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Design of a test rig for stress visualisation using photoelasticimetry
Doležel, Miroslav ; Rebenda, David (referee) ; Michalec, Michal (advisor)
The purpose of this work is to construct a specific loading device for the observation of moving samples in the existing polariscope. The experimental method of photoelasticity is often used to observe stationary samples, but the observation of moving samples is less common. However, the time-varying development of the stress profile is very important for understanding of the stress cycles in the machine components. The theoretical part contains a basic information about the method of photoelasticity, its advantages and limitations and the possibility of its use. Then the dynamically stressed machine elements are mentioned, from which the gear is selected as a preferable element for observation in the polariscope. Furthermore, attention is focused on materials and techniques of sample production. The determination of the required load of the gear sample is based on these findings. The most suitable design of the loading device capable of inducing specified stress in the samples is proposed and the critical nodes of the structure are supported by the strength calculations. This design offers variability for clamping different sample sizes and can thus be used to investigate stress in other gear configurations as well.
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Propagation of inclined cracks to the interface of ceramic laminates
Novotná, Lenka ; Trunec, Martin (referee) ; Chlup, Zdeněk (advisor)
Composite materials with laminated structure provide advantages which are utilised during component design. Low density, temperature and chemical stability are the profitable properties predetermining application of ceramic laminates. The main obstacle for wide spread of ceramic materials is their inherent brittleness. Therefore, in this thesis, the crack propagation in ceramics laminates has been extensively studied. Laminated structures with various volume fractions of components (alumina and zirconia) were prepared by electrophoretic deposition. Evaluation of crack propagation through the interface and determination of basic mechanical properties was conducted on the basis of extensive literature search. Crack deflection originated in both presence of internal stresses and differences in elastic modulus during the crack interface passing was monitored. A special type of specimen geometry was employed with the aim to set arbitrary angle between crack and interface. It was experimentally found that the degree of crack deflection is dependent on entering angle and volume fraction of components. Higher crack deflection was already found in the bulk of the test piece comparing to the test piece surface. The 3D fracture surface reconstruction generated using laser confocal microscopy was used in this detailed crack propagation study. Further basic elastic and strength characteristics of laminates were determined and compared to those obtained from monolithic materials. The validity of the mix rule for elastic characteristics was confirmed by comparing of elastics modulus. The most reliable method for elastic modulus determination was marked the dynamic resonance method due to low scatter and consistency in measurement. The flexural strength of all laminates tends to be close to the flexural strength of the weakest component. Therefore the mix rule is not applicable for flexural strength estimation on the contrary of elastic characteristics. The change of component volume fraction leads only to change of flexural strength scatter. Thanks to gained knowledge about crack propagation and basic characteristic determination will be possible to design ceramic laminates more efficiently for given needs of application.
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Numerická předpěťová modální analýza kmene
Skokan, Vojtěch
This work is investigating the effect of prestress on the results of the numerical modal analysis of tree stem and the effects of the degree of simplification of the geometry of the numerical model on the values of natural frequencies and modes of natural oscillation. The work aims to create credible numerical models of trunks and to use prestress to induce such a change in the diameter of the trunk that occurs in trees during the diumal cycle, thus simulating the transpiration stress in the trunk. During the work, three different methods of inducing prestress in the trunk are investigated and their impact on the values of the observed frequencies of strain models is assessed. In addition to artificial prestress, the work also assesses the impacts of the co-effect of gravity on the values of natural frequencies. This work is one of the first attempts to investigate the effect of mechanical stress caused by the transpiration flow using numerical simulation and can thus lay the foundation for future research in this field.
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Design of a test rig for stress visualisation using photoelasticimetry
Doležel, Miroslav ; Rebenda, David (referee) ; Michalec, Michal (advisor)
The purpose of this work is to construct a specific loading device for the observation of moving samples in the existing polariscope. The experimental method of photoelasticity is often used to observe stationary samples, but the observation of moving samples is less common. However, the time-varying development of the stress profile is very important for understanding of the stress cycles in the machine components. The theoretical part contains a basic information about the method of photoelasticity, its advantages and limitations and the possibility of its use. Then the dynamically stressed machine elements are mentioned, from which the gear is selected as a preferable element for observation in the polariscope. Furthermore, attention is focused on materials and techniques of sample production. The determination of the required load of the gear sample is based on these findings. The most suitable design of the loading device capable of inducing specified stress in the samples is proposed and the critical nodes of the structure are supported by the strength calculations. This design offers variability for clamping different sample sizes and can thus be used to investigate stress in other gear configurations as well.
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Propagation of inclined cracks to the interface of ceramic laminates
Novotná, Lenka ; Trunec, Martin (referee) ; Chlup, Zdeněk (advisor)
Composite materials with laminated structure provide advantages which are utilised during component design. Low density, temperature and chemical stability are the profitable properties predetermining application of ceramic laminates. The main obstacle for wide spread of ceramic materials is their inherent brittleness. Therefore, in this thesis, the crack propagation in ceramics laminates has been extensively studied. Laminated structures with various volume fractions of components (alumina and zirconia) were prepared by electrophoretic deposition. Evaluation of crack propagation through the interface and determination of basic mechanical properties was conducted on the basis of extensive literature search. Crack deflection originated in both presence of internal stresses and differences in elastic modulus during the crack interface passing was monitored. A special type of specimen geometry was employed with the aim to set arbitrary angle between crack and interface. It was experimentally found that the degree of crack deflection is dependent on entering angle and volume fraction of components. Higher crack deflection was already found in the bulk of the test piece comparing to the test piece surface. The 3D fracture surface reconstruction generated using laser confocal microscopy was used in this detailed crack propagation study. Further basic elastic and strength characteristics of laminates were determined and compared to those obtained from monolithic materials. The validity of the mix rule for elastic characteristics was confirmed by comparing of elastics modulus. The most reliable method for elastic modulus determination was marked the dynamic resonance method due to low scatter and consistency in measurement. The flexural strength of all laminates tends to be close to the flexural strength of the weakest component. Therefore the mix rule is not applicable for flexural strength estimation on the contrary of elastic characteristics. The change of component volume fraction leads only to change of flexural strength scatter. Thanks to gained knowledge about crack propagation and basic characteristic determination will be possible to design ceramic laminates more efficiently for given needs of application.
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