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Special Issue "Shape Memory Materials"

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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (28 February 2014)

Special Issue Editor

Guest Editor
Dr. Trevor Finlayson (Website)

Associate Professor and Honorary Principal Fellow, School of Physics, University of Melbourne, Victoria. 3010, Australia

Special Issue Information

Dear Colleagues,

Shape memory materials rely on a shape change in response to an environmental stimulus. While such stimuli are commonly changes in temperature, other environmental stimuli, such as an electric or magnetic field, or a light pulse, are growing in importance for special classes of materials. At a microscopic level, the shape change is a consequence of a crystallographic or phase change within the material. Of particular importance to applications are both the temperature at which the shape change will occur and the magnitude of the strain associated with the effect itself. Shape memory is now known to occur for a long list of materials. Consequently, applications for such materials are many and varied and include areas such as actuators, medical implants, orthodontics, industrial couplings, automotive components and optometry. This special issue will cover both the fundamental science of materials exhibiting the effect as well as existing and proposed applications for specific materials. The issue will comprise a comprehensive overview of the topic and include articles reporting new research results, as well as reviews of particular classes of materials and their applications. Manuscripts will be welcomed from both fundamental researchers and authors from industrial companies involved in the field.

Dr. Trevor Finlayson
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Keywords

  • shape memory materials
  • shape memory alloys
  • shape memory ceramics
  • shape memory polymers
  • magnetic shape memory
  • martensitic transformation
  • applications of shape memory materials
  • actuator design

Published Papers (8 papers)

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Research

Open AccessArticle Damping Characteristics of Ti50Ni50−xCux (x = 0~30 at.%) Shape Memory Alloys at a Low Frequency
Materials 2014, 7(6), 4574-4586; doi:10.3390/ma7064574
Received: 27 February 2014 / Revised: 3 April 2014 / Accepted: 11 June 2014 / Published: 16 June 2014
Cited by 2 | PDF Full-text (2493 KB) | HTML Full-text | XML Full-text
Abstract
The damping characteristics of Ti50Ni50−xCux (x = 0~30 at.%) shape memory alloys (SMAs) at a low frequency have been studied using a dynamic mechanical analyzer. The magnitude of the tan δ value and the values [...] Read more.
The damping characteristics of Ti50Ni50−xCux (x = 0~30 at.%) shape memory alloys (SMAs) at a low frequency have been studied using a dynamic mechanical analyzer. The magnitude of the tan δ value and the values of the storage modulus (E0) softening/hardening and the strain variation exhibited in B2↔B19 transformation are all higher than those in B2↔B19’ transformation. The larger E0 softening/hardening in B2↔B19 can induce higher strain variation in this transformation. It is suggested that the greater mobility of the twin boundaries and the larger magnitude of the strain variation both cause the higher tan δ value exhibited in B2↔B19 transformation, as compared with B2↔B19’ transformation. In comparison with that in B19’ martensite, the E0 value in B19 martensite is low and not affected so greatly by changes in temperature. Relaxation peaks are observed in B19’ martensite, but not in B19 martensite, because the latter has rare twinned variants. The activation energy of the relaxation peak is calculated and found to increase as the Cu-content increases in these SMAs. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle Magnetic Properties of the Ferromagnetic Shape Memory Alloys Ni50+xMn27−xGa23 in Magnetic Fields
Materials 2014, 7(5), 3715-3734; doi:10.3390/ma7053715
Received: 23 February 2014 / Revised: 2 April 2014 / Accepted: 4 May 2014 / Published: 8 May 2014
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Abstract
Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni50+xMn27−xGa23 (x = 2.0, 2.5, 2.7) were performed. For x = 2.7, in which the martensite transition and the ferromagnetic transition occur [...] Read more.
Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni50+xMn27−xGa23 (x = 2.0, 2.5, 2.7) were performed. For x = 2.7, in which the martensite transition and the ferromagnetic transition occur at the same temperature, the martensite transition starting temperature TMs shift in magnetic fields around a zero magnetic field was estimated to be dTMs/dB = 1.1 ± 0.2 K/T, thus indicating that magnetic fields influences martensite transition. We discussed the itinerant electron magnetism of x = 2.0 and 2.5. As for x = 2.5, the M4 vs. B/M plot crosses the origin of the coordinate axis at the Curie temperature, and the plot indicates a good linear relation behavior around the Curie temperature. The result is in agreement with the theory by Takahashi, concerning itinerant electron ferromagnets. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Figures

Open AccessArticle Anodic Fabrication of Ti-Ni-O Nanotube Arrays on Shape Memory Alloy
Materials 2014, 7(4), 3262-3273; doi:10.3390/ma7043262
Received: 27 January 2014 / Revised: 26 March 2014 / Accepted: 17 April 2014 / Published: 22 April 2014
Cited by 6 | PDF Full-text (2137 KB) | HTML Full-text | XML Full-text
Abstract
Surface modification with oxide nanostructures is one of the efficient ways to improve physical or biomedical properties of shape memory alloys. This work reports a fabrication of highly ordered Ti-Ni-O nanotube arrays on Ti-Ni alloy substrates through pulse anodization in glycerol-based electrolytes. [...] Read more.
Surface modification with oxide nanostructures is one of the efficient ways to improve physical or biomedical properties of shape memory alloys. This work reports a fabrication of highly ordered Ti-Ni-O nanotube arrays on Ti-Ni alloy substrates through pulse anodization in glycerol-based electrolytes. The effects of anodization parameters and the annealing process on the microstructures and surface morphology of Ti-Ni-O were studied using scanning electron microscope and Raman spectroscopy. The electrolyte type greatly affected the formation of nanotube arrays. A formation of anatase phase was found with the Ti-Ni-O nanotube arrays annealed at 450 °C. The oxide nanotubes could be crystallized to rutile phase after annealing treatment at 650 °C. The Ti-Ni-O nanotube arrays demonstrated an excellent thermal stability by keeping their nanotubular structures up to 650 °C. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle Transformation-Induced Relaxation and Stress Recovery of TiNi Shape Memory Alloy
Materials 2014, 7(3), 1912-1926; doi:10.3390/ma7031912
Received: 4 December 2013 / Revised: 15 January 2014 / Accepted: 24 February 2014 / Published: 6 March 2014
Cited by 3 | PDF Full-text (1283 KB) | HTML Full-text | XML Full-text
Abstract
The transformation-induced stress relaxation and stress recovery of TiNi shape memory alloy (SMA) in stress-controlled subloop loading were investigated based on the local variation in temperature and transformation band on the surface of the tape in the tension test. The results obtained [...] Read more.
The transformation-induced stress relaxation and stress recovery of TiNi shape memory alloy (SMA) in stress-controlled subloop loading were investigated based on the local variation in temperature and transformation band on the surface of the tape in the tension test. The results obtained are summarized as follows. (1) In the loading process, temperature increases due to the exothermic martensitic transformation (MT) until the holding strain and thereafter temperature decreases while holding the strain constant, resulting in stress relaxation due to the MT; (2) In the unloading process, temperature decreases due to the endothermic reverse transformation until the holding strain and thereafter temperature increases while holding the strain constant, resulting in stress recovery due to the reverse transformation; (3) Stress varies markedly in the initial stage followed by gradual change while holding the strain constant; (4) If the stress rate is high until the holding strain in the loading and unloading processes, both stress relaxation and stress recovery are large; (5) It is important to take into account this behavior in the design of SMA elements, since the force of SMA elements varies even if the atmospheric temperature is kept constant. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle Properties of Graphene/Shape Memory Thermoplastic Polyurethane Composites Actuating by Various Methods
Materials 2014, 7(3), 1520-1538; doi:10.3390/ma7031520
Received: 15 October 2013 / Revised: 10 January 2014 / Accepted: 11 February 2014 / Published: 27 February 2014
Cited by 10 | PDF Full-text (1312 KB) | HTML Full-text | XML Full-text
Abstract
Shape memory behavior of crystalline shape memory polyurethane (SPU) reinforced with graphene, which utilizes melting temperature as a shape recovery temperature, was examined with various external actuating stimuli such as direct heating, resistive heating, and infrared (IR) heating. Compatibility of graphene with [...] Read more.
Shape memory behavior of crystalline shape memory polyurethane (SPU) reinforced with graphene, which utilizes melting temperature as a shape recovery temperature, was examined with various external actuating stimuli such as direct heating, resistive heating, and infrared (IR) heating. Compatibility of graphene with crystalline SPU was adjusted by altering the structure of the hard segment of the SPU, by changing the structure of the graphene, and by changing the preparation method of the graphene/SPU composite. The SPU made of aromatic 4,4′-diphenylmethane diisocyanate (MSPU) exhibited better compatibility with graphene, having an aromatic structure, compared to that made of the aliphatic hexamethylene diisocyanate. The finely dispersed graphene effectively reinforced MSPU, improved shape recovery of MSPU, and served effectively as a filler, triggering shape recovery by resistive or IR heating. Compatibility was enhanced when the graphene was modified with methanol. This improved shape recovery by direct heating, but worsened the conductivity of the composite, and consequently the efficiency of resistive heating for shape recovery also declined. Graphene modified with methanol was more effective than pristine graphene in terms of shape recovery by IR heating. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Figures

Open AccessArticle Investigation on the Cyclic Response of Superelastic Shape Memory Alloy (SMA) Slit Damper Devices Simulated by Quasi-Static Finite Element (FE) Analyses
Materials 2014, 7(2), 1122-1141; doi:10.3390/ma7021122
Received: 5 January 2014 / Revised: 23 January 2014 / Accepted: 24 January 2014 / Published: 11 February 2014
Cited by 3 | PDF Full-text (1776 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the superelastic shape memory alloy (SMA) slit damper system as an alternative design approach for steel structures is intended to be evaluated with respect to inelastic behavior simulated by refined finite element (FE) analyses. Although the steel slit dampers [...] Read more.
In this paper, the superelastic shape memory alloy (SMA) slit damper system as an alternative design approach for steel structures is intended to be evaluated with respect to inelastic behavior simulated by refined finite element (FE) analyses. Although the steel slit dampers conventionally used for aseismic design are able to dissipate a considerable amount of energy generated by the plastic yielding of the base materials, large permanent deformation may occur in the entire structure. After strong seismic events, extra damage repair costs are required to restore the original configuration and to replace defective devices with new ones. Innovative slit dampers fabricated by superelastic SMAs that automatically recover their initial conditions only by the removal of stresses without heat treatment are introduced with a view toward mitigating the problem of permanent deformation. The cyclically tested FE models are calibrated to experimental results for the purpose of predicting accurate behavior. This study also focuses on the material constitutive model that is able to reproduce the inherent behavior of superelastic SMA materials by taking phase transformation between austenite and martensite into consideration. The responses of SMA slit dampers are compared to those of steel slit dampers. Axial stress and strain components are also investigated on the FE models under cyclic loading in an effort to validate the adequacy of FE modeling and then to compare between two slit damper systems. It can be shown that SMA slit dampers exhibit many structural advantages in terms of ultimate strength, moderate energy dissipation and recentering capability. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle A Constitutive Description for Shape Memory Alloys with the Growth of Martensite Band
Materials 2014, 7(1), 576-590; doi:10.3390/ma7010576
Received: 25 November 2013 / Revised: 23 December 2013 / Accepted: 15 January 2014 / Published: 20 January 2014
Cited by 1 | PDF Full-text (370 KB) | HTML Full-text | XML Full-text
Abstract
Based on the experimental results and the finite element analysis, a constitutive model is proposed for two phase shape memory alloys by introducing a compensative volumetric strain into a constrained relationship between the two phases, accounting for the reduced constraint due to [...] Read more.
Based on the experimental results and the finite element analysis, a constitutive model is proposed for two phase shape memory alloys by introducing a compensative volumetric strain into a constrained relationship between the two phases, accounting for the reduced constraint due to the growth of martensite band. The pseudoelasticity of NiTi shape memory alloy micro-tube, subjected to pure tension, is analyzed and compared with the experimental results. It can be seen that the pseudoelastic behavior, especially the phenomena of a stress drop during tension processes, can be well described with the proposed model. The proposed model separates the complicated constitutive behavior of a shape memory alloy (SMA) into simple responses arising respectively from its two phases, taking into account laminar microstructure, the thickness of martensite phase and the interaction between the two phases, and provides an easy but comprehensive method for the description of the constitutive behavior of SMAs under complex thermomechanical loading. Full article
(This article belongs to the Special Issue Shape Memory Materials)
Open AccessArticle Towards Low-Cost Effective and Homogeneous Thermal Activation of Shape Memory Polymers
Materials 2013, 6(12), 5447-5465; doi:10.3390/ma6125447
Received: 7 October 2013 / Revised: 30 October 2013 / Accepted: 12 November 2013 / Published: 27 November 2013
Cited by 2 | PDF Full-text (752 KB) | HTML Full-text | XML Full-text
Abstract
A typical limitation of intelligent devices based on the use of shape-memory polymers as actuators is linked to the widespread use of distributed heating resistors, via Joule effect, as activation method, which involves several relevant issues needing attention, such as: (a) Final [...] Read more.
A typical limitation of intelligent devices based on the use of shape-memory polymers as actuators is linked to the widespread use of distributed heating resistors, via Joule effect, as activation method, which involves several relevant issues needing attention, such as: (a) Final device size is importantly increased due to the additional space required for the resistances; (b) the use of resistances limits materials’ strength and the obtained devices are normally weaker; (c) the activation process through heating resistances is not homogeneous, thus leading to important temperature differences among the polymeric structure and to undesirable thermal gradients and stresses, also limiting the application fields of shape-memory polymers. In our present work we describe interesting activation alternatives, based on coating shape-memory polymers with different kinds of conductive materials, including textiles, conductive threads and conductive paint, which stand out for their easy, rapid and very cheap implementation. Distributed heating and homogeneous activation can be achieved in several of the alternatives studied and the technical results are comparable to those obtained by using advanced shape-memory nanocomposites, which have to deal with complex synthesis, processing and security aspects. Different combinations of shape memory epoxy resin with several coating electrotextiles, conductive films and paints are prepared, simulated with the help of thermal finite element method based resources and characterized using infrared thermography for validating the simulations and overall design process. A final application linked to an active catheter pincer is detailed and the advantages of using distributed heating instead of conventional resistors are discussed. Full article
(This article belongs to the Special Issue Shape Memory Materials)

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