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The detailed analytical and experimental investigation of the fracture behaviour of quasi-brittle materials is an endeavour which has been ongoing worldwide for many years. Such materials are usually characterized in terms of their mechanical fracture parameters, which are determined based on the evaluation of quasi-static fracture experiments. One of the most commonly used building materials with a quasi-brittle response is concrete, which is most often based on a cement matrix. It is sometimes also necessary to characterize concrete included in existing structures. In this case, test specimens are obtained by core drilling, and the investigation is conducted with the requirement to maximize the number of parameters obtained while minimizing the number of test specimens drilled from the structure. This paper focuses on the mechanical fracture parameters of core-drilled specimens taken from a selected concrete structure. Tests were performed on cylindrical specimens with a chevron-notched stress concentrator in the three-point bending configuration in order to determine modulus of elasticity, fracture toughness and fracture energy. Subsequently, theoretical compressive strength was estimated and tests for the determination of compressive strength values were performed focusing on dependence on the slenderness ratio, i.e. the relationship between the compressive strength and the length to diameter ratio of the cylindrical specimens. In relation to the obtained mechanical fracture parameters, selected specimens were analysed and three-dimensionally characterized via high-resolution X-ray computed tomography.

Quasi-brittle materials like cement-based composites, rocks, and bricks are subjected to a number of environmental loadings throughout the life cycle of buildings. For instance, fluctuation of the ambient temperature (climatic cycles or fire) causing a variety of physical and chemical transitions resulting in structural changes and affecting the mechanical properties. In this work a special mixture containing glass spheres and Portland cement was evaluated by a combination of four-point bending and time-lapse X-ray computed tomography to verify the feasibility of this novel combined method. The effect of temperature on the behavior of investigated material in terms of sphericity of the present glass spheres and the way of crack propagation under load together with its influence to mechanical fracture parameters was studied. The described methodology was used especially to be able to monitor these changes throughout the loading process, as the characterization of the fracture surface using conventional optical methods is possible only after the complete fracture of the specimen and total damage of used material results in loosening of the matrix and filler to such an extent, that the results of these methods may be very distorted. It has been proven that the developed method can be used to characterize the internal structural changes in building materials and thus contribute to the understanding of the fracture processes during mechanical loading. Up to 600 degrees C the glass spheres stay spherical and the crack is propagating through the interfacial transition zone, while at higher temperatures the glass loses its shape and the newly formed pores cause also cracks within the inclusions. The relationship between compressive strength and the maximum loading temperature was confirmed.

In the case of quasi-brittle material, there is a zone of non-linear behaving material, near the crack tip. A major part of this zone forms a so-called fracture process zone (FPZ), where mechanisms of material toughening take place. The main idea is to estimate the size of the fracture process zone under various types of load by using X-ray tomography. The estimation of the zone is supported by the theory of linear elastic fracture mechanics (LEFM) that could be a limit case of quasi-brittle mechanics. The size of the zone envelop is provided in X-ray snaps and compared with the theoretical size form LEFM.

The aim of this work is the evaluation of the fracture process zone while loading a quasi-brittle concrete compound. The regularly used optical observation of the specimen surface does not provide accurate information regarding the fracture zone shape, particularly when this zone is tunnelled inside of the specimen body. Therefore, X-ray dynamic defectoscopy and computed tomography were employed as tools for an extended investigation of process zone evolution. A notched specimen manufactured from silicate composite was subjected to the three-point bending test in a special table-top loading device. On-line radiographic observation of the process zone during the loading experiment serves for overall evaluation, while a tomographic measurement which is conducted during temporal loading interruption - provides information about the spatial distribution of the newly developed cracks.

Úkolem této diplomové práce je seznámit čtenáře se základy problematiky ionizujícího záření od jeho druhů a zdrojů, přes mechanismy jeho působení a účinky na lidský organismus až po možnosti výpočtu různých charakteristik. Značná pozornost je věnována využití ionizujícího záření v moderních lékařských přístupech, je zde detailně popsán postup při plánování radioterapeutického výkonu a popis plánovacích systémů. Součástí diplomové práce je rovněž program RT-Plan zpracovaný v programovém prostředí MatLab. Program simuluje plánovací systém pro zevní terapii ionizujícím zářením využívaný v léčbě, je doplněn o podrobnou nápovědu a několik testů pro zadané charakteristiky plánu. Je vhodný pro případné využití ve výuce., The task of this thesis is to familiarize readers with the basics of the problem of ionizing radiation from its types and resources, through mechanisms of action and its effects on the human organism, to the possibility of calculating various characteristics. Close attention is paid to the use of ionizing radiation in medical approaches. There is in detail described process of radiotherapy planning and a basic properties of planning systems. Part of the thesis is also program RT-Plan processed in Matlab. The program simulates the planning system for external ionizing radiation therapy used in treatment. There is supplemented a detailed help and series of tests for the plan. It is suitable for possible use in teaching.