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Optimalization of evaluation of initiation of temperature ageing processes of selected cable isolation
Štěpánová, Lucie ; Štěpánek, Ivo ; Mertová, Andrea ; Šimečková, Lucie
The paper is devoted of verification of possibilities of evaluation of initial changing of properties and behaviour of selected polymeric isolation of cables after defined temperature loading simulated of external operational conditions and simulated temperature loading evoked by current loading. There are evaluated initial properties and behaviour of selected polymeric cable isolations and properties and behaviour after natural ageing process and controlled accelerated ageing process during higher temperature loading and different time of exposition to the higher temperature. The method of x-ray fluorescence analysis is used for evaluation of differences of changing of properties and behaviour of polymeric isolation cable materials after natural ageing process and after accelerated controlled ageing processes. There are verificated the possibilities for analysis differences in behaviour of polymeric insulation materials after different ageing process. The paper is namely devoted by verification of the possibilities analytic methods for evaluation initial of changing of properties and behaviour by nanoindentation methods for analysis very small differences in mechanical properties and behaviour of surface layers of polymeric materials used in the application isolation of cables. There are optimized the parameters of nanoindentation measurements for analysis of differences in hardness and elastic plastic behaviour.
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Study of mechanical properties of nanolayered Ti/Ni coatings
Zábranský, L. ; Václavík, R. ; Přibyl, R. ; Ženíšek, J. ; Souček, P. ; Buršík, Jiří ; Fořt, Tomáš ; Buršíková, V.
The aim of the present work was to study the dependence of mechanical properties of Ti/Ni multilayer thin films on the thicknesses of constituent Ti and Ni layers. The multilayer thin films were synthesized by deposition of Ti and Ni layers alternately on single crystalline silicon substrates using direct current magnetron sputtering method. Thicknesses of Ti and Ni layers varied from 1.7 nm to 100 nm. The micro-structure of the multilayer films was studied using X-ray diffraction technique, scanning electron microscopy with focused ion beam technique and transmission electron microscopy. Mechanical properties obtained from nanoindentation experiments were discussed in relation to microstructural observations.
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Early stage microstructure development of cement paste modified by crystalline admixture
Hrbek, V. ; Petráňová, Veronika ; Němeček, J.
This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on reference specimens consisting of pure cement. Samples of pure CA and cement modified by 1% of CA with the same w/c ratio were examined and compared in this paper. By investigation of these materials on the micro-scale, it is possible to identify the development of the microstructure of each and determine the impact of the modification. For this purpose, backscattered electrons microscopy (BSE) with energy-dispersive X-ray spectroscopy (EDX) was used for phase analysis as well as instrumental nano-indentation to obtain micro-mechanical properties. Presented results show the evolution of mechanical properties and microstructure in time and the impact of the crystalline admixture on modified cement.
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Fracture of selected building composites in the vicinity of aggregate-matrix-interface
Vyhlídal, Michal ; Malíková, Lucie (referee) ; Keršner, Zbyněk (advisor)
The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.
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Advanced techniques in nanoindentation testing
Břečka, Jan ; Tkachenko, Serhii (referee) ; Čížek, Jan (advisor)
The aim of this thesis is to determine the suitability of using advanced indentation methods for various materials. These advanced measurement methods are described in detail and subsequently compared in terms of time complexity and accuracy of the elastic modulus and the hardness measurement. The tested materials were copper and silica. The comparison of the methods is carried out at different views and gives a general overview of advantages of these methods.
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Microscopic features of cement paste modified by fine perlite
Hrbek, V. ; Koudelková, Veronika ; Padevět, P. ; Šašek, Petr
The use of waste material and replacement of binder element in cementitious composites is in focus of material development. Perlite in the construction industry is usually used in form of lightweight aggregate enhancing the insulating performance of concrete. This paper focuses on integration of fine perlite into the cement matrix and possible replacement of the cement binder in the composition of the material. The macromechanical performance of the modified paste is tested on specimens with 5, 10, 15 and 20% fine perlite substitution and pure cement sample. To distinguish the effect of the perlite on the microstructural level, pure cement material and specimen containing 10% of fine perlite are investigated by the electron microscopy. Furthermore, the mechanical properties of individual phases are examined and compared on same samples by instrumented indentation. The presented results enabled estimation of fine perlite impact on the macro and microscopic performance of the material..
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Wood microstructure analysis onto the strength parameters
Martinek, Radomír ; Kuklík,, Pavel (referee) ; Vaněrek, Jan (advisor)
This work focuses on a closer examination of the microstructure of wood and the relationship between microscopic and mechanical properties of wood. The main point of the practical part of this study is a measurement of microfibril angle (MFA) in the S2 layer of a wood cell wall. This layer occupies more than 80 % of the total thickness of the cell wall and thus has the greatest influence on the mechanical properties of the wood cells. MFA values as well as values of bulk density show a strong dependence on the modulus of elasticity in the longitudinal direction, as well as on the values of shrinkage. The theoretical part involves methods for measuring MFA, variations of MFA, wood properties evolving from the MFA and also mechanical properties of wood cell walls measured by nanoindentation.
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Surface topography and mechanical properties of thin films on tetravinylsilane basis
Plichta, Tomáš ; Klapetek, Petr (referee) ; Čech, Vladimír (advisor)
Proposed diploma thesis is focused on preparation and characterization of the plasma polymer thin films based on tetravinylsilane monomer (TVS). Plasma enhanced chemical vapour deposition (PECVD) method involving pulse and continual plasma discharge modes were used for thin film deposition on silicon wafer pieces. Reactive plasma composition was containing pure TVS or mixtures of TVS and argon or oxygen gas. Atomic force microscopy was used for surface topography and roughness characterization. Cyclic nanoindentation was involved to measurements to determine the Young’s modulus and hardness of prepared films and scratch test was performed to evaluate the degree of adhesion. Special attention was drawn to the characterization of films with a Young’s modulus below 10 GPa. Tip geometry of indenter influence on scratch test was also commented. Surface and mechanical properties of thin films in relation to the deposition conditions were correlated to the obtained results and final analysis of deposition conditions influence is proposed.
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THE APPLICATION OF NANOMATERIALS FOR LEAD FREE SOLDERS DEVELOPMENT
Pešina, Zbyněk ; Pinkas, Jiří (referee) ; Spousta, Jiří (referee) ; Sopoušek, Jiří (advisor)
The present dissertation is motivated by the search for alternatives of lead-free soldering by nanoparticles of metals and their alloys. The research focuses on the possibility of replacing lead-free solders by nanoparticles. This issue is currently being addressed by the use of lead-free solders but their properties are not entirely equivalent to properties of lead-tin based alloys. The theoretical part of the dissertation first summarizes up-to date knowledge on the development of lead-free alloys currently used for soldering in the electronics. The work compares these lead-free solder candidates with previously used Pb-Sn alloys. The second section of the theoretical part is devoted to nanotechnology that offers possible solutions of problems associated with the use of lead-free solders. The text contains a description of the properties of nanocrystalline materials in comparison with those of compact alloys having the same chemical composition. The possibility of preparation of nanoparticles and potential problems associated with small particle sizes are also presented. Introduction of the experimental part focuses on the preparation of nanoparticles of pure metals and alloys by chemical and physical ways as well as on an instrumentation for characterisation and analysis. Attention is focused on the silver in nanoparticle form that exhibits the low temperature sintering effect, which is thermally activated by decomposition of oxide envelope covering the Ag nanoparticles. This factor is critical for low-temperature sintering and thus also for possible future applications. The thermal effects of the low sintering process were studied by methods of thermal analysis. The preparation of the Cu / Ag nano / Cu joints was carried out in-situ in inert atmosphere and under the action of atmospheric oxygen. In both cases varying conditions of thermal treatment were used. The cross sections of the prepared joints were then used for the metallographic analysis of the local mechanical properties of the resulting silver layer, for the chemical composition evaluation of the resulting layers of the joint, and for the microstructure study. Strength characteristics are represented by testing shear strength of individual joints.
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Characterisation of Nanostructure Deposited by PVD and CVD Technology
Fořt, Tomáš ; Boušek, Jaroslav (referee) ; RNDr.Vilma Buršíková, Ph.D. (referee) ; Sobota, Jaroslav (advisor)
The thesis deals with mechanical properties of thin hard wear-resistant coatings. The work presents a method of dynamic testing of thin hard coatings on a newly constructed prototype of impact wear tester. It provides a comparison with standard methods of layer testing and presents new experimental results of dynamic impact wear test of the coatings. Finally, the thesis covers preparation techniques of thin film systems deposited on various substrates and their characterization using optical and electron microscopy.
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