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Role of Plasticity in Nitinol Fatigue
Shayanfard, Pejman ; Seiner,, Hanuš (referee) ; Dlouhý, Antonín (referee) ; Šandera, Pavel (advisor)
Disertace analyzuje vliv koncentrátorů napětí na průběh martensitické transformace, vznik plastické deformace a její vliv na přerozdělení napětí a vznik zbytkového pnutí a reziduálního martenzitu v okolí koncentrátorů v prvcích ze slitin s tvarovou pamětí NiTi. Vliv je analyzován v režimech superelastického isotermálního cyklování a aktuačního cyklování, t.j. teplotního cyklování pod vnějším napětím. Disertace využívá pro vyhodnocení vlivu experimentální přístup spolu s numerickými simulacemi metodou konečných prvků na modelových případech tenkých pásků ze slitin NiTi opatřených půlkruhovými vruby. V experimentální části je vyhodnocován vliv koncentrátorů pomocí termomechanických experimentů s využitím metod obrazové korelace a rentgenové mikrodifrakce pro lokální analýzu deformací a fázových objemových podílů v průběhu cyklování v okolí vrubů. Simulace metodou konečných prvků poskytují komplementární informace o průběhu napětí, deformací a martensitické transformaci, zejména o vývoji jednotlivých složek celkové deformace, tj. elastické a plastické, a vývoji zbytkového pnutí a s ním souvisejícím zbytkovým martensitem.Disertace je dále doplněna o numerickou analýzu vlivu konstrukce stentů na lokální cyklický průběh martensitické transformace a jeho vliv na únavové vlastnosti.
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Fatigue life of crankshaft
Wolf, David ; Kučera, Pavel (referee) ; Vopařil, Jan (advisor)
This thesis is focused on the crankshaft as one of the most dynamically stressed component of internal combustion engines. At the beginning describes in the wider context how is the crankshaft of internal combustion engines strained. Then it considers individual parts of crankshaft, which are affecting its construction in terms of fatigue life. And in the last section describes the different ways to eliminate the damage caused by cyclic loading and modern methods of fatigue life prediction of crankshafts.
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Microstructural stability of austenitic steels during fatigue loading
Kudelka, Martin ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This diploma thesis studies the structure of selected austenitic stainless steels which were fatigued at room and depressed temperatures. The theoretical part is divided into three parts. The first one defines the austenitic stainless steels with accent to their chemical composition and microstructure. Second part is dedicated to deformation-induced martensite formation. The third part shows the mechanisms and stages of damage due to cyclic straining. The experimental part is focused especially on the observing of microstructural changes by methods of colour metallography and their relation to stress-strain response of material under selected conditions of fatigue loading. Series of samples of 304 and 316L steels were prepared by colour etching and their microstructures were documented using optical microscopy. Then the semi-quantitative measurements of presence and morphology of deformation-induced martensite were done and the results were discussed and correlated with fatigue damage level.
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Verification of nonlinear material models of concrete
Král, Petr ; Němec, Ivan (referee) ; Hradil, Petr (advisor)
Diploma thesis is focused on the description of the parameters of nonlinear material models of concrete, which are implemented in a computational system LS-DYNA, interacting with performance of nonlinear test calculations in system LS-DYNA on selected problems, which are formed mainly by simulations of tests of mechanical and physical properties of concrete in uniaxial compressive and tensile on cylinders with applying different boundary conditions and by simulation of bending slab, with subsequent comparison of some results of test calculations with results of the experiment. The thesis includes creation of appropriate geometric models of selected problems, meshing of these geometric models, description of parameters and application of nonlinear material models of concrete on selected problems, application of loads and boundary conditions on selected problems and performance of nonlinear calculations in a computational system LS-DYNA. Evaluation of results is made on the basis of stress-strain diagrams and load-displacement diagrams based on nonlinear calculations taking into account strain rate effects and on the basis of hysteresis curves based on nonlinear calculations in case of application of cyclic loading on selected problems. Verification of nonlinear material models of concrete is made on the basis of comparison of some results of test calculations with results obtained from the experiment.
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The effect of cyclic loading assessment on the deformation characteristics of hardened concrete
Potočková, Michaela ; Kocáb, Dalibor (referee) ; Misák, Petr (advisor)
This thesis deals with the influence of multiple cyclic loading on the deformation characteristics of hardened concrete. The influence on static modulus of elasticity in compression was studied. In this thesis deformation during multiple cyclic loading test was measured. Afterwards, from the test results the static modulus of elasticity in pressure was defined. The main output of this research is grafical and percentual representation of decrease of static modulus of elasticity values in compression in dependence of increasing number of cycles.
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Contributions to the experimental investigation and numerical description of soil cyclic behavior
Duque Felfle, Jose Alejandro ; Mašín, David (advisor) ; Herle, Ivo (referee) ; Wichtmann, Torsten (referee)
A wide range of geotechnical structures are subjected to episodes of cyclic loading. Among them, we can for example mention onshore and offshore foundations subjected to environmental loadings, pavements subjected to traffic loading, filling-emptying cycles on silos and water tanks, among many others. In order to develop constitutive models or numerical tools that accurately reproduce the soil behavior on the aforementioned geotechnical problems, a deep understanding on how soil behaves under cyclic loading is necessary. This behavior is, however, not trivial since non-linearity, small strain stiffness, stiffness degradation, cyclic hysteresis and recent stress history play a significant role. This dissertation presents some contributions to the experimental evidence and numerical description of soil cyclic behavior. It begins with comprehensive experimental databases on Malaysian kaolin and Zbraslav sand. In each database, several monotonic and cyclic tests were performed and analyzed considering a wide range of initial conditions and loading characteristics. In particular, the influence of the deviatoric stress amplitude, soil plasticity, initial stress ratio, drained cyclic preloading and sequence of packages of cycles with different deviatoric stress amplitudes was investigated on Malaysian...
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Role of Plasticity in Nitinol Fatigue
Shayanfard, Pejman ; Seiner,, Hanuš (referee) ; Dlouhý, Antonín (referee) ; Šandera, Pavel (advisor)
Disertace analyzuje vliv koncentrátorů napětí na průběh martensitické transformace, vznik plastické deformace a její vliv na přerozdělení napětí a vznik zbytkového pnutí a reziduálního martenzitu v okolí koncentrátorů v prvcích ze slitin s tvarovou pamětí NiTi. Vliv je analyzován v režimech superelastického isotermálního cyklování a aktuačního cyklování, t.j. teplotního cyklování pod vnějším napětím. Disertace využívá pro vyhodnocení vlivu experimentální přístup spolu s numerickými simulacemi metodou konečných prvků na modelových případech tenkých pásků ze slitin NiTi opatřených půlkruhovými vruby. V experimentální části je vyhodnocován vliv koncentrátorů pomocí termomechanických experimentů s využitím metod obrazové korelace a rentgenové mikrodifrakce pro lokální analýzu deformací a fázových objemových podílů v průběhu cyklování v okolí vrubů. Simulace metodou konečných prvků poskytují komplementární informace o průběhu napětí, deformací a martensitické transformaci, zejména o vývoji jednotlivých složek celkové deformace, tj. elastické a plastické, a vývoji zbytkového pnutí a s ním souvisejícím zbytkovým martensitem.Disertace je dále doplněna o numerickou analýzu vlivu konstrukce stentů na lokální cyklický průběh martensitické transformace a jeho vliv na únavové vlastnosti.
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Microstructural stability of austenitic steels during fatigue loading
Kudelka, Martin ; Válka, Libor (referee) ; Pantělejev, Libor (advisor)
This diploma thesis studies the structure of selected austenitic stainless steels which were fatigued at room and depressed temperatures. The theoretical part is divided into three parts. The first one defines the austenitic stainless steels with accent to their chemical composition and microstructure. Second part is dedicated to deformation-induced martensite formation. The third part shows the mechanisms and stages of damage due to cyclic straining. The experimental part is focused especially on the observing of microstructural changes by methods of colour metallography and their relation to stress-strain response of material under selected conditions of fatigue loading. Series of samples of 304 and 316L steels were prepared by colour etching and their microstructures were documented using optical microscopy. Then the semi-quantitative measurements of presence and morphology of deformation-induced martensite were done and the results were discussed and correlated with fatigue damage level.
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Verification of nonlinear material models of concrete
Král, Petr ; Němec, Ivan (referee) ; Hradil, Petr (advisor)
Diploma thesis is focused on the description of the parameters of nonlinear material models of concrete, which are implemented in a computational system LS-DYNA, interacting with performance of nonlinear test calculations in system LS-DYNA on selected problems, which are formed mainly by simulations of tests of mechanical and physical properties of concrete in uniaxial compressive and tensile on cylinders with applying different boundary conditions and by simulation of bending slab, with subsequent comparison of some results of test calculations with results of the experiment. The thesis includes creation of appropriate geometric models of selected problems, meshing of these geometric models, description of parameters and application of nonlinear material models of concrete on selected problems, application of loads and boundary conditions on selected problems and performance of nonlinear calculations in a computational system LS-DYNA. Evaluation of results is made on the basis of stress-strain diagrams and load-displacement diagrams based on nonlinear calculations taking into account strain rate effects and on the basis of hysteresis curves based on nonlinear calculations in case of application of cyclic loading on selected problems. Verification of nonlinear material models of concrete is made on the basis of comparison of some results of test calculations with results obtained from the experiment.
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