BRJ – Volume 58, Number 1–2, 2010

Jan Sladek, Vladimir Sladek, Chuanzeng Zhang and Michael Wünsche:
Influences of electromagnetic crack-face boundary conditions on crack-tip parameters
in mgnetoelectroelastic composites . . . 1 – 21

Alexander Ekhlakov, Oksana Khay, Chuanzeng Zhang, Jan Sladek and Vladimir Sladek:
Crack analysis in functionally graded materials under thermal shock loading . . . 23 – 42

Ján Jerga:
Time development of autogenous and drying shrinkage of cement composite
with lightweight aggregate . . . 43 – 56

Ľubomír Bágeľ:
Effect of aggregate surface pretreatment onproperties of mortars.
Role of wettability and interfacial transitionzone . . . 57 – 74

Jan Sladek and Vladimír Sladek:
Bending of functionally graded plates under a thermal load . . . 75 – 94

Vladimír Živica, Martin-Tchingnabé Palou, Ľubomír Bágeľ and Blažena Vasilkovová:
Cements and geothermal deep borehole environment . . . 95 – 115

Peter Matiašovský and Peter Mihálka:
Numerical analysisof hygro-thermal performance of external envelope of historical buildings
with internal insulation plaster . . . 117 – 135

Abstracts

Influencesof electromagneticcrack-faceboundary conditionson crack-tip parametersin magnetoelectroelasticcomposites

Jan Sladek, Vladimir Sladek, Chuanzeng Zhang and Michael Wünsche

The paper presents an influence of various electromagnetic boundary condi¬tions on crack faces on crack quantities and intensity factors in magnetoelectroelas¬tic materials. The meshless method based on the local Petrov-Galerkin approach is proposed to solve initial-boundary value crack problems of magnetoelectroelastic solids with nonlinear electrical and magnetic boundary conditions on crack faces. A Heaviside step function as the test functions is applied in the weak-form to de¬rive local integral equations. Nodal points are spread on the analyzed domain, and each node is surrounded by a small circle for simplicity. The spatial variations of the displacements, electric and magnetic potentials are approximated by the Moving Least-Squares (MLS) scheme. The Newton-Raphson scheme is applied to consider nonlinear crack face boundary conditions.

Keywords: MLPGmethod, Moving least-squares (MLS) approximation, Newton-Raphson scheme, magnetoelectroelastic composites, intensity factors

Crack analysisin functionally gradedmaterialsunderthermalshock loading

Alexander Ekhlakov, Oksana Khay, Chuanzeng Zhang, Jan Sladek and Vladimir Sladek

In this paper a boundary-domain element method for solving transient crack problems of linear coupled thermoelasticity in two-dimensional, isotropic, continu¬ously non-homogeneous and linear elastic functionally graded materials subjected to tensile stress impact and thermal shock is presented. Laplace-domain fundamental solutions of transient coupled thermoelasticity for infinite, isotropic, homogeneous and linear elastic solids are employed to derive boundary-domain integral represen¬tations. The numerical implementation is performed by using a collocation method for the spatial discretization. Numerical solutions are first obtained in the Laplace-transformed domain. The final time-dependent solutions are subsequently acquired by the Stehfest’s Laplace-inversion algorithm. Numerical results for the dynamic stress intensity factors are presented and discussed for a finite edge crack in a finite domain.

Keywords: Functionally graded materials, Edge Cracks, Transient linear coupled thermoelasticity, Boundary-domain element method, Boundary-domain integral equa¬tions, Laplace-transform, Stehfest’s algorithm, Dynamic stress intensity factors

Timedevelopment of autogenousanddryingshrinkageof cement compositewithlightweight aggregate

Ján Jerga

Arecent attitude towards concrete sets equality among requirements on strength and a wide range of physico-mechanical properties. The behaviour modifica¬tion of the material is achieved by a proper replacement of mineral aggregate, often by waste products. The enhanced shrinkage is an unavoidable consequence to which the attention must be paid to prevent from structural damage. The question of time development of the long-term deformation is critical, considering the interaction of concrete components of various compositions and different ages. The advantage is an expression of the deformation increase by a simple parameter called the halftime of deformation. The drying and autogenous shrinkage were focused on in the analysis. Based on available experimental results a research into the dependence of a halftime and the limit value of shrinkage on the degree of mineral aggregate replacement was carried out. Some topics for the future research have been proposed.

Keywords: cement composite, lightweight aggregate, rheology, halftime of deforma¬tion

Effect of aggregate surface pretreatment onproperties of mortars
Role of wettability and interfacial transitionzone

Ľubomír Bágeľ

Asurface texture is one of the most important factors affecting the bond strength between aggregate and cement matrix in mortars. The aggregate–matrix interfacial zone (ITZ) also plays a broad role in the global strength and durability of cement composites. In this work, the influence of the pretreatment of the sand surface on the macroscopic properties (strengths) as well as microscopic parameters (pore structure) of mortars is investigated. Because there is a high volume fraction of ITZin tested mortars (68.90 %) there is an assumption that given treatments of the aggregate surface will affect the ITZin the great degree. Four different mortars with the constant sand volume contents and the same water to cement ratio were cast and several treating solutions were applied to alter the ability to wet the surface of the sand particles. The test results indicate that treated aggregates modify not only the strength but also the microstructure as well as the transport properties (perme¬ability) of mortars. The dominant role of the wettability degree of aggregate surface on the performance of mortars was also demonstrated. First of all the flexural and compressive strength of mortars were determined, followed by the pore structure analysis by the mercury intrusion porosimetry. Significant differences in the meas¬ured strengths and structural parameters of mortar specimens were observed among the different pretreatment processes applied. The changes detected in the pore size distribution of the mortars also indicate that the volume of ITZmay alter due to the sand treatment.

Keywords: mortar, interfacial transition zone, aggregate, surface treating, pore structure, MIP

Bendingof functionally gradedplatesundera thermalload

Jan Sladek and Vladimír Sladek

The Reissner-Mindlin theory is applied to describe plate bending problem un¬der a thermal load. Functionally graded material properties with continuous varia¬tion in the plate thickness direction are considered here. The meshless local Petrov-Galerkin (MLPG) method is applied to solve considered problems. Thermal shock loads are considered here. A weak formulation for the set of governing equations in the Reissner-Mindlin theory is transformed into local integral equations on local subdomains in the mean surface of the plate by using a unit test function. Nodal points are randomly spread on the surface of the plate and each node is surrounded by a circular subdomain to which local integral equations are applied. The meshless approximation based on the Moving Least-Squares (MLS) method is employed for the implementation. After performing the spatial integrations, one obtains a system of ordinary differential equations for certain nodal unknowns. That system is solved numerically by the Houbolt finite-difference scheme as a time-stepping method.

Keywords: Local integral equations, MLSapproximation, functionally graded ma¬terial, orthotropic properties, Houbolt finite-difference scheme

Cementsandgeothermaldeep boreholeenvironment

Vladimír Živica, Martin-Tchingnabé Palou, Ľubomír Bágeľ and Blažena Vasilkovová

High temperatures up to 400 °Cand pressures up to 150 MPa can be reached in deep boreholes. The borehole conditions under which the cement and cement com¬posites mixtures are used differ from the commonly used conditions for cement ma¬terials. Moreover the chemistry of geothermal reservoir fluids to which the cement is exposed differs from the essentially fresh waters. They contain 10 times larger amount of salinities in comparison to the amount in the sea water. Non condensable gases, notably H2Sand C02, are also frequently present. Cements and composite mix¬tures should comply with these conditions. Therefore special cements with superior cementing properties, hardening characteristics under high-temperature and high-pressure conditions are taken into consideration.

Keywords: geothermy, borehole, temperature, pressure, w/c ratio, chemical aggres¬sivity, biological activity

Numericalanalysisof Hygro-Thermalperformanceof Externalenvelopeof Historicalbuildingswithinternalinsulation Plaster

Peter Matiašovský and Peter Mihálka

The internal thermal insulation of external wall is an alternative solution enabling the additional thermal insulation of historical buildings providing their original external look. This solution requires specific design steps, using detailed numerical simulation tools. Characteristic structural details of historical buildings were selected and analysed in order to evaluate the temperature and humidity fields in the application of internal thermal insulation made from the capillary active plaster. The evaluation gave results confirming applicability of the proposed design solutions.

Keywords: external walls, internal thermal insulation, capillary activity, hygro¬thermal performance, numerical simulations