Micromechanical analysis of heterogeneous structural materials

This paper shows an efficient methodology based on micromechanical framework and grid nanoindentation for the assessment of effective elastic properties on several types of microscopically heterogeneous structural materials. Such task is a prerequisite for successful nano- and micro-structural material characterization, development and optimization. The grid nanoindentation and statistical deconvolution methods previously described in the literature e.g. for cementitious materials [1,2], alkali activated materials [3] or high-performance concretes [4] have been employed. In this paper we demonstrate their utilization also for other types of structural composites with crystalline nature and we validate the results by using enhanced numerical method based on fast Fourier transform (FFT). The direct procedure of using grid nanoindentation data in the FFT method simplifies the evaluation of effective composite properties and leads to the assemblage of the full stiffness matrix compared to simple analytical approaches. The paper deals namely with cement paste, gypsum and aluminum alloy. Nanoindentation is used for the determination of phase properties in grid points at the scale below one micrometer. Statistical approach and deconvolution methods are applied to assess intrinsic phase properties. Elastic properties obtained by nanoindentation are homogenized in the frame of the representative volume element (RVE) by means of analytical and numerical FFT-based schemes. Good correlation of the results from all methods was found for the tested materials due to the close-to-isotropic nature of the composites in the RVE having dimensions similar to 100-200 mu m. Results were also verified against macroscopic experimental results. The proposed and validated numerical approach can be successively used for the material modeling in finite element software or for optimization of materials with inhomogeneous microstructures. (C) 2012 Elsevier Ltd. All rights reserved.