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Creating conditions for evaluation of high-strength concrete characteristics using non-destructive testing methods
Procházka, David ; Horký,, Ondřej (referee) ; Kolář,, Karel (referee) ; Adámek, Jiří (referee) ; Brožovský, Jiří (advisor)
High-strength concrete (HSC) belongs in the recent years to frequently used types of concrete. It allows realization of static challenging structures and also shows due to its dense structure greater durability especially against aggressive media. Currently HSC construction realization abroad is not exceptional. It’s using in the Czech Republic is still limited. When realized, then in a small scale in civil engineering works. The realization of high-strength concrete structures is closely related with the concrete construction quality verification. Good efficiency of the quality control methods can provide non-destructive testing methods (NDT), especially when investigating strength of concrete built in structure. A lack on relevant data for non-destructive testing of HSC in technical and normative rules is to be considered as a significant deficiency. Evident for HSC generally is the lack in literature on deeper analysis of the factors affecting their non-destructive testing, as well a meaningful methodology or practically usable calibration relationships. HSC differs from ordinary concrete not only by used components, but also by more compact structure with different strength – elastic characteristics. Considering these differences, HSC strength prediction can not be performed by using calibration relationships developed for ordinary concrete. Moreover, the question is to what extent the current knowledge of the NDT results influencing factors can be considered as valid. The paper presents findings on the effects of the key factors affecting the measurement results of Schmidt hardness method and ultrasonic pulse method, including recommendations for the practical application of these methods. The problematic of static vs. dynamic modulus of elasticity was also solved. Calibration equations for predicting the compressive strength of HSC from the non-destructive testing parameter were elaborated, showing high cohesion among variables and practically usability.
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The influence of multiple cyclic loading on the properties of ordinary concrete
Pešek, Lukáš ; Topolář, Libor (referee) ; Kocáb, Dalibor (advisor)
The diploma thesis deals with the observation of elastic and strength properties (primary moduli of elasticity and Poisson's ratio) of ordinary concrete before and after multiple cyclic loading. Test specimens with cylinder shape and diameter of 150 mm and height of a 300 mm were cyclically loaded up to 5000 loading cycles with resistive strain gauges to measure deformations so static modulus of elasticity could be determined. Further on the test specimens were performed tests to determine the dynamic modulus of elasticity and whole testing was finished with compressive strength test. The results were processed and selected properties evaluated in tabular and graphical form to determine statistical data and formulate a conclusion.
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Stiffness anisotropy of Brno Tegel determined by continuous loading in triaxial tests
Mohyla, Tomáš ; Boháč, Jan (advisor) ; Miča, Lumír (referee)
This Thesis deals with the determination of Young's modulus and Poisson's ratio from the measurement of small strains (10-3 - 10-5 ) in triaxial tests on the overconsolidated Miocene clay from Moravia (Brno Tegel). The tests were performed in a hydraulic triaxial chamber, fitted with submersible local LVDT sensors, which were fixed directly on the sample. The tests were carried out on undisturbed samples of standard height and diameter (76x38 mm). There were three types of tests - isotropic loading probe, axial loading probe and shear test to the failure. The measured data were analyzed and the results were discussed. The research part of the Thesis briefly describes previous works on stiffness of Brno Tegel and also some works on stiffness of similar material to Brno Tegel - London Clay.
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Analysis of the mechanical behavior of wood by means of digital image correlation
Brabec, Martin
The full-field optical techniques such as e.g. a digital image correlation are capable to fully reflect the natural wood heterogeneity. Therefore, this thesis aspires to contribute to the experimental mechanics of wood and wood-based composites by the implementation of the full-field optical technique based on the digital image correlation to the standard mechanical tests. A supplementation of the conventional displacement sensors should help to obtain more precise mechanical characteristics and to do more sophisticated analyses of the deformation behaviour of wood and wood-based composites. The experimental part of the thesis is divided into the five independent case studies listed as the original papers. The measurements were carried out on the most wide-spread wood species in central Europe such as European beech (Fagus sylvatica, L.) and Norway spruce (Picea abies, L. Karst). Beside the solid wood, the new wood-based sandwich structure, which consists of a core made from birch plywood and the particleboard facings, was investigated too. The loading of the samples was carried out using of the standard mechanical tests such as tension, compression, three-point bending and torsion test. In the first study, the full-field deformation data were used to indentify reasons for the non-standard deformation behaviour of spruce and beech wood during compression parallel to grain. Reason for this was recognized in the abrubt compression of damage zones located near the compression plates, which induced the expansion of the middle zone located between them. The second study aimed to find out neutral axis position in native and thermally modified beech wood during the conventional three-point bending test. The relative neutral axis position was obtained from mutual position of the neutral axis and centroidal axis, which was determined based on the appropriate image processing methods. It was found that the neutral axis and centroidal sample axis are almost coincident. Objective of the third study was to determine both longitudinal shear moduli of beech wood with help of the full-field shear strains, obtained from a single torsion test, together with use of the appropriate analytical solutions for the calculation of the stress distribution within the radial and tangential direction on the longitudinal-radial and longitudinal-tangential sample surfaces. Both longitudinal shear moduli increasingly mutually differed as the load increases. Within the fourth study, verification of the elastic material model used in finite-element analyses was carried out with help of full-field deformations induced around notches within dog-bone shaped sample during the uniaxial tension. Great correlation was found between numerically predicted and experimentally measured strain data sets for both longitudinal-radial and longitudinal-tangential shear planes. The fifth study dealed with the characterization of elastic deformation behaviour of newly developed wood-based composite with a sandwich structure. Based on the full-field strain analysis the local strain concentrations were identified. They took place within the core during flatwise compression, and within the facings, when the edgewise compression test was done. A variety of presented results confirmed widespread applicability of optical methods in the mechanics of materials. Therefore, the utilization of full-field optical method based on digital image correlation in experimental mechanics of wood and wood-based composites can be highly recommended.
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Methodological detection solution scaffolds response to mechanical stress, depending on the degree of hydration
Mejzlíková, Kateřina ; Jelen, Karel (advisor) ; Kubový, Petr (referee)
Title: Methodological detection solution scaffolds response to mechanical stress, depending on the degree of hydration Objectives: Determining the extent of lateral deformation u scaffolds made of PVA polymer electrospinning technique. Identify the extent of differences in transverse deformation for different groups of nanofiber scaffolds made of PVA polymer electrospinning technique. Methods: Research scaffolds, we used a measuring device μ-tester, which has two jaws. For the measurement, we chose uniaxial tension test in -tester and record the fluorescence microscope was used with HD camera Olympus 320 for online video recording. Results: The results of this study showed that the ratio of the samples U: L and crosslinking time affects the degree of lateral deformation of the samples scaffolds. Samples scaffolds are compressible, some groups even reached the limits of incompressibility 0.5 Poisson's ratio. Keywords: Poisson, Poisson's ratio, scaffold, nanofiber scaffold, scaffold hydrated, electrospun scaffold, lateral deformation
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Stiffness anisotropy of Brno Tegel determined by continuous loading in triaxial tests
Mohyla, Tomáš ; Boháč, Jan (advisor) ; Miča, Lumír (referee)
This Thesis deals with the determination of Young's modulus and Poisson's ratio from the measurement of small strains (10-3 - 10-5 ) in triaxial tests on the overconsolidated Miocene clay from Moravia (Brno Tegel). The tests were performed in a hydraulic triaxial chamber, fitted with submersible local LVDT sensors, which were fixed directly on the sample. The tests were carried out on undisturbed samples of standard height and diameter (76x38 mm). There were three types of tests - isotropic loading probe, axial loading probe and shear test to the failure. The measured data were analyzed and the results were discussed. The research part of the Thesis briefly describes previous works on stiffness of Brno Tegel and also some works on stiffness of similar material to Brno Tegel - London Clay.
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Creating conditions for evaluation of high-strength concrete characteristics using non-destructive testing methods
Procházka, David ; Horký,, Ondřej (referee) ; Kolář,, Karel (referee) ; Adámek, Jiří (referee) ; Brožovský, Jiří (advisor)
High-strength concrete (HSC) belongs in the recent years to frequently used types of concrete. It allows realization of static challenging structures and also shows due to its dense structure greater durability especially against aggressive media. Currently HSC construction realization abroad is not exceptional. It’s using in the Czech Republic is still limited. When realized, then in a small scale in civil engineering works. The realization of high-strength concrete structures is closely related with the concrete construction quality verification. Good efficiency of the quality control methods can provide non-destructive testing methods (NDT), especially when investigating strength of concrete built in structure. A lack on relevant data for non-destructive testing of HSC in technical and normative rules is to be considered as a significant deficiency. Evident for HSC generally is the lack in literature on deeper analysis of the factors affecting their non-destructive testing, as well a meaningful methodology or practically usable calibration relationships. HSC differs from ordinary concrete not only by used components, but also by more compact structure with different strength – elastic characteristics. Considering these differences, HSC strength prediction can not be performed by using calibration relationships developed for ordinary concrete. Moreover, the question is to what extent the current knowledge of the NDT results influencing factors can be considered as valid. The paper presents findings on the effects of the key factors affecting the measurement results of Schmidt hardness method and ultrasonic pulse method, including recommendations for the practical application of these methods. The problematic of static vs. dynamic modulus of elasticity was also solved. Calibration equations for predicting the compressive strength of HSC from the non-destructive testing parameter were elaborated, showing high cohesion among variables and practically usability.
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Analýza mechanických vlastností balzového dřeva na mesoúrovni pomocí zkušebního stroje iErudio
Grossová, Olga
This thesis analysis the mechanical properties of balsa wood mesolevel using the test machine iErudio. The thesis aim is to experimentally determine the mechanical properties of balsa wood (Ochroma lagopus). On the prototype minimachine iErudio is a set of measurements. Specifically, tensile and bending tests. Another objective is to determine the Poisson ratio on measured levels. These properties will be obtained from image data recorded device iErudio and calculated using the digital image correlation. Another objective is to evaluate the work done with the prototype device, point out the advantages and disadvantages. To analyse data using a commercial computer program VIC 3D and Mercury RT, which process the results using digital image correlation. The work has provided us with confirmation of mechanical characteristics of balsa and the suitability of using "minimachine" iErudio the performed tests.
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