The Measurement of Microdeformations in Structured Solids

Abstract

Over the past decades various test procedures have been developed in the Micromechanics Laboratory to verify the analytically predicted microdeformations of structured solids. In accordance with the probabilistic mechanics theory [1],[2] these predictions involve the distributions of the (internal) deformations or strains over a particular domain of the microstructure. They are also accessible from appropriate experimental observations. Hence this paper is concerned with a brief review of two of the test procedures developed for the determination of microdeformations in metallic, composite and fibrous structures. In order to comply with the requirements of the probabilistic theory of deformation [2], it is necessary to conduct the experiments and associated measurements on three levels, i.e., the microscopic, mesoscopic and macroscopic one. The first level concerns a microelement of the structure, which can be a single crystal in a polycrystalline solid, a solid particle of the dispersed phase in a matrix material or a single fibre in a fibrous structure, etc. For the observation at this level scanning — electron microscopy with special adaptions can be used. For the testing of an “ensemble of micro-elements” pertaining to a “meso-domain” of the material structure, it has been found convenient to employ the “stress-holographic interferometry” technique [3] yielding measurements of surface deformation. The latter must be linked to the microdeformations, however, by the application of quantitative stereology [4]. The observations of the macroscopic deformations occur by the usual non-destructive testing procedures adopted in engineering.