Strain gradient effects on microscopic strain field in a metal matrix composite

The purpose of this paper is to demonstrate the improved modeling accuracy of a finite-deformation strain gradient crystal plasticity formulation over its classical counterpart by conducting a joint experimental and numerical investigation of the microscopic details of the deformation of a whisker-r einforced metal-matrix composite. The lattice rotation distribution around whiskers is obtained in thin foils using a TEM technique and is then correl ated with numerical predictions based on finite element analyses of a unit- cell of a single crystal matrix containing a rigid whisker. The matrix mate rial is first characterized by a classical, scale-independent crystal plast icity theory. It is found that the classical theory predicts a lattice rota tion distribution with a spatial gradient much higher than experimentally m easured. A strain gradient crystal plasticity formulation is then applied t o model the matrix. The strain gradient formulation accounts for both strai n hardening and strain gradient hardening. The deformation thus predicted e xhibits a strong dependence on the size of the whisker. For a constitutive length scale comparable to the whisker diameter? the spatial gradient of th e lattice rotation is several times lower than that predicted by the classi cal theory, and hence correlates significantly better with the experimental results. (C) 2000 Elsevier Science Ltd. All rights reserved.