1.1 本试验方法包括在环境温度下测定高级陶瓷材料的弯曲强度。四点- 1. / 4. -规定跨度的点荷载和三点荷载为标准荷载，如 图1 规定横截面尺寸的矩形试样与规定的试样夹具组合中的规定特征一起使用。试样尺寸可为3×4×45至50 mm，在40 mm外跨四点或三点夹具上进行测试。或者，可以使用这些尺寸的一半或两倍的试样和夹具跨度。该方法允许对机加工或烧制试样进行测试。加工准备的几个选项包括:应用匹配加工、常规程序或指定的标准程序。 本方法描述了仪器、试样要求、试验程序、计算和报告要求。本试验方法适用于单片或颗粒或晶须增强陶瓷。它也可以用于眼镜。它不适用于连续纤维增强陶瓷复合材料。 1.2 以国际单位制表示的数值应视为标准。括号中给出的值仅供参考。 1.3 本标准并不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。 1.4 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《国际标准、指南和建议制定原则决定》中确立的国际公认标准化原则制定的。 =====意义和用途====== 4.1 该测试方法可用于材料开发、质量控制、表征和设计数据生成。本试验方法适用于强度为50 MPa（~7 ksi）或更高的陶瓷。 4.2 弯曲应力是基于简单梁理论计算的，假设材料是各向同性和均质的，拉伸和压缩弹性模量相同，材料是线性弹性的。 平均晶粒尺寸应不大于梁厚度的五十分之一。标准中的均匀性和各向同性假设排除了对连续纤维增强陶瓷使用该试验的可能性。 4.3 一组试样的抗弯强度受与试验程序相关的几个参数的影响。这些因素包括加载速率、试验环境、试样尺寸、试样制备和试验夹具。如MIL-STD-1942（MR）和参考文献所述，选择样本尺寸和夹具以在实际配置和由此产生的误差之间提供平衡 ( 1. , 2. ) . 4. 指定了特定的夹具和样本配置，以便在无需威布尔的情况下对数据进行快速比较- 尺寸缩放。 4.4 陶瓷材料的弯曲强度取决于其固有的抗断裂能力以及缺陷的大小和严重程度。这些变化会导致试样样本的测试结果自然分散。尽管断裂表面的断口分析超出了本标准的范围，但强烈建议用于所有目的，特别是如果数据将用于MIL-STD-1942（MR）和参考文献 ( 2- 5. ) 和实践 第1322页 和 第123页 . 4.5 三点试验配置仅使试样的一小部分暴露在最大应力下。因此，三点弯曲强度可能远大于四点弯曲强度。 三点弯曲有一些优点。它使用更简单的测试夹具，更容易适应高温和断裂韧性测试，有时在威布尔统计研究中也很有用。然而，对于大多数表征目的，首选并推荐四点弯曲。 4.6 该方法确定了环境温度和环境条件下的弯曲强度。环境条件下的弯曲强度可以是或不一定是惰性弯曲强度。 注7: 通过使用惰性测试气氛（如干燥氮气、油或真空），可以将时间相关的影响降至最低。或者，可以使用比本标准规定的更快的测试速率。 氧化物陶瓷、玻璃和含有界面相玻璃的陶瓷即使在室温下也容易发生缓慢的裂纹扩展。即使在本标准规定的速率下，液体形式的水或空气中的湿度也会产生显著影响。另一方面，许多陶瓷如碳化硼、碳化硅、氮化铝和许多氮化硅在室温下对缓慢的裂纹生长不敏感，实验室环境条件下的弯曲强度是惰性弯曲强度。

1.1 This test method covers the determination of flexural strength of advanced ceramic materials at ambient temperature. Four-point- 1 / 4 -point and three-point loadings with prescribed spans are the standard as shown in Fig. 1 . Rectangular specimens of prescribed cross-section sizes are used with specified features in prescribed specimen-fixture combinations. Test specimens may be 3 by 4 by 45 to 50 mm in size that are tested on 40-mm outer span four-point or three-point fixtures. Alternatively, test specimens and fixture spans half or twice these sizes may be used. The method permits testing of machined or as-fired test specimens. Several options for machining preparation are included: application matched machining, customary procedure, or a specified standard procedure. This method describes the apparatus, specimen requirements, test procedure, calculations, and reporting requirements. The test method is applicable to monolithic or particulate- or whisker-reinforced ceramics. It may also be used for glasses. It is not applicable to continuous fiber-reinforced ceramic composites. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.3 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. 1.4 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 This test method may be used for material development, quality control, characterization, and design data generation purposes. This test method is intended to be used with ceramics whose strength is 50 MPa (~7 ksi) or greater. 4.2 The flexure stress is computed based on simple beam theory with 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 average grain size should be no greater than one-fiftieth of the beam thickness. The homogeneity and isotropy assumption in the standard rule out the use of this test for continuous fiber-reinforced ceramics. 4.3 Flexural strength of a group of test specimens is influenced by several parameters associated with the test procedure. Such factors include the loading rate, test environment, specimen size, specimen preparation, and test fixtures. Specimen sizes and fixtures were chosen to provide a balance between practical configurations and resulting errors, as discussed in MIL-STD-1942(MR) and Refs ( 1 , 2 ) . 4 Specific fixture and specimen configurations were designated in order to permit ready comparison of data without the need for Weibull-size scaling. 4.4 The flexural strength of a ceramic material is dependent on both its inherent resistance to fracture and the size and severity of flaws. Variations in these cause a natural scatter in test results for a sample of test specimens. Fractographic analysis of fracture surfaces, although beyond the scope of this standard, is highly recommended for all purposes, especially if the data will be used for design as discussed in MIL-STD-1942(MR) and Refs ( 2- 5 ) and Practices C1322 and C1239 . 4.5 The three-point test configuration exposes only a very small portion of the specimen to the maximum stress. Therefore, three-point flexural strengths are likely to be much greater than four-point flexural strengths. Three-point flexure has some advantages. It uses simpler test fixtures, it is easier to adapt to high temperature and fracture toughness testing, and it is sometimes helpful in Weibull statistical studies. However, four-point flexure is preferred and recommended for most characterization purposes. 4.6 This method determines the flexural strength at ambient temperature and environmental conditions. The flexural strength under ambient conditions may or may not necessarily be the inert flexural strength. Note 7: time dependent effects may be minimized through the use of inert testing atmosphere such as dry nitrogen gas, oil, or vacuum. Alternatively, testing rates faster than specified in this standard may be used. Oxide ceramics, glasses, and ceramics containing boundary phase glass are susceptible to slow crack growth even at room temperature. Water, either in the form of liquid or as humidity in air, can have a significant effect, even at the rates specified in this standard. On the other hand, many ceramics such as boron carbide, silicon carbide, aluminum nitride, and many silicon nitrides have no sensitivity to slow crack growth at room temperature and the flexural strength in laboratory ambient conditions is the inert flexural strength.