Cyclic fatigue-crack growth in grain bridging ceramics

Article Abstract:

The principle toughening mechanism in polycrystalline ceramics that exhibit grain bridging is the cyclic fatigue degradation. Repetitive sliding wear degradation of frictional grain bridges is based on frictional-wear mechanism. The effects of salient mechanical and microstructural variables on the grain and matrix interface are explained by the development of a micromechanical model. Experimentally determined values show that the fatigue crack growth rates in coarse grained alumina and silicon nitride are the same as those predicted by theory.

Fatigue (Materials), Materials

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Nondestructive detection of damage produced by a sharp indenter in ceramics

Article Abstract:

An ultrasonic technique using normal-incident compressional waves and a thermal wave measurement technique using an optical beam deflection method allow nondestructive detection of damage in ceramics. The indentation of material with Vickers and Knoop diamond pyramidal indenters causes a permanent mark on the surface. The damage also involves radial, median and lateral cracks below and around the indentation.

Methods, Usage, Ultrasonic testing, Non-destructive testing, Nondestructive testing

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The influence of grain size on the toughness of monolithic ceramics

Article Abstract:

The toughness of polycrystalline ceramics is increased by the existence of an optimal grain size, whose effect is predicted by a model developed theoretically. The model shows that three principal mechanisms influence the toughness of ceramics, the distributed microcracking, crack trapping by tough grains and the dissipation of fictional energy when grains are pulled out because of the crack.

Causes of, Residual stresses

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