MECHANICAL PROPERTIES AND BEHAVIOR

The overriding concern with regard to the mechanical performance of ceramics is their brittieness and hence sensitivity to flaws. There is usually htfle or no warning that failure is imminent because deformation strain prior to failure is usually less than 0.1%. As a result, a primary thmst of stmctural ceramics research has been the development of tougher ceramics. Ceramics now exist that have toughness values of 20 and strengths that 

Elastic Behavior. Elastic deformation is defined as the reversible deformation that occurs when a load is appHed. Most ceramics deform in a linear elastic fashion, ie, the amount of reversible deformation is a linear function of the appHed stress up to a certain stress level. If the appHed stress is increased any further the ceramic fractures catastrophically. This is in contrast to most metals which initially deform elastically and then begin to deform plastically. Plastic deformation allows stresses to be dissipated rather than building to the point where bonds break irreversibly. 

Elastic behavior is commonly quantified by the Young s modulus E, the proportionality constant between the appHed tensile stress O, and the tensile strain (A length/original length). 

Materials having high elastic moduH deform less for a given stress. Typical E values are shown in Table 1. 

Values for the Poisson s ratio of ice are highly dependent on composition, stmcture, and strain rate (4). 

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Young s modulus for [CERAMICS - MECHANICAL PROPERTIES AND BEHAVIOR] (Vol 5)... 

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