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Studies on Non-Newtonian Behavior in Slit-flow rheometer at Unsteady flow
Halama, Lukáš ; Vimmr, Jan (referee) ; Roupec, Jakub (advisor)
The thesis deals with the description of the unstable flow of non-Newtonian fluid in a slit-flow rheometer, which negatively affects its behaviour. The initiators of unstable fluid flow are the roughness of the rheometer slit walls, the slip on the rheometer walls, and the influence of the inlet and outlet region geometry of the rheometer slit. The work contains methodical procedures for mathematical consideration of individual unstable fluid flow initiators and design of change of slit geometry of slit-flow rheometer. Part of the work is also a comparison of the most commonly used rheological models, derivation of general relations for the creation of the velocity profile of individual rheological models and their subsequent implementation in the rheological application, which significantly simplifies the process of evaluation of measured data when measured on slit-flow rheometer. This application can be used to determine basic parameters in CFD simulations or as a teaching aid.
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The Effect of Temperature Annealing on Structure-Property Relationship of Oriented Polypropylene
Sadílek, Jiří ; Jančář, Josef (referee) ; Kohout,, Jan (referee) ; Hell,, Jaroslav (referee) ; Kučera, Jaroslav (advisor)
The aim of this work is to study the effect of thermal history to structure and properties not only of oriented polypropylene monofilaments with different orientation but of course of isotropic non-oriented polypropylene. Term thermal history includes thermal regimes from alpha relaxation temperature (T?) to melting temperature (Tm). This work consists of three parts. The changes of dynamic mechanical properties, strength, deformation and tensile modulus of polypropylene samples according to annealing temperature (Ta) are described in the first part of this work. In the second part, the changes of crystal phase are observed. Preferentially, calorimetric behaviour (DSC), changes of crystal dimensions and orientation function of crystal phase (X-ray) are observed. Measured values from the first and the second part of this work were used for calculation of total orientation function of PP samples. Rheological measurements are shown in the third part of this thesis. Rheological measurements consist of short isothermal creep, shrinkage of free tapes and static deformation at higher temperatures. Measured rheological values were performed using rheological models. Using these models characteristics of entropic spring, instantaneous elasticity and viscosity and tendency to get to state of ease were calculated.
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Experimental and numerical analysis of rheological processes during the concrete maturation.
Zvolánek, Lukáš ; Navrátil, Jaroslav (referee) ; Vítek,, Jan (referee) ; Terzijski, Ivailo (advisor)
This doctoral thesis deals with the volume changes of structural concrete caused by its shrinkage. Great importance is given to the evaluation of concrete resistance against shrinkage cracking, too. A lot of physical and numerical experiments were carried out before results and conclusion of observed phenomena was publicized. The amount of physical tests and utilization rate of the experiments can be enlarged and intensified due to the usage of materials made of micro-concrete. Consequently, the design of concrete mixtures with the ordinary size of aggregate particle reflected the large knowledge obtained by micro-concrete. In this work, the effect of different fibres and its different amount was also researched. Finally, the optimized fibre concrete mixture was designed. During the testing, the unique method referred to as “Complex experiment” was developed. Obtained data from the Complex experiment allows predicting when the shrinkage cracks may occur. The final comparison between all tested materials made of concrete was performed by means of unique parameter referred to as “Critical degree of restraint”. It was proofed that the resistance of optimized fibre concrete against to shrinkage cracking is twice of ordinary concrete. Moreover, the shrinkage cracks did not occur in the developed fibre concrete during the observed period. Based on the obtained results the new scaling factors for the rheological model B4 were derived. Due to the new scaling factors, the model B4 describes the real behavior of special composite materials very well.
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Studies on Non-Newtonian Behavior in Slit-flow rheometer at Unsteady flow
Halama, Lukáš ; Vimmr, Jan (referee) ; Roupec, Jakub (advisor)
The thesis deals with the description of the unstable flow of non-Newtonian fluid in a slit-flow rheometer, which negatively affects its behaviour. The initiators of unstable fluid flow are the roughness of the rheometer slit walls, the slip on the rheometer walls, and the influence of the inlet and outlet region geometry of the rheometer slit. The work contains methodical procedures for mathematical consideration of individual unstable fluid flow initiators and design of change of slit geometry of slit-flow rheometer. Part of the work is also a comparison of the most commonly used rheological models, derivation of general relations for the creation of the velocity profile of individual rheological models and their subsequent implementation in the rheological application, which significantly simplifies the process of evaluation of measured data when measured on slit-flow rheometer. This application can be used to determine basic parameters in CFD simulations or as a teaching aid.
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Experimental and numerical analysis of rheological processes during the concrete maturation.
Zvolánek, Lukáš ; Navrátil, Jaroslav (referee) ; Vítek,, Jan (referee) ; Terzijski, Ivailo (advisor)
This doctoral thesis deals with the volume changes of structural concrete caused by its shrinkage. Great importance is given to the evaluation of concrete resistance against shrinkage cracking, too. A lot of physical and numerical experiments were carried out before results and conclusion of observed phenomena was publicized. The amount of physical tests and utilization rate of the experiments can be enlarged and intensified due to the usage of materials made of micro-concrete. Consequently, the design of concrete mixtures with the ordinary size of aggregate particle reflected the large knowledge obtained by micro-concrete. In this work, the effect of different fibres and its different amount was also researched. Finally, the optimized fibre concrete mixture was designed. During the testing, the unique method referred to as “Complex experiment” was developed. Obtained data from the Complex experiment allows predicting when the shrinkage cracks may occur. The final comparison between all tested materials made of concrete was performed by means of unique parameter referred to as “Critical degree of restraint”. It was proofed that the resistance of optimized fibre concrete against to shrinkage cracking is twice of ordinary concrete. Moreover, the shrinkage cracks did not occur in the developed fibre concrete during the observed period. Based on the obtained results the new scaling factors for the rheological model B4 were derived. Due to the new scaling factors, the model B4 describes the real behavior of special composite materials very well.
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The Effect of Temperature Annealing on Structure-Property Relationship of Oriented Polypropylene
Sadílek, Jiří ; Jančář, Josef (referee) ; Kohout,, Jan (referee) ; Hell,, Jaroslav (referee) ; Kučera, Jaroslav (advisor)
The aim of this work is to study the effect of thermal history to structure and properties not only of oriented polypropylene monofilaments with different orientation but of course of isotropic non-oriented polypropylene. Term thermal history includes thermal regimes from alpha relaxation temperature (T?) to melting temperature (Tm). This work consists of three parts. The changes of dynamic mechanical properties, strength, deformation and tensile modulus of polypropylene samples according to annealing temperature (Ta) are described in the first part of this work. In the second part, the changes of crystal phase are observed. Preferentially, calorimetric behaviour (DSC), changes of crystal dimensions and orientation function of crystal phase (X-ray) are observed. Measured values from the first and the second part of this work were used for calculation of total orientation function of PP samples. Rheological measurements are shown in the third part of this thesis. Rheological measurements consist of short isothermal creep, shrinkage of free tapes and static deformation at higher temperatures. Measured rheological values were performed using rheological models. Using these models characteristics of entropic spring, instantaneous elasticity and viscosity and tendency to get to state of ease were calculated.
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