The prediction of a size effect in micro-indentation

The indentation hardness of metals depends upon the size of the indent. for indents in the size range of 0.1-10 mu m. A finite element method is used to predict this size effect, based on Fleck-Hutchinson strain gradient plasticity theory. The material is treated as a power law, deformation theory solid such that the strain energy density depends upon both strain and strain gradient. An indentation size effect is predicted for axisymmetric indenters of various head-shape (flat, conical and spherical), and the role of contact friction is explored. It is found that the predicted hardness increases significantly when the size of the indent is comparable to the material micro-length scale. (C) 1998 Elsevier Science Ltd.