Shape Memory Effect Research Papers

This special issue addresses the possible connections and mutual benefits of examining together two analytic concepts – memory and periphery. These concepts receive much attention in various scholarly discussions, yet they have done so... more

are tabs for Home (taking the user back to the main page), Disability and Difference (outlining the project rationale), Stories (a statement describing the importance of life stories for sharing experience), Reflections (calling on audiences to think about common themes such as love, community and self-esteem), Accessibility (to select viewing options to facilitate the use of the site by the visual and audio impaired), and Contact (to contact a project practitioner). On the left-hand side are the names of fourteen artists—one of whom has chosen to remain anonymous—and links to their series of work produced within the ENMDD project. This turn to self-reflexivity and self-esteem can be mapped across wider neoliberal and postfeminist discourses, where neoliberalism operates as a “mobile, calculatec technology for governing subjects who are constituted as self-managing, autonomous and enterprising” and postfeminism as the media terrain in which political engagements become subservient and sometimes evacuated in favor of reflexive explorations of identity, body, choice, individualism and self-transformation issues (Gill and Scharff. 2013:5). On the home page of the ENMDD website, an indication of the meaning of the project title is provided: “En-vi-sion: To picture in the mind, to imagine possible.’ The contours again appear interior, rather than community or collectively orientated While the MoP USA site posits shared social memories as a resource for building empathetic routes to equality and social justice, the ENMDD website suggests more softly that “Some of the stories and photos ask others to explore their own responses tc

Figure 1. Museum of the Person USA website (www.museumoftheperson.org, January 2014).

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Magnetically controlled shape memory effect in Ni 2MnGa intermetallics

by J. K. HUG

1997, Scripta Materialia

Magnetocrystalline anisotropy energy favors magnetization along certain crystallographic axes called directions of easy magnetization. When the external magnetic field is applied, the magnetization tends to turn from the easy directions of the unit cells to the direction of the external magnetic field. If the anisotropy energy is high and the energy of twin boundary motion is low, the magnetization turns the unit cells of one twin variant into another as the magnetization turns to the direction of the external field. Magnetization then remains in the easy direction in the turned unit cells. This phenomenon es- sentially differs from magnetostriction in which magnetization rotates to the field direction without changing the unit cell orientations. Magnetic-field-induced turning of the unit cells of one twin variant into another that results in a strain of the actuator material is possible if

Figure 4. Strains induced by the magnetic field H applied in the [110] and [001] directions. The strain was measured in the [001] direction. The measurements were performed at 283 K (left) and at 265 K (right). OV) bAtw ORE SEE POEL OEE VV REAWwEh CL a — We Yws PIWhotiw Gb oO AS AW VN Vid LE 446: Tv Figure 4 also shows the contraction of the sample induced by the magnetic field at 265 K. The sample was first cooled from room temperature to 265 K in the absence of the magnetic field, which resulted in the formation of non-preferentially oriented martensite. As the magnetic field of 10 kO« was applied in the [001] direction, the material contracted by as much as 1.3 x 10°. This value is abou 10 times higher than magnetostriction measured at 283 K. That portion of the strain which remains after returning the field to zero is denoted by Ly. The recoverable portion of the strain is about 10°. The strains were also measured for the field direction [110]. Before that measurement, the sample was heated to room temperature and cooled back to 265 K to remove the preferentially oriented twir structure (denoted Lt) produced by the application of the field in [001] direction in the previous meas: urement. The strains measured in the field directed along [110] are observed to be substantially smaller than those induced by the [001] field, as shown in Fig. 4. The difference in the field needed to initiate the strain for the two field orientations is a reflection of the sample shape and crystallography. In the

The martensitic transformation occurs at 275 K on cooling, and it causes a strain of -2 x 10°. Dur- ing heating the reverse transformation takes place at 281 K. The strain induced by the martensitic transformation during cooling in the applied magnetic field of 10 kOe is 1.45 x 10°. This value is about 7 times larger than the strain induced in the absence of the field. This strongly suggests that the maenetic field aligns the twin structure of the transforming martensite. The difference between the

Figure 2. Magnetically induced growth of the twin variant which is in favorable orientation to the external magnetic fielc (Hy < Hh). AO UY CIPI Sy IVYUUOU LUE POULISTILIE Ut CVV OULU LU tall a Ola! oid (by UMIVIUUe WIC Te chanical work done in the matrix) [5,6]. W is the work done by the actuator material. Appropriate field energies E required for driving the actuators are Ux > E> E,+ W. Control of the shape memory effect by a magnetic field is expected to be possible in several ferro- magnetic materials. In some alloys twin boundaries or martensite interfaces are highly mobile. Growth of the martensite plates by low magnetic fields was recently demonstrated in an Fe-33.5Ni alloy [5,6]. Magnetic-field-induced shape changes attributed to the reorientation of the twin structure were previ- ously observed in ferromagnetic steels that exhibit a shape memory effect [8]. As the reorientation of

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Single pile simulation and analysis subjected to lateral load

by Jasim M Abbas

2008, Elect. J. Geotech. Eng

The results of the 3D finite element analysis on the behavior of single pile under lateral loadings are presented in this paper. The effect of pile shape for both circular and square cross-section on pile response was investigated. In... more

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Effect of Thermal Cycling on the Transformation Temperatures of a Ni-Ti Shape Memory Alloy

by João Paulo H G Canejo and

2004, Materials Science Forum

The effect of thermal cycling on the transformation temperatures was investigated in TimNi alloys which were subjected to various types of thermo-mechanical treatments.

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Shaping an Origami shading device through visual and thermal simulation

by Francesco Fiorito and

2015

This paper presents the first results of a research work aimed at the optimisation of a shading system through parameters of visual comfort – Useful Daylight Illuminance (UDI), Daylight autonomy (DA) and Daylight Glare Probability (DGP) –... more

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An overview of vibration and seismic applications of NiTi shape memory alloy

by I. Bar-on and

2002, Smart Materials and Structures

Shape memory alloys (SMAs) exhibit peculiar thermomechanical, thermoelectrical and thermochemical behaviors under mechanical, thermal, electrical and chemical conditions. Examples of these materials are Cu-based SMAs, NiTi SMAs, ferrous... more

Figure 1. Schematic diagrams of (a) stress-free temperature-induced phase transformation, and (b) effect of the applied stress on temperature-induced transformation.

Figure 2. Schematic diagrams of (a) isothermal stress-induced phase transformation, and (b) transformation stresses versus temperature.

Figure 3. Schematic diagrams of (a) free recovery, (b) restrained recovery and (c) controlled recovery.

Figure 4. (a) Schematic of internal yield and recovery, (b) pseudoelastic hysteresis.

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Shape memory behaviour in auxetic foams: Mechanical properties

by Fabrizio Scarpa

2010, Acta Materialia

Shape memory is the property of a material to remember its original shape despite subsequent plastic deformation. The exposure to specific temperature profiles induces a shape memory effect on auxetic (negative Poisson's ratio) foam... more

Fig. 1. SEM images of: (A) conventional grey open-cell foam; (B) conventional blue open-cell foam.

Fig. 5. Tangent modulus vs Poisson’s ratio resulted from the compressive (A) and tensile (B) loading related to the conventional, first auxetic, returned and second auxetic phases.

Fig. 2. SEM images of: (A) returned grey open-cell foam; (B) returned blue open-cell foam. The label indicates where kinking of the cell wall is visible. The results of a Student’s ¢ test show that all the tangent modulus values in the second auxetic phase are markedly lower (probability <0.0001) in comparison with those of the first auxetic phase, showing average values of 59% and 40% smaller in the compressive and tensile tests respec- tively. However, the Poisson’s ratio results do not show sig- nificant differences (probability of approximately 0.28) between the auxetic phases, with values ranging between —0.06 and —0.23 in compression and —0.09 and —0.26 in tension. The specimens returned from the auxetic phase to their native dimensions lost their auxetic properties as expected, showing positive Poisson’s ratio values between Quasi-static cyclic tests in compression and in tension were performed in order to mechanically characterize each specimen. The mean values of v.,, E, and energy dissipa- tion for each group are shown in Table 3. Fig. 5A and B shows the behaviour of the tangent modulus vs the Poisson’s ratio resulting from both compressive and tensile tests respectively for all the different families. The errors associated with the average tangent modulus for the differ-

Fig. 7. Final density ratio vs tangent modulus resulted from the compressive and tensile loading related to the first auxetic, returned and second auxetic phases. Figs. 7 and 8 show the correlation between the final den- sity ratio (FDR) vs the tangent modulus (£) and the Pois- son’s ratio respectively for the foam series constituted by the first auxetic, returned and second auxetic phases. All the mechanical properties were identified with a 95% confi- dence (Student’s ¢ test). In Fig. 7, the error bounds of the average tangent modulus were +6.8 kPa, +23.7 kPa and +3.2 kPa. The FDR error bars were +0.3, +0.04 and

Fig. 3. SEM images of: (A) first auxetic grey open-cell foam; (B) first auxetic blue open-cell foam.

Fig. 4. SEM images of: (A) second auxetic grey open-cell foam; (B) second auxetic blue open-cell foam

Fig. 6. Dissipation of energy vs Poisson’s ratio resulted from the compressive (A) and tensile (B) loading related to the conventional, first auxetic, returned and second auxetic phases. d t Fig. 6A and B shows the comparison between the energy issipation and the Poisson’s ratio from the compressive and tensile tests. The results related to the various speci- mens appear to group in clusters of the same phase. Using he Student’s ¢ test, the average energy dissipation per unit volume (Fig. 6A) was identified with a confidence of 95%, with error bounds of +0.049 mJ cm~*, +0.029 mJ cm7?, +0.016 mJ cm~* and +0.083 mJ cm~? for the series with the following sequence (conventional, rst auxetic, returned and second auxetic phases). The Poisson’s ratio was determined also with 95% confidence, with error bars of +0.08, +0.02, +0.06 and 0.02. Similar considerations are valid also for the data shown in Fig. 6B, with the error bounds associated with the average energy dissipation being +0.272 mJ cm~?, +0.010 mJ cm~*, +0.018 mJ cm? and +0.024 mJ cm. The Poisson’s ratios error bars were 0.07, +0.02, +0.08, and +0.02 for the series in the sequence adopted. For the compressive tests (Fig. 6A), he auxetic phase specimens form two tightly packed clus- ers underlining a great consistency of the results in term of Poisson’s ratio, with the first auxetic phase more correlated han the second auxetic phase. In contrast, the native and returned specimens form two large clusters less densely packed in comparison with the auxetic versions. In tension Fig. 6B), the reverse is apparent with the auxetic speci- mens forming more compact groups than the conventional

Mean results gathered from the quasi-static tests on the specimens in the different phases. Table 3 trend of the results shows that the values of Poisson’s ratio, tangent modulus and dissipated energy are larger in magni- tude under tension loading rather than compression (Table 3) with the exception of the first auxetic phase (tangent modulus and dissipated energy larger under compressive loading). However, performing a non-parametric Kruskal Wallis test (akin to analysis of variance) [42], no significant differences were found in the results of Poisson’s ratios comparing within each test state (i.e. compressive and ten- sile loading), a result confirmed using the non-parametric Mann-Whitney method [43]. Similar results were also 0.05 and 0.74 and tangent modulus up to one order in mag- nitude larger than their auxetic phase (Table 3). The returned specimens, compared with their native forms, had mean values of Poisson’s ratio 15% and 24% lower in compression and tension respectively. Conversely, in compression the native foam showed a mean tangent mod- ulus 33% lower than the returned specimens. No significant differences were found for the results from the tensile tests. A marked difference of Poisson’s ratio was found between auxetic and native-returned specimens, being negative and more positive with respect to original values. The general

Fig. 8. Final density ratio vs Poisson’s ratio resulted from the compressive and tensile loading related to the first auxetic, returned and second auxetic phases.

Details about the conversion of the specimens into the auxetic phases. Table 2

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The effects of vacuum induction melting and electron beam melting techniques on the purity of NiTi shape memory alloys

by Jorge otubo

2006, Materials Science and Engineering A-structural Materials Properties Microstructure and Processing

The usual process to produce NiTi shape memory alloys is by vacuum induction melting (VIM) using graphite crucible that contaminates the bath with carbon. The contamination by oxygen comes from residual oxygen inside the melting chamber.... more

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Micro artificial muscle fiber using NiTi spring for soft robotics

by Matt Jolda

2009, … Robots and Systems …

For a new class of soft robotic platforms, development of flexible and robust actuators is quintessential. Remarkable resilience, shape memory effect, high energy density, and scalability are attributed to nickel titanium (NiTi) making it... more

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Chromogenic Photonic Crystals Enabled by Novel Vapor-Responsive Shape-Memory Polymers

by Baeck B Choi

2015, Advanced Materials

Figure 1. Schematic illustration showing the SM effects of the new vapor-responsive SMP. a) Thin macroporous SMP photonic crystal with 3D ordere structure can diffract light with specific wavelengths. b) The unusual “cold” programming process deforms the ordered macropores into disordere array with rough surface and no light diffraction. c) The recovery of the permanent photonic crystal structure can be triggered by exposing the deforme membrane to various organic vapors (e.g., acetone).

Figure 4. Normal-incidence optical reflection spectra comparing a macroporous SMP membrane with 280 nm macropores dried out of water, liquid ethanol, and acetone vapor. The calculated spectrum using a SWA model is also shown to compare with the experimental results. reflection spectra obtained from a water-dried SMP membrane with 280 nm macropores (black line), and the same sample after exposed to acetone vapor (red line) and liquid ethanol (blue line). No apparent Bragg diffraction peaks are shown in the spectrum of the water-dried sample, while distinct dif- fraction peaks with well-defined Fabry-Perot fringes are pre- sent in the spectra of the samples triggered by acetone vapor and liquid ethanol, confirming the high crystalline quality of the recovered macroporous photonic crystals.'*! Additionally,

Figure 6. a—c) Photographs showing a macroporous SMP membrane exposed to acetone vapor above liquid acetone at different locations. d) Norma incidence optical reflection spectra obtained from a macroporous SMP membrane exposed to acetone vapors with different partial pressures. The ins shows dependence of In P versus the reciprocal of the radius of curvature of the condensed acetone films. The pressure is in units of “mm Hg” an the radius of curvature is in unit of nanometer.

Figure 5. a) Normal-incidence optical reflection spectra obtained from a macroporous SMP membrane with 280 nm macropores exposed to acetone vapor for ten times. b) Normal-incidence reflection spectra of the same sample after drying out of water for ten times. c) Reflection amplitudes of the spectra in (a) and (b) taken at 500 nm wavelength.

Table 1. Roughness of 10 pm x 10 pm AFM scan area of SMP sample surface.

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Shape recovery behaviour of NiTi strips in bending: experiments and modelling

by Raffaella Rizzoni

2013, Continuum Mechanics and Thermodynamics, 03/2013; 25(2-4):207-227. DOI:10.1007/s00161-012-0242-0

We present a theoretical and experimental investigation of the bending recovery performances for a commercial NiTi shape-memory alloy strip. We evaluate the mechanical properties and the shape setting parameters, and estimate the... more

Table 2 Material properties estimated from uniaxial tensile tests at 25 °C and 150 °C. Table 3 Curvature values measured in shape recovery tests on strips with memorised curvature of 12.50 m7?.

Fig. 14 Single-variant martensite volume fraction (left, continuous line), multi-variant martensite volume fraction (left, dot-dashed line), and residual stress (right) after bending and unloading in simulation I.

Fig. 13 Moment-curvature response in simulation II.

Table 4 Curvature values measured in shape recovery tests on strips with memorised curvature of 57.01 m7?.

Fig. 17 Evolution of the residual stress during shape recovery in simulation II.

Shape recovery behaviour of NiTi strips in bending: experiments and modelling Fig. 7 Single-variant martensite volume fraction (left, continuous line), multi-variant martensite volume frac- tion (left, dot-dashed line), and residual stress (right) after bending and unloading in simulation I.

Fig. 4 Moment-curvature response during uniform bending in the martensitic phase.

Shape recovery behaviour of NiTi strips in bending: experiments and modelling

Table 6 Parameters of the residual volume fractions and stress distributions calculated in the two simulations

Fig. 11 Evolution of the single-variant martensite volume fraction (continuous line) and the multi-variant martensite volume fraction (dot-dashed line) during shape recovery in simulation I.

These expressions, chosen so as to take into account (25-27), are explicit in the variable z. On the other hand, the dependence on the temperature is unknown because the function T + x(T) describing the evolution of the beam curvature is also unknown. This function can be calculated by imposing the condition of equilibrium (24) to hold true at each T > Ag. Substituting (48) into (24), after few calculations, we obtain the following nonlinear equation in x : where we have omitted the dependence upon T for the sake of clarity. Note that in (49), the unknown x also enters through z+, 29 and zm (see (39), (40) and (45)). In the next section, after numerically solving (49) with respect to x for assigned values of the temperature T, we substitute the result into (39), (40) and (45). The resulting curvature values, substituted back into (46-48), allow to calculate the evolution of the martensite volume fractions and of the stress. So far we have not enforced the incremental conditions (5) of activation of the phase transforma- tions. We now discuss a set of conditions sufficient to ensure the validity of the conditions (5) and which can be verified a posteriori after numerically solving (49). Let T > Ag and let (zo(T), 24 (T)) C Is(T), be the set of points at which the phase transformations $,M — A occur in traction. Note that, in view of (48), the appropriate activation condition at a generic point z € (zo(T), z4(T)) is

Fig. 9 Evolutions of the transformation fronts z, (continuous line), z_ (——~ — — — (—— — ——) during shape recovery in simulation I.

Fig. 2 DSC heating (red line) and cooling (blue line) curves and the measurement of transformation temper- atures of the alloy.

Fig. 15 Theoretical evolution of the curvature during shape recovery in simulation II and comparison with experimental data drawn from table 4.

Table 5 Values of curvatures and bending moments in the two simulations.

Fig. 19 Evolution of the austenite volume fraction during shape recovery in simulation II.

Fig. 18 Evolution of the single-variant martensite volume fraction (continuous line) and the multi-variant martensite volume fraction (dot-dashed line) during shape recovery in simulation II.

Fig. 5 (a) Residual stress distribution and (b) single-variant martensite fraction distribution in the upper half of the cross-section after uniform bending in the martensitic phase.

Fig. 6 Moment-curvature response in simulation I.

Fig. 10 Evolution of the residual stress during shape recovery in simulation I. Raffaella Rizzoni et al.

Fig. 8 Theoretical evolution of the curvature during shape recovery in simulation I and comparison with experimental data drawn from table 3.

Table 1 Transformation temperatures and latent heats per unit mass (AH) determined by DSC.

Fig. 12 Evolution of the austenite volume fraction during shape recovery in simulation I. Shape recovery behaviour of NiTi strips in bending: experiments and modelling

Fig. 1 Percentage of recovered shape after heat treatments performed for 25 minutes at different temperatures. Shape recovery behaviour of NiTi strips in bending: experiments and modelling

Fig. 3 Geometry of the curved beam modelling the NiTi strip. Shape recovery behaviour of NiTi strips in bending: experiments and modelling

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Theoretical and numerical modeling of solid–solid phase change: Application to the description of the thermomechanical behavior of shape memory alloys

by quoc nguyen

2008, International Journal of Plasticity

The mechanical behavior of a solid capable of undergoing internal phase change is considered. Reversible and dissipative constitutive equations are established within the framework of generalized standard materials with internal... more

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Multiple healing effect of thermally activated self-healing composites based on Diels–Alder reaction

by Thomas Hahn

2010, Composites Science and Technology

a b s t r a c t Self-healing composites using a thermally mendable polymer, bis-maleimide tetrafuran (2MEP4F), based on Diels-Alder reaction and electrical resistive heating were fabricated using a vacuum assisted injection molding... more

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Thermomechanics of the shape memory effect in polymers for biomedical applications

by Kristi Anseth

2005, Journal of Biomedical Materials Research Part A

We examine the shape memory effect in polymer networks intended for biomedical, and specifically cardiovascular, applications. The polymers were synthesized by photopolymerization from a tert-butyl acrylate monomer with a diethyleneglycol... more

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Modelling of SMA materials: Training and two way memory effects

by Elio Sacco

2003, Computers & Structures

The present work addresses a simple and effective one-dimensional model able to reproduce the superelastic behaviour as well as the shape memory effect. In particular, it considers the transformations from austenite to single variant... more

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One-dimensional constitutive SMA model with two martensite variants: Analytical and numerical solutions

by Raffaella Rizzoni

2013, European Journal of Mechanics - A/Solids. 07/2013, 40:166–185. DOI:10.1016/j.euromechsol.2013.01.007

This paper deals with the one-dimensional modeling of a shape memory alloy (SMA) in order to reproduce the special thermo-mechanical response of the material. In particular, new analytical solutions are developed using a simple... more

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A three-dimensional model describing stress-induced solid phase transformation with permanent inelasticity

by Ferdinando Auricchio and

2007, International Journal of Plasticity

The employment of shape memory alloys (SMA) in a large number of applications in the fields of aeronautical, biomedical, and structural engineering has been the motivation for an increasing interest in the direction of a correct and... more

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Modeling and simulation of an artificial muscle and its application to biomimetic robot posture control

by Koray Safak and

2002, Robotics and Autonomous Systems

The shape memory effect exhibited by Nitinol wire can be utilized to construct an artificial muscle. The muscle is activated by an electric current, which produces heat and initiates a phase transformation. The Nitinol artificial muscle... more

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On the origin of the improvement of shape memory effect by precipitating VC in FeeMneSi-based shape memory alloys

by Dierk Raabe

2018, Acta Materialia

We studied the role of VC precipitation in improving the shape memory effect (SME) of the as-solution treated FeeMneSi-based shape memory alloys by examining the microstructures developed during aging and deformation using transmission... more

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Potential applications of shape memory alloys in seismic retrofitting of an exterior RC beam-column joint

by Daniel McCrum and

2015, SECED 2015 Conference: Earthquake Risk and Engineering towards a Resilient World

Shape memory alloys (SMAs) have the ability to undergo large deformations with minimum residual strain and also the extraordinary ability to undergo reversible hysteretic shape change known as the shape memory effect. The shape memory... more

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FUNDAMENTAL CHARACTERISTICS AND DESIGN METHOD FOR NICKEL-TITANIUM SHAPE MEMORY ALLOY

by István Mihálcz

2001, paper

Shape memory alloys (SMA), because of their unique mechanical characteristics and shape memory effect (SME), have been widely used as force and displacement actuators in many fields [DUERING et al, 1990]. In the industrial applications,... more

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Factors influencing shape memory effect and phase transformation behaviour of Fe–Mn–Si based shape memory alloys

by Druce Dunne and

1999, Materials Science and Engineering: A

The objective of this research work was to investigate the factors influencing the shape memory effect and phase transformation behaviour of three Fe-Mn-Si based shape memory alloys: Fe-28Mn-6Si, Fe-13Mn -5Si-10Cr-6Ni and... more

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Austenite stability in Fe–Mn–Si-based shape memory alloys

by Brian Monaghan

2007, Journal of Alloys and Compounds

The stability of austenite in a number of Fe–Mn–Si-based shape memory alloys has been investigated. It was found that a grain boundary precipitate of BCC structure is formed over a wide range of alloy compositions and heat treatment... more

Fig. 6. Tensile behaviour of Alloy #1 after (a) austenitizing at 1000°C for 1h and (b) austenitizing at 1000 °C followed by 4h at 700°C.

Fig. 7. SEM micrographs of fracture surfaces resulting from tensile testing of Alloy #1 shown in Fig. 6. (a) As-austenitized condition. (b) Heat treated for 4h at 700°C. of 0.3 im, is shown in Fig. 8b for all 40 indents, and number 21 is indicated by an arrow. The grain boundary phase in this case does have a slightly higher hardness value than the grain inte- rior at either side. However, the average hardness of the grain

Nominal alloy compositions in weight percentage measured using EDS Table 2 in an attempt to form fine austenite strengthening precipitates of carbide or intermetallic Ni3Al.

Explanation of the labels used in Fig. 9 Table 5

Fig. 9. (a) An isopleth section through metal compositions “start” (Fe-0.0353% C) and “end” (Fe—0.0353% C, 13.25% Mn, 5.05% Si, 7.05% Ni, 8.7% Cr) showing the equilibrium phase stability. The phase field denoted A through to E are A=BCC_A2+CEMENTITE, B (and C)=BCC_A2+FCC_A1 + M7C3, D=BCC_A2 + CUB_A13 + FCC_A1 + M23C6 + CR3SLA15+ SIGMA and E=BCC_A2+CUB_A13 + M23C6 + CR3SI_A15+SIGMA. (b) An isopleth section through metal compositions “start” (Fe—0.0353% C) and “end” (Fe—0.0353% C, 13.25% Mn, 5.05% Si, 7.05% Ni, 8.7% Cr) where carbide and intermetallics phases were excluded from the calculation. This is a metastable phase diagram. The BCC_A2 +CBCC_A12+FCC_A1 phase boundary denoted by the line and circular symbols is only considered provisional. Also included in this diagram is the BCC_A2 +CBCC_A12+FCC_A1 phase boundary as calculated for a similar but non-carbon containing alloy system. This is shown on the diagram as a line with triangular symbols.

Fig. 5. (a) Shape memory behaviour of alloys in the austenitized condition, measured in bending. The curves labelled 1—3 are further discussed in the text. (b) Shape memory behaviour, measured in bending, of Alloy #4 after the indicated heat treatments. Curve 2 from (a) is reproduced in (b).

2 Measured using inert gas fusion. Composition of the base alloy (Alloy #1) measured using atomic emission spectroscopy Table | Table 3

* A, estimated by the onset of shape change. Transformation temperatures for each of the alloys measured using DSC

Fig. 4. TEM diffraction patterns of grain boundary precipitate in Alloy #3 after heat treatment at 700°C for 15h. Since the grain boundary preci by XRD, selected samp diffraction in the TEM. boundary precipitate in a ite and the precipitate p 8.8A. Alloy #2 1 of the ot pitate could not be identified es were analysed using selected area was not further investigated because it’s microstructure is inappropriate for SME. The grain her alloys was found to be the same. Fig. 4 shows the electron diffraction patterns of austen- hase in A loy #3. The grain boundary phase was identified as BCC phase, with a lattice parameter of The mechanical behaviour of Alloy #1 was investigated in more detail, and the stress-strain curves obtained by tensile testing are shown in Fig. 6. There were two different heat treat- ment conditions tested; Fig. 6a is from a sample of Alloy #1 in the as-austenitized condition, and Fig. 6b shows the same alloy after austenitizing followed by 4h at 700°C. As can be seen, heat treatment at 700 °C increases the yield point and ten- sile strength, and decreases the elongation to failure from 80 to 64% strain. The fracture surfaces from these two tensile tests are shown in Fig. 7. After the 700°C heat treatment the alloy

Fig. 1. Optical micrographs of (a) Alloy #1 and (b) Alloy #2 after austenitizing heat treatment for 1h at 1000°C. The lighter etching phase in (b) is ferrite. Fig. la shows an optical micrograph of the base alloy, Alloy #1, after annealing at 1000°C for 1h and water quenching. The structure is fully austenite and the austenite grain size was

Fig. 3. XRD of (a) Alloy #1 after heat treatment at 700 °C for 4h, and (b) Alloy #2 after austenitizing heat treatment for 1h at 1000°C followed by cold water quench: ¢=hexagonal martensite, y = fcc austenite, a =bec ferrite.

Fig. 8. Nano-indentation of the parent and grain boundary phases measured using UMIS nano-indentor. A SEM micrograph of the indents after etching is shown in (a). The hardness of all indents are shown in (b), and indent 21 identified in (a) is arrowed in (b). The filled squares represent indents that were on the precipitate. The hardness measurements were taken at a penetration depth of 0.3 wm.

TEM EDS of grain boundary precipitates in weight percent (average of three or more particles/matrix measurements)

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A review on the machining of Nickel-Titanium shape memory alloys

by Angelos P Markopoulos and

2015, Reviews on Advanced Materials Science, 42(1), pp. 28-35

In this review paper the machining performance pertaining to the processing of Nickel-Titanium shape memory alloys is presented. High accuracy products for specialized applications need to be machined in order to be shaped to their final... more

Fig.3. Typical shear stress-shear strain curve.

Fig.1. Stress-temperature (left) and stress-strain (right) curves that describe the SE behaviour.

wedge with the surface of the workpiece, given tha there is a relative movement between them. These machining operations include turning, milling anc drilling among others and are usually referred as conventional machining processes. Abrasive pro- cesses such as grinding are also part of cuttinc processes of great importance in contemporary in- dustry. Other non-conventional machining operations that may or may not include physical contact be- tween cutting tool and workpiece or may not have é cutting tool in the same sense as conventional pro- cesses or utilize thermal or chemical energy for re- moving material from workpiece, are electrodischarge machining, laser machining, wa:- ter jet machining and electrochemical machininc just to name some.

The shape memory effect refers to the recovery of plastic strains in an initially deformed in low tem- perature material, through the mechanism of auste- nite-martensite phase transformation. The shape in which the material returns to, after the phase trans- formation, can be memorized by the material through its deformation in high temperature, at austenite phase. Thus, a material deformed in the martensite phase can recover its plastic strain and return to its high-temperature shape via heating to the austenite phase. In other cases, the material can return to its low-temperature shape from the austenite phase via cooling to the martensite phase. In order to clarify the SME mechanism, Fig. 2 is given. In this graph a thermo-mechanical loading path in a stress-strain- temperature space is presented. It is worth notic- ing, that the below described phenomenon is the simplest case of the SME, termed as one-way shape memory effect or SME for short. The data for the graph of Fig. 2 represent the SME mechanism of a typical NiTi wire, tested under uniaxial loading.

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Laser welding of a NiTi alloy: Mechanical and shape memory behaviour

by Carmine Maletta

2005, Materials Science and Engineering: A

The present paper reports the effect of Nd:YAG laser welding on the mechanical and functional properties of Ni-51 at.% Ti alloy. The specimens were prepared from thin sheets and tested in martensitic conditions. The mechanical and shape... more

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Thermo-mechanical processing and the shape memory effect in an Fe–Mn–Si-based shape memory alloy

by Druce Dunne

2006, Materials Science and Engineering: A

The effect of cold rolling and annealing on the shape memory effect (SME) in an Fe-Mn-Si-based alloy has been studied. It has been found that the SME in these alloys can be significantly increased by the appropriate thermo-mechanical... more

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A finite element model for shape memory alloys considering thermomechanical couplings at large strains

by Daniel Juhre

2009, International Journal of Solids and Structures

In the present work we propose a new thermomechanically coupled material model for shape memory alloys (SMA) which describes two important phenomena typical for the material behaviour of shape memory alloys: pseudoelasticity as well as... more

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Synthesis and characterization of novel biodegradable polymers composed of hydroxycinnamic acid andD,L-lactic acid

by Mehdi Barikani

2001, Journal of Applied Polymer Science

Biodegradable polyurethane (PU) elastomers with potential for biomedical and industrial applications with tunable thermal properties were synthesized by the reaction of poly(e-caprolactone) and 4,4 0 -diphenylmethane diisocyanate and... more

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Texture evolution during thermomechanical treatments in Fe–Mn–Si shape memory alloys

by Jorge Malarria and

2008, Materials Science and Engineering: A

Texture evolution and shape memory behaviour were investigated in an Fe-30Mn-4Si (at.%) alloy showing the ␥↔ martensitic transformation. The alloy was subjected to different rolling and annealing treatments. Texture mapping and shape... more

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Cyclic behavior of shape memory alloys: Material characterization and optimization

by Jason McCormick

2006

2-1 Schematic view of a typical SMA microstructure: (a) multi-variant twinned martensite, (b) single variant detwinned martensite, (c) austenite.

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Characterization and mechanical properties of calcium silicate/citric acid-based polymer composite materials

by Azim Ataollahi Oshkour

International Journal of Applied Ceramic Technology

Optimal implants for bone tissue engineering require sufficient mechanical strength as well as apt bioactivity and biodegradability. Calcium silicate (CaSiO 3 -CS) ceramics have been studied for tissue engineering and implantation for... more

Table I. Porosity of Different Ratios of CaSiO3/ Poly (1.8-octanediol citrate) (POC) Composite

Fig. 4. Bending strength (left) and bending Young’s modulus (right) for different ratios of poly (1.8-octanediol citrate) (POC)

Fig. 5. Field emission scanning electron microscopy (FESEM) of different ratios of poly (1.8-octanediol citrate) (POC): (A) 30 POC wt%. (B) 40 POC wt%, (C) 50 POC wt%, and (D) 70 POC wt%.

3. Compressive strength (left) and compressive Young’s modulus (right) for different ratios of poly (1.8-octanediol citrate) (POC). Figure 3 indicates the compressive strength and compressive Young’s modulus of different CS/POC com- posites. It is observed that with increase in CS content up to 60 wt%, the compressive strength was greatly improved. However, increasing the amount of CaSiO, to 70 wt%, the compressive strength was decreased sig- nificantly which is due to the brittleness of composite. In this case, the majority of composites were made of the brittle component which brings about brittle composite. Fig. 2. Fourier transformation infrared (FTIR) of different ratio of poly (1.8-octanediol citrate) (POC): (A) pure POC wt%, (B) 60 POC wt%, (C) 50 POC wt%, and (D) 40 POC wt%.

Fig. 1. Thermogravimetric analysis (TGA) of different ratio of poly (1.8-octanediol citrate) (POC): (A) pure POC wt%, (B) 60 POC wt%, (C) 50 POC wt%, and (D) 40 POC wt%.

of polyster groups.'’ The aforementioned peaks are also found in other composites. The peaks at 2845 and 2917/cm signify the symmetrical stretching vibration of —CH; and —CH) groups that exist in polymer materi-

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Comparative assessment of two constitutive models for superelastic shape-memory wires against experimental measurements, R. Rizzoni, A. Chiozzi, M. Merlin and A. Tralli

by Raffaella Rizzoni

Two constitutive models representative of two well-known modeling techniques for superelastic shape-memory wires are reviewed. The first model has been proposed by Kim and Aberayatne in the framework of finite thermo-elasticity with... more

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Thermomechanical aspects of NiTi

by John Shaw

1995, Journal of the Mechanics and Physics of Solids

The uniaxial behavior of a nearly equiatomic NiTi alloy is studied experimentally. Experiments are conducted in a temperature and deformation regime in which the alloy exhibits the shape memory effect and pseudoelasticity. These... more

Fig. 13. Comparison of local and global stress-strain responses, strain histories and temperature histories for experiments in 70°C air and water at four displacement rates.

Fig. 18. Comparison of responses of as-received material (R phase) and material that had been quenched in liquid nitrogen (M phase) at three different temperatures.

Fig. 10. (a) Local stress-strain responses at four axial positions for 6/L = 4x 10-* s~', (b) corresponding strain and temperature histories.

Fig. 11. (a) Stress, strain and temperature histories at several axial positions for 6/L = 4x 107° s7', (b) x-1 diagram of significant events. 4.4.1. 6/L =4x10-> s~'. Figure 11 shows results from an experiment conducted

Fig. 17. (a) Measured transformation stresses as a function of temperature, (b) measured transformation strains as a function of temperature.

2.2.2. Deformation twinning and the shape memory effect. We now consider a similat isothermal uniaxial test carried out at 10°C shown in Fig. 3. In this case, the specimer was cooled to —196°C (in liquid nitrogen) and allowed to warm up to room tem- perature before being tested at 10°C. The microstructure of martensite produced ir this fashion differs from SIM. Lattices with a low degree of symmetry, such a: monoclinic, have energetically equivalent configurations, called variants, which are

Fig. 14. Transformation stresses in 70°C water and air at different displacement rates. nterface fronts, thereby approximating homogeneous deformation. Because of the ignificant increase in temperature, continuation of the transformation requires an ncrease in the applied stress. The combined effect of these interacting events is the tabilization of the transformation processes which is demonstrated by the monotonic lature of the stress-strain response and by the absence of significant strain jumps in he local strain history.

ahd OF8FL CI Vi GPP evsasitiawiy 7 /Y. Unloading from within the plateau is initially elastic and leaves behind intermixed martensite and austenite. Unloading from the end of the plateau (point b) results, at least initially, in elastic unloading of the predominantly martensite phase. Similar to the austenite instability during loading, martensite becomes unstable when the stress drops below a certain critical level (point b’, nucleation of austenite) and the materia! starts to transform back to austenite. Under displacement controlled unloading this

Fig. 9. (a) Stress and strain histories at four axial positions from an experiment conducted at a displacement rate of 6/L = 4x 10~*s~', (b) x-1 diagram of significant events.

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Structural transformations in Mn 2 NiGa due to residual stress

by Rajeev Ranjan

Powder x-ray diffraction study of Mn 2 NiGa ferromagnetic shape memory alloy shows the existence of a 7M monoclinic modulated structure at room temperature ͑RT͒. The structure of Mn 2 NiGa is found to be highly dependent on residual... more

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SHS of shape memory CuZnAl alloys

by Mohamed Amiour

2008, International Journal of Self-propagating High-temperature Synthesis

Aiming at preparation of shape memory alloys (SMAs), we explored the SHS of Cu1 − x Zn1 − y Al1 − z alloys (0.29 x y z

data. The CuZnAl alloys have a very large grain size, which makes them brittle. It is reported that the addi- tion of grain refiner (Ti or Zr) restricts the grain size, thus solving the brittleness problem [16, 17]. Figure 8 shows the microstructure of alloy 6 at a higher magnification (x1000). Here the gray color cor- responds to the dominant phase (with pores, cavities, and buffing streaks) which surrounds another lucid phase with weak open porosity. Generally, the contrast in all images confirms the existence of a phase respon- sible for the SME. Samples remain to be uniform and relatively dense. These results agree with the XRD

Fig. 2. Schematic of one-way and two-way memory effects [5]. In terms of the above mechanisms, SMAs are assumed to undergo a crystallographically reversible martensitic transformation. At high temperatures, the SMA exists as an austenite phase with a long-range ordering. Upon cooling down below the transformation temperature, austenite transforms to thermoelastic mar- tensite of varied structure, typically sheared platelets. Martensite deforms by twinning mechanism that trans- forms various structural forms to that one which can undergo maximal elongation alongside the applied force. The interfaces between platelets in the martensite phase slip very readily and the material is deformed at low applied stresses. The austenite phase has only one possible orientation, thus when heated, all of possible deformed structures of the martensite phase must revert to this one orientation of the austenite memory phase and the material recovers its original shape. In the two-way shape memory effect (TWSME), the material remembers two different shapes: one at low temperature and another at high temperature. SMAs exhibit the capability to recover a specific shape upon heating and then return to an alternate shape when

Fig. 1. Evolution of the martensite volume fraction vs. tem- perature: M, is the temperature at which martensite starts to form, M,the temperature at which conversion to martensite is complete, A, the temperature at which austenite starts to form, and A, the temperature at which conversion to austen- ite is complete [5].

Table 1. Basic properties of the elements used as reagents

R-type thermocouple. Burned specimens were cut ver- tically, impregnated with resin, and polished. The com- position of products was determined by XRD (INEL XRG3000, Ag, 1.5405 A), optical microscopy (Olym- pus BX51M, DP12) and scanning electron microscopy (JEOL, Model JSM 6400F).

Table 2. Synthesized alloys and their stoichiometry Table 3. Some process parameters for synthesis of CuZnAl alloys

Fig. 3. Composition diagram of CuZnAl alloys and the M, temperature [5].

Fig. 4. Experimental setup: (/) reaction vessel, (2) transpar- ent window, (3) sample, (4) graphite plate, (5) electric power source, and (6) to vacuum pump.

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Training effect in Fe-Mn-Si shape-memory alloys

by Yoshimi Watanabe

1993, Journal of Materials Science

The training effect in Fe-Mn-Si shape-memory alloys has been examined by length change and electrical resistivity measurements. After 13 deformation-heating cycles, it was found that the major recovery took place at a temperature lower by... more

Figure I (a) Crystallographic geometry of the primary shear system expected to operate in the present specimen. (b) Location of indenta- tion markings used for length change measurements.

Figure 2 Temperature dependences of CRSSs resolved on <112) {111} and <110) {111} shear systems.

Figure 3 Stress—strain diagrams obtained at room temperature be- fore and after repeated deformation—heating cycles. Cycle number: (O) 1, (A) 2, (G) 3, (©) 4, (@) 8, (A) 9, (MD) 13.

Figure 4 Fraction of recovery strain plotted against annealing temperature.

Figure 5 Variation of local strains induced by repeated tensile deformations at different locations of a specimen.

Figure 6 Optical micrographs taken on the (18 1) surface of the present specimen: (a) before deformation, (b) after the first deformation, (c) after the third deformation, (d) after the seventh deformation.

Figure 7 Electrical resistance versus temperature curves for a polycrystalline Fe~30 wt% Mn-6 wt% Si alloy. Run: (©) 1, (A) 8, (C4) 14

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Synergic effect of carbon black and short carbon fiber on shape memory polymer actuation by electricity

by Jinsong Leng

2008, Journal of Applied Physics

This paper presents a study on the effect of carbon black (CB) and short carbon fibers (SCFs) on shape memory polymer (SMP) actuation by applying electric current. The coexistence of CB and SCF electrically conductive networks, supporting... more

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SMA Numerical Modeling Versus Experimental Results: Parameter Identification and Model Prediction Capabilities

by Alberto Coda

2009, Journal of Materials Engineering and Performance

In this work, we briefly review the one-dimensional version of a well-known phenomenological shape memory alloy (SMA) constitutive model able to represent the main macroscopic SMA macroscopic behaviors (i.e., superelasticity and... more

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CARACTERIZACIÓN DE ALEACIONES DE TiNi CON MEMORIA DE FORMA MEDIANTE NANOINDENTACION INSTRUMENTADA

by mur tini

2007

El objetivo de este trabajo es caracterizar la transformación de fase termoelástica en aleaciones TiNi, mediante nanoindentación instrumentada. Para ello, se han preparado, en condición de pulido especular, muestras de aleaciones TiNi en... more

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Contrasting magnetic behavior of Ni50Mn35In15 and Ni50Mn34.5In15.5 alloys

by Vishal Tiwari

2010

We have studied the electrical resistivity, magnetization, and heat capacity of the off-stoichiometric Heusler alloys Ni 50 Mn 35 In 15 and Ni 50 Mn 34.5 In 15.5 as functions of temperature and magnetic field. The results show that the... more

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Effect of solution hardening on the shape memory effect of FeMn based alloys

by Yo Tomota

Scripta Metallurgica et Materialia

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A finite-deformation-based phenomenological theory for shape-memory alloys

by Prakash Thamburaja

2010, International Journal of Plasticity

In this work we develop a finite-deformation-based, thermo-mechanically-coupled and non-local phenomenological theory for polycrystalline shape-memory alloys (SMAs) capable of undergoing austenite $ martensite phase transformations. The... more

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Phenomenological Modeling of Shape Memory Alloys

by Marcelo Savi and

2008, AIP Conference Proceedings

Shape memory alloys exhibit two characteristic effects, viz., shape memory and superelasticity or pseudoelasticity, due to a reversible solid‐solid transformation brought about by either temperature or stress or both. The two important... more

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Effect of Heat Treatment Temperature and Heat Treatment Time on Properties and use of NiTi Shape Memory Implant Material

by Levent Öncel

2017, Effect of Heat Treatment Temperature and Heat Treatment Time on Properties and use of NiTi Shape Memory Implant Material

In this study, effect of heat treatment parameters, which is applied in order to achieve superelasticity and shape memory, on the nitinol microstructure was investigated. Nitinol is a commonly used material in cardiovascular and... more

Fig. 2. TTT diagram describing aging behaviour for Ti- 52Ni [6] Precipitation sequence for Ti-52Ni (at.%) was revealed as Ti, )Nij4-TipNi;-TiNi, by Nishida et. al in 1986. TTT diagram of Ti-52Ni is seen in Fig. 2 [6]. Ti;,Nij, was correctly determined as Ni,Ti; by further EDS analysis later [7].

Fig. 5. EDS analysis of precipitates in the sample heat treated at 540 °C for 10 minutes In these four heat treatment conditions, precipitates were determined as Ni,Ti; by EDS analyses. In EDS analyses, it was seen that chemical composition of the precipitates were close to NiyTi3. Previous studies also indicated that precipitates which were formed in these heat treatment conditions were Ni4Ti3[6, 12]. Fig.5 shows EDS analysis of precipitates in the sample heat treated at 540 °C for 10 minutes.

Fig. 7. EDS analysis of precipitates in the sample heat treated at 550 °C for 14 minutes

behaviour is seen in Fig. 1. In nitinol, if critical stress for slip is high enough (Critical Stress for Slip: A), material exhibits shape memory effect below austenite start (Ag) temperature, superelasticity occurs above A,temperature but full recovery of superelasticity shape change occurs above austenite finish (As) temperature. In nitinol, critical stress for slip is improved by precipitation hardening [4].

Vol. 4, Issue 1, January 2017 Fig. 6. (Continuum 2) Optical microscope micrographs of Ti-50.6Ni wires heat treated at 550 °C; (G) 14 minutes

Fig. 6. Optical microscope micrographs of Ti-50.6Ni wires heat treated at 550 °C; (A) 8 minutes and (B) 9 minutes In heat treatments applied at 550 °C between 8 and 14 minutes, precipitates were determined as NiyTi; by EDS analyses. Chemical composition of the precipitates was close to Ni,Ti; as in heat treatments applied between 540 °C and 570 °C. Previous studies also indicated that precipitates formed in these heat treatment conditions were NiyTis [6, 12].

Fig. 3. Optical microscope micrograph of Ti-50.6Ni wire supplied from the manufacturer Fig. 3 shows optical microscope micrograph of Ti-50.6Ni wires which were supplied from the manufacturer. Because of the standard wire production procedure, which includes cold drawing and subsequent annealing, its structure was composed of recrystallised grains [10].

y International Advanced Research Journal in Science, Engineering and Technology

Fig. 6. (Continuum) Optical microscope micrographs of Ti-50.6Ni wires heat treated at 550 °C; (C) 10 minutes, (D) 11 minutes, (E) 12 minutes and (F) 13 minutes Fig.7 shows EDS analysis of precipitates in the sample heat treated at 550 °C for 14 minutes.

TABLE IT MECHANICAL TEST RESULTS OF TI- 50.6NI SAMPLES HEAT TREATED AT DIFFERENT TEMPERATURES AND TIMES

Vol. 4, Issue 1, January 2017 Heat treatment was applied to nitinol wires in Nabertherm N 30/65 HA heat treatment furnace. Nitinol wires were heat treated at 540 °C, 550 °C, 560 °C and 570 °C for 10 minutes. Then, heat treatment was applied at 550 °C for 8, 9, 10, 11, 12, 13 and 14 minutes.

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Phase diagram kinetics for shape memory alloys: a robust finite element implementation

by L. Brinson

2007, Smart Materials and Structures

A physically based one-dimensional shape memory alloy (SMA) model is implemented into the finite element software ABAQUS via a user interface. Linearization of the SMA constitutive law together with complete transformation kinetics is... more

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A computational model for shape memory alloys

by Garrett Hall

2000, International Journal of Solids and Structures

An investigation into the computational aspects of a multi-well mixture approach to shape memory modeling is undertaken with the goals of determining its qualitative behavior as well as its eciency in a numerical setting. A basic rate... more

Fig. 5. Truss system configuration. Each bay measures 0.2 m square, with each bar having a cross sectional area of 0.000123 m? (0.00625 m radius).

Fig. 7. Simulation of truss system response to a mechanical-thermal closed cycle starting from the state € = ét = 3 and a tem- perature of 283 K. The circle denotes the start and finish points, while the path direction is indicated by the arrows. The structure is that of Fig. 5.

Fig. 3. Mechanical load cycle of TiNi bar under isothermal conditions. The solid, dashed, and dash—dot lines indicate runs at 263, 293, 323 K. The + points indicate experimental data by Liang as per Brinson and Lammering (1993). presented first. Then, as a test of the constitutive algorithm under spatially inhomogeneous loading patterns, a truss system similar to that suggested by Govindjee and Kasper (1999) is run. The final examples are of a shape memory beam undergoing large rotations, a simulation of an SMA mechanism, and a plastically deformed shape memory beam.

Fig. 4. Thermal load cycle of TiNi bar under isostress conditions. The solid, dashed and dashed—dot lines indicate loads of 100, 300, and 500 MPa, respectively.

Fig. 6. Simulation of truss system response to mechanical cycling. The progression from left to right and top to bottom shows iden- tical load paths at 253, 283, 313, 333, 353, and 373 K. The structural system is shown in Fig. 5. The second series of tests considered an isostress thermal load cycle of a one-dimensional bar under several values of an applied tension. The results of the three runs, loaded at 100, 300 and 500 MPa, respectively, are shown in Fig. 4.

Fig. Al. Geometric interpretation of constraint set. The * locates the projection of a random point into the plane €*+é~+é* =1, with the bounded triangular area indicating the interior of the constraint set. Once in the plane, a solution satisfying the remaining constraints is found by a closest point projection to the constraint surface. the initial techniques described by Parlett (1976) for computing functions of a triangular matrix have since been refined to largely overcome such difficulties. While the cost of a Schur decomposition is still conservatively O(25(v)*) (or O(25(v — 1)*) with reduction in dimensionality) (Demmel, 1997), this coefficient may prove to be smaller than the previous estimate when |IQll,, is large.

Approximate material properties for TiNi Table 1

Fig. 1. Graphical interpretation of barrier energy for a fixed stress value.

Fig. 8. Beam simulation: mechanical cycles at various temperatures. Initial conditions (from top to bottom) were & = é* 253 K, €°=1 at 313 K, and €*°=1 at 373 K. Nie

where once again the time subscripts (m + 1) have been neglected in the interest of notational clarity. The remaining terms 0),,/00 and 0b,,/0S must be worked out individually based on the particular values of a and f indicated in Eq. (30), and as such are not explicitly written here. However, by allowing H and L to, respectively, represent the compilation of the first and second terms in Eq. (B6), the variation of the volume fractions is given by where Z is the tangent of the chosen integration method. The evaluation of 6Q=@At6Q requires an expression for the variation of each unique term comprising Q. Based on Eq. (29) and the relation (bop)n + 1 = bap (Sn + 1. On + 1), the symbolic evaluation of a typical term is carried out in the following manner

Fig. 2. Plot of the norm of the residual function over the phase space domain. The upper figure provides a contour plot of the sur- face shown below.

Fig. 9. Beam simulation: thermo-mechanical cycle with initial conditions & = é+ = 3 at 253 K. The circle marks the start and fin- ish points along the path; the arrows indicate the direction traveled.

Fig. 11. Shape memory beam simulation incorporating plasticity. The bottom deflected shape shows the residual deformation induced by the mechanical load/unload cycle, whereas the intermediate configuration demonstrates partial recovery following a thermal cycle. The original geometry is given at the top; see Fig. 12 for the response curves. Note that the region of the cantilever beyond the zone of plasticity completely recovers the initial shape following the thermal cycle.

Fig. 12. Thermomechanical cycling of a shape memory beam accounting for plasticity. The circled points coincide with the deflected shapes given in Fig. 11. Despite the large residual deformation following unload, over 50% of the residual deformation is recovered by the thermal cycle.

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Improvement in shape memory in magnesium niobate modified PZST

by Abhishek Pathak

2010, Ceramics International

A modified lead zirconate stannate titanate system (PZST) has been studied for shape memory effect. Addition of magnesium niobate (MN) slows down the dipole relaxation process, leading to increased ($3-fold improvement) remnant strain in... more

Fig. 1. Variation of dielectric constant (¢’) of unmodified and modified PZST composition with temperature (30 °C < T < 210 °C), at different frequencies (1 kHz < f < 500 kHz).

Fig. 4. X-ray diffraction of modified composition before and after application of electric field.

Fig. 3. Field-induced strain loops of 0.99PZST-0.01PMN composition at different temperatures.

Fig. 2. P-E hysteresis loops of 0.99PZST-0.01PMN composition at different temperatures.

* The reported value of remnant strain is for 50 Hz. > The reported value of remnant strain is for 0.05 Hz. A comparison of relevant properties of Pb-based systems with those obtained from present work. Table |

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Processing methodology to embedding NiTi shape memory fibers into a polymer-based composite plate

by Wanderley Amorim

The objective of this work was the development of a processing methodology to embedding NiTi fibers into a polymer-based composite plate. A carbon fiber reinforced polymer (CFRP) prepreg and NiTi thin wires were used. A uniaxial hot press... more

Figure 6 - Rectangular CFRP test specimens with dimensions of 153 x 24 mm without embedded wires.

Figura 9 - Storage modulus as a function of temperature for the CFRP with embedded NiTi wires.

Figure 4. Dynamic Mechanical Analyzer (DMA) Q800 model from TA Instruments.

Figure 3 — (a) Alignment and fixation fixture installed in the press and (b) the wire alignment components in the fixture.

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Effects of aging on the microstructure of a Cu-Al-Ni-Mn shape memory alloy

by fatih sari

2011, International Journal of Minerals Metallurgy and Materials

The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy (SMA) was studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray... more

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Submicron-sized actuators based on enhanced shape memory composite material fabricated by FIB-CVD

by Alexey Mashirov

2012, Smart Materials & Structures

An enhanced scheme for a functional bilayered composite material with shape memory effect has been successfully applied on the microscale to fabricate a thermally controlled microactuator. Fabrication of cantilever-type microactuators... more

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Shape Memory Effect

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