Development of small specimen test techniques

根据JIS R1601，用10多个尺寸为3x4x36mm的试样来评估陶瓷的抗弯强度。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样品无法从中子辐照材料中获得。因此，测量中子辐照材料的力学性能需要小试样试验技术。由于陶瓷的强度取决于测试条件，因此必须开发一种适当的实验方法来从小样品中获得可靠的数据。众所周知，陶瓷的强度取决于试样的尺寸。用小体积试件的强度估算大体积构件强度的方法也很重要。因此，必须研究尺寸对强度的影响。本研究从易于操作和精确测量的角度出发，设计了适用于小试件的弯曲夹具。由于小试件比标准试件在更小的载荷和更小的挠度下断裂，因此研制了小试件试验机。研究了表面粗糙度、扭转和应变速率对弯曲强度的影响。确定了试验条件，使误差最小化。利用弯曲夹具和试验条件，研究了尺寸对强度的影响。发现试样尺寸的Weibull尺度关系可以很好地描述尺寸效应。因此，用威布尔关系从小试件的强度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.