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Role of Plasticity in Nitinol Fatigue
Shayanfard, Pejman ; Seiner,, Hanuš (oponent) ; Dlouhý, Antonín (oponent) ; Šandera, Pavel (vedoucí práce)
This doctoral thesis deals with the analysis of the role of stress risers in NiTi elements on the local cyclic evolutions of martensitic transformation, plastic deformations, and mechanical gradients at the stress risers, under both iso-thermal cyclic loading in the superelastic regime and thermal cycling under external load in actuator regime. The methodology of investigation includes both experimental measurements and finite element simulations of notched thin NiTi superelastic/shape-memory ribbons. In the experimental part of the work, the DIC method is used to capture the spatial evolutions of strain gradients around the notch, and the X-ray microdiffraction is used to analyze the local strain fields around the notch and the plasticity induced remnant martensite at the notch-tip. Besides, the finite element results help assess the corresponding evolutions of stresses and strains, martensitic transformation, and the partitioning of total strains into elastic, plastic and residual strains around the notch. In addition, the thesis includes numerical analysis investigating the effect of the design of self-expanding NiTi stents on local cyclic evolution of martensitic transformation and its relation to fatigue performance.
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Evaluation of mechanical characteristics of shape memory alloys under cyclic loading in torsion
German, Roman ; Štěpánek, Roman (oponent) ; Horníková, Jana (vedoucí práce)
The main aim of this thesis is to process the results of fatigue tests of wires of a NiTi shape memory alloy subjected to symmetric cyclic torsion. The first part of this work is dedicated to literature research about NiTi alloys, their response to cyclic loading and the specific features of torsion loading. The second part contains a review of the influence of heat treatment and strain amplitude on the ability to dissipate mechanical energy, changes in mechanical properties and fatigue life of the tested material.
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Smart materiály
Valenová, Ludmila ; Němec, Karel (oponent) ; Molliková, Eva (vedoucí práce)
Bakalářská práce se zabývá smart materiály. Souhrnně popisuje obecné rozdělení smart materiálů do jednotlivých skupin, uvádí vlastnosti jednotlivých skupin a využití těchto materiálů v praxi. Detailněji jsou popsány skupiny materiálů s tvarovou pamětí, materiály měnící barvu za působení vnějšího podnětu, materiály vyzařující světlo a materiály fungující na principu piezoelektrického jevu.
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Zpracování NiTi slitiny technologií SLM
Lukačovič, Samuel ; Dočekalová, Kateřina (oponent) ; Koutný, Daniel (vedoucí práce)
Táto diplomová práca sa zaoberá vývojom procesných parametrov vhodných na spracovanie zliatiny niklu a titánu, taktiež známu pod názvom nitinol, pomocou technológie Selective laser melting. Hlavným cieľom tejto diplomovej práce je návrh SLM procesných parametrov vhodných na výrobu objemových a tenkostenných dielov. Vedľajšími cieľmi je popis vplyvu procesných parametrov na chemické zloženie, termomechanické a mechanické vlastnosti výtlačkov. Analýzou experimentov vykonaných na návaroch, objemových telesách a tenkých stenách bola určená optimálna kombinácia procesných parametrov. Použitím tejto kombinácie boli vyrobené neporézne tenkostenné a objemové diely disponujúce efektom superelasticity. Pomocou analýz chemického zloženia a termomechanických vlastností boli stanovené závislosti odparovania niklu a zmeny tranzitných teplôt na procesných parametroch.
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Role of Plasticity in Nitinol Fatigue
Shayanfard, Pejman ; Seiner,, Hanuš (oponent) ; Dlouhý, Antonín (oponent) ; Šandera, Pavel (vedoucí práce)
This doctoral thesis deals with the analysis of the role of stress risers in NiTi elements on the local cyclic evolutions of martensitic transformation, plastic deformations, and mechanical gradients at the stress risers, under both iso-thermal cyclic loading in the superelastic regime and thermal cycling under external load in actuator regime. The methodology of investigation includes both experimental measurements and finite element simulations of notched thin NiTi superelastic/shape-memory ribbons. In the experimental part of the work, the DIC method is used to capture the spatial evolutions of strain gradients around the notch, and the X-ray microdiffraction is used to analyze the local strain fields around the notch and the plasticity induced remnant martensite at the notch-tip. Besides, the finite element results help assess the corresponding evolutions of stresses and strains, martensitic transformation, and the partitioning of total strains into elastic, plastic and residual strains around the notch. In addition, the thesis includes numerical analysis investigating the effect of the design of self-expanding NiTi stents on local cyclic evolution of martensitic transformation and its relation to fatigue performance.
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Untraditional Actuators Sma Type -Modeling Of Hysteresis
Vašina, Michal
The shape memory materials are known since first half of the twentieth century. The example of these materials could be a Shape Memory Alloys (SMA). Because of their attributes, the engineers usually call them a „smart materials“. The SMA can be used in many static or dynamic applications for example in problem of actuators. Thanks to the SMA materials sophistication and associated shape memory effect, there are some issues (hysteresis, degradation etc.), which can complicate their prospective usage. The attributes of SMA classified these actuators to the category of non-linear system with hysteresis. This article deals with the SMA use and potential hysteresis modeling approaches. Several model examples are discussed.
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Smart materiály
Valenová, Ludmila ; Němec, Karel (oponent) ; Molliková, Eva (vedoucí práce)
Bakalářská práce se zabývá smart materiály. Souhrnně popisuje obecné rozdělení smart materiálů do jednotlivých skupin, uvádí vlastnosti jednotlivých skupin a využití těchto materiálů v praxi. Detailněji jsou popsány skupiny materiálů s tvarovou pamětí, materiály měnící barvu za působení vnějšího podnětu, materiály vyzařující světlo a materiály fungující na principu piezoelektrického jevu.
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Evaluation of mechanical characteristics of shape memory alloys under cyclic loading in torsion
German, Roman ; Štěpánek, Roman (oponent) ; Horníková, Jana (vedoucí práce)
The main aim of this thesis is to process the results of fatigue tests of wires of a NiTi shape memory alloy subjected to symmetric cyclic torsion. The first part of this work is dedicated to literature research about NiTi alloys, their response to cyclic loading and the specific features of torsion loading. The second part contains a review of the influence of heat treatment and strain amplitude on the ability to dissipate mechanical energy, changes in mechanical properties and fatigue life of the tested material.
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The Common Mechanical Factor of Shape Memory
Kafka, Vratislav ; Vokoun, David
Shape memory is observed in elastic bodies, springs, bi-metals, in many mechanical actuators, such as thermostats and others, in many biological materials, and in special "shape memory alloys". It is shown that all systems or materials have one common factor: at least one elastic or thermoelastic continuous substructure, in the case of "shape memoryalloys" this substructure is on the atomic scale.
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