Wyniki wyszukiwania - BazTech

1

Large Deformation Constitutive Theory for a Two-Phase Shape Memory Alloy

Panoskaltsis V., Polymenakos L. C., Soldatos D.

Engineering Transactions

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2014

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Vol. 62, iss. 4

355–-380

EN

In this work we examine significant theoretical issues related to the constitutive modelling of a two-phase shape memory alloy which undergoes large deformations. For this purpose, we propose a new generalized plasticity based model. The model is based on a standard fractions approach and considers a local multiplicative decomposition of the deformation gradient into elastic and inelastic (transformation induced) parts, as its basic kinematic assumption. We also assess the ability of the model in simulating several patterns of the complex behavior of the material in question, by three representative numerical examples. These examples comprise a standard uniaxial tension problem, a torsion problem and an additional problem dealing with non-conventional pseudoelastic response.

2

TiNi shape memory alloy tension at various temperatures - infrared imaging of shape memory effect and pseudoelasticity

Pieczyska E., Tobushi H.

Mechanics and Control

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2011

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Vol. 30, no. 1

20-26

EN

The mechanical characteristics and the infrared imaging of stress-induced martensite transformation developing in TiNi shape memory alloy (SMA) subjected to tension in various conditions with respect to the SMA austenite finish parameter have been presented. Based on the mechanical curves and their related temperature changes it was found that onset of the martensitic transformation appears at the end of the elastic part of the stress-strain curve, since the temperature starts to increase before the knee in the curve. The uniform temperature distribution observed on the specimen surface at this stage confirms that the initial martensite transformation is macroscopically homogeneous. For the shape memory effect behavior the uniform temperature distribution on the specimen surface was observed during the complete process of the SMA loading which means that the transformation process is macroscopically homogeneous. For the shape memory alloy pseudoelasticity behavior bands of higher temperature have been recorded during the specimen loading and bands of lower temperature during its unloading, manifesting localized Lü ;ders-like deformation, caused by the transformation process. As the transformation advances, the higher temperature changes have been recorded. Taking advantages from the infrared technique a new results concerning nucleation and development of the martensite forward and reverse transformation have been obtained. Finally, some examples of the SMA new applications due to the SMA shape memory effect have been presented and discussed.

PL

W pracy omówiono właściwości stopów z pamięcią kształtu, przedstawiono wyniki własnych badań parametrów mechanicznych w procesie jednoosiowego rozciągania oraz zmian temperatury próbek, otrzymane w sposób bezstykowy za pomocą kamery termowizyjnej o wysokiej czułości. Na podstawie charakterystyk mechanicznych oraz zmian temperatury próbek tego stopu stwierdzono, że indukowana naprężeniem przemiana fazowa inicjuje się pod koniec zakresu sprężystego, zdecydowanie przed plateau, charakterystycznym dla przebiegu przemiany. Zarejestrowane rozkłady zmian temperatury na powierzchni obciążanych próbek pozwoliły wykazać, że przemiana martenzytyczna wprost i odwrotna, odpowiedzialna za pseudosprężystość SMA, zachodzi w sposób niejednorodny. Inicjuje się w postaci cienkich pasm, podobnych do pasm Lü ;dersa, które następnie rozwijają się w dwóch prawie prostopadłych kierunkach. Niejednorodność przebiegu przemiany martenzytycznej udokumentowano w technice badań w podczerwieni oraz fotografując relief na powierzchni próbki. Omówiono przykłady nowych zastosowań stopu z pamięcią kształtu.

3

On the elastic energy invariance of crystal twins

Glüge R.

Archives of Mechanics

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2010

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Vol. 62, nr 6

441-464

EN

An analysis by Zanzotto (1992, 1996) showed that, if crystal twinning is considered as a material symmetry operation, the symmetry groups of many crystals that form twins correspond to the unimodular group, which is the symmetry group of elastic fluids. It is therefore evident that an elastic modelling based on an elastic energy that includes any possible combination of twin system activation must fail. However, one may try to construct an elastic energy which includes only the stressfree configurations of the parent and the first order twins. It is known that, even under this restriction, many twinning modes exhibit an elastic energy invariance, which renders them indistinguishable in terms of the elastic energy. In this article, it is demonstrated that this energy invariance holds for all compound twins. The implications of the latter are discussed. It is suggested to distinguish between crystallographically equivalent and crystallographically distinct compound twins, since different implications regarding the elastic energy invariance emerge.

4

Dynamic Problem Formulation for Shape Memory Alloys

Grzesikiewicz W., Zbiciak A.

Machine Dynamics Problems

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2004

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Vol. 28, No. 3

113-118

EN

The main goal of the paper is the formulation of three-dimensional constitutive relations of shape memory alloys (SMAs). We will propose a rheological model of such material providing a simple illustration of physical equations. Using this model we will introduce an additional variable describing the strain state. The equation we formulate can be used in dynamic analysis of structures. The proposed methods involves notions of non-smooth mechanics.

5

Thermomechanical investigations of martensitic and reverse transformations in TiNi shape memory alloy

Pieczyska E. A., Gadaj S. P., Nowacki W. K., Tobushi H.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2004

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Vol. 52, nr 3

165-171

EN

Shape memory alloys are characterised by interesting properties, i.e. shape memory effect and pseudoelasticity, which enable their increasing application. Thermomechanical aspects of martensitic and reverse transformations in TiNi shape memory alloy subjected to tension tests were investigated. The stress-strain characteristics obtained during the tests were completed by the temperature characteristics. The temperature changes were calculated on the basis of thermograms determined by an infrared camera. Taking advantages from the infrared technique, the temperature distributions on the specimen's surface were found. Heterogeneous temperature distributions, related to the nucleation and development of the new martensite phase, were registered and analysed. A significant temperature increase, up to 30 K, was registered during the martensitic transformation. The similar effects of the heterogeneous temperature distribution were observed during unloading, while the reverse transformation, martensite into austenite took place, accompanied by significant temperature decrease.

6

In-situ observations of reversible martensitic transformations in shape memory alloys

Morgiel J., Dutkiewicz J.

Archives of Metallurgy and Materials

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2004

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Vol. 49, iss. 4

839-854

EN

The conditions of performing in-situ TEM and OM straining and in-situ TEM heating experiments with CuAlMn and TiNiCu shape memory alloys were discussed. It was shown that correlating the bulk straining tests with in-situ straining experiments allow to determine the strain temperature phase diagrams for CuAlMn martensitic phases. The in-situ heating experiments helped to explain the influence of different elements of microstructure, like grain size, precipitates or dislocations in TiNiCu alloy on nucleation and grow of martensite.

PL

W pracy przedyskutowano wyniki prowadzenia eksperymentów in-situ odkształcania oraz in-situ grzania stopów wykazujących efekt pamięci kształtu z wykorzystaniem transmisyjnego mikroskopu elektronowego oraz mikroskopu optycznego. Wykazano, że porównanie serii pomiarów odkształcenia próbek masywnych z obserwacjami amian mikrostruktury w czasie odkształcenia cienkich folii z wykorzystaniem mikroskopu transmisyjnego umożliwiatworzenie diagramów stabilności faz pseudo-sprężystego stopu CuAlMn w funkcji temperatura-naprężenie. Eksperymenty in-situ cienkich folii z taśm TiCuNi pozwoliły na kreślenie wpływu poszczególnych elementów mikrostruktury jak wielkości ziarna, gęstości wydzieleń, czy dyslokacji na zarodkowanie i wzrost przemiany martenzytycznej.