作者：Dr. Donald F. Adams;
作者單位：
刊名：HIGH-PERFORMANCE Composites
ISSN：1081-9223
出版年：2008-01-05
卷：16
期：4
起頁：11
止頁：13
分類號：TQ175
語種：英文
關鍵詞：
內容簡介Because of their brittle nature, ceramics, fiber-reinforced or unreinforced, are difficult to test in pure tension, compression and shear, primarily due to difficulties in gripping and uniformly loading the brittle specimen. In contrast, a flexural specimen simply rests on two supports and is loaded at one or two points along its length, making the test very easy to perform. This explains why those involved with ceramic-matrix composites and bulk ceramics use flexural testing of a beam more commonly than those working with less brittle materials. There are other factors as well. The tensile strength of the material can be very sensitive to flaws and defects, including those induced during specimen fabrication, as well as stress concentrations induced by the gripping method. Thus, despite extremely careful preparation, there can be considerable scatter in test data. Compressive strength is difficult to obtain because the materials tend to be much stronger in compression than in shear. Even in a pure compression test, the shear stresses that occur at 45 deg to the direction of applied compressive load can cause a premature shear failure. Shear strength is the most difficult to determine. Ceramics are typically brittle materials, which by definition means that they are weaker in tension than in shear. Thus, even if a pure shear stress state is induced in the specimen, then at 45 deg to the direction of shear loading a tensile stress of magnitude equal to the applied shear stress is present. As a result, the material actually fails in tension.
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