogeneous, continuous behavior, and the application of this test method to these materials is not recommended. 1.3 This test method is intended for use with various test environments such as air, other gaseous environments, and liquids. 1.4 The values stated in SI units are to be regarded as the standard and in accordance with IEEE/ASTM SI 10 Standard. 1.5 This test method may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. ====== Significance And Use ====== 4.1 The service life of many structural ceramic components is often limited by the subcritical growth of cracks. This test method provides an approach for appraising the relative slow crack growth susceptibility of ceramic materials under specified environments at ambient temperature. Furthermore, this test method may establish the influences of processing variables and composition on slow crack growth as well as on strength behavior of newly developed or existing materials, thus allowing tailoring and optimizing material processing for further modification. In summary, this test method may be used for material development, quality control, characterization, design code or model verification, and limited design data generation purposes. Note 4: Data generated by this test method do not necessarily correspond to crack velocities that may be encountered in service conditions. The use of data generated by this test method for design purposes, depending on the range and magnitude of applied stresses used, may entail extrapolation and uncertainty. 4.2 This test method is related to Test Method C1368 (“constant stress-rate flexural testing”), however, C1368 uses constant stress rates to determine corresponding flexural strengths whereas this test method employs constant stress to determine corresponding times to failure. In general, the data generated by this test method may be more representative of actual service conditions as compared with those by constant stress-rate testing. However, in terms of test time, constant stress testing is inherently and significantly more time consuming than constant stress rate testing. 4.3 The flexural stress computation in this test method is based on simple elastic beam theory, with the assumptions that the material is isotropic and homogeneous, the moduli of elasticity in tension and compression are identical, and the material is linearly elastic. The grain size should be no greater than one-fiftieth ( 1 / 50 ) of the beam depth as measured by the mean linear intercept method (Test Methods E112 ). In cases where the material grain size is bimodal or the grain size distribution is wide, the limit should apply to the larger grains. 4.4 The test specimen sizes and test fixtures have been selected in accordance with Test Methods C1161 and C1368 , which provides a balance between practical configurations and resulting errors, as discussed in Ref ( 4 , 5 ) . 4.5 The data are evaluated by regression of log applied stress versus log time to failure to the experimental data. The recommendation is to determine the slow crack growth parameters by applying the power law crack velocity function. For derivation of this, and for alternative crack velocity functions, see Appendix X1 . Note 5: A variety of crack velocity functions exist in the literature. A comparison of the functions for the prediction of long-term static fatigue data from short-term dynamic fatigue data ( 6 ) indicates that the exponential forms better predict the data than the power-law form. Further, the exponential form has a theoretical basis ( 7- 10 ) , however, the power law form is simpler mathematically. Both have been shown to fit short-term test data well. 4.6 The approach used in this method assumes that the material displays no rising R-curve behavior, that is, no increasing fracture resistance (or crack-extension resistance) with increasing crack length. The existence of such behavior cannot be determined from this test method. The analysis further assumes that the same flaw type controls all times-to-failure. 4.7 Slow crack growth behavior of ceramic materials can vary as a function of mechanical, material, thermal, and environmental variables. Therefore, it is essential that test results accurately reflect the effects of specific variables under study. Only then can data be compared from one investigation to another on a valid basis, or serve as a valid basis for characterizing materials and assessing structural behavior. 4.8 Like strength, time to failure of advanced ceramics subjected to slow crack growth is probabilistic in nature. Therefore, slow crack growth that is determined from times to failure under given constant applied stresses is also a probabilistic phenomenon. The scatter in time to failure in constant stress testing is much greater than the scatter in strength in constant stress-rate (or any strength) testing ( 1 , 11- 13 ) , see Appendix X2 . Hence, a proper range and number of constant applied stresses, in conjunction with an appropriate number of test specimens, are required for statistical reproducibility and reliable design data generation ( 1- 3 ) . This standard provides guidance in this regard. 4.9 The time to failure of a ceramic material for a given test specimen and test fixture configuration is dependent on its inherent resistance to fracture, the presence of flaws, applied stress, and environmental effects. Fractographic analysis to verify the failure mechanisms has proven to be a valuable tool in the analysis of SCG data to verify that the same flaw type is dominant over the entire test range Ref ( 14 , 15 ) , and it is to be used in this standard (refer to Practice C1322 ).