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The use of indentation testing as a method for investigating the deformation and fracture properties of intrinsically brittle materials, glasses, and ceramics is examined. It is argued that the traditional plasticity models of hardness phenomena can be deficient in some important respects, notably in the underlying assumptions of homogeneity and volume conservation. The penetrating indenter is accommodated by an intermittent “shear faulting” mode, plus (to a greater or lesser extent, depending on the material) some structural compaction or expansion. These faults provide the sources for initiation of the indentation cracks. Once generated, the cracks can grow under the action of subsequent external tensile stresses, thereby taking the specimen to failure.
In this presentation the mechanical basis for describing these phenomena will be out-lined, with particular emphasis on the interrelations between hardness and other characteristic material parameters, such as elastic modulus and fracture toughness. Procedures for quantitative determination of these parameters will be discussed. Extension of the procedures to the measurement of surface residual stresses in brittle materials will be made to illustrate the power of the indentation method as an analytical tool for materials evaluation.
Microindentation hardness testing, brittleness, cracks, elastic recovery, fracture mechanics, indentation, residual stress, shear faults, toughness
Manager, Rockwell International Science Center, Thousand Oaks, CA
Physicist, Center for Materials Science, National Bureau of Standards, Gaithersburg, MD