Micromechanics

About: Micromechanics is a research topic. Over the lifetime, 6000 publications have been published within this topic receiving 162635 citations.

Mechanical properties of porous materials

Abstract: Porous materials are commonly found in nature and as industrial materials such as wood, carbon, foams, ceramics and bricks. In order to use them effectively, their mechanical properties must be understood in relation to their micro-structures. This paper studies the mechanical properties of a few common porous materials: carbon rods, ceramics, polymeric foams and bricks. The characterisation of pore structures was performed using a Mercury Porosimeter. Detailed information was obtained on the density, porosity, surface area and pore size distribution. A large number of experiments on either bending or compression were conducted in order to obtain their macro-mechanical properties such as Young's modulus, hardness and strength. Based on the experimental observations, theoretical models were employed to predict the macro-properties from the micromechanics viewpoint. By studying the deformation of pores the global behaviour was calculated. Two simple formulae for the elastic modulus, E, were proposed: for low values of porosity, φ, E = E0(1 − 2φ) (1 + 4φ2) where E0 is the elastic modulus when the porosity is zero; for high value of porosity such as for foams E = E0 (1 − φ)2. The theoretical results agreed well with the experimental ones. The study has provided insights into the mechanical properties of porous materials over a wide range of porosity values.

Linear Thermoelastic Higher-Order Theory for Periodic Multiphase Materials

Abstract: A new micromechanics model is presented which is capable of accurately estimating both the effective elastic constants of a periodic multiphase composite and the local stress and strain fields in the individual phases. The model is presently limited to materials characterized by constituent phases that are continuous in one direction, but arbitrarily distributed within the repeating unit cell which characterizes the material's periodic microstructure. The model's analytical framework is based on the homogenization technique for periodic media, but the method of solution for the local displacement and stress fields borrows concepts previously employed by the authors in constructing the higher-order theory for functionally graded materials, in contrast with the standard finite element solution method typically used in conjunction with the homogenization technique. The present approach produces a closed-form macroscopic constitutive equation for a periodic multiphase material valid for both uniaxial and multiaxial loading which, in turn, can be incorporated into a structural analysis computer code. The model's predictive accuracy is demonstrated by comparison with reported results of detailed finite element analyses of periodic composites as well as with the classical elasticity solution for an inclusion in an infinite matrix.

Prediction of thermo-mechanical properties for compression moulded composites

Abstract: We present a method to determine the thermo-mechanical properties of compression moulded composite parts. The flow-induced fibre orientation is first calculated by numerical simulation, and the resulting orientation state is used as input in a micromechanical model that predicts the thermo-mechanical properties of the part. A two-step homogenization scheme based on the grain model approach is followed. First, the properties of a reference composite with aligned fibres are estimated by means of a mixture rule between the upper and lower Hashin-Shtrikman bounds (derived by Willis). This method is in agreement with the Mori-Tanaka estimates for moderate concentrations, and gives better results for higher concentrations. Next, the properties of the composite are obtained by averaging several reference composites with different fibre directions. An example of a 3-D compression moulded composite part is analyzed and the results are discussed. (C) 1997 Elsevier Science Limited.