1.1 本试验方法涵盖了在给定的高温试验环境中测定先进陶瓷的慢裂纹扩展（SCG）参数，其中四点失效时间- 1. / 4. 点弯曲试样（见 图1 )被确定为不同水平的恒定施加应力的函数。这种SCG恒定应力测试程序也称为慢裂纹扩展（SCG）应力断裂测试。该测试方法涉及测试设备、试样制造、测试应力水平和实验程序、数据收集和分析以及报告要求。 1.2 在该试验方法中，测量了在特定试验条件和温度下，随着施加应力水平的增加，失效时间的减少，并用于分析陶瓷的缓慢裂纹扩展参数。优选的分析方法基于裂纹速度和施加应力强度之间的幂律关系；还讨论了幂律关系不适用的情况下的替代分析方法。 注1: 该试验方法在早期的技术文献中被称为静态疲劳试验（参考文献 1. 3. ) 2. 其中疲劳一词与术语可互换使用 缓慢裂纹扩展 为了避免与仅在循环应力载荷下发生的材料疲劳现象混淆，如 E1823 ，本测试方法使用术语 恒定应力测试 而不是静态疲劳测试。 1.3 该测试方法使用四点- 1. / 4. 点弯曲试验模式，主要适用于宏观均匀和各向同性的单片高级陶瓷。该试验方法也可应用于某些须晶- 或颗粒增强陶瓷以及表现出宏观均匀行为的某些不连续纤维增强复合陶瓷。通常，连续纤维陶瓷复合材料不会表现出宏观各向同性、均匀、弹性连续的行为，不建议对这些材料应用这种测试方法。 1.4 本试验方法适用于高温和各种试验环境，如空气、真空、惰性气体和蒸汽。该试验方法类似于试验方法 C1576 增加了在高温下进行测试的规定，以确定这些温度对缓慢裂纹扩展的影响。高温试验规定源自试验方法 C1211 和 C1465 . 1.5 某些陶瓷在高温下会发生蠕变变形，这是一种缓慢裂纹扩展的竞争机制。这些蠕变效应可能会相互作用并干扰缓慢裂纹扩展效应（见 5.5 ). 本试验方法主要用于蠕变可忽略不计的陶瓷试样。 本试验方法对断裂或跳动时测得的最大蠕变应变施加了特定的上限（根据 5.5 ). 1.6 以国际单位制表示的值应被视为标准，并符合 IEEE/asm SI 10 . 1.7 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。 1.8 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====== 4.1 许多结构陶瓷部件的使用寿命通常受到裂纹随时间、在规定温度下的应力下和在规定化学环境中亚临界增长的限制（参考文献 1. 3. ). 当一个或多个裂纹扩展到临界尺寸时，部件可能会发生脆性灾难性失效。陶瓷中的缓慢裂纹扩展通常在高温下加速。该试验方法提供了一种测量长期承载能力和评估陶瓷材料在高温下相对缓慢裂纹扩展敏感性的程序，该敏感性是时间、温度和环境的函数。本试验方法基于试验方法 C1576 增加了高温测试的规定。 4.2 该测试方法还用于确定加工变量和成分对高温下缓慢裂纹扩展的影响，以及对新开发或现有材料强度行为的影响，从而可以定制和优化材料加工以进行进一步修改。 4.3 该测试方法可用于材料开发、质量控制、表征、设计代码或模型验证、失效时间和有限的设计数据生成目的。 注2: 该试验方法产生的数据不一定与使用条件下可能遇到的裂纹速度相对应。 根据所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。 4.4 本试验方法和试验方法 C1576 与测试方法相似且相关 C1368 和 C1465 ; 然而， C1368 和 C1465 使用恒定应力率（随时间线性增加的应力）来确定相应的抗弯强度，而本试验方法和 C1576 采用恒定应力（随时间变化的固定应力水平）来确定相应的时间- 失败。一般来说，与恒定应力率测试的数据相比，该测试方法生成的数据可能更能代表实际使用条件。然而，就测试时间而言，恒定压力测试本质上比恒定压力率测试更耗时。 4.5 该试验方法中的弯曲应力计算基于简单的弹性梁理论，假设如下:材料是各向同性和均匀的；拉伸和压缩的弹性模量是相同的； 并且该材料是线性弹性的。这些假设是基于陶瓷试样中的小晶粒尺寸。粒径不应大于 1. / 50 用平均线性截距法测量的光束深度( E112 ). 在材料粒度为双峰或粒度分布较宽的情况下，该限制应适用于较大的晶粒。 4.6 已根据试验方法选择了试样尺寸和试验夹具 C1211 如参考文献所述，该方法在实际配置和由此产生的误差之间实现了平衡 4. 和 5. .试验方法 C1211 还规定了提高测试温度稳定性和功能性的夹具材料要求。 4.7 通过将施加的应力对数与失效时间对数回归到实验数据来评估SCG数据。建议通过应用幂律裂纹速度函数来确定慢裂纹扩展参数。关于这一点的推导以及其他裂纹速度函数，请参见 附录X1 . 注3: 文献中存在多种裂纹速度函数。 从短期恒定应力率（动态疲劳）数据预测长期恒定应力（静态疲劳）数据的函数比较（参考 6. )表明指数形式比幂律形式更好地预测数据。此外，指数形式有理论基础（参考文献 7. 10 ); 然而，幂律形式在数学上更简单。这两种形式都被证明与短期测试数据非常吻合。 4.8 本测试方法中使用的方法假设陶瓷材料没有显示上升的R- 曲线行为，即在给定的试验温度下，随着裂纹长度的增加，断裂阻力（或裂纹扩展阻力）没有增加。通过这种测试方法无法确定是否存在这种R曲线行为。该分析进一步假设，在给定的测试温度下，相同的缺陷类型始终控制着故障。 4.9 陶瓷材料的慢裂纹扩展行为可能因材料性能、热条件和环境变量而异。因此，测试结果必须准确反映所研究的特定变量的影响。 只有这样，才能在有效的基础上对一项调查的数据进行比较，或者作为表征材料和评估结构行为的有效依据。 4.10 与机械强度一样，先进陶瓷的SCG失效时间本质上是概率性的。因此，在给定的恒定施加应力下，由失效时间决定的缓慢裂纹扩展也是一种概率现象。恒定应力测试中失效时间的分散远大于恒定应力下强度的分散- 速率（或任何强度）测试（参考 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水平范围和数量，以及适当数量的试样（参考 1. 3. ). 本试验方法在这方面提供了指导。 4.11 给定试样和测试夹具配置的陶瓷材料的失效时间取决于陶瓷材料的固有抗断裂性、缺陷的存在、施加的应力以及温度和环境影响。 用于验证失效机制的断口分析已被证明是分析SCG数据的有价值的工具，以验证相同的缺陷类型在整个测试范围内占主导地位（参考文献 14 , 15 )，本试验方法中建议使用断口图（参见规程 C1322 ).

1.1 This test method covers the determination of the slow crack growth (SCG) parameters of advanced ceramics in a given test environment at elevated temperatures in which the time-to-failure of four-point- 1 / 4 point flexural test specimens (see Fig. 1 ) is determined as a function of different levels of constant applied stress. This SCG constant stress test procedure is also called a slow crack growth (SCG) stress rupture test. The test method addresses the test equipment, test specimen fabrication, test stress levels and experimental procedures, data collection and analysis, and reporting requirements. 1.2 In this test method the decrease in time-to-failure with increasing levels of applied stress in specified test conditions and temperatures is measured and used to analyze the slow crack growth parameters of the ceramic. The preferred analysis 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: This test method is historically referred to in earlier technical literature as static fatigue testing (Refs 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 stress loading, as defined in E1823 , this test method uses the term constant stress testing rather than static fatigue testing. 1.3 This test method uses a four-point- 1 / 4 point flexural test mode and 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, elastic continuous behavior, and the application of this test method to these materials is not recommended. 1.4 This test method is intended for use at elevated temperatures with various test environments such as air, vacuum, inert gas, and steam. This test method is similar to Test Method C1576 with the addition of provisions for testing at elevated temperatures to establish the effects of those temperatures on slow crack growth. The elevated temperature testing provisions are derived from Test Methods C1211 and C1465 . 1.5 Creep deformation at elevated temperatures can occur in some ceramics as a competitive mechanism with slow crack growth. Those creep effects may interact and interfere with the slow crack growth effects (see 5.5 ). This test method is intended to be used primarily for ceramic test specimens with negligible creep. This test method imposes specific upper-bound limits on measured maximum creep strain at fracture or run-out (no more than 0.1 %, in accordance with 5.5 ). 1.6 The values stated in SI units are to be regarded as the standard and in accordance with IEEE/ASTM SI 10 . 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 ====== 4.1 The service life of many structural ceramic components is often limited by the subcritical growth of cracks over time, under stress at a defined temperature, and in a defined chemical environment (Refs 1- 3 ). When one or more cracks grow to a critical size, brittle catastrophic failure may occur in the component. Slow crack growth in ceramics is commonly accelerated at elevated temperatures. This test method provides a procedure for measuring the long term load-carrying ability and appraising the relative slow crack growth susceptibility of ceramic materials at elevated temperatures as a function of time, temperature, and environment. This test method is based on Test Method C1576 with the addition of provisions for elevated temperature testing. 4.2 This test method is also used to determine the influences of processing variables and composition on slow crack growth at elevated temperatures, as well as on strength behavior of newly developed or existing materials, thus allowing tailoring and optimizing material processing for further modification. 4.3 This test method may be used for material development, quality control, characterization, design code or model verification, time-to-failure, and limited design data generation purposes. Note 2: 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. 4.4 This test method and Test Method C1576 are similar and related to Test Methods C1368 and C1465 ; however, C1368 and C1465 use constant stress-rates (linearly increasing stress over time) to determine corresponding flexural strengths, whereas this test method and C1576 employ a constant stress (fixed stress levels over time) 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 data from 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. 4.5 The flexural stress computation in this test method is based on simple elastic beam theory, with the following assumptions: the material is isotropic and homogeneous; the moduli of elasticity in tension and compression are identical; and the material is linearly elastic. These assumptions are based on small grain size in the ceramic specimens. The grain size should be no greater than 1 / 50 of the beam depth as measured by the mean linear intercept method ( 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. 4.6 The test specimen sizes and test fixtures have been selected in accordance with Test Method C1211 which provides a balance between practical configurations and resulting errors, as discussed in Refs 4 and 5 . Test Method C1211 also specifies fixture material requirements for elevated test temperature stability and functionality. 4.7 The SCG data are evaluated by regression of log applied-stress vs. 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 3: A variety of crack velocity functions exist in the literature. A comparison of the functions for the prediction of long-term constant stress (static fatigue) data from short-term constant stress rate (dynamic fatigue) data (Ref 6 ) indicates that the exponential forms better predict the data than the power-law form. Further, the exponential form has a theoretical basis (Refs 7- 10 ); however, the power law form is simpler mathematically. Both forms have been shown to fit short-term test data well. 4.8 The approach used in this test method assumes that the ceramic material displays no rising R-curve behavior, that is, no increasing fracture resistance (or crack-extension resistance) with increasing crack length for a given test temperature. The existence of such R-curve behavior cannot be determined from this test method. The analysis further assumes that the same flaw type controls all times-to-failure for a given test temperature. 4.9 Slow crack growth behavior of ceramic materials can vary as a function of material properties, thermal conditions, and environmental variables. Therefore, it is essential that test results accurately reflect the effects of the 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. 4.10 Like mechanical strength, the SCG time-to-failure of advanced ceramics 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 (Refs 1 , 11- 13 ; see Appendix X2 ). Hence, a proper range and number of constant applied stress levels, in conjunction with an appropriate number of test specimens, are required for statistical reproducibility and reliable design data generation (Ref 1- 3 ). This test method provides guidance in this regard. 4.11 The time-to-failure of a ceramic material for a given test specimen and test fixture configuration is dependent on the ceramic material’s inherent resistance to fracture, the presence of flaws, the applied stress, and the temperature 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 (Refs 14 , 15 ), and fractography is recommended in this test method (refer to Practice C1322 ).