Development of small specimen test techniques

根据JIS R1601，陶瓷的弯曲强度用10个以上尺寸为3x4x36 mm的试样进行评估。然而，由于辐照空间和辐照废物的限制，许多这种尺寸的标准试样无法从中子辐照材料中获得。因此，小试样试验技术是测量中子辐照材料力学性能的必要手段，陶瓷材料的强度取决于试验条件，因此必须发展一种合适的试验方法，以便从小试样上获得可靠的数据。众所周知，陶瓷的强度取决于试样的尺寸。从小试样强度估算大体积构件强度的方法也很重要。本研究从操作方便、测量精确的角度出发，设计了小试样弯曲夹具。一台试验机也被开发用于小样本，因为小样本是在低得多的负载和低挠度比标准试样的断裂。研究了表面粗糙度、扭转和应变速率对弯曲强度的影响。确定了测试条件，以使误差最小化。研究了弯曲夹具和试验条件对强度的尺寸效应。结果表明，试样尺寸的威布尔比例关系能很好地描述尺寸效应。因此，用威布尔关系估计标准试件的强度似乎是有效的。用这种技术实际测量了辐照AlN的强度。

According to JIS R1601, bending strength of ceramics is evaluated with more than 10 specimens whose sizes are 3x4x36 mm. However, many standard specimens of this size are not available from neutron-irradiated materials because of limitations of irradiation space and irradiation waste. Therefore small specimen test techniques are necessary to measure mechanical properties of neutron-irradiated materials.An adequate experimental method must be developed to get reliable data from small specimens because the strength of ceramics depends on testing condition. It is well known that the strength of ceramics depends on the specimen size. Estimation methods of the strength of larger volume component from that of smaller specimen are important as well. Therefore the size effect on the strength must be studied.In this study, bend fixtures for small specimens were designed from the stand point of easy operation and precise measurement. A testing machine was also developed for small specimens because small specimens are fractured at much lower load and lower deflection than those of standard specimens. The effects of surface roughness, twisting and strain rate on the bending strength were studied. The testing condition was determined to minimize the errors. The size effect on the strength was studied with the bending fixtures and the testing condition. It was found that the size effect was well described by Weibull's scaling relationship of specimen size. Therefore estimation of the strength of the standard specimens from that of the small specimens seemed to be valid with the Weibull's relationship. Strength of irradiated AlN was actually measured with this technique.