The micropolar elastic behaviour of model macroscopically heterogeneous materials

This paper describes the design, manufacture, testing and analysis of two model heterogeneous materials that exhibit non classical elastic behaviour when loaded. In particular both materials demonstrate a size effect in which stiffness increases as test sample size reduces; an effect that is unrecognized by classical elasticity but predicted by more generalized elasticity theories that are thought to describe the behaviour of heterogeneous materials more fully. The size effect has been observed by both experimental testing and finite element analysis that fully incorporates the details of the underlying heterogeneity designed into each material. The size effect has been quantified thus enabling both the modulus and also the characteristic length, an additional constitutive parameter present within micropolar and other generalized elasticity theories, to be determined for each material. These characteristic length values are extraordinarily similar to the length scales associated with the structure of the materials. An additional constitutive parameter present within plane micropolar elasticity theory that quantifies shear stress asymmetry has also been determined for one of the materials by using an iterative process that seeks to minimize the differences between numerical predictions and test results.