,bibour, M69,

Keywords:Shape memory alloyShape memory materials

s) bir p. SM

butes of SMAs that make them ideally suited to actuators in various applications, and addresses their

marteatures

considerable progress in the eld of automotive sensors and con-trol electronics. However, the technical progress for automotiveactuators is relatively poorly advanced [2]. Currently, there are

ince then, the de-lications haas in conctures an

robotics [2224], biomedical [16,18,2530] and even in fashion[31]. Although iron-based and copper-based SMAs, such as FeMnSi, CuZnAl and CuAlNi, are low-cost and commerciallyavailable, due to their instability, impracticability (e.g. brittleness)[3234] and poor thermo-mechanic performance [35]; NiTi-basedSMAs are much more preferable for most applications. However,each material has their own advantage for particular requirementsor applications.

Corresponding author at: School of Aerospace, Mechanical and ManufacturingEngineering, RMIT University, Melbourne 3083, Australia. Tel.: +61 405552605.

E-mail addresses: jaronie@iprom.unikl.edu.my (J. Mohd Jani), martin.leary@rmit.edu.au (M. Leary), aleksandar.subic@rmit.edu.au (A. Subic), mark.gibson@

Materials and Design 56 (2014) 10781113

Contents lists availab

Materials an

elscsiro.au (M.A. Gibson).existing technologies [1]. The integration and miniaturisation ofintegrated micro-controllers and advanced software has enabled

posites [11], automotive [2,12,13], aerospace [1417], mini actua-tors and micro-electromechanical systems (MEMS) [16,1821],results in increased fuel consumption, and automotive suppliersare highly cost-constrained. Research on the application of smarttechnologies must concentrate on ensuring that these smartsystems are compatible with the automotive environment and

nation of NiTi and Naval Ordnance Laboratory). Smand for SMAs for engineering and technical appincreasing in numerous commercial elds; suchproducts and industrial applications [810], stru0261-3069/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.matdes.2013.11.084s beensumerd com-creased use of sensors, actuators and micro-controllers; therebyresulting in an undesirable increase in weight and volume of theassociated machine components. The development of high func-tional density and smart applications must overcome technicaland commercial restrictions, such as available space, operatingenvironment, response time and allowable cost [1]. In particular,for automotive construction and design: increased mass directly

by Arne lander in 1932 [4], and the term shape-memory wasrst described by Vernon in 1941 [5] for his polymeric dentalmaterial. The importance of shape memory materials (SMMs)was not recognised until William Buehler and Frederick Wang re-vealed the shape memory effect (SME) in a nickel-titanium (NiTi)alloy in 1962 [6,7], which is also known as nitinol (derived fromthe material composition and the place of discovery, i.e. a combi-AutomotiveAerospaceBiomedicalRobotics

1. Introduction

The technology push, towards sand/or intelligent functions and fassociated limitations to clarify the design challenges faced by SMA developers. This work provides atimely review of recent SMA research and commercial applications, with over 100 state-of-the-art pat-ents; which are categorised against relevant commercial domains and rated according to design objec-tives of relevance to these domains (particularly automotive, aerospace, robotic and biomedical).Although this work presents an extensive review of SMAs, other categories of SMMs are also discussed;including a historical overview, summary of recent advances and new application opportunities.

2013 Elsevier Ltd. All rights reserved.

systems with adaptive, necessitates the in-

about 200 actuation tasks are performed on vehicles with conven-tional electro-magnetic motors, which are potentially sub-optimalfor weight, volume and reliability [3].

Shape memory alloy (SMA) or smart alloy was rst discoveredAvailable online 17 December 2013 range of commercial applications, due to their unique and superior properties; this commercial develop-ment has been supported by fundamental and applied research studies. This work describes the attri-Review

A review of shape memory alloy researchand opportunities

Jaronie Mohd Jani a,b,, Martin Leary a, Aleksandar Sua School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melb Institute of Product Design and Manufacturing, Universiti Kuala Lumpur, Kuala LumpucCSIRO Process Science and Engineering, Private Bag 33, Clayton South MDC, Victoria 31

a r t i c l e i n f o

Article history:Received 17 September 2013Accepted 16 November 2013

a b s t r a c t

Shape memory alloys (SMAto memorise or retain theical or magnetic variations

journal homepage: www.applications

c a, Mark A. Gibson c

rne 3083, AustraliaalaysiaAustralia

elong to a class of shape memory materials (SMMs), which have the abilityrevious form when subjected to certain stimulus such as thermomechan-As have drawn signicant attention and interest in recent years in a broad

le at ScienceDirect

d Design

evier .com/locate /matdes

Inthe vaappliction dical, as

ture (As) is the temperature where this transformation starts and

characteristics as follows:

[44]. Various training methods have been proposed[42,4549], and two of them are: Spontaneous and externalload-assisted induction [50].

(3) Pseudoelasticity (PE) or Superelasticity (SE):The SMA reverts to its original shape after applying mechan-ical loading at temperatures between Af and Md, without theneed for any thermal activation.

In addition to the material TWSME above, a biased OWSMAactuator could also act as a mechanical TWSME at a macroscopic(structural) level; which is more powerful, reliable and is widelyimplemented in many engineering applications [18].

The SME is a diffusionless solid phase transition betweenmartensitic and austenitic crystal structures [49,5153]. Thereare other transformations associated with shape memory such asrhombohedral (R-phase), bainite [49,54] and the rubberlikebehaviour (RLB) in martensite stage [55,56], which are not dis-cussed in detail, in this work.

Hysteresis is a measure of the difference in the transition tem-peratures between heating and cooling (i.e. DT = Af Ms), which isgenerally dened between the temperatures at which the materialis in 50% transformed to austenite upon heating and in 50% trans-formed to martensite upon cooling [53]. This property is importantand requires careful consideration during SMA material selectionfor targeted technical applications; e.g. a small hysteresis is re-

Fig. 2. Flexinol NiTi SMA (HT) phase transformation [57].

and(1) One-way shape memory effect (OWSME):The one-way SMA (OWSMA) retains a deformed state afterthe removal of an external force, and then recovers to its ori-ginal shape upon heating.

(2) Two-way shape memory effect (TWSME) or reversible SME:In addition to the one-way effect, a two-way SMA (TWSMA)can remember its shape at both high and low temperatures.However, TWSMA is less applied commercially due to thetraining requirements and to the fact that it usually pro-duces about half of the recovery strain provided by OWSMAthe austenite-nish-temperature (Af) is the temperature wherethis transformation is complete. Once a SMA is heated beyond Asit begins to contract and transform into the austenite structure,i.e. to recover into its original form. This transformation is possibleeven under high applied loads, and therefore, results in highactuation energy densities [38]. During the cooling process, thetransformation starts to revert to the martensite at martensite-start-temperature (Ms) and is complete when it reaches themartensite-nish-temperature (Mf) [6] (see Fig. 2). The highesttemperature at which martensite can no longer be stress inducedis called Md, and above this temperature the SMA is permanentlydeformed like any ordinary metallic material [39]. These shapechange effects, which are known as the SME and pseudoelasticity(or superelasticity), can be categorised into three shape memoryHowever, intensive topics such as metallurgy, thermodynamicsand mechanics of materials will not be addressed in detail.

2. Shape memory alloy overview

SMAs are a group of metallic alloys that can return to their ori-ginal form (shape or size) when subjected to a memorisation pro-cess between two transformation phases, which is temperature ormagnetic eld dependent. This transformation phenomenon isknown as the shape memory effect (SME).

The basic application of these materials is quite simple, wherethe material can be readily deformed by applying an external force,and will contract or recover to its original form when heated be-yond a certain temperature either by external or internal heating(Joule heating); or other relevant stimuli such as a magnetic eldfor MSMAs.

2.1. Shape memory effect and Pseudoelasticity

Practically, SMAs can exist in two different phases with threedifferent crystal structures (i.e. twinned martensite, detwinnedmartensite and austenite) and six possible transformations[36,37] (see Fig. 1). The austenite structure is stable at high tem-perature, and the martensite structure is stable at lower tempera-tures. When a SMA is heated, it begins to transform frommartensite into the austenite phase. The austenite-start-tempera-emphasis on NiTi SMAs, but other forms or types of smart materi-als such as high temperature shape memory alloys (HTSMAs),magnetic shape memory alloys (MSMAs), SMM thin lm (e.g. NiTithin lm) and shape memory polymers (SMPs) are also discussed.this work, a brief summary of SMA, its design feasibility andriety of SMA applications are compiled and presented. SMAations are divided into several sections based on the applica-omain, such as automotive, aerospace, robotics and biomed-well in other areas. Most of the work presented here has an

J. Mohd Jani et al. /Materialsfor the same material [4042] and it strain tends to deterio-rate quickly, especially at high temperatures [43]. Therefore,OWSMA provides more reliable and economical solutionFig. 1. SMA phases and crystal structures [3638].

Design 56 (2014) 10781113 1079quired for fast actuation applications (such as MEMSs and robot-ics), larger hysteresis is required to retain the predened shapewithin a large temperature range (such as in deployable structures

and pipe joining) [58]. In addition, the transition temperaturesreferred to identify the operating range of an application. Thesetransition temperatures and the hysteresis loop behaviour areinuenced by the composition of SMA material, the thermome-chanical processing tailored to the SMA and the working environ-ment of the application itself (e.g. applied stress) [44]. Thesetransition temperatures can be directly measured with varioustechniques such as differential scanning calorimetry (DSC), dila-tometry, electrical resistivity measurement as a function of tem-perature, and can be indirectly determined from a series ofconstant stress thermal cycling experiments [43].

Some of the SMAs physical and mechanical properties also vary

coupler in 1969 for the F-14 jet ghter built by the Grumman Aero-space Corporation and followed subsequently by the orthodonticbridge wires by George B. Andreasen in 1971 [7].

Since the 1980s, the commercial application of NiTi alloys hasdeveloped in many areas due to the greater demands for lighterand more compact actuators, especially in the biomedical sector(see Figs. 4 and 3).

2.3. Recent developments

In the 1990s, the term shape memory technology (SMT) was

vibration [70] and actuation applications. Therefore, much system-

Martensite Austenite

1080 J. Mohd Jani et al. /Materials and Design 56 (2014) 10781113between these two phases such as Youngs modulus, electricalresistivity, thermal conductivity and thermal expansion coefcient[37,59,60]. The austenite structure is relatively hard and has amuch higher Youngs modulus; whereas the martensite structureis softer and more malleable; i.e. can be readily deformed by appli-cation of an external force [34,37] (see Table 1).

When an external stress is applied below the martensite yieldstrength (approximately 8.5% strain for NiTi alloys and 45% forcopper-based alloys [34,57,61]), the SMA deforms elastically withrecoverable strain. However, a large non-elastic deformation (per-manent plastic deformation) will result beyond this point. Mostapplications will restrict the strain level; e.g. to 4% or less, for NiTialloys [35,57].

2.2. History of SMA development

In 1932, the solid phase transformation in SMA was rst discov-ered by lander [4], a Swedish physicist who determined that thegold-cadmium (AuCd) alloys could be plastically deformed whencool, and returned to its original conguration when heated. Laterin 1938, Greninger and Mooradian [62] rst observed the SME forcopper-zinc (CuZn) alloys and copper-tin (CuSn) alloys. The fun-damental phenomenon of the memory effect governed by the ther-moelastic behaviour of the martensite phase was widely reported adecade later by Kurdjumov and Khandros [63] in 1949 and also byChang and Read [64] in 1951. Similar affects in other alloys suchInTl and CuAlNi were also observed in the 1950s. These discov-eries had captured the interest of many researchers and inventors,but practical and industrial applications could not be realised dueto their material high costs, manufacturing complexity and unat-tractive mechanical properties.

Although the NiTi alloy was discovered by William Buehler in1959 [7], the potential to commercialise SMA applications wasonly became available after the SME in NiTi alloy was revealedby William Buehler and Frederick Wang in 1962 [6,7]. Nitinolalloys are cheaper to produce, easier and safer to handle, and havebetter mechanical properties compared to other existing SMAs atthat time [6,53]. The rst commercial success for a SMA applicationwas the Raychem Corporations CryoFit shrink-to-t pipe

Table 1Commercial NiTi SMA physical properties [34,46].

Property Symbol Units

Corrosion Resistance Density qD kg/m3

Electrical Resistivity (approx.) qR lX cmSpecic Heat Capacity c J/kg KThermal Conductivity k W/m KThermal Expansion Coefcient a m/m K1

Ultimate Tensile Strength rUTS MPaYoungs Modulus (approx.) E GPaYield Strength r MPaYPoissons Ratio m Magnetic Susceptibility v lemu gSimilar to 300 series SS or Ti-alloy645065007680 82100836.8 836.88.610 186.6 106 11.0 106895 (Fully annealed)/1900 (Hardened)2841 758370140 195690atic and intensive research work is still needed to enhance the per-formance of SMAs [71,72], especially to increase their bandwidth,fatigue life and stability [73].

Recently, many researchers have taken an experimental ap-proach to enhance the attributes of SMAs, by improving thematerial compositions (quantifying the SMA phase transition tem-perature [7478]) to achieve a wider operating temperature range,and better material stability, as well as to improve the material re-sponse and stroke with better mechanical design (or approach),controller systems and fabrication processes. Research into alter-native SMMs, forms or shapes, such as MSMA, HTSMA, SMP, shapememory ceramic, SMM thin lm or a combination of them (i.e. hy-brid or composite SMMs), are also intensively being conducted,and the number of commercial applications is growing each year(see Fig. 4). More details of recent applications and developmentof SMA are described in the subsequent sections.

A literature analysis has been carried out using the Scopus andUSPTO search engines with search keywords of shape memory al-loy or nitinol for related areas are presented in Figs. 3 and 4.

BCC research [79] reported that the global market for smartmaterials was about USD19.6 billion in 2010, estimated to ap-proach USD22 billion in 2011 and forecasted to reach overUSD40 billion by 2016 with a compound annual growth rate(CAGR) of 12.8% between 2011 and 2016. The largest applicationsegment of the market is actuators and motors, with sales of nearlyUSD10.8 billion (55% of the total market) in 2010 and forecasted toreach USD25.4 billion (approximately 64% of the market) by 2016with CAGR of 15.4% between 2011 and 2016 (see Fig. 5).

3. Designing with SMAs

To date, more than 10,000 United States patents and over20,000 worldwide patents have been issued on SMAs and their

Valueintroduced into the SMM community [65]. SMA application designhas changed in many ways since then and has found commercialapplication in a broad range of industries including automotive,aerospace, robotics and biomedical [16,18,23,6669]. Currently,SMA actuators have been successfully applied in low frequency0.332.5 3.8

and Design 56 (2014) 10781113 1081J. Mohd Jani et al. /Materialsapplications, but the realisation of viable products from all thisintellectual property has thus far been limited [61,80,81]. The rea-son for this lies primarily with the lack of understanding by scien-tists and engineers on both the technical limitations of SMAs andthe methods to apply SMAs in a robust manner to achieve technicalrequirements of longevity and stability [69,8083].

3.1. SMA design advantages

Recent research work has shown that SMA actuators provide anexcellent technological opportunity to replace conventional actua-tors such as electric motors, pneumatics and hydraulics [15,84],

Fig. 3. SMA publications and US patent

Fig. 4. Number of Shape Memory Alloy articles and patents by years-group.due to their unique characteristics and ability to react directly toenvironmental stimuli [81]; thus promoting the development ofmore advanced and cheaper actuators with a signicant reductionin mechanical complexity and size [2,85]. For instance, the NiTiSMA displays one of the highest work density at 10 J cm3 (seeTable 2), which is a factor of 25 times greater than the work densityof electric motors [19] and is able to lift more than 100 times of itsweight [86]. Furthermore, the NiTi SMA is bio-compatible [29,87],exhibits high wear resistance [34,53], and the tribological behav-iour has been investigated and compared to many conventional

s from January 1990 to June 2013.

Fig. 5. Global market forecast for smart materials for 20102016 [79].

engineering materials such as steels, Ni-based and Stellite alloys[19,8890].

With reference to Table 2, the NiTi SMA is the obvious choice fordesigners for actuators that provide signicant displacement andforces, with no critical requirements for a short response time orhigh efciency. This makes NiTi SMA an attractive candidate fora variety of industrial applications, smart structures and intelli-gent systems [94,95]. A composite airframe with a combinationof piezoelectric crystals, as the vibration sensors, and NiTi as theactuators to counteract the vibration, is a good example of a smartstructure application [81].

Commonly, designers make use of the benet of the engineeringeffects described above to design their applications, where the SMEis primarily employed for actuation and pseudo-elasticity forvibration isolation and dampening (see Table 3). For example, thetwo unique pseudoelastic behaviours of SMA, provide a valuableadvantage in dampening vibrations, where its non-linear behav-iour allows vibration isolation and a large deformation recovery,and its hysteresis behaviour dissipates the energy [96,97]. SMAsare also capable of actuating in a fully three-dimensional manner,allowing the fabrication of actuation components which can ex-tend, bend, twist, in isolation or combination; and can be used in

low actuation frequency, low controllability, low accuracy andlow energy efciency. The major obstacle is the low operationalfrequency and narrow bandwidth of SMA materials, which havea relatively high heat capacity and density, and as a result theyexperience difculty in transferring the heat rapidly into and moreimportantly out of the active element, which leads to a severebandwidth problem. In several studies [101103], it has beenshown that rapid heating of SMA actuators can be achieved easilywith several methods, such as applying large electrical currents(Joule heating) to increase the heating rate. However, withoutproper monitoring and control this may overheat and damagethe actuator. Nonetheless, the most signicant concern in band-width limitation is the very slow cooling process, where the heatenergy removal rate is limited by the mechanisms of heat conduc-tion and convection. The size and shape of the SMA actuator affectsthe actuator response time, where actuators with smaller diameterheat faster due to their higher resistivity, and cool faster due totheir higher surface-to-volume ratio [57,104]. Therefore changingthe wire diameter could change the application bandwidth dra-matically (see Table 4). In addition, the preloading stress, loadingcondition and amplitude of activation potential also inuence theresponse time of SMA actuators [105]. Several strategies have been

B

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1082 J. Mohd Jani et al. /Materials and Design 56 (2014) 10781113various congurations and shapes such as helical springs, torsionsprings, straight wires, cantilever strips, and torsion tubes[13,98]. SMAs can provide a highly innovative approach to solvea wide range of engineering problems and may in fact be the onlyviable technical option for complex applications, due to their attri-butes and unique advantages.

An overview of the features and possibilities of SMA actuators isprovided in Fig. 6, which characterises the SMA actuators accord-ing to their relevant requirements and can be considered as a use-ful checklist for the development of SMA applications [99]. A seriesof charts to aid the selection of SMAs (NiTi, CuZnAl and CuAlNi) is also presented by Huang [35], based on a number of perfor-mance indices and criteria [100], with special reference to the un-ique features of SMA actuators.

3.2. SMA design challenges

The challenges in designing SMA applications are to overcometheir limitations, which include a relatively small usable strain,

Table 2Comparison of actuator performance [9193].

Actuator type Stress (MPa) Strain (%) Efciency (%)

NiTi SMA 200 10 3Piezoceramic 35 0.2 50Single crystal piezoelectric 300 1.7 90Human Muscle 0.0070.8 1100 35Hydraulic 20 50 80Pneumatic 0.7 50 90

Table 3Summary of various SMA properties and their effects [15].

SMA traits Practical consequences

Shape memory effect Material can be used as an actuator,Pseudoelasticity Material can be stressed to provide lHysteresis Allows for dissipation of energy duriHigh actuation stress (400700 MPa) Small component cross-sections canHigh actuation strain (ca. 8%) Small component lengths can providHigh energy density (ca. 1200 J/kg) Small amount of material required tThree-dimensional actuation Polycrystalline SMA components fabActuation frequency Difculty in achieving high compone

Energy efciency (1015%) Amount of thermal energy required for aTransformation induced plasticity Plastic accumulation during cyclic respodeveloped to improve the control of the heating process [35,106]and to expedite the cooling process with active cooling such asforced air [105,107,108], owing liquids [105,109111], thermo-electric modules (i.e. Peltier or semiconductor heat pumps) [112117], heat sinks [103,105,118] and conductive materials[85,119,120]. Table 4 shows the ratio of actuation speed improve-ment with several cooling methods [57].

Higher cooling rates are obtained when cooling with a uidicmedium, but this requires a special design to prevent any leakageto the environment. A small amount of air circulation around thewire is sufcient to obtain a substantial improvement comparedto the natural convection case, however, several studies have alsoindicated that increasing the air ow would only produce a minoreffect on the cooling performance and has several drawbacks suchas higher energy consumption and noise production [84]. There-fore, active cooling is not practical in numerous situations sinceit contributes to increases in cost, weight, physical volume, as wellthe mechanical and control complexity [38,106]. Alternatively,bandwidth improvement with passive cooling is also achievable

andwidth (Hz) Work per Volume (J/cm3) Power per Volume (W/cm3)

10 30000 0.035 175800 2.55 15,000173 0.035 0.35

5 200 0.175 3.5

viding force during shape recovery, recoverable deformations at relatively constant stress levelsseudo-elastic responsevide substantial forcesrge displacementsovide substantial actuation workted in a variety of shapes, providing a variety of useful geometric congurationsooling rates limits use in high frequency applications

ctuation is much larger than mechanical work outputnse eventually degrades material and leads to failure

and Design 56 (2014) 10781113 1083J. Mohd Jani et al. /Materialsvia improvements in mechanical design and control systems, suchas the application of an agonistic-antagonistic system [83,121],high surface-to-volume ratio design (e.g. thin lm SMA), and con-troller optimisation (e.g. gain optimisation [106]). An assessmentof transient cooling opportunities has been completed by Huanget al. [122].

The second challenge is the low associated energy efciency.Theoretically the maximum energy efciency of SMAs is in therange of 1015% [123], which may fall to 10% [124] based on theCarnot cycle efciency in some studies, and is often less than 1%in practical applications [16]. Hence SMA actuator applicationsmust be limited to areas where energy efciency is not an issue,and it should be noted that there is a difference between SMA ef-ciency and actuator efciency (i.e. efciency of the entire systemversus efciency of SMA wire) [125]. Mechanically, SMA actuatorscome in various loading congurations. Most of the proposed actu-ator designs are based on a SMA spring as the active element,where large macroscopic displacements can be generated out ofa relatively small microscopic strain. However, the stress distribu-tion over the cross-section of the SMA spring is not constant, andtherefore requires greater material volume to generate the sameforce, which has a negative effect on the efciency and the band-width of the actuator (i.e. for the same output, a larger material

Fig. 6. SMA actuator ele

Table 4Cooling methods [57].

Cooling methods Improvement in speed

Increasing Stress 1.2:1Using higher temperature wire 2:1Using solid Heat Sink materials 2:1Forced air 4:1Heat conductive grease 10:1Oil immersion 25:1Water with Glycol 100:1

Note: Typical heating (joule heating) and cooling time (passive cooling) for HT-type(90 C) Flexinol wire at standard environmental condition (i.e. static air, verticalposition and atmospheric pressure): 0.05 mm: Heating (85 mA) = 1 s, Cooling = 0.3 s. 0.51 mm: Heating (4000 mA) = 1 s, Cooling = 14 s.volume has to be heated and cooled) [60,84]. Therefore, straightSMA wires are more advantageous due to the optimal use of mate-rial (i.e. more work generated from a minimal amount of SMAmaterial) and the loading in tension conguration (see Table 5).

The next challenge is the durability and reliability of SMA actu-ators when subjected to multiple transformation cycles, which issignicantly important to be assured of long-term stability, func-tionality and safety for any applications such as in automotivesafety systems [66]. Many factors inuence the long-term perfor-

ment features [99].mance and reliability of SMA actuators such as maximum temper-ature, stress, strain and the number of transformation cyclesaccumulated. SMAs have been shown to exhibit a softening ofbehaviour (i.e. reducing the amount of recoverable strain) as theactuator is cycled, either by heating and cooling the SMA underload [77,126128] or by mechanically cycling the wire in itssuper-elastic state [129]. Many researchers have concluded thatthermal effects are highly relevant in determining fatigue-life,particularly for the NiTi SMA [130138]. For fatigue-limited appli-cations, the SMA actuator temperature should be controlled pre-cisely and overheating the SMAs reduces the fatigue lifeconsiderably [73]. Recent studies [77,128,139] have also shownthat SMA actuators with constant loading, which are higher thanthe recommended load (stress), experienced a reduction in stroke(strain) as the number of cycles increased. It was also reported thatoverstraining of the SMA material also degraded performance,either in tension [140], torsion [141] or bending [142,143]. Increas-ing both stress and strain reduces the lifetime of SMA materials,and it is therefore essential to select the appropriate working

Table 5Comparison of loading conguration for SMA actuators [84].

Loading conguration Efciency (%) Energy density (J/kg)

Tension 1.3 446Torsion 0.23 82Bending 0.013 4.6

Note: The values in this table are calculated based on a pure elastic deformationwhich is only a rough estimate for comparing the three loading congurations.

boundary conditions to obtain high fatigue resistance and highreliability from SMA materials (see Fig. 7) [140]. In terms of fatigueperformance, SMA wires were reported to be better than SMAsprings, where the recovery force and strain of SMA springs de-creased by 30% after 1000 cycles and by 60% after 10,000 cycles[144]; in addition, the SMA springs deection against the bias forcedegraded by at least 20% after ageing at 95 C for 2000 h [145].

Therefore, SMA actuators should be prevented from overheat-ing, overstressing and overstraining for long durations. Generally,to guarantee the applications are designed to perform safely overa large number of cycles (about 106 cycles) before reaching yield

[152,153], fabrication processes [154,155], thermomechanicaltreatments [156159] and mechanical design optimisation [83]are not discussed in this work.

4. Other forms or types of shape memory materials

Other forms or types of SMMs have been explored due to someobvious limitations or disadvantages of SMA, such as high manu-facturing cost, limited recoverable deformation, limited operatingtemperature and low bandwidth. Some of the SMMs can be catego-rised in multiple forms or types, such as CoNiGa and NiMnGacan be categorised as HTSMA and MSMA, and NiTiPt/Pd also canbe fabricated as SMM thin lm.

4.1. High temperature shape memory alloys

Extensive research for HTSMAs with other ternary additions tothe NiTi SMA (e.g. Au, Hf, Pd, Pt and Zr) has been undertaken[43,160,161], due to the increasing demands for high-temperatureapplications. Practically, HTSMAs are dened as SMAs that areoperating at temperatures above 100 C, and can be categorisedinto three groups based on their martensitic transformation ranges[43] (see Table 6).

Unfortunately, most HTSMAs are very difcult to process and to

Fig. 7. Fatigue lifetime for Smartex 76 under different stressstrain [140].

) St

2

33

13

1084 J. Mohd Jani et al. /Materials and Design 56 (2014) 10781113point and mechanical breakage, the active elements should pre-vented from overheating; and not allowed exceed the recom-mended fatigue strength and strain of the SMA material (i.e.maximum load of 350 MPa [35], safe design load at 100 MPa [84]and 34% strain [35,57,146]). The advancement in materials devel-opment and processing has reduced degradation and fatigue, andas a result over millions of cycles are readily achievable withappropriate training and usage [57]. Application of electronics con-trollers such as temperature sensors [147], position feedback [148],resistance feedback [149,150], limit curve [151], and adaptiveresetting [83] are capable to resolve the overstress and overheatingproblems in commercial applications. Other methods to enhancethe fatigue life of SMAs such as improvement of materials

Table 6HTSMA groups and their properties [43,162164].

Group Alloy composition Transformationtemperature range (C)

Thermal hysteresis (C

100400 C TiNiPd 100530 2026

TiNiPt 1101100 3155NiTiHf 100400 60

NiTiZr 100250 54CuAlNi 100400 21.5CuAlNb 59170 5CoAl 100400 121 2

CoNiAl 15.5 5NiAl 100300 - -

NiMn 100670 20 3NiMnGa 100400 85 1ZrCu 100600 70 8TiNb 100200 50 2

UNb 100200 35 7400700 C TiPd 100510 40 10 88 Good ductility (TiPd), but high materials cost (TiPt)

TiAu 100630 35 3>700 C TiPtIr 9901184 66.5 1

TaRu 9001150 20 4

NbRu 425900 4

Note: PE = Pseudoelastic.1000PE 40PE High yield strength.

50 Stable microstructural, but poor oxidation resistanceand small hysteresistrain due to their limited ductility or poor fatigue resistance atroom temperature, and making them very expensive to manufac-ture. Therefore, alternative low cost materials or compositionssuch as copper and cobalt have been researched. At present, onlyTiNiPd, TiNiPt, NiTiHf, NiTiZr and CuAlMnNi alloys are useful at100300 C, and the rest of them had signicant challenges tocommercial application and require further work [43].

4.2. Magnetic shape memory alloys

Magnetic shape memory alloys (MSMAs), which are also knownas ferromagnetic shape memory alloys (FSMAs) can actuate athigher frequencies (up to 1 kHz) because the actuation energy is

rain (%) Recovery (%) Comments

.65.4 90PE-100 High work output, most commercial ready and highmaterials cost

4 100100 Reasonable SME, large hysteresis and relatively low

materials cost.8 1005PE 8090PE Low cost, poor to reasonable SME, and brittle in tension

(CuAlNi).57.6

90 Good workability, large hysteresis and high temperaturePE (CoNiAl)

PE 100PE

- Low materials cost, low hysteresis and poor tensileductility

.9 900 70

44 Good ductility and workability, but poor SME3 97100 Good ductility and SME, but suspect to oxidation and

contain Uranium (UNb).2 88

transmitted via magnetic elds and is not hindered by the rela-tively slow heat transfer mechanism [165]. FSMA strain rate isquite comparable to magnetostrictive and piezoelectrics active ele-ments, but at strains as large as SMAs (see Fig. 8, [43]). FSMA canalso provide the same specic power as SMAs, but deliver it athigher frequencies (see Fig. 8, [43]). The maximum strain of FSMAis 32 times more than the giant magnetostrictive Terfenol-D(TbDyFe2), and the trade-off for greater strain is 46 times lowerfor lower elastic modulus (stiffness) [166]. Consequently, FSMAsare suitable to ll the technological gaps between SMAs and mag-netostrictive materials, and would be a niche for motor and valveapplications [167] that require signicantly larger displacementat lower actuation force [166].

addition, SMPs can sustain two or more shape changes [181

either thermo- or chemo-responsive [184]. When one considers

Table 7Micro-actuators comparison [172174].

Micro-actuators Maximum energydensity (J/m3)

Maximumfrequency (Hz)

Efciency(%)

NiTi thin lm 2.5 107

ond p0)

l mm K

D10

pres

ndmemory element as shown in Table 10 [34,201]; where the SMEcan be used to generate motion and/or force, and the SE can storethe deformation energy. [44].

The unique behaviour of NiTi SMAs have spawn new innovativeapplications in the aerospace, automotive, automation and control,appliance, energy, chemical processing, heating and ventilation,safety and security, and electronics (MEMS devices) industries.Some of these applications apply similar methods, concepts ortechniques, which are also applicable for other areas; such as theNiTi thermovariable rate (TVR) springs, which are used to controlthe opening door in the self-cleaning oven, is also used to offersmooth gear shifting for Mercedez-Benz automatic transmissions,for domestic safety devices to control the hot water ow (e.g.Memrysafe antiscald valves from Memry Corporation), and forindustrial safety valves to prevent ammable and dangerousgasses from owing (e.g. Firechek from Memry Corporation)[44,201203] (see Fig. 9). More interesting, these actuators canact as both a sensor and an actuator in these applications [202].

Selected state-of-the-art and relevant SMA applications andpatents are presented in this section, particularly from the automo-tive, aerospace, robotics and biomedical domains. A brief summaryof other related SMA applications and discoveries till mid 2013 aresummarised in the appendices.

5.1. Automotive applications

Table 8Comparison of SMP and SMA properties [177,178].

Property SMP

Density (g cm3) 0.91.25Transition breath (C) 1050Phase transformations Glass transitiStrain (%) Up to 400, anYoungs modulus (GPa) at T < TTrans at T > TTrans 0.013 (0.11Deform stress (MPa) 13Recovery stress (MPa) 13Recovery speeds (s)

iTiC

Fe-based alloys: FePt, FeMnSi, FeNiC . . .

. . .

and Ag-based alloys: AgCd . . . Au-based alloys: AuCd . . . Co-based alloys: CoNiAl. . .

MSMA/FSMA:

NiMnGa, FePd, NiMnAl, FePt, Dy, Tb, LaSrCuO, ReCu, NiMnIn, CoNiGa

HTSMA:Table 9Materials with SME [19,43,166,178].

Materials Examples

Metals SMA:

NiTi-based alloys: NiTi, NiTiCu, NiTiPd, NiTiFe, NiTiNb, NiFeGa, N Cu-based alloys: CuZn, CuZnAl, CuAlNi, CuAlNiMn, CuSn . . .

J. Mohd Jani et al. /Materialsin locations with higher temperatures such as under the enginehood. The SMAs should have an Mf temperature well above themaximum operating temperatures (see the red dotted lines inFig. 13) in order to work properly [13]. The comparison of thetransformation temperature ranges of the most common SMAs un-der development in Fig. 13 shows that the cheaper CuAlNi SMAscan perform the transformation with temperatures up to 200 C,but these SMAs are brittle, unstable, have low fatigue strengthand not suitable for multiple cyclic operations [13,32,34,44,160].A wide selection of HTSMAs are available, but these materials arestill expensive for automotive applications [13].

5.2. Aerospace applications

Since the success of the SMA coupling for hydraulic lines in theF-14 ghter jets in the 1970s [219], the unique properties of SMAshave gathered greater interest in aerospace applications[16,17,96,220], which are subjected to high dynamic loads andgeometric space constraints. A few examples of these applicationsare actuators [15,221], structural connectors, vibration dampers,sealers, release or deployment mechanisms [222226], inatable

TiNiPd, TiNiPt, NiTiHf, NiTiZr, ZrRh, ZrCu, ZrCuNiCo, ZrCuNiCoTi, TiMo, TiNTiTa, TiAu, UNb, TaRu, NbRu, FeMnSi and etc.

Polymers PTFE, PU, Poly-caprolactone, EVA + nitrile rubber, PE, Poly-cyclooctene, PCCPE blend, PCLBA copolymer, Poly(ODVE)-co-BA, EVA + CSM, PMMA,Copolyesters, PET-PEG . . .

Ceramics ZrO2 (PSZ), MgO, CeO2, PLZT, PNZST . . .

Others SMM thin lm:

NiTi, SMP and etc.Notes

The best choice is NiTi SMAE.g. NiTi-based:

o Frequency: 63 Hz, dia. 100 lm with natural cooling (Very Slow).Strain:max. 10% (High), Recommended: 4%.Stress: up to 500 MPa (High),Recommended: 100 MPa.Max. operating temp: ca. 100 C (Low).

NiMnGa was rst discovered in 1984 [411] and have received increasinginterest since the principle of the MSMA was presented by Ullakko et al.[412,413]

E.g. NiMnGa:Frequency: max. 2 kHz (High), Recommended: 500 HzStrain: max. 10% (High), Typical: 6%Stress: max. 9 MPa (Low), Typical: 3.4 MPaYoung modulus: 0.5 GPa (Very Low)Max. operating temp: 72 C. (Low), full austenite transition at 48 C.

So far, TiNiPd and TiNiPt produced the best results and commercially ready

Design 56 (2014) 10781113 1087structures [227,228], manipulators [229,230], and the pathnderapplication [96,231].

In the 1990s, aerospace researchers focussed on active andadaptive structures toward morphing capability and system-leveloptimisation under various ight conditions, such as in the DefenseAdvanced Research Projects Agency (DARPA) program for aircraftsmart wings [232], the Smart Aircraft and Marine Propulsion Sys-tem Demonstration (SAMPSON) program for jet engines [233], anda number of other programs [234237]. Boeing has developed anactive serrated aerodynamic device with SMA actuators, which isalso known as a variable geometry chevron (VGC) and has been in-stalled on a GE90-115B jet engine (for the Boeing 777-300 ER com-mercial aircraft). This device has proven to be very effective inreducing noise during take-off by maximising the chevron deec-tion, and also increasing the cruise efciency by minimising thechevron deection during the remainder of the ight [238240](see Fig. 14). The high temperature requirement for a core exhaustchevron design was resolved by the identication, testing, andvalidation of the new TiNiPt HTSMA at the NASA Glenn ResearchCenter [241,242].

Following the VGC success, more SMA based technologyprograms have been initiated by Boeing, DARPA, NASA and other

b,

E.g. TiNiPd [414]:Frequency: 800% (Very High)Stress: 3 MPa (Low)

Shape memory ceramics has limited shape memory effect (below 0.5 %)[33,415,416]E.g. PNZST:

Frequency: ca. 1 kHz (High)Strain:

nd1088 J. Mohd Jani et al. /Materials arelated research agencies, which have been reviewed by Calkinsand Mabe [243], such as in the smart inlet that could provideghter aircrafts with a variable engine inlet capability, the

Table 10Shape memory application categories [34,44,201].

Category Description

Free recovery The sole function of the memory element is to causon the applicationsWorking principle: The memory element is stretcreleased (no load applied). It remains in stretchedheated above the transition temperature and shrioriginal form, and subsequent cooling below the ttemperature does not cause any macroscopic shapOWSMA)

Constrained recovery The memory element is prevented from changingthereby generates a stress or force on the applicat

Working principle: The memory element is prevereturning to its original form after being stretchedforce generated if heated above the transition tem

Actuator or work production There is motion against a stress and thus work is bmemory element on the applications

(Force actuator, proportionalcontrol and two-way-effectwith external reset force)

Most of applications fall in this category. Can be eTWSMA. Three types of actuators:

Force actuator:The memory element exerts force over a considermotion, and often for many cyclesProportional control:The memory element used only part of its selectedrecovery to accurately position the mechanism, btransformation occurs over a range of temperaturesingle temperatureTwo-way-effect with external reset force:The memory element generates motion to overcoforce, and thus do work. The memory element coheating to lift a load, and the load will stretch theand reset the mechanism upon cooling (e.g. TWSM

Superelasticity The applications are isothermal in nature and invopotential energy

Fig. 9. NiTi thermovariable rate (TVRDesign 56 (2014) 10781113recongurable rotor blade, which is highly robust, and the twist-able rotor blade to optimise rotor aerodynamic characteristics.Most recently, the variable geometry fan nozzle, which is based

Examples

emotion or strain NiTi eyeglass frames (TiFlex, TITANFlex) and Simon IVClter

hed and thencondition until

nk back to itsransitione change (e.g.

shape andions

Hydraulic couplings, fasteners and connectors: CryoFit,Cryocon, UniLok, CryOlive, CryoFlare, CryoTact,Permacouple, Tinel Lock and BetaFlex

nted fromand considerableperature

eing done by the Electrical actuators (VEASE, SMArt Clamp), thermalactuators (Memrysafe, circuit breaker, window or louvreopener, valves), and heat engines

ither OWSMA or

able range of

portion of shapeecause thes rather than at a

me the opposingntracts uponheating elementA)

lve the storage of Eyeglass frame, orthodontic archwire, Mammelok breasthook, guidewires, anchors and underwire brassiere

) springs applications [202,203].

andTable 11Existing and potential SMA applications in the automotive domain [13,67,205].

J. Mohd Jani et al. /Materialson the VGC technology, has demonstrated to improve jet engineperformance.

Soa et al. [235] have provided a comprehensive review of air-craft wing morphing technologies, and they have also developed ashape morphing wing design for small aircraft by applying antag-onistic SMA-actuated exural structural forms that enable thechanging of the wing prole by bending and twisting, to improve

Parts References

ENGINE ROOM /UNDERHOOD

Radiator [417420]Fan clutch [423]Engine control (sensors and actuators) [426]Start-up clutch [430]Tumble aps [211]Fuel injector/fuel system [435438]Piston rings [439]Booster/charger [13]Valves [13,441]Battery [446]

DRIVETRAINTransmission control [13,448,449]

SUSPENSION/STEERING/WHEEL AND TYREBrake [449,455]Absorber [13]Tyre [456]

Table 12Comparison of DC-Drive and SMA-Drive for fuel door actuator [206].

Parameters DC-Drive

Actuation time (Complete cycle open-close) 3 sInstallation space CompactAcoustics emission (from drive) Slight noiseMechanical complexity HighMass Approx. 65 gm.Positioning accuracy 1.5Energy consumption 1 W during ap mDesign 56 (2014) 10781113 1089the aerodynamic performance (refer Fig. 15). A preliminary designstudy with nite element simulations presented by Icardi and Fer-rero [236] has veried that an adaptive wing for a small unmannedaircraft (UAV), which is totally driven by SMA devices, could bearthe aerodynamic pressure under any ight conditions, withoutweight increase or stiffness loss compared to other conventionalactuators.

Parts References

BODY AND EXTERIOR

Headlights/lamps [13,421,422]Wiper [13,424,425]Sunroof/sunshade [418,427429]Door and locking mechanism [13,210,431434]Side mirror [213,214,216]Boot [3,431]Engine hood [212,440]Petrol cap [206]Bumpers and crash structures [442445]Air dams [210,447]

Grill/louver [210,417,418]Spoiler [450]Structural parts/panels [418,451454]

INTERIOR/PASSENGER ROOMDashboard [444]Rear view mirror [207]Seats [442,453,457463]Airbags [464,465]Structural parts/impact structures [444,451,466]

SMA-Drive

23 sStretched along the air ductNo noiseLowApprox. 20 gm2.25

ovements 1 W permanent

nd1090 J. Mohd Jani et al. /Materials aThere has also been signicant research in rotor technology(rotorcraft) with SMAs conducted by several researchers, includingrotor blade twisting [229,244,245], rotor blade tracking tab[220,246], rotor control [247] and rotor blade tip morphing [248].

SMAs have been used for many years in spacecraft as low-shockrelease mechanisms because they can be actuated slowly by grad-ual heating, can absorb vibration very well and can be fabricated insimple and compact designs, which are most suitable for averageand smaller sized spacecraft (e.g. microsatellite) [96,250,251]. Afew samples of small devices with SMA are the QWKNUT [252],Frangibolt [253], Micro-Sep-Nut, and Rotary Latch; as describedin previous reviews [15,224,254].

Fig. 10. EAGLE mirror

Fig. 11. Emerging General Motors

Fig. 12. Other SMA application in the automotive domain [211213,217].prototype [207].

SMA applications [3,209,210].

Design 56 (2014) 10781113As mentioned earlier, SMAs are suitable for vibration damperand isolator applications due to their unique behaviour [96,97].Considerable new research has been performed to study this in de-tail [255257], and a few patents have been led to exploit theseadvantages [258260]. Several other proposed or developed SMAapplications for aerospace are the telescopic wing system [261],wing span morphing [262], retractable landing gear [263], jet en-gine components [264268], morphing structures [269], ap edgefence [270], aircraft related actuators [271] and aerostructures[272274] (see Table 14).

5.3. Robotic applications

Since the 1980s, SMAs have been used in a diverse range ofcommercial robotic systems, especially as micro-actuators or arti-cial muscles [275279]; as described by Furuya and Shimada [24]and Sreekumar et al. [23]. Today, most of the SMA robotic applica-tions are biologically inspired (i.e. biomechanics) and widely uti-lised in biomedical areas but are also used extensively in otherelds as well. The primary challenges relevant to the robotics do-main are: to increase the performance and miniaturisation of thehardware platform and to increase the intelligence of the inte-grated system (i.e. small, faster, reliable and autonomous). Severaltechnical issues have been highlighted and need to be resolved,such as clamping difculties, low electrical resistance, miniatureelectrical connection (for micro-robots), small strain output, con-trol issues and very low efciency. However, some of these issueshave been tackled by selecting suitable modelling techniques, con-trol techniques and feedback sensors. As an example, the resis-tance feedback control is ideal for micro-robots as it eliminatesthe necessity of additional sensors, although with limited accuracy[23].

As mentioned earlier, the SMA actuators response rate dependssignicantly upon its shape and size, and these have a high impact

d to

andTable 13Typical automotive electronic components specications [12].

Requirements Engine room

Operating temperature 40 C to +125 C (+175 C for some parts mounteStorage temperature +100 C for 500 hThermal shock 100 Thermal cyclesRelative humidity 0100%Shock 20 gDrop test 4 ft. dropVibration 502000 Hz, 10 g RMS, 16 h

J. Mohd Jani et al. /Materialson the overall size and degrees of freedom of the robotic device.Resistive heating is generally used for small SMA actuators (up to400 lm diameter), and indirect heating techniques are appliedfor thicker actuators [23]. To increase the actuation frequency,capacitors are incorporated with thicker actuators to obtained a ra-pid heating response, and several cooling strategies can be adoptedas mentioned earlier, to enhance the cooling process, but thesewould make the device bulkier [23]. Furthermore, to increase thedegrees of freedom of the robots, the number of actuators has tobe increased, which leads to complex control problems.

A new SMA actuator design for a prosthetic hand was intro-duced by Chee Siong et al. [103], where two SMA actuators are

Operating voltage 5 V, 0.5 VReliability 95% Reliable for 10 years, 120 k milesOther

Contaminant resistance Salt spray, engine oil, ATF, windshield washer uid, ethsteering uid, battery acid, engine cleaner, methanol, m

Fig. 13. Operating temperature range for automobiles applications and thetransformation temperatures for selected commercially available and developedSMAs [13,34,161,218].

Fig. 14. Boeings variable geometry chevron (VGC) [238].Passenger room

engine) 40 C to +85 C50 C to 100 C for 500 h20 Thermal cycles95% @ +65 C for 100 hMaximum 25 g4 ft. drop502000 Hz, 4 g RMS12 V, 4.0 V90% Reliable for 10 years, 100 k milesMinimal radiated or conducted emissions. Notsusceptible to conducted/radiated emissions

ylene, glycol, gasoline, powerud and exhaust gases

Design 56 (2014) 10781113 1091used to actuate the robotic nger, instead of using the conventionalpushpull type and the biased spring type (see Fig. 16). The twoactuators are inserted from both ends of the outer stainless tube,which functions as a heat sink and guide simultaneously. The cur-rent passed asynchronously through the wires via electrode points,which are located at the centre of the tube (where the wires join)and each end of the tube. The two actuators are used to actuate therobotic nger, which can almost replicate the actions of the humannger actions (exion and extension). A PWM controller is used topulse periodically high voltage in milliseconds to the actuators toavoid overheating and excessive power usage.

In a recent review by Kheirikhah et al. [22], they divided the ro-bots into several categories based on their locomotion styles andapplications such as crawler, jumper, ower, sh, walker, medicaland biomimetic robotic hand. Many robotics researchers are moreinterested in developing biomemitics and humanoid robots. Theserobots are useful in solving problems that are challenging for hu-mans, by providing pertinent information from underwater, space,air and land. Comprehensive details and challenges in developingthese robots are summarised by several researchers, focusing onthe actuation technologies, especially SMA actuators (see Table 15).Tao et al. [280] designed a robotic sh with a caudal peduncle actu-ator based on the concept of a FSMA hybrid mechanism that canprovide fast response and a strong thrust.

Mohamed Ali and Takahata [281] have developed passive (i.e.without internal power source) micro-grippers (i.e. about 600 lmdisplacement) that can be actuated wirelessly with a RF magneticeld. The fabrication of the micro-gripper is similar to the waferfabrication processes in the semiconductor industry, where theSMA actuator is bonded to or near an inductor-capacitor (LC) res-onant circuit with photo-dened electroplating technology, and

Fig. 15. Wing morphing with antagonistic SMA actuators [235,249].

ndTable 14Existing and potential SMA applications in the aerospace domain [14,15].

1092 J. Mohd Jani et al. /Materials athen micro-machined with a lEDM process. The working principleof the micro-gripper is quite simple. The frequency-sensitive LCresonant circuit is heated when a RF magnetic eld passes throughit, and then transfers the heat energy to the SMA actuator foractivation. The opportunity to control multiple selections ofmicro-SMA actuators is possible by applying different resonant fre-quencies, either selectively or simultaneously to the actuators (seeFig. 17).

Parts References

FUSELAGE

Aerostructure/composite body [274,467]Skin/panel [273]Wing/n/stabilizerWing [232,235,249,261,262]Winglet [467]Vortex generator [469]Flap edge [270]Structure/spars [470]

Fig. 16. Prosthetic hand powereDesign 56 (2014) 10781113A novel sensory system for robotics has been developed byresearchers at Northwestern University, Illinois applying the SEcharacteristic of a NiTi SMA to create an articial rat whisker,utilising the rats sensing capabilities. The articial whisker tech-nology has the great potential to enhance robotic sensing capabil-ities, and could be used to examine and navigate into small andtight interiors, or to locate and identify micro-features on surfaces[282].

Parts References

ENGINE

Inlet [233,405,468]Nozzle [239,269,405]Rotor [220,229,230,244,246]LANDING GEAR [263]ELECTRO-MECHANICAL CONTROLHydraulic lines [219]

d by SMA actuators [103].

Table 15Existing and potential SMA applications in the robotics domain[2224].

J. Mohd Jani et al. /Materials andSeveral ying robots have been developed with SMAs, such asthe BATMAV [283,284] and Bat Robot [285]. Recently, a 44 cmlength dragony with a wingspan of 63 cm was developed by FestoGroup, equipped with four SMA actuators to control the move-ments of its head from side to side and its tail up and down foright manoeuvre and stability. The dragony, also known asBionicOpter, has 13 degrees of freedom, can hover in mid-airand manoeuvre in all directions [286] (see Fig. 18).

5.4. Biomedical applications

After the discovery of the SME in nitinol by Buehler et al. i1962, they proposed to use this material for implants in dentistrand a few years later, the rst superelastic braces made from a NiTalloy were introduced by Andreasen in 1971 [7,287,288]. SMmade a signicant breakthrough into biomedical domain after itintroduction in minimally invasive surgery (MIS) [26], and morbiomedical applications are developed and introduced into thmarket after the approval of the Mitek surgical product (i.e. MiteAnchor) for orthopaedic surgery by US Food and Drug Administration (FDA) in September 1989.

Although NiTi alloys are signicantly more expensive thastainless steels, SMAs have exhibited excellent behaviour for biomedical applications such as high corrosion resistance [34,53bio-compatible [29,87], non-magnetic [37], the unique physicaproperties, which replicate those of human tissues and bone[27] (see Fig. 19), and can be manufactured to respond an

Categories References Categories References

BIOMIMETICS BIOMEDICAL ROBOTS

Crawling/snaking [471479] Endoscopic [480482]Walking/jumping [476,483486] HUMANOID ROBOTSRolling/skating [485,487] Fingers/hands [103,488494]Climbing [495,496] Head/facial expression [497,498]Swimming [280,499502] MISCELLANEOUSFlying [284286] Controller [147,278,503,504]Others [505] Actuators [281]

Sensors [282]

Fig. 17. Micro-gripper with SMA actuator [281].

Fig. 18. Festo BionicOpter inspiration dragony ight [286].ny,iAseek-

n-],Design 56 (2014) 10781113 1093lsd

ange at the temperature of the human body [28]. The need forecise and reliable miniature instruments to achieve accuratesitioning and functioning for complex medical treatments andrgical procedures provides SMAs with substantial advantagesd great opportunities for further commercial success in thisea. SMAs are used in medical equipment and devices in manylds including orthopaedics, neurology, cardiology and interven-nal radiology [27]; and other medical applications include:dodontics [289], stents [26], medical tweezers, sutures, anchors

for attaching tendon to bone, implants [290,291], aneurismtreatments [292], eyeglass frames [9] and guide wires [293](see Table 16).

The superelastic behaviour of SMA, which ts the stressstrainbehaviour of human bone and tendons, makes it an excellent mate-rial to meet some of the challenges presented by stenting opera-tions. SMA stents are much more compliant to bends in thevessels and contours in the lumen, whereas stainless steel stentstend to force blood vessel straight. In addition, the superelastichysteresis behaviour of SMA can resist crushing during the normalphysiological process (provide radial resistive force) and exert asmall outward force on the vessel during recovery, which is idealfor stenting applications [27] (see Fig. 20). The rst SMA stentwas made by Dotters group in 1983 [294], and since then it hasevolved remarkably (from simple coiled wire form to the complexlaser cut structures), growing in the global market (nearly half ofstent products are fabricated from SMA and was forecast to reachUSD6.3 billion by 2010 [295]), and has expanded the usage to otherparts of the human body [26].

. 19. The stress versus strain relationship for superelastic nitinol, stainless steel,ne and tendon tissues [27].

Table 16Existing and potential SMA applications in the biomedical domain [2528,30].

TRU

scop

94 J. Mohd Jani et al. /Materials and Design 56 (2014) 10781113Fields References Fields

ORTHODONTIC BIOMEDICAL/SURGICAL INS

Braces/brackets [288,506,507] Catheters/snaresPalatal arches [510] Scopes (Ureteroscopy, endoFiles [516]

Suturechprposuanaretioen

Figbo

10ORTHOPAEDIC MISCELLANEOUS

Head [518] Cardiology (Heart)Spine [519523] Hepatology (Liver, gallbladder,Bone [291,526,527]Muscles [28] Otorhinolaryngology (Ear, noseHands/ngers [103,532]Legs [300,533] Gastroenterology (Gullet, stoma

VASCULAR

Aorta [541,542] Urology (Kidneys, adrenal glandArteries [549]Vena cava lter [550554]Ventricular Septal Defect (VSD) [555557] Plastic, reconstructive and aestVessels [559561]Valves [562564] Ophthalmology (Eye)References

MENTS

[508,509]y, laparoscopy) [511515]

[517]

[301,302]biliary tree and pancreas) [524,525]

and throat) [528531]

ch and intestine) [534540]

s, ureters, urinary bladder, urethra and the male reproductive organs) [543548]

hetic surgery [558][565]

heart stroke, as well as cardiac massage during a lifesaving emer-gency for recovery from ventricular brillation. Recently, they havedeveloped another mechanical circulation support device usingSMA bres for Fontan circulation to assist pulmonary circulationin patients with congenital heart diseases (see Fig. 23) [302].

An alterable stiffness implant might help the bone to healfaster, thus able to bear weight earlier and avoid a follow-on oper-ation. Currently, this alteration is only possible with a biodegrad-able implant, xateur externe or a second surgery. Therefore, analterable stiffness implant made of NiTi-SMA has been developedto alter the stiffness of the implant with contactless heat induction[291] (see Fig. 24).

In the last few years, there have been concerns from medical

sues with SMPs and SMHs [457].

still considered to be low [61,80,81].

J. Mohd Jani et al. /Materials and Design 56 (2014) 10781113 1095Today, catheter-based surgeries have become increasinglypopular due to the demand for MIS treatment, which will furtherminimise operation trauma. The application of SMAs has improvedthe active catheter capability to move accurately with larger bend-ing angles, which enables novel diagnosis and therapy to be treated[293,296,297]. A laser machined SMA actuator from NiTi tubing asproposed by Tung et al. [298], allows for the creation of custom-tailored SMA actuators with force, elongation and size characteris-tics, which are not achievable with common straight wire or coilspring actuators, leading to another viable option for developingactuators for steerable catheters (see Fig. 21).

A micro-muscle bre crafted from NiTi SMA coiled springs waspresented by Kim et al. [299], utilising many of the SMAs attributes(resilience, high energy density, exibility and scalability) to pro-duce a novel mesh-worm prototype that employs a bio-inspiredantagonistic actuation for its body deformation and locomotion,and this could make an excellent actuator candidate for meso-scaleapplications. Similar work has also been done by Stirling et al.[300], to develop an active, soft orthotic for the knee. They con-cluded that even though SMA springs could provide the soft char-acteristics as required and produce a large energy density; it wasnot appropriate for this application due to the poor response timeand would be difcult to operate if not tethered to an externalpower supply. However, it could be appropriate for applicationswith a slower time scales or reduced forces requirements (seeFig. 22).

An articial myocardium was developed by Shiraishi et al. [301]using a nanotech covalent type SMA bre with a parallel-linkstructured myocardial assist device, which is capable of supporting

Fig. 20. (a) Model of stent laser cut from nitinol tubing. (b) The radial resistanceforce and chronic outward force as a function of superelastic hysteresis loop [27].natural contractile functions from the outside of the ventriclewithout blood contacting the surface. The researchers concludedthat their system might be applied in patients with exertional

Fig. 21. SMA active ca6.1. Future trends in SMAs

The future trends in SMAs can be expected at three differentlevels [218]: (1) development of new or improved SMAs, (2) com-bination of the functional properties of SMAs with the structuralproperties of other materials (e.g. hybrid or composite SMMs),and (3) search for new markets.6. Opportunities and future direction of SMA applications

The commercial and research interest in SMMs, particularly inSMAs are rapidly increasing, and many potential new applicationshave been proposed, such as listed in Table 17 [307]. The chance ofsuccess of a new idea can be evaluated and ranked into three dif-ferent categories of applications, i.e. substitution, simplicationand novel applications [218]. Applications with higher noveltyand good competitive price are more interesting and have a betterchance to penetrate the market. A few successful mass producedSMA applications in the market are the underwire brassiere, themobile-phone antenna, eyeglass frames, the SMA pneumatic valvesdeveloped by Alfmeier Przision AG (now Actuator SolutionsGmbH) for the lumbar support device in car seats and the Xlineaautofocus (AF) module for smart phones [201,308,309]. However,the percentages of commercially successful SMA applications arepractitioners and researchers about the fatigue and fracture behav-iour of SMA materials, and several observations and follow-up pro-cedures were conducted to understand these behaviours and todesign better biomedical applications in the future [27,303,304].The concern of biocompatibility of the NiTi SMAs has also beenraised due to the known toxic, allergenic and carcinogenic proper-ties of nickel, and an alternative material composition has beenconsidered [291,305,306]; such as the new ideas of shaping the tis-theter [297,298].

nd1096 J. Mohd Jani et al. /Materials aThe developments of new or improved SMAs have signicantlyenhanced SMAs attributes and performances (see Fig. 25). Manyresearchers are recently interested in programming the SMMsby locally embedding multiple shape memories into SMMs withvarious techniques to set the temporary shapes without perma-nently changing the material properties, instead of utilising thetraditional training method [310,311]. For example, a new processknown as multiple memory material technology (MMMT) devel-oped by researchers at University of Waterloo, Canada has trans-formed SMAs into multiple shapes at various temperatures [310].A new single-crystal SMA (SCSMA) made of copperaluminiumnickel (CuAlNi) developed by TiNi Aerospace has exhibited betterperformance over NiTi SMA, i.e. higher operation temperature(>200 C), fully resettable (repeatable with 100% recovery), up to

Fig. 22. Muscle like Ni

Fig. 23. Articial heart support dDesign 56 (2014) 10781113one million of cycles operation, greater strain recovery (9%), widertranformation temperature range (270 C to +250 C) and verynarrow loading hysteresis (

The future of SMAs is full of potential as SMAs becoming more

andJ. Mohd Jani et al. /Materialschanging [321] and self-healing capability [196]. An advancedcomposite structure constructed from CFRP composites withembedded SMA wires has also been employed as a structuralhealth monitoring (SHM) system (i.e. for sensing and damagedetection) with structural ice protection capacity [322].

The unique properties of SMAs result in high damping, com-bined with the capability to resist extreme, repetitive and variousloading conditions (e.g. earthquake), substantially make SMAshighly compatible with for civil engineering applications, espe-cially in damping and vibration control [323,324]. Several potentialSMA applications in bridge and building structures are bearings,columns, beams, and connecting elements between beams and col-umns [325]. However, there are still limitations such as greater

tal data. These are considered essential to speed up the develop-

Fig. 24. An alterable stiffness implant [291].

Table 17Potential SMA applications [307].

Conguration Potential applications

SMA tendons, wires and cylinders Adaptive control and actuation ofaircraft ight surfaces

Embedded SMA wires Shape-adaptive composite materialsSMA actuators Transmission line sag control and ice

removal from overhead power linesSMA energy absorbers and tendons Earthquake-resistant building and

bridges, bridge and structural repairsSMA dampers Engine mountings, structural

supportsSMA wires, wings, legs, actuators, etc. Mobile micro-robots, robot arms and

grippersSMA wires, composites, etc. Prosthetics, articial muscles

Fig. 25. Comparison stress and strain of new developed SMA with other materials[100,317].ment process, especially for preliminary studies and validation ofhigh risk and/or expensive projects.

7. Discussion

Although, more than 10,000 US SMA related patents have beenproposed in many sectors [61,81,336] (see Fig. 4), only the four ma-jor sectors are presented in this work, due to the huge classicationof sectors and applications. The most recent developments ofSMMs, others than SMAs are also omitted; due to the objectivemultifunctional and capable to perform more active roles in com-plex systems [317].

6.2. Future directions of SMA applications

Many potential areas and topics of research have been proposed[332], butmost of the research onSMAs that has been conducted hasfocused mainly on the metallurgical properties, and less on thedesign perspective. It was concluded that to utilise the SMA applica-tions, closer collaborationbetweenmaterial scientists andengineer-ing designers is essential, due to the available informationoffered bymaterial scientists is not transparent and difcult to digest directly(i.e. too specialised inmaterial scienceand technology)by thedesignengineers [80,82,332]. Therefore, the challenges in designing SMAactuators arenotmainly the SMA limitations, but alsohowto conveythe information effectively. As example, Spaggiari et al. [333] de-scribed that the three main challenges for SMA actuator designare: (1) obtaining a simple and reliable material model, (2) increas-ing the stroke of the actuator, and (3) nding design equations toguide the engineer in dimensioning the actuator.

For this reason, the development of an effective informationplatform or database for SMA applications is important to reducethe development time and cost, to minimise the risk of failureproducts and to identify potential applications effectively withpatents screening and analysis (see Fig. 26) [80]. An optimumdesign of SMA actuators could be realised by providing designengineers with appropriate design procedures and guidelines[13,80,82,332,333].

Actually, there is no lack in vision or ideas for creating the SMAapplications, but there is a serious problem in making it market-able [334]. Involvement of marketing personnel in SMM communi-ties is also essential in shaping SMA applications to adapt to thecommercial market with different approaches and strategies,where smart marketing is the key to an unconditional break-through [218]. A few standards and requirements for SMMs havebeen drafted by several SMM communities as guidelines in variouselds and applications, such as for terminology, testings, fabrica-tions and treatments [335].

Furthermore, the importance of incorporating modern com-puter design and analysis tools such as CAD and FEA into develop-ing innovative and reliable SMA applications has led to an interestin more accurate 3D constitutive models, which are calibratedfrom carefully obtained material characterisation and experimen-cost compared to structural steel, much slower response timeand larger power consumption requirement for activation due tothe larger cross-section of the structure, and difculties in bothmachining and welding [326]. Other new potential industries forSMA applications are oil and gas industry [310,327], industrialand manufacturing [8], sports [328330] and arts [331] (seeappendices).

Design 56 (2014) 10781113 1097of this review is to focus on SMAs. After the rst commercially suc-cess SMA application as pipe coupler in 1969 [7], the demand forSMAs are increasing after 1980s, especially in the biomedical sec-

app

1098 J. Mohd Jani et al. /Materials andtor (see Fig. 3). Consequently, major manufacturers such as ATIWah Chang Corporation, Dynalloy Inc., Johnson-Mattheys, Mem-ory-Metalle GmbH, Memry Corporation, SAES Group and Toki Cor-poration have continued to grow in both size and knowledge base.

The advancement in the process and manufacturing technolo-gies (see Appendix D) has led to an increase in production quantityand quality, and at the same time reduced the material price. NewSMA materials (e.g. MSMAs and HTSMAs) or forms (e.g. NiTi thinlms, composites or hybrids) have been researched, and morepromising attributes and enhancements are being offered (see Sec-tion 6), and further outweigh their challenges (see Section 3.2).

The current research or development trends of SMAs, in the se-lected sectors are (see Section 5):

(a) Automotive and aerospace: Self-healing and sensing structures/components (e.g.

smart tyre and airbags). Morphing capability for aerodynamic and aesthetic

features. High temperature actuators. Noise, vibration and harshness (NVH) dampers/isolators. Rotary actuators.

(b) Robotics: Micro and fast actuators. Efcient, stable and accurate actuators. Rotary actuators.

(c) Biomedical: Articial muscles. Shape memory implants.

Fig. 26. Current situation and proposed Toxic (i.e. Nickel) free SMAs.

The self-healing capability of SMHs (i.e. combination of SMAsand SMMs, particularly SMPs) [196,337339] has potentially cre-ated new applications, such as healable composites, coatings andbrake pads. The potential of SMAs to work as both sensor and actu-ator simultaneously is favourable for miniature actuators. The fab-rication of mini- and micro-actuators such as NiTi thin lms (seeSection 4.3) is possible, with the new fabrication technologies,which further enhanced SMAs attributes and functionality.

8. Conclusions

In general, the important designing factors to be considered forSMA applications are as listed below:

Operating temperature range for the actuator: Selection ofSMA material and heat transfer technique to be considered. Force required for deforming the actuator: Selection of SMAshape, size, loading conguration and design technique tobe considered.

The required speed of the actuator: Selection of SMA mate-rial, shape, size and cooling technique.

The stroke required: Selection of SMA material, shape, size,loading conguration and design technique to beconsidered.

Type of sensors and controller to incorporate with the actu-ator (e.g. position, temperature, force or resistance) toensure long life and stability.

Durability and reliability of the actuator: Selection of SMAmaterial, size, loading conguration and number of cyclesto be considered.

Proposed actions to be taken to increase the commercialisationof SMA applications:

Good collaboration within the SMM community (i.e.between material scientists, engineering designers andmarketing personnel) and utilisation of information plat-form or database to share the knowledge of SMAs anddesigning SMA applications.

Utilisation of new SMA materials, including hybrid orcomposite SMMs to enhance its performance andfunctionality.

Exploration of new markets for SMA applications. Incorporation of modern computer design and analysis

tools such as CAD and FEA into the design and develop-

roach for SMA in product design [80].

Design 56 (2014) 10781113ment process.

Future development

The identied future development for SMA applications:

Development of more efcient and effective informationplatform or base for knowledge sharing within SMMcommunities.

Development of new materials (including compositesand hybrid SMMs), fabrication technologies and treat-ment processes for SMAs, which are more stable, moredurable and can be utilised in a broad range ofindustries.

Development of new design approaches or guidelines forcreation of novel SMA applications, in existing and newmarkets.

Development of robust computational models of SMAbehaviour.

e o -i r

A

Remarks Year Inventor/researcher

Linear type.Self-regulated

1985 Morganand Yaeger[340]

Linear type 1986 Hosodaet al. [341]

Linear type 1987 Sampson[342]

Rotary type 1987 Gabrielet al. [343]

volume with minimal

Rotary type.Bi-directional

1992 Swenson[344]

SM

Remarks Year Inventor/researcher

strain

system andChristian[346]

1999

[347]

Rotary type 2000 Weems[348]

Rotary type 2000 Jacot et al.[349]

Rotary type 2001 Williams[350]

Enhance life 2004

sequential activation

switch et al. [352]

ls andsystem in which ableto move freely with astroke in the range of1500 lm

Folding et al. [345]

An invention forincreasing the life of a

Linear/Rotary type.

1995 Thomaet al. [146]A micro-actuation

for activation

Linear type. 1994 Komatsupower consumptionSMA actuator by Controlone another to providetwo stable positionsand smooth motionbetween the two withmore describesuniform heating, thusdeliver maximumwork output per unitAn actuator consisting oftwo concentric tubesof SMA, torsional alongtheir longitudinal axis,with the endsconstrained relative toapplying variousselective voltage.Aimed primarily forrobotics but is deemedmore widelyapplicableA temperature tractiondevice suited toclosing doorsautomaticallyfollowing a short delayafter opening

An actuator comprisingof a SMA wire andcontrol element rotateto different section byActuators and motorsDescription

Self-regulating actuatorthat cut-off the powerwhen reach its stroke.Also protect actuatorand connectedmechanism fromdamage due to jam ormalfunction

An actuator withmultiple SMA wiresarranged around aresilient member(such as spring) toincrease bandwidthpact, fast and intell

ppendix A. SMA actuators Development of int grated actuatgent controller systems).s (with comJ. Mohd Jani et al. /MateriaA rotary actuatormaintained until thenext activation cycle

Rotary type 2006 Jacot et al.of a SMA element, andcomposed of a SMA(continuedstable workingpositions that willswitch between thesepositions uponenhance service life(more than 100 kcycles), with limitedtensile stress(100 MPa)

An actuator with two Two states 2005 Biasiottooperate in bothdirections using asingle SMA member

A rotary drive systemthat incorporates SMAelements for use in amotorised camera

A method of designing aSMA actuator to cycleHomma[351]constant force fromapplied heat. Canrotate either aclockwise or anti-clockwise dependingon which spring isactivated

A rotary actuator whichcan provide eithersmall or large amountsof torque and is able toa heating device and tothe object at the otherend

An actuator consists ofSMA strips (coiled intosprings) and SMAsprings that produce afrom one position toanother by the actionof a SMA at springattached at one end tocontrol multiple SMAelements in a matrixconguration thatreduces the electricalconnections by 50%

A linear actuator totranslate an objectLinear type Foss andSiebrechtActuators and motorsDescription

maintaining amartensite strain onthe SMA element at

SM

Remarks Year Inventor/

Linear and 2006,

[353,354]

Behrens

Linear type 2008 Yson et al.

Rotary type 2008 Garschaet al. [357]

Linear type 2009 Takahashi

Rotary type 2010 Taya et al.

[360]

Linear type 2010 Altali andBenjamin[362]

An actuator device with Linear type 2010

SM

Remarks Year Inventor/researcher

system [364]

A ining

and clampsRemarks Year Inventor/

researcher

1990 Romanelliand

[365]

Releasemech

1992 Johson[253]

and Larson[367]

controllable to allow a

Releasemech. PCB

1996

clamp Summers

components by simple

Fasteners 2001 White [370]

11 ls and Desresponse timethermal conduction tobase to improvesliding elements andA device and method for Control 2013Yang [363]based on MSMAcomposites (A hybridelectromagnet and apermanent magnet toactivate FSMA spring)

An SMA wire actuatormade in a series toincrease applied load

A solar trackingmechanism driven bySMA motorLinear type 2010 Butera[361]two bias springspositioned in acylinder

A torque actuatorincorporating SMA andMSMA composites

A linear actuator design Linear type 2010[359]

Taya et al.element in such a wayit can rotates in bothdirection

A SMA linear actuatorwith a SMA wire, twomoving bodies and[358]are set coaxially toprovide a telescopicextension

A turn-actuator with atensile element madeof three SMAelements, which arexed to a rotationalvariable return force toimpart motion in anoutput shaft

A linear actuator withseveral SMA membersin tubular shape and[356]with severalprotectionmechanisms and[355]with combination ofSMA elements tocreate a long outputstroke from ascompact unit

An actuator assembly Linear type 2006 VonspringSeveral linear androtational actuators Rotary types 2007Gumminet al.torque tube connectedwith a biassuperelastic returnA actuators (continued)

Actuators and motorsDescriptionresearcher00 J. Mohd Jani et al. /MateriaGao et al.one of the componentsbeing a super-elasticmaterialrelative motion, withA sealing assembly that Seals 2002 Wincorporating a SMAelement for the easyclamping and release ofa work piece

An effective connectionbetween twodesiredA novel clamping device Release/ 1998 Schron andmech [369]withdrawn when so

in place and to be

Board) to be held rmly

heat exchanger (on PCBinterference t fastenerfabricated from SMAmaterial

A heat operated releasemechanism with SMAelement that is applicationPorter [368]fatigue lifetime aroundholes formed instructural membersthrough cold workingusing a tool or anuse in a wellbore thatincorporates a SMAelement

A method to enhance Fasteners 1993 Kennedyapplications (e.g.clamping mechanismfor space station)

A device for the non-explosive separation ofcoupled componentswith SMA element in acontrolled fashion

A metal to metal seal for Seals 1993 Ross [366]ppendix B. Bonding and jo

Fasteners, seals, connectorsDescription

A pre-tensioned SMAactuator for high loadsand long period idlingClampsOtterstedttemperature of ashape memory alloy.Developed byDynalloy and GMA actuators (continued)

Actuators and motorsDescription

controlling a phasetransformationign 56 (2014) 10781113hite [371]

Bo ed)

and clampsRemarks Year Inventor/

researcher

Fasteners 2004 Cheng et al.

Releasemech

2004 Carmanet al. [373]

Fasteners 2006 Cheng et al.

Fasteners 2006 Johnsonet al. [375]

Fasteners 2007 Rudduck

member made of a

Fasteners 2008 White [377]

Bo d

aRemarks Year Inventor/

researcher

Fasteners 2008

Fasteners 2009 Rudducket al. [379]

Clamps 2011

A a

gRemarks Year Inventor/

researcher

Valve 1990 Homma

inexpensive, lightweight

Valve 1993

Tool andDie

2007 Browne et al.[385]

Valve 2008 Vasques andGarrod [386]

SMA by varying aperture

Valve 2008 Me

ls andxed relative positionwhich lock twomembers together in asuper-elastic alloy,upon activationmechanicalDevices and methods forfasteners (such asbolts) made of singlecrystal SMA capable ofadjusting the tension inthe assembly

SMA as fastening systemfor instrument panels,e.g. in a motor vehiclewhich can improve thexing or releasing oftrim panel and canchange the approach todashboard design

A torque transmittingcoupling assemblyincorporates anelongated shaftet al. [376]CrN coating andaluminium) withinterlayer of SMAmaterial between themby compensating themismatches ofreleasable engagementA system consists of tworelease mechanism ofdifferent structurestates (pseudoelasticand martensite-austenite)

To improve adhesionbetween two dissimilarmetals (such as a hard[374](composed of a brethat has a non-axisymmetric coatingof a SMA) that whenpressed together theyinterlock to form ato seal between twoconnecting memberswhen the sealingsurfaces are fullyengaged

A releasable fastenersystem comprising aseries of loops[372]nding and joining (continu

Fasteners, seals, connectorsDescription

incorporates a atwasher gasket made ofa super-elastic alloythat deforms elasticallyJ. Mohd Jani et al. /Materiathe frameAdjusting the nozzle tipheight and hot runner

Injectionmoulding

2009 Jenko [388]size (rotary motion) ofseals in an injection(continueA resettable thermal valvefor uid ow controlusing a SMA actuatorthat permits the valve tomove from an open to aclosed position whenheated to apredeterminedtemperature

To control the gas ow rate(ow controller) withacGregort al. [387]Same tool/die to formdifferent geometrieswith changeable SMAsurfaceSMA actuator for theclamping forcearrington384]An invention for a pressbrake tool holder with

Pressbrake

2007 Moreheadandtool H[SMA element [383]

A uid control valves with

few parts as possible

Valve 2001 Hines et al.and constructed from asthe linear valveA linearly actuated valvewith SMA wire that isCoffee [382]Industrial and manufacturinDescription

A SMA wire as its drivingsource to open or close [381]ppendix C. Industrial and mA ratchet mechanismwith SMAnufacturingJohnsonet al. [380]Several types of fastener,fastener systems andfastener assembliesusing SMA elementstogether andpermanently deforms abolt to adjust thecomponents to a pre-determined distancewithout being fullydetached fully byselective activation ofSMA elementFasteners, seals, connectorsDescription

A device and method forholding componentsJohnsonet al. [378]nding and joining (continue )

nd clampsDesign 56 (2014) 10781113 1101d on next page)

In u

Y Ir

A ial and process and materialim

rial improvementsRemarks Year Inventor/

researcher

TransformOWSME toTWSME

1998 Ingram[389]

the force

variability

Reducehysteresisvariability

2000 Carpenterand Draper[390]

SM ocess and material improvements

r

researcher

2006 Jacot et al.

minimum of about

Improve fatigueresistance

2007 Berendt[392]

11 ls and Des(Ti50Ni47Fe3)which responds tochanges in

with narrowtemperaturerange

[391]

A novel SMA SMAambientmaterial 2002 Ashursttemperatures andtherefore producesa reduction in thehysteresiscontrol over theforward andreversetransformationyields greater

application, toaustenitictransformationnish temperature,but below themaximumtemperature atwhich theaustenitic-martensitictransformationwill be effected bymoulding machineeffectively andefciently with SMAelement

ppendix D. SMA materprovements

SMA process and mateDescription

Producing a two-waySME from one-waymemory materialby deforming thematerial into apredeterminedshape and thenwork hardening,such as throughshot peening

A process (training)for conditioning aSMA by coldworking andannealing prior toforce application/release cycling at atemperature abovethe martensitic-dustrial and manufact

Industrial and manufacDescriptionring (continued)

turingRemarks ear nventor/

esearcher02 J. Mohd Jani et al. /Materiaare linked togetherA system of amultitude SMAsegments, which

SMA controllersystem

2007 Asada et al.[393]ve cycles)but controlledhole in acondensatecollector pan of anair conditionerwhen the ambienttemperatureapproachesfreezing

An apparatus toimprove thecontrol andoperatingefciency of a SMAdevice by using athermoelectric(TEC) material topump heatbetween the SMAand a heat sink

A method ofpreparing nitinolfor use inmanufacturinginstruments withimproved fatigueresistance bysubjecting thenitinol to a strainand thermalcycling process(between a coldbath of about 010 C and a hotbath of about 100180 C for aSMAimprovementwith TEC[245]Description

temperature over anarrowertemperature range(2 C) by takingadvantage of atransition to the R-phase rather thanthe martensitephase to reducehysteresis effects.A specicapplication forsuch an actuator isto control an anti-freeze plug foropening a drainageA material and pr(continued)

SMA process and mate ial improvementsRemarks Year Inventor/ign 56 (2014) 10781113

SM ocess and material improvements

rial improvementsRemarks Year Inventor/

researcher

SMA et al. [394]

HTSMA 2009 Noebe et al.[242]

Thin lm SMAforming

2009 Johnson[171]

CuNiAl SMAshape-settingmethod

2009 Johnsonet al. [395]

These SMAs

SMA et al. [396]

SM ocess and material improvements

rial improvementsRemarks Year Inventor/

researcher

Higher strainand strength

et al. [313]

NiTiCo SMA.Increasestiffness ofmaterial

2011 Faschinget al. [397]

TransformOWSME to

2012 Tang et al.[311]

Four ways SME 2012 Meng et al.[398]

FSMA 2013 CRDFGlobal[314]

could be achieved

SMA [310]

ls andthere are no graingradual changeduring repeatedcycling becauseexhibit no creep orboundaries (Cusingle crystal CuNiAl SMA

Hyperelastic SMAsingle crystalmaterial which iscapable of arecoverable strainof 9% (and inexceptionalcircumstances aslarge as 22%).Hyperelastic 2010 J