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International audience; The homogenization theory in linear elasticity is applied to a periodic array of cylindrical inclusions in rectangular pattern extending to infinity in the inclusions axial direction, such that the deformation of tissue along this last direction is negligible. In the plane of deformation, the homogenization scheme is based on the average strain energy whereas in the third direction it is based on the average normal stress along this direction. Namely, these average quantities have to be the same on a Repeating Unit Cell (RUC) of heterogeneous and homogenized media when using a special form of boundary conditions forming by a periodic part and an affine part of displacement. It exists an infinity of RUCs generating the considered array. The computing procedure is tested with different choices of RUC to control that the results of the homogenization process are independent of the kind of RUC we employ. Then, the dependence of the homogenized coefficients on the microstructure can be studied. For instance, a special anisotropy and the role of the inclusion volume are investigated. In the second part of this work, mechanical traction tests are simulated. We consider two kinds of loading, applying a density of force or imposing a displacement. We test five samples of periodic array containing one, four, sixteen, sixty-four and one hundred of RUCs. The evolution of mean stresses, strains and energy with the numbers of inclusions is studied. Evolutions depend on the kind of loading, but not their limits, which could be predicted by simulating traction test of the homogenized medium.

Paper deals with the problem of crack propagation in the vicinity of the interface in layered materials. Layered materials are often used in practice, primarily because of their better mechanical properties in comparison with properties of individual materials components. The configuration of a crack with its tip at the bi-material inter-face can be created during the crack propagation in the structure. It is important to decide if the crack propagates into the second material in this case. The step change of material properties at bi-material interface causes that the classical linear elastic fracture mechanics cannot be used. A generalized approach has to be applied. In this paper, two criteria are applied for the determination of the critical value of applied load. Knowledge of these values is important for the estimation of service life time of such structures. Results obtained can be used espe-cially for multi-layer polymer composites design. On the basis of presented procedures, suitable material combi-nation can be suggested for composite structures. Článek se zabývá šířením trhlin v blízkosti rozhraní ve vrstevnatých materiálech. V případě, kdy se vrchol trhliny dostane na rozhraní, je nutné rozhodnout, zda se bude trhlina šířit dál do druhého materiálu nebo ne. Skoková změna materiálových vlastností na rozhraní zabraňuje možnosti použít klasický přístup lineárně elastické lomové mechaniky. Je nutné použít zobecněný přístup. Pro určení kritické hodnoty aplikovaného zatížení byla použita dvě kritéria.

The present paper deals with the low cycle fatigue analysis of the low pressure (LP) steam turbine blade. The blade is cyclically loaded by the centrifugal force because of the repeated startups of the turbine. The goal of the research is to develop a technique to assess fatigue life of the blade and to determine the number of startups to the crack initiation. Two approaches were employed. First approach is based on the elastic finite element analysis. Fictive ‘elastic’ results are recalculated using Neuber’s rule and the equivalent energy method. Triaxial state of stress is reduced using von Mises theory. Strain amplitude is calculated employing the cyclic deformation curve. Second approach is based on elastic-plastic FE analysis. Strain amplitude is determined directly from the FE analysis by reducing the triaxial state of strain. Fatigue life was assessed using uniaxial damage parameters. Both approaches are compared and their applicability is discussed. Factors that can influence the fatigue life are introduced. Experimental low cycle fatigue testing is shortly described.