Arturo Domínguez Rodríguez

Evolution of specimen shape for uniaxial compression of single crystals

Compression tests for the study of plastic deformation of single crystals have been widely used, especially for those materials which are brittle and/or difficult to machine in the form of specimens. The present work was stimulated by unexpected observations of the shape evolution of sapphire specimens after a few per cent deformation by basal slip. The crystals were oriented to avoid rhombohedral twinning, using an orientation quite different from previous studies. Here, the authors examine the shape changes for a parallelepiped specimen subjected to a homogeneous strain in compression; it is based on a simple geometrical approach derived from previous calculations. The key parameters are the initial angle {var_phi}{sub 0} between the slip plane and the compression face and the deformation represented by the homogeneous shear strain {gamma} or the specimen shortening (l/l{sub 0}) (l and l{sub 0} are the final and initial lengths).

Recent Insights on the Superplastic Behaviour of Ceramics

Superplasticity is the ability exhibited by some fine-grained materials to be elongated a great deal with no failure. Such phenomenological definition accounts for the engineering view point of this remarkable property. From a fundamental basis, there is a full consensus to admit that it is essentially linked to the grain boundary motion under invariance of microstructure. Despite the great scientific effort carried out during the two last decades, or probably due to that, there is still a gap on the scientific comprehension of the equation describing superplasticity from a basic point of view, not to say about its potential extension to nanostructured materials. This paper presents the essential basis of a new model proposed to account for the main features of structural ceramics.