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1

Mechanical properties and advanced subjects in shape memory alloys and polymers

Matsui R., Takeda K., Tobushi H., Pieczyska E. A.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 2

447--456

EN

Advanced subjects in mechanical properties of shape memory alloys and polymers are discussed. In the subloop loading under a stress-controlled condition of the shape memory alloy, the transformation-induced stress relaxation appears due to variation in temperature. The enhancement of corrosion and corrosion fatigue life of the shape memory alloy is discussed. The development of a functionally-graded shape memory alloy and polymer is expected to obtain better performance. Three-way motion appears in the shape memory composite with the shape memory alloy and polymer.

2

Torsional deformation properties of SMA tapes and their application to bias-type reciprocating rotary driving actuator

Takeda K., Matsui R., Tobushi H., Pieczyska E. A.

Archives of Mechanics

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2017

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Vol. 69, nr 4-5

289--303

EN

In order to develop the reciprocating rotary driving actuator with a simple mechanism using shape memory alloy (SMA) tapes, the graphical method to design the actuator was proposed based on the torsional deformation properties of SMA tapes. The torsional deformation properties of the SME tape showing the shape memory effect (SME) and the SE tape showing superelasticity (SE) were obtained. The bias-type reciprocating rotary actuator was composed of the pretwisted SME tape and the flat SE tape in series. The design chart expressed by the relationship between torque and twisting angle of the SME tape and the SE tape was proposed. The rotational angle and torque, which vary depending on temperature, can be estimated based on the design chart. The rotational angle is controlled by adjusting the mounting angle of the SME tape and the heating temperature. The automatically opening and closing blind driven by sunlight was demonstrated. The blind was controlled by using the reciprocating rotary element composed of the SME tape and the SE tape. The behavior of the blind can be achieved based on the proposed design method of the reciprocating rotary driving element.

3

Investigation of thermal effects accompanying tensile deformation of Shape Memory Polymer PU-SMP

Pieczyska E. A., Staszczak M, Maj M., Tobushi H., Hayashi S.

Measurement Automation Monitoring

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2015

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Vol. 61, No. 6

203--205

EN

Experimental results of effects of thermomechanical couplings occurring in shape memory polymer subjected to tension are presented. Stress-strain curves were recorded by testing machine, while their related temperature changes were measured with infrared camera. The mechanical and thermal characteristics were used to investigate the polymer properties. Three various stages were distinguished during the deformation process. The first, elastic, is accompanied by a drop in the specimen temperature; the second, plastic, is associated with change of the material structure and the temperature increase; the third stage, related to the specimen rupture and damage mechanisms, is accompanied by the significant increase in temperature.

4

Enhancement of bending fatigue life in TiNi shape-memory alloy tape by nitrogen ion implantation

Takeda K., Matsui R., Tobushi H., Homma S., Levintant-Zayonts N., Kucharski S.

Archives of Mechanics

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2015

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Vol. 67, nr 4

293--310

EN

A shape-memory alloy (SMA) is expected to be applied as intelligent or smart material since it shows the functional characteristics of the shape memory effect and superelasticity. Most SMA elements, with these characteristics, perform cyclic motions. In these cases, the fatigue property of SMA is one of the most important issues in view of evaluating functional characteristics of SMA elements. The fatigue properties are complex since they depend on stress, strain, temperature and their hysteresis. If an SMA is implanted with high-energy ions, the thermomechanical properties of the material may change, resulting in long fatigue life. In the present study, the nitrogen ion implantation was applied to modify the surface of a TiNi SMA tape and the influence of implantation treatment on the bending fatigue properties was investigated.

5

Właściwości mechaniczne oraz zmiany temperatury polimeru z pamięcią kształtu w procesie rozciągania

Staszczak M, Pieczyska E. A., Maj M., Urbański L., Tobushi H.

Pomiary Automatyka Kontrola

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2013

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R. 59, nr 9

1002--1005

PL

W pracy zawarto opis podstawowych właściwości, przykłady zastosowań oraz wyniki badań efektów sprzężeń termomechanicznych poliuretanu z pamięcią kształtu w procesie rozciągania. Otrzymane charakterystyki mechaniczne i temperaturowe wskazują na dużą wrażliwość tego polimeru na prędkość deformacji. Wykorzystując efekt termosprężysty wyznaczono granice odwracalnego odkształcenia (plastyczności) dla różnych prędkości odkształcania. Pokazano, że metoda bazująca na minimum temperatury próbki pozwala na wyznaczenie granicy plastyczności z dużą dokładnością, w tym materiałów wykazujących nieliniową sprężystość.

EN

Mechanical properties and temperature changes of a new multifunctional material - polyurethane shape memory polymer (PU-SMP) subjected to tension at room temperature with various strain rates are presented (Figs. 1-3), [1, 2]. The stress and strain data were recorded by an MTS 858 testing machine. The temperature changes were measured by a fast and sensitive infrared camera ThermaCam PhoenixTM. Basing on the obtained mechanical and corresponding temperature data, experimental effects of thermomechanical couplings occurring in the SMP during loading were studied (Figs. 4-7). The stress and temperature changes vs. strain obtained for tension with strain rates 2x10-1s-1 and 2x100s-1 until the sample rupture show that the SMP exhibits a hardening-like behavior and its elongation limit is over 180 % in case of the true strains (Figs. 4, 5). The higher strain rate, the higher temperature changes were recorded, since the mechanisms of deformation occurred very fast and the process was more close to adiabatic conditions. The significant temperature changes, accompanying the SMP loading with higher strain rate, influence the SMP mechanical behavior. Namely, a maximum of the stress value was recorded at the advanced loading stage, followed by its drop and increase preceding the sample rupture (Fig. 5). The initial reversible tension of any solids is accompanied by a temperature decrease, called thermoelastic effect, whereas the following plastic deformation is always related to energy dissipation and increase in the sample temperature [3-5]. Thus, the maximum drop in temperature of the sample subjected to tension indicates a limit of the reversible material deformation. The higher strain rate, the higher drops in temperature for the SMP were recorded and the larger values of the yield point for the polymer were obtained (Figs. 6, 7), [9, 10].

6

Influence of nitrogen ion implantation on deformation and fatigue properties of TiNi shape-memory alloy wire

Takeda K., Mitsui K., Tobushi H., Levintant-Zayonts N., Kucharski S.

Archives of Mechanics

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2013

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Vol. 65, nr 5

391--405

EN

A shape memory alloy (SMA) is expected to be applied as intelligent material since it shows the unique characteristics of the shape memory effect and superelasticity. Most SMA elements, with these characteristics, perform cyclic motions. In these cases, fatigue of SMA is one of the important properties in view of evaluating functional characteristics. The fatigue properties are complex since they depend on stress, strain, temperature and time. If SMA is implanted by high energy ions, the thermomechanical properties may change, resulting in long fatigue life. In the present study, the nitrogen ion implantation was applied to modify TiNi SMA wire surface and the influence of implantation treatment on the tensile deformation and bending fatigue properties was investigated.

7

Creep and creep recovery under stress-controlled subloop loading in TiNi shape memory alloy

Takeda K., Matsui R., Tobushi H., Pieczyska E. A.

Archives of Mechanics

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2013

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Vol. 65, nr 5

429-444

EN

If a shape memory alloy (SMA) is subjected to the subloop loading under the stress-controlled condition, creep and creep recovery can appear based on the martensitic transformation. In the design of SMA elements, these deformation properties are important since the deflection of SMA elements can change under constant load. The conditions for the progress of the martensitic transformation are discussed based on the kinetics of the martensitic transformation for the SMA. The creep deformation properties are investigated experimentally for TiNi SMA. The creep strain rate increases in proportion to the martensitic transformation strain; the creep recovery strain rate increases in proportion to the reverse transformation strain.

8

Performance and design of precision-cast shape memory alloy brain spatula

Tobushi H., Mitsui K., Takeda K.

Journal of Theoretical and Applied Mechanics

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2012

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Vol. 50 nr 3

855-869

EN

In order to develop a brain spatula made of a shape memory alloy (SMA), this paper discusses the bending characteristics of a new brain spatula precision-cast in a TiNi SMA. The results obtained can be summed up as follows. (1) With respect to an SMA-brain spatula having the same length and width as the existing type made of copper, if the new cast SMA spatula is 1.2 times as great in thickness as the existing copper spatula, or if a conventionally rolled SMA spatula is 1.3 times as great, the SMA instrument will offer the same bending rigidity and withstand almost as great a bending force as the copper one. (2) Expressing the bending fatigue life of the copper or SMA in the region of low-cycle fatigue as a power function of the maximum bending strain, the fatigue life of the SMA is longer than that of the copper. For both the cast and the rolled SMAs, the fatigue life is longer under pulsating-plane bending than under alternating plane bending.

PL

W pracy opisano problem projektowania szpatułki używanej w chirurgii mózgu, wykonanej ze stopu z pamięcią kształtu (SMA). Przedyskutowano charakterystyki zginania nowej szpatułki wykonanej z precyzyjnie odlewanego stopu TiNi. Wyniki badań podsumowano w następujący sposób: (1) w porównaniu do konwencjonalnych, miedzianych szpatułek o tej samej długości i szerokości, jeśli odlewana szpatułka SMA jest 1.2 raza grubsza od miedzianej, lub 1.3 raza, gdy wykonana została przez walcowanie, instrument ten będzie posiadał taką samą sztywność giętną i wytrzyma niemalże to samo obciążenie zginające, jak w przypadku narzędzia miedzianego; (2) wyrażając wytrzymałość zmęczeniową szpatułki miedzianej w rejonie niskocyklicznych obciążeń jako funkcję potęgową maksymalnego odkształcenia przy zginaniu, stwierdzono, że szpatułki SMA wykazują dłuższą żywotność od konwencjonalnych. W obydwu przypadkach – odlewanej i walcowanej szpatułki SMA – wytrzymałość zmęczeniowa jest większa dla płaskiego jednostronnego zginania od wytrzymałości przy zginaniu przemiennym.

9

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.

10

Novel shape memory actuators

Tobushi H., Miyamoto K., Nishimura Y., Mitsui K.

Journal of Theoretical and Applied Mechanics

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2011

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Vol. 49 nr 3

927-943

EN

In order to develop novel shape memory actuators, the torsional deformation of a shape memory alloy (SMA) tape and the actuator models driven by the tape were investigated. The shape memory composite (SMC) belt composed of SMA tapes and a shape memory polymer (SMP) was fabricated, and the three-way bending characteristics were also investigated. The results obtained can be summarized as follows. In the SMA tape subjected to torsion, the martensitic transformation appears along the edge of the tape due to elongation of the edge of the tape and grows to the central part. The fatigue life in both the pulsating torsion and alternating torsion is expressed by a unified relationship of the dissipated work in each cycle. Based on the two-way motion of an opening and closing door model and a solar-powered active blind model driven by two kinds of SMA tape, it is confirmed that the two-way rotary driving actuator with a small and simple mechanism can be developed by using torsion of the SMA-tape. The SMC belt laminated with the SMP tape and SMA tapes was fabricated. The three-way bending movement of the SMC belt was achieved during heating and cooling based on the charac- teristics of the SMA tapes and the SMP tape. The active SMC actuator with various three-dimentional movements can be developed by applying the three-way properties of the SMC.

PL

W pracy zajęto się aktuatorami nowego typu, w których zastosowano stop z pamięcią kształtu (SMA) w postaci skręcającej się taśmy SMA wywołującej ruch aktuatora. Opracowano kompozytowy pas (SMC) z taśm SMA oraz polimeru wykazującego efekt pamięci kształtu (SMP) oraz zbadano charakterystyki takiego kompozytu przy zginaniu trójosiowym. Rezultaty badań pokazały, że taśma SMA poddana skręcaniu doznaje przemiany martenzytycznej wzdłuż krawędzi z powodu jej wydłużania, która stopniowo przechodzi do środkowej części taśmy. Problem wytrzymałości zmęczeniowej taśmy obciążonej jednokierunkowym i naprzemiennym skręcaniem opisano ujednoliconym wyrażeniem określającym pracę dyssypacji na każdy cykl obciążenia. Zbadano model aktuatora dwustronnego działania do otwierania i zamykania drzwi oraz do sterowania przesłony zasilanej energią słoneczną. Potwierdzono skuteczność torsyjnego aktuatora SMA przy utrzymaniu prostoty konstrukcji takiego mechanizmu. Przeanalizowano przestrzenny ruch kompozytowego pasa SMC indukowanego ogrzewaniem i chłodzeniem w zależności od charakterystyk taśm SMA i SMP. Pokazano, że dzięki właściwościom kompozytu SMC różnych w trzech kierunkach, uzyskanie zdolności ruchowej aktuatora w przestrzeni (3D) jest możliwe.

11

Three-way actuation of shape memory composite

Tobushi H., Hayashi S., Pieczyska E., Date K., Nishimura Y.

Archives of Mechanics

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2011

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Vol. 63, nr 5-6

443-443

EN

The SMC belt composed of two kinds of SMAs with different phase transformation temperatures and SMP, was fabricated and the three-way (reciprocating) movement and recovery force in bending actuation were investigated. The results obtained can be summarized as follows. 1) The three-way bending movement was achived during heating and cooling, based on the characteristics of the SMA tapes and the SMP tape. 2) The recovery force decreased at first and increased thereafter during heating and decreased during cooling. The recovery force was roughly estimated by the proposed model. 3) The development and application of multi-functional SMCs with simple structure for three-dimensional actuators are highly expected.

12

Two-way rotary shape memory alloy thin strip actuator

Tobushi H., Pieczyska E. A., Nowacki W. K., Date K., Miyamoto K.

Journal of Theoretical and Applied Mechanics

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2010

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Vol. 48 nr 4

1043-1056

EN

In order to develop a two-way rotary shape memory alloy thin strip actuator, the torsional deformation and fatigue properties of a TiNi SMA thin strip were investigated. The results obtained are summarized as follows. (1) In the SMA thin strip subjected to torsion, the MT appears along the edge of the strip due to elongation of the edge of the strip and grows to the central part. (2) The number of cycles to failure decreases with an increase in the maximum angle of twist in torsion fatigue. The fatigue life in pulsating torsion is longer than that in alternating torsion by five times. The fatigue limit exists in a certain value of dissipated work of the strip in each cycle. (3) Based on the two-way motion of a lifting actuator model driven by two kinds of SMA thin strip, it is confirmed that the two-way rotary actuator with a small and simple mechanism can be developed by using the SMA thin strips.

PL

Wpracy zbadano termomechaniczne właściwości skręcania i zmęczenia stopu TiNi z pamięcią kształtu (SMA) w celu zbudowania skrętnego siłownika taśmowego zaprojektowanego na bazie dwukierunkowego efektu pamięci kształtu. Otrzymane wyniki podsumowano w sposób następujący. (1) W cienkich taśmach SMA poddawanych skręcaniu, przemiana martenzytyczna (MT) inicjuje się na krawędzi taśmy w związku ze składową rozciągania, a następnie rozwija w kierunku jej środka. (2) W badaniach zmęczeniowych ilość cykli do zniszczenia maleje wraz ze wzrostem maksymalnego kąta skręcania. Wytrzymałość na męczenie w przypadku skręcania pulsującego jest pięciokrotnie dłuższa niż w przypadku obciążania symetrycznego. (3) Przeprowadzone badania dwukierunkowego ruchu na zaprojektowanym modelu siłownika poruszanego przy pomocy dwóch rodzajów cienkiej taśmy SMA potwierdziły możliwość zbudowania skrętnego siłownika z małym i prostym mechanizmem na bazie dwukierunkowego efektu pamięci kształtu.

13

Torsional deformation and rotary driving characteristics of SMA thin strip

Tobushi H., Pieczyska E. A., Nowacki W. K., Sakuragi T., Sugimoto Y.

Archives of Mechanics

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2009

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Vol. 61, nr 3-4

241-257

EN

The torsional deformation properties of a TiNi shape-memory alloy thin strip were investigated. The results obtained are summarized as follows. (1) The martensitic transformation starts at the edge of the thin strip. (2) The torsional deformation properties change slightly under thermomechanical cycling. (3) The fatigue life in pulsating torsion is longer than that in alternating torsion. (4) A simple rotary driving element can be developed by using the SMA thin strip.

14

Temperature measurement as a new technique applied to the phase transformation study in a TiNi shape memory alloy subjected to tension

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

Archives of Metallurgy and Materials

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2005

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Vol. 50, iss. 3

661-674

EN

Temperature distributions obtained from studying the stress induced phase transformations in a TiNi shape memory alloy (SMA) were employed for the investigation into nucleation and further development of the bands of martensite and reverse transformations. A thermovision camera was used to register the distribution of infrared radiation emitted by the specimen surface and constructed thermograms with of 50 Hz frequency. Basing on temperature changes and the relevant mechanical characteristics it was noticed that just after crossing a certain threshold stress, narrow lines of considerably higher temperature — up to 10 K, corresponding to the martensite phase, appeared starting from the central part of the specimen and developing towards the specimen grips. Their angle of inclination was about 42°. At higher stresses, a few such lines parallel to each other occurred and moved towards the specimen borders, as well as the next “family” of them, developing in the perpendicular direction. The heterogeneous field of the temperature distribution was observed also during the unloading process of TiNi SMA, while the reverse transformation — austenite into martensite, took place. The reverse transformation was accompanied by a significant temperature decrease. The lines of reverse transformation were observed when the unloading process started and developed in the whole material volume, however the process remained inhomogeneous. The processes of relaxation do not bring about any changes in the nature of phase transitions, however, the relaxation involved temperature changes cause stress changes as the deformation (unloading) develops after relaxation.

PL

Pomiary rozkładów temperatury podczas przemiany martenzytycznej i przemiany odwrotnej stopu TiNi z pamiecia kształtu, stymulowanych odkształceniem, wykorzystano do badania inicjacji i rozwoju tych przemian oraz wpływu parametrów odkształcania na te przemiany. Rozkłady temperaury mierzono za pomocą kamery termowizyjnej, umożliwiającej uzyskiwanie obrazów termicznych z częstotliwością do 50 Hz. Na podstawie badań charakterystyk mechanicznych i zmian temperatury stwierdzono, że mertenzytyczna przemiana fazowa rozpoczyna sie pod katem ok. 42° do kierunku rozciągania próbki. W miarę odkształcania pojawia się coraz więcej pasm, zarówno równoległych, jak i skierowanych przeciwnie, aż obejmują one całą próbkę. Skok temperatury w miejscu pojawienia się pojedynczego pasma wynosi ok. 6 K. Przemiana odwrotna jest również procesem niejednorodnym, przy czym w pasmach tej przemiany następuje spadek temperatury. Przyrost średniej temperatury próbki podczas przemiany martenzytycznej może przekraczać 40 K, co powoduje przyrost naprężeń w miarę rozciągania. Procesy relaksacji nie powodują zmian charakteru przemian fazowych, jednak związane z relaksacją zmiany temperatury wywołują zmiany naprężeń przy kontynuacji odkształcania (odciążania) po relaksacji.

15

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.

16

Pseudoviscoelastic behavior of TiNi shape memory alloys under stress-controlled subloop loadings

Tobushi H., Endo M., Ikawa T., Shimada D.

Archives of Mechanics

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2003

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Vol. 55, nr 5-6

519-530

EN

The superelastic behavior of TiNi shape memory alloy under various subloop loadings were investigated. The results obtained can be summarized as follows. (1) In the case of subloop loading under strain-controlled conditions, the reloading curve passes through the unloading-start point. In the case of stress-controlled conditions, the return-point memory does not appear. (2) In the case of subloop loading under stress-controlled conditions, strain increases under constant stress in the loading process and decreases in the unloading process. (3) In the case of subloop loading under stress-controlled conditions, stress decreases under constant strain in the loading process and increases in the unloading process. (4) The above-mentioned behavior concerning the return-point memory and the pseudoviscoelastic behavior similar to creep and stress relaxation, appear according to the martensitic transformation and the reverse transformation based on the variation in stress and temperature.

17

Deformation behavior of TiNi shape-memory alloy under strain- or stress-controlled conditions

Tobushi H., Okumara K., Endo M., Tanaka K.

Archives of Mechanics

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2002

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Vol. 54, nr 1

75-91

EN

The deformation properties of TiNi shape-memory alloy subjected to strain control and stress control were investigated experimentally. The results obtained are summarized as follows. (1) In the case of a full loop, the stress-strain curves under stress-controlled conditions are similar to those under strain-controlled conditions with high strain rate. The overshoot and undershoot do not appear at the start points of the stress-induced martensitic transformation in these curves. (2) In the case of subloop under stress-controlled conditions, temperature decreases and therefore the strain increases owing to the martensitic transformation at the early stage of the unloading process. At the early stage in the reloading process, temperature increases and therefore the strain decreases owing to the reverse transformation. (3) In the case of subloop under stress-controlled conditions, the starting stresses of the martensitic transformation and the reverse transformation in the loading and unloading processes coincide with the transformation stresses under strain-controlled conditions with low strain rate, respectively. (4) The deformation behaviours for a subloop under stress-controlled conditions are prescribed by the condition for progress of the martensitic transformation based on the transformation kinetics. (5) The deformation behaviors subjected to cyclic loading under stress-controlled conditions at constant temperature are also prescribed by the conditions for progress of the martensitic transformation.

18

Temperature evolution during tensile test of TiNi shape memory alloy

Gadaj S., Nowacki W., Tobushi H.

Archives of Mechanics

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1999

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Vol. 51, nr 6

649-663

EN

Experimental results containing both the mechanical characteristics and the changes of temperature obtained during tensile test of TiNi shape memory alloy strained at various strain rates have been presented. The investigations were carried out at room temperature (~ 295 K) and at chamber temperature equal to 333 K. The temperature changes were measured in a contactless way by recording the infrared radiation emitted by the surface of the sample. It was found that during loading at room temperature, the phase transformation process is homogeneous but at temperature 333 K the process seems to be heterogeneous. The martensitic transformation was accompanied by an increase in temperature. Both the stresses and the temperature changes were higher for the tests carried out at elevated temperature. Decreases in temperature during unloading were higher too. For tests carried out in the same conditions, the temperature increments in the range of the martensitic transformation plotted as a function of stress, turned out to lie on the same curve, independently of the strain rate.

19

Fatigue properties of TiNi shape memory alloy and applications to a heat engine and an actuator

Tobushi H., Nakahara T., Hashimoto T., Shimeno Y., Tanaka K.

Archives of Mechanics

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1999

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Vol. 51, nr 6

833-845

EN

The fatigue properties of a TiNi shape-memory alloy (SMA) wire in the region of the martensitic transformation and the R-phase transformation are investigated. The rotating-bending fatigue life of a wire in the region of the R-phase transformation is longer than 10'7 cycles. A tilt-disk offset SMA heat engine and an indirect-heated SMA thermal actuator are developed.