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Journal of Alloys and Compounds 577S (2013) S745–S748

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

journa l homepage: www.e lsev ier .com/ locate / ja l l com

orsional deformation characteristics of TiNi SMA tape and application tootary actuator

isaaki Tobushia,∗, Elzbieta Pieczyskab, Kouji Miyamotoc, Kento Mitsuia

Aichi Institute of Technology, 1247 Yachigusa, Yakusa-cho, Toyota 470-0392 JapanInstitute of Fundamental Technological Research, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, PolandChuryo Engineering Co., Ltd., 60-1 Kutanjo, Iwatsuka-cho, Nakamura-ku, Nagoya 453-0862, Japan

a r t i c l e i n f o

rticle history:eceived 26 September 2011eceived in revised form 27 October 2011ccepted 29 October 2011vailable online 26 November 2011

a b s t r a c t

In order to develop novel shape memory actuators, the torsional deformation of a shape memory alloy(SMA) tape and the actuator models driven by the tape were investigated. The results obtained can besummarized as follows. In the SMA tape subjected to torsion, the martensitic transformation appearsalong the edge of the tape due to elongation of the edge of the tape and grows to the central part. Thefatigue life in both the pulsating torsion and the alternating torsion is expressed by the unified relationshipof the dissipated work in each cycle. Based on an opening and closing door model and a solar-powered

eywords:hape memory alloyctuatorwo-wayapeorsion

active blind model, the two-way rotary driving actuator with a small and simple mechanism can bedeveloped by using torsion of the SMA-tape.

© 2011 Elsevier B.V. All rights reserved.

atigue

. Introduction

One of the main materials which have activated the researchn the intelligent materials is shape memory alloy (SMA) [1]. Theain characteristics of SMA are the shape memory effect (SME)

nd superelasticity (SE). Thanks to these characteristics, SMAs aresed in the driving elements of actuators, heat engines and robots.he SME and SE appear as a result of a martensitic transforma-ion (MT). In a recent study using the torsional deformation of aiNi SMA tube, twist in the blades of rotor aircraft was investi-ated in order to improve the flight performance [2]. In practicalpplications making use of SMA-tapes, torsional deformation cane obtained simply by gripping both ends without any mechanicalrocess. If the characteristics of SE are exploited, a high perfor-ance of energy storage can be achieved similar to that of a torsion

ar. In this way of using torsional characteristics of SMA-tapes,imple and small actuators can be developed. The authors inves-igated therefore the basic deformation properties of an SMA-tapen torsion [3].

In the present paper, in order to develop the rotary actuatorsriven by SMA tapes, the torsional deformation properties of TiNiMA tapes are investigated. The two-way motions of an opening

∗ Corresponding author.E-mail address: tobushi@aitech.ac.jp (H. Tobushi).

925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.jallcom.2011.10.108

and closing door model and a solar-powered active blind modeldriven by SMA tapes are demonstrated.

2. Materials

The materials used in the experiment on torsional deformation and fatigue wereTi–50.18 at.%Ni SMA tapes with a thickness of t = 0.25 mm and a width of w = 5 mm.The specimen was a uniform flat tape of length L = 60 mm. The gauge length of thespecimen was l = 40 mm. The transformation temperatures obtained from the DSCtest were Ms = 304 K, Mf = 266 K, As = 319 K and Af = 359 K.

The superelastic alloy (SEA) tapes used in the rotary actuator wereTi–50.89 at.%Ni alloy tapes with a thickness of t = 0.25 mm and a width of w = 2.9 mm.The transformation temperatures obtained from the DSC test were Ms = 237 K,Mf = 220 K, As = 279 K and Af = 295 K.

3. Torsional deformation and fatigue properties of SMAtape

3.1. Observation of martensitic transformation by thermography

The temperature distribution on the surface of the SMA tape ateach angle of twist during the torsional deformation obtained bythe infrared thermography is shown in Fig. 1. In Fig. 1, the upperside in each case shows the twisting part and the lower side shows

the fixed part. Maximum temperature Tmax on the surface of thespecimen appears along the edge of the tape, and the exothermicMT occurs in this part and grows toward the central part of thespecimen. The temperature rise along the edge of the tape starts

S746 H. Tobushi et al. / Journal of Alloys and Compounds 577S (2013) S745–S748

Fig. 1. Thermograms showing temperature distribution on the surface of the SMAt

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the same line. Both fatigue life is therefore expressed by the unified

ape appeared due to the phase transformation under torsion.

t the angle of twist per unit length � = 26.2 rad m−1. This angle ofwist per unit length corresponds to the tensile strain at the edgef the tape of 0.3% and coincides with the MT starting condition.he maximum temperature of the specimen occurs along the edgef the tape and the high temperature region propagates toward theentral part with an increase in angle of twist. Therefore, the MTrows preferentially based on the elongation along the edge of theape.

.2. Torsional deformation

The relationships between torque M and angle of twist per unitength � obtained by the pulsating torsion test and the alternatingorsion test for the maximum angle �m = 78.5 rad m−1 are shown inig. 2(a) and (b), respectively. In the case of the pulsating torsion,he curve between M and � is expressed almost by a straight linen the initial loading process. In the unloading process, the earlylope of the curve is steep and thereafter becomes to be the plateautage. In the reloading process, the early curve is almost parallelo the initial loading curve and thereafter the slope of the curveecomes steep. In the case of the alternating torsion, the twisting

n the reverse direction to the initial twisting direction was carriedut. The reverse loading and unloading curves are almost similar tohe initial loading and unloading curves except for the early stage,losely symmetric with respect to an origin. The point at the end ofhe reloading curve almost coincides with the point at which thenitial unloading started, showing the return-point memory in the

ulsating and alternating torsion.

The area surrounded by the hysteresis loop of the torque-angleurve of twist shown in Fig. 2 expresses the dissipated work per

Fig. 2. Relationship between torque M and angle of twist per unit length � obtained by

Fig. 3. Relationship between maximum angle of twist per unit length and numberof cycles to failure.

unit length Wd. The value of Wd in the alternating torsion is largerthan that in the pulsating torsion by 3.5 times.

3.3. Torsional fatigue properties

The relations between the maximum angle of twist per unitlength �m and the number of cycles to failure Nf obtained fromthe torsion fatigue test are shown in Fig. 3. The number of cycles tofailure Nf decreases with an increase in the maximum angle of twistper unit length �m. This relation is approximated by a straight lineon the logarithmic graph. The fatigue life curve seems therefore tobe expressible by the following equation:

�m · Nˇf

= ˛ (1)

where ˛ and ˇ represent �m in Nf = 1 and the slope of thelog �m − log Nf curve, respectively. The calculated results obtainedfrom Eq. (1) for ˇ = 0.1, ˛ = 265 rad m−1 in pulsating torsion and forˇ = 0.13, ˛ = 310 rad m−1 in alternating torsion are shown by thesolid lines in Fig. 3. As can be seen, the fatigue life curves are wellmatched by the solid calculation lines. The number of cycles tofailure Nf for alternating torsion is smaller than that for pulsatingtorsion by 1/5.

The relationship between the dissipated work Wd and the num-ber of cycles to failure Nf is shown in Fig. 4. The relationships for thepulsating torsion and the alternating torsion are located almost on

relationship between Nf and Wd in Eq. (2):

Wd · N�f = � (2)

the pulsating and alternating torsion tests for maximum angle �m = 78.5 rad m−1.

H. Tobushi et al. / Journal of Alloys and Co

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recovers a flat plane, resulting in closing the door. Thus, if two kinds

ig. 4. Relationship between dissipated work per unit length and number of cycleso failure.

here � and � represent Wd at Nf = 1 and the slope of the logd − log Nf curve, respectively. The calculated result by Eq. (2) for

= 0.382 and � = 9 J/m is shown by the solid line in Fig. 4. As cane seen, the overall inclinations are approximated by the solid line.he dissipated work corresponding to the fatigue limit may existt 0.04–0.05 J/m.

Fig. 5. Photographs of two-way rotary movement of a door driven by SMA ta

Fig. 6. Solar-powered ac

mpounds 577S (2013) S745–S748 S747

4. Rotary actuator driven by SMA tape

4.1. Two-way opening and closing door model

Photographs of the rotary movement of an opening and clos-ing door model using an SMA tape which shows the SME andan SEA tape which shows the SE at room temperature (RT) areshown in Fig. 5. The SMA tape is the same as the specimen usedin the torsion test. The SEA tape with a thickness of t = 0.25 mmand a width of w = 2.5 mm was heat-treated to memorize a flatplane. In the initial state at RT, the SEA tape was mounted to bein a flat plane and the SMA tape was mounted at the total angleof twist � = �/2. The SMA tape was heated by joule heat throughelectric current. As can be seen in Fig. 5, the door is closed inthe initial state, since torque of SEA tape MSEA is larger than thatof the SMA tape MSMA. Since recovery torque appears by heat-ing the SMA tape and the relation of the torque changes intoMSMA > MSEA, the SMA tape recovers a flat plane and therefore thedoor is opened. When the SMA tape is cooled thereafter, the rela-tion of torque varies again into MSMA < MSEA. Therefore, the SEA tape

of SMA tapes which show the SME and SE are used, a two-wayrotary driving element with a small and simple mechanism can bedeveloped.

pe and SEA tape during heating and cooling at room temperature (RT).

tive blind model.

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748 H. Tobushi et al. / Journal of Alloys

.2. Solar-powered active blind model

The structure of the solar-powered active blind model and thehotographs of two-way motion are shown in Fig. 6. Both the SMAape and the SEA tape were the same as those used in the door

odel. In the initial state, the SEA tape was mounted to be in a flatlane and the SMA tape was mounted at the total angle of twist= �/2. The SMA tape was heated by sunlight through a Fresnel

ens. Since recovery torque appears in SMA tape by heating the tape,he blind is closed through a crank and a lever. When the sunlights shut out, the SMA tape is cooled and the SEA tape recovers a flatlane, resulting in opening the blind.

In the two actuator models mentioned above, the SMA ele-ents were subjected to pulsating torsion with a total angle

f twist of �/2. At this angle of twist, the hysteresis loop inhe relationship between the torque and the angle of twist isarrow in width and the amount of dissipated work in eachycle is small, resulting in a fatigue life longer than 107 cycles.MA elements can therefore be used safely in practical applicationsithout any risk of fatigue failure.

. Conclusions

In order to develop the rotary driving element with SMA tapes,he torsional deformation properties of a TiNi SMA tape and actu-tor models driven by SMA tapes were investigated. The results

btained can be summarized as follows:

1) In the SMA tape subjected to torsion, the MT appears alongthe edge of the tape due to elongation of the edge of the

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mpounds 577S (2013) S745–S748

tape and grows to the central part. The relationship betweentorque and angle of twist per unit length is expressed by astraight line in the initial loading process. In the case of thealternating torsion, the initial and reverse twisting curves aresymmetric with respect to an origin. The return point mem-ory in the twisting curve appears in both the pulsating andthe alternating torsions. The dissipated work per unit lengthin the alternating torsion is larger than that in the pulsatingtorsion.

(2) The fatigue life in the alternating torsion is shorter than thatin the pulsating torsion. The fatigue life in both the pul-sating torsion and the alternating torsion is expressed bya unified power function of the dissipated work in eachcycle.

(3) Based on the two-way motion of an opening and closing doormodel and a solar-powered active blind model driven by twokinds of SMA tape, it is confirmed that the two-way rotarydriving actuator with a small and simple mechanism can bedeveloped by using torsion of the SMA tapes.

(4) At a total angle of twist of �/2 in pulsating torsion for the SMAelements applied to the two actuator models, the fatigue lifeis longer than 107 cycles. SMA elements can therefore be usedsafely in practical applications without any risk of fatigue fail-ure.

References

1] H. Funakubo (Ed.), Shape Memory Alloys, Gordon and Breach Science, New York,1987.

2] J.H. Mabe, F.T. Calkins, R.T. Ruggeri, Proc. of SPIE 6525–65251C (2007) 1–12.3] H. Tobushi, T. Sakuragi, Y. Sugimoto, Mater. Trans. 49 (1) (2008) 151–157.