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A zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed around underground excavation in the deep geological layers considered for the high level radioactive waste disposal. The present study concerns the modeling of this phenomena by a micromechanical damage model, based on a Mori-Tanaka homogenization on a cracked media. This anisotropic model is derived from Eshelby homogenized scheme, on which a coupling between damage and friction is taking into account on cracks. Compared to elastoplastic model on tunnel drilling modeling, micromechanical modeling seems very promising: both approaches provide similar EDZ sizes and shapes even if they do not have the same effects on perturbed mechanical behavior; micromechanical model also overcomes the elastoplastic one by a realistic characterization of crack processes.

This study presents a two-scale homogenization scheme for determining effective thermal, mechanical, electrical, and piezoelectric properties of smart laminated composites. The studied smart composite is composed of a unidirectional fiber reinforced laminated system as a host structure and an active unidirectional fiber reinforced piezocomposite. The effective response of the composites, in a representative unit-cell model, is formulated based on a volume average of the field quantities of the constituents. Each unit-cell is divided into a number of subcells. A unit-cell model, consisting of four fiber and matrix subcells, is generated to homogenize mechanical and non-mechanical responses of a lamina. Material parameters in the constitutive models of the constituents, i.e., fiber and matrix, are allowed to vary with temperature and time. The macro-scale consists of a sublaminate model that homogenizes responses of representative layers in the laminated systems. Perfect bonds are assumed at the fiber–matrix interphases and at the interphases between laminae. The effective properties obtained from the present micromechanical model are comparable to the ones generated using an asymptotic homogenization scheme. Available experimental data in the literature are used to verify the multi-scale model formulation. The effects of temperature dependent material constants on the overall coupled electro-mechanical properties of composites during transient heat conduction are also examined.

Considering the nucleation sites around the crack tip as the events of a Poisson’s process with intensity λ, a micromechanical model for the prediction of the fracture toughness of materials is developed. Stress and strain ahead of a crack under mode-III loading are reviwed[1] and it is shown that the distribution of the critical stress intensity factors (SIF) for stress controlled failure can be expressed by $$ G(K) = 1 - \exp \left( { - \lambda \frac{{K^4 }} {{4\pi \tau _c^4 }}} \right) $$ (1) where τ c is the critical stress for decohesion or cracking of the second phase particles. On the other hand the distribution of critical K for strain controlled failure is $$ G(K) = 1 - \exp \left( { - \lambda \left( {\frac{{(K - K_{\min } )^4 }} {M}} \right)} \right) $$ (2) where μ is the elastic shear modulus, τ y is the yield stress in shear and γ c is the critical strain for crack growth. The results are then modified and extended for the mode-I case. The distribution of K is shown to be $$ G(K) = 1 - \exp \left( { - \lambda \frac{{K^4 }} {{4\pi \mu ^2 \tau _y^4 \gamma _c^2 }}} \right) $$ (3) where K min is a material parameter reflecting the finite size of the inclusion, M is the counterpart of Mode-I as in the Eq(1) or (2). .Interpreting Eq(3) as failure probability of a specimen under a given K, the theoretical models are then compared to other statistical models[2,3].

Herein we derive, under the micromechanical model we proposed earlier, Man and Paroni [14], a complete set of formulae for the twelve material constants in the acoustoelastic constitutive equation for orthorhombic aggregates of cubic crystallites. We present also a second model and compare its predictions on the material constants with those of the first model. Both these models lead to constitutive equations which are indifferent to rotation of reference placement. This allows us to appeal to a new representation theorem (Paroni and Man [15]), which greatly facilitates our derivation of the formulae for the material constants. The second model introduced in this paper is intimately related to some previous averaging theories in the literature. We explain why and in what sense our second model could be taken as a generalization of its predecessors.

An orthotropic plasticity model was developed for unidirectionally reinforced fibrous composites. A simplified plastic potential function with a single parameter was proposed for the flow rule. The parameters of the plasticity model were determined by simple tension tests on off-axis composite specimens. It was shown that this plasticity model was able to characterize the nonlinear behavior of polymeric and metal-matrix composites.

To calculate the plastic flow properties of two-phase materials, a large number of micromechanical models based on continuum mechanics principles has been established throughout the past years. Self consistent methods [1–3], rules of mixture (ROM) [4–9], non-linear generalizations of the classical Hashin-Shtrikman bounds [10–12] and the finite-element (FE) method [6, 13–19] have been used for this purpose. All these approaches aim to predict the properties of two-phase materials from the given properties of their constituent phases. Quantitative information from the microstructure, however, is incorporated seldomly in the models, with the exception of those with specific reference to matrix-inclusion-type microstructures. Up to now, only little attention was paid to microstructures different from these special types due to the lack of stereological parameters to characterize general two-phase microstructures quantitatively, and so even finite element based micromechanical modeling methods have been restricted to more or less special two-phase microstructures [21]. It is the aim of this report to present a micromechanical model applicable to general two-phase microstructures. In this course, a stereological parameter is introduced, which fully quantifies the geometrical continuity (GC) of the constituent phases. GC is a quantity of eminent importance, when dealing with various physical properties of coarse grained two-phase alloys possessing interpenetrating phases [20].

A micromechanical model for composite materials is proposed in which the components are assumed to obey continuum laws, and where the interfaces between the components are modelled with nonlinear springs. A homogenization procedure is used to obtain a constitutive relation of a fictitious homogeneous material body, that best represents the real heterogeneous composite. The latter relation shows a strain-softening behaviour which gives rise to mesh-dependent finite element solutions. A nonlocal formulation of this macroscopic relation can solve these problems.

A micromechanical model is presented which is used to analyse thermal cycling experiments of duplex stainless steel specimens. Varyiing the temperature leads to a remarkable internal stress state as consequence of the different thermal expansion coefficients of the austenite and ferrit phase. The internal stresses exceed the yield strength of in both phases. Plasticity effects together with the anisotropic microstructure of the material investigated result in irreversible deformations in thermal cycling experiments. Experiments and calculations are compared.

Major elements of a technique of the theoretical and experimental study of the mechanical properties of fiber-reinforced laminates are presented. A package of programs is based on macro- and micromechanical models of the composite. Analysis of the composite material strain in the neighbourhood of the loading application and close to the surface of the specimen was carried out on the basis of a finite-elements method.

The present paper offers a cursory review of the state-of-art in analytical modelling of brittle response. The discussion is formally divided to considerations of discrete (statistical) and continuum (micromechanical and phenomenological) models. An effort was made to point out the relations between these three classes of models and ascertain the manner of using these relations in improving currently existing modeling techniques.

The purpose of this study is to develop constitutive equations valid for HCP textured metals, with special applications to pure zirconium. A viscoplastic micromechanical approach is proposed, with the constitutive equations written on slip systems.The first results, shown in this paper, concern qualitative simulations of loading surfaces and of 1D tension test, performed with various assumptions on the active slip systems.

First, a review of some theories of toughening mechanisms in quasi-brittle materials was presented by Professor C. Atkinson. The spring model that includes the bridging mechanism was explained. Micromechanical models for various bridging mechanisms are summarized. As an example of studies on micromechanics of bridging, analyses of crack growth along the interface between short fiber and matrix are presented. In the discussion, mechanisms other than bridging such as crack deflection, crack branching, and microcracking are discussed.