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Repair formulations for fine-grained stone arte-facts
Tišlová, R. ; Novotná, Adéla
Stone restoration practice continuously deals with the problem of the selection of suitable repair materials. In establishing the requirements that guide their specification, the fundamental aim should always be to achieve the best compatibility between the substrate and the repair. When dealing with the restoration of stone, several aspects must be taken into consideration: not only the way in which compatibility influences the durability and structural and environmental resistance of the repair, but also the properties of the stone substrate itself must be considered. Compatibility is a highly complex problem but when considering the above mentioned aspects, functional compatibility – the compliance between physical and mechanical characteristics of the materials – is the most critical in prolonging the sustainability of the repair.
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Modification of protective lime coating systems for the porous limestone using lime nanomaterials: assessment of mechanical properties and ageing resistance
Navrátilová, Michaela ; Bayer, K. ; Ghaffari, E. ; Macounová, Dana ; Slížková, Zuzana ; Weber, J.
Within the area of care for sculptural and architectonic monuments of limestone in Austria there has been a historic continuity of use of protective lime coatings. In the regions of Upper and Lower Austria, Vienna and Burgenland mainly Leitha limestone (named after the Leitha Mountains) are dealt with. In Czech lands such approach was disrupted from 19th century by application of the “purist” idea of bare surface of stone. Nevertheless, this treatment of stone surface has been coming back into use for many various reasons in the past few decades. Requirements for preservation of pieces of art and handcraft made of limestone using lime coatings are most often applied in the regions of Vyso!ina, South Moravia and South Bohemia, which directly border on the Northern States of Austria. Owing to the resource locations of Leitha limestone in these regions, there is a higher representation of cultural heritage monuments made of this type of stone in the Czech Republic.
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Variation of Strouhal number on iced cable in sub-transitional range
Pospíšil, Stanislav ; Górski, P. ; Kuznetsov, Sergeii ; Tatara, M. ; Marušić, A.
The influence of ice accretion, angle of attack and Reynolds number on the flow field around iced cables of the cable-supported bridges is not clearly understood. The paper presents results of a wind tunnel investigations of Strouhal number of stationary iced cable model of cable-supported bridges. The investigations were carried out in a Climatic Wind Tunnel Laboratory of ITAM. The methodology leading to the experimental icing of the inclined cable model in the climatic section of the laboratory was prepared. For the aerodynamic investigations the iced cable model in a smaller scale was reproduced with combination of photography and 3-D printing procedure. The Strouhal number (St) was determined within the range of the Reynolds number (Re) between 2.4×10^4 and 16.4×10^4, based on the dominant vortex shedding frequency measured in the flow behind the model. The model was orientated at three principal angles of wind attack for each of the Re. Good agreement with the generally reported value in the sub-critical Re range for a circular cylinder was obtained.
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Microindentation assessment of climatic loading impacts on polymer sealants
Minster, Jiří ; Šašek, Petr
Sun light, especially the short-wave ultra-violet part of the sun spectrum, together with influence of moisture, are the most enlarged and the most effective sources of climatic damage of polymers. The effects of the both influences became stronger with enhanced temperature. Sun light on the one hand supports the forming of transverse chemical bonds between macromolecules and on the other hand results in their breakdown. This causes a strengthening or softening of polymers. The amount of changes and the dominant process depends on the radiation dose and on the influencing wave length. Every kind of chemical bond has its own critical wave length, which, with sufficient amount of energy, brings a reaction. Ageing, as a result of climatic loading, is therefore very closely connected with a structure of a real material. Microindentation is one of possible methods for assessing influences of a climatic loading on mechanical properties of polymers. Indentation test is checked by the history either of a power or an indent depth. The information about the hardness, Young modulus and viscoelastic properties of the investigated material can be received afterwards from measured data. The investigated materials were tested in their native standard form and also after four model types of physical-chemical ageing. Time-dependent properties of the sealants were assessed by the method of indentation creep. One hundred indentation creep tests were conducted for each sealant and type of ageing. A motivation for this work was a requirement to assess an influence of a climatic loading on the basic mechanical properties of sealants, used for a creation and a repair of mosaics.
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Mechanics of laser cut stent grafts
Major, Štěpán ; Kocour, Vladimír ; Hubálovský, Š.
This article is dedicated to a finite element analysis of tubular, laser cut stent grafts with peak-to peak bridge geometry under representative cyclic loading conditions for abdominal aortic aneurysm repair. Cardiovascular diseases are the principal cause of death in the developed world. For computational analysis, ANSYS software was employed to study the mechanical behavior of stents. Contrary to conventional engineering materials, nitinol stent fracture is not stress based but strain based. The effects of crimpling and cyclic pressure loading on stent–graft fatigue life were simulated and analyzed.
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Consolidation testing of porous limestone using lime nanomaterials: optimization, assessment of stone mechanical and structural characteristics
Macounová, Dana ; Bayer, K. ; Ghaffari, E. ; Navrátilová, Michaela ; Slížková, Zuzana ; Weber, J.
In consequence of an array of degradation mechanisms there is a change of stone characteristics used in historic objects. One of the negative changes is deterioration of mechanical properties, which may often lead to losses of original substance and gradual disintegration of works of art or handcraft made of stone. To prolong the lifespan of such damaged cultural-heritage objects a process called consolidation is often carried out within the framework of conservation treatment. During the process of conservation treatment the damaged stone is impregnated with a consolidating material, which is to provide the stone with a new binder capable of renewing its cohesion to a certain extent. Currently, a wide range of organic and inorganic consolidating agents of various characteristics is available, from synthetic polymers to silicic acid esters. Long-term experience shows that not only is the consolidating effect of the actual agent important, but also its lifespan and impact on the subsequent aging of the treated stone. Thus, in the past few years more emphasis has been laid on the compatibility or – to express it more precisely – the material similarity of the agents used in the process of conservation and restoration of works of art or handcraft.
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Mechanical properties of 3D auxetic structures produced by additive manufacturing
Jiroušek, O. ; Koudelka_ml., Petr ; Fíla, Tomáš
Three distinct auxetic structures were produced by direct 3D printing based on parametric CAD models. Mechanical properties of the structures were established by static compression tests where strain fields on the surface of the specimens was measured by non-contact optical method. Parametric finite element (FE) model of each structure was then subjected to a virtual compression test and mechanical properties obtained from the FE simulations were compared to the experimentally assessed values. After verification, the parametric FE models were used to establish relationships between various design parameters (porosity, rod thickness, internal angles, etc.) and overall mechanical properties (particularly stiffness).
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Approximate calculation of eigen-values of linear viscously damped system with passive damping element
Hračov, Stanislav
The paper presents an approximative method for eigen-solution of non-classically damped linear system representing classically damped structure equipped with passive damping element (viscous damper). The proposed procedure avoids using a numerically demanding state-space approach. It operates in the original dimension of the problem and utilizes the real eigen-modes for its further size reduction. The method is based on the dividing of the damping matrix to classical and non-classical part and the application of the perturbation strategy. The accuracy of the procedure is demonstrated by considering numerical examples.
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Fracture toughness testing for improving the safety of gas pipeline
Gajdoš, Lubomír ; Šperl, Martin
For standard fracture mechanical tests flat specimens (principally CT or SENB) are required. This brings problems for investigating fracture mechanical properties of thin-walled pipes because it is necessary to straighten the pipe bands [1]. However, this operation causes internal stresses to be induced not only in the semi-product subjected to straightening but also in finished specimens. A question therefore arises to what extent are then the magnitudes of the fracture toughness determined representative for the actual cylindrical wall. To solve this problem fracture mechanics tests were carried out on flat (straightened) CT specimens as well as on curved CT specimens with the natural curvature. The R – curves as well as the resulting parameters of the fracture toughness, obtained for both types of CT specimens, were compared and it was concluded that the fracture toughness of the pipe material determined on straightened CT specimens was practically the same as that obtained on curved CT specimens.
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