Indian Journal of Fibre & Textile Research Vol. 38, June 2013, pp. 193-197 Actuation performance of shape memory alloy friction-spun yarns M R Ahmad, M H M Yahya a, W Y W Ahmad, J Salleh & N Hassim Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia Received 11 July 2012; accepted 24 July 2012 This paper reports study on the determination of the actuation performance of shape memory alloy (SMA) friction-spun yarns (SMA FSY). Thin SMA actuator wire has been spun with 100% cotton fibres into the core of the friction spun yarn structure using DREF 3000 friction spinning. The delivery speed (m/min) and suction pressure (rpm) are varied, while the spinning drum speed as well as the core-sheath ratio are kept constant during production. The SMA FSY has been electrically heated using a customized instrument and the results are reported as the work done (potential energy) and output power (Watt) needed to lift the load (constant weight) from staticcondition. The actuation performances of the SMA FSY are compared with SMA wires actuation performance without sheath. The changes in spinning parameters show different actuation performance of SMA FSY, which is measured as the height to lift the load and the time taken for the SMA core to return to the pre-determined shape. The cohesion between the sheath and the wire may have contributed to the difference in the actuation performance based on the internal friction test. Keywords: Electrical actuation performance, Friction-spun yarn, Resistive heating, Shape memory alloy, Spinning parameters The incorporation of shape memory alloy (SMA) into textile substrates has received great attention among researchers and manufacturers. The SMA posses two unique behaviours which are superelastic effect and shape memory effect (SME). SME is widely used in the making of actuator rather than superelastic effect 1. The SME occured due to the changes in SMA microstructure. At low temperature, the SMA microstructure is in the form of martensite while at high temperature the microstructure change shifts to austenite form. When SMA is in the martensite form, the SMA microstructure is more flexible, thus easy to be deformed into any shape, and when it is in the a Corresponding author. E-mail: harris_6556@yahoo.com austenite form, the microstructure is more stronger, thus become very stiff and strong 2. Due to these unique temperature sensitive advantages, the SMA is able to return into pre-set shape by applying direct heat either thermally or resistively. The SMA metal compound can be obtained from the mixture of copper-zinc-aluminium-nickel, copperaluminium-nickel or nickel-titanium 3. Among them, nickel-titanium (NiTi) is the most employed SMA due to the great performance of shape recovery and more stable equiatomic structure 4. The marriage of SMA actuator either in the form of bar, rod, thin film or thin wire with textile is creating textile end products that have shape memory effect. This new textile materials is also known as smart textiles as it is now able to sense temperature changes and react to the temperature by modifying its shape. Heat can be applied either by thermal means (such as using hair dryer) or resistivity method (allowing current to pass through the smart textile) to detect its actuating performance. The microscopic view of SMA at different condition is shown in Fig. 1. There are many methods of combining SMA into textiles including spinning, weaving, knitting, braiding and spun bonding. Different methods of integration gives different kinds of SMA textile s surface appearance and function, thus suitable for certain applications. Bailleul and Boussu 5 produced a woven SMA for the purpose of technical fabric and possibilities to be used within a rigid composite. It was noted that there are some difficulties to weave the wire since the wire is more rigid and twistsensitive. Vasile et al. 6 reported the weaving of SMA Fig. 1 Microscopic view of SMA in different conditions
194 INDIAN J. FIBRE TEXT. RES., JUNE 2013 wire to be used for crease recovery of natural fiber and found that slippage problems increased during the weaving process due to the non-textile aspect of the wire. In another study, Vasile et al. 7 reported that they have overcome the obstacles by wrapping the SMA through hollow spinning technique to give the wire a textile surface. All of the studies above used SMA in the form of superelastic effect. Besides, the used of SMA actuator wire will produce a textile material that able to sense and change it shape due to the heat either by thermal heating or resistive heating. Yvonne and Vili 8 reported weaving of the SMA actuator wire to form an attractive moveable woven fabric. The wire was wrapped using a fancy yarn spinning machine to allow the wire to be at the centre of the yarn. An optimum speed of the delivery rollers and suction pressure are needed to ensure that the SMA actuator wire in the yarn turns the yarn into the coil shape (pre-set shape). It can be said that the spinning process is important to achieve a textile surface like wire, which is smooth and soft wire surface, before proceeding to weaving or other fabric formation process. The prospect of utilizing SMA wires into textiles for technical textiles applications seems promising and that is the aim of this study. DREF 3000 spinning technology was used to produce SMA core-sheath friction-spun yarn with different process parameters. The actuation capability was evaluated through a resistive heating test to evaluate the work done and output power to lift the constant load at static condition. In the study, 100% cotton carded slivers were used as the sheath and core fibres of the yarn. The cotton carded sliver size was 4 ktex and 5 ktex. The SMA actuator wire (MEMRY GMBH) has a diameter of 0.175 mm with a linear density of 130 tex and a tensile strength of 17.513 cn/tex. The wire was set to a coil shape using high temperature (550 C) in the furnace before spinning. The core-sheath friction-spun yarns were produced with the linear density of 350 tex using the DREF 3000 spinning machine. Three cotton carded slivers (5 ktex each) were used as the input materials from the creel of the machine, while 4 ktex sliver was fed to the second drafting unit. The SMA wire was supplied through a yarn guide from the back of the machine. The spinning drum speed and the core sheath ratio were kept contstant at 4400 rpm and 60/40 respectively. The yarns were spun according to the process parameters, listed in Table 1. Resistive Heating Test The test was conducted using a fabricated testing instrument as there is no specific device for measuring single wire actuating performance especially in the form of coil. The idea was to place a 20 cm length SMA FSY vertically as a conductor in the circuit. When the current is passed through the circuit, the wire is heated and then the actuated into a coil. A transparent covered box was used to maintain the temperature inside. A load was clipped at the bottom edge of the yarn to act as the connector to the SMA FSY conductor. The weights of the load as well as the wire (attached to the load) were measured to ensure that they do not give much influence while testing. The height and time taken for lifting were determined after the wire completely form a coil. A mirror was usedto avoid the parallax error while taking the measurement. A CANON digital camera was used to record the time of wire movement at the initial and complete actuation. Figures 2 (a) and (b) Spinning parameter Table 1 Spinning parameters Delivery speed m/min S1 100 S2 130 S3 160 S4 190 S5 220 S6 250 S7 100 S8 130 S9 160 S10 190 S11 220 S12 250 Main suction fan speed rpm 3400 4800 Fig. 2 Instrument setup (a) front view and (b) side view
SHORT COMMUNICATIONS 195 show the front and side views of the instrument set-up for resistive heating test. Upon heating, a reversible effect was expected by the SMA FSY where it will be in the form of coil shape. The height (length) of the SMA FSY after the yarn stop moving was taken. The difference in length (from the height of initial length) was calculated and used in equation W = mgh to measure the amount of work done (potential energy) for lifting the object [m = mass of the load (constant), g = gravitational field strength, h = height of lifting and W = amount of work done]. The time of actuation was taken to calculate the amount of output power for lifting the object using the equation P = W / t [P= value of output power, W = amount of work done, and t = difference of time between the initial and stop]. The schematic of the yarn actuation tests is given in Fig. 3. The core-sheath yarn surface and cross-section are shown in Figs 4(a) and (b), captured under the LEICA digital microscope. It can be seen that the SMA wire is positioned at the center of the yarn. Figure 5 shows the comparison of actuation capabilities of the SMA Fig. 4 (a) yarn surface appearance and (b) cross-section, observed under LEICA microscope Internal Friction Test The internal friction test was conducted using a Universal Testometric Instrument and following JIS standard for yarn tensile strength. The test was conducted to evaluate the grip strength of the sheath material to the core material. The test speed and gauge length were set at 50 mm/min and 18 cm respectively. The sample was cut into 20 cm length. Then, about 1 cm of sheath was strip away from the yarn so that part of the wire is exposed. The sample was put to grip by a special gripper where the top gripper holds the stripped region (exposed wire) and the bottom gripper holds the yarn. It is important to note that 1 cm region needed to be carefully stripped to avoid the initial pulling force that have been given to the yarn before the internal friction test being conducted. The wire was pulled upward until completely taken out from the sheath. Fig. 3 Schematic diagram of yarn actuation test [(I) before heating the yarn, (II) during heating and (III) after switching off current] Fig. 5 Relationship between work done and delivery speeds at different volts
196 INDIAN J. FIBRE TEXT. RES., JUNE 2013 FSY (S1 S12) and SMA wire (W). It can be seen that the changes in the delivery speed and the suction fan influence the SMA wire actuation capability. The S6 yarn exhibits the highest amount of work done while S2 shows the lowest work done value for all the 4, 6 and 8 voltages. The change in the delivery speed as well as the main suction fan speed have influenced the actuation performance. With increasing delivery speeds (while maintaining the suction fan speed at 3400 rpm), with the exception of S2, there is an increase in the work done. However, at higher suction fan speeds, the trend (samples S7 - S12) is not obvious as they may have about the same values for the work done. The differences in terms of the actuation performance among of these samples are probably due to the amount of fibre that covers the yarn, the number of twist given to the yarn and tightness of the sheath wrapping the SMA wire. It is observed that there are some problems in spinning the S6 and S12 yarns due to the high delivery roller speed (250 m/min). The spinning process could not run more than 5 min after which it will stop running producing yarns of less than 5 m in length. It is also found that the yarn spun at the lowest and highest delivery speeds (100 m/min and 250 m/min) results in yarns of high bulkiness. In addition, the SMA wire is loosely gripped by the sheath fibres as there is a small gap that exists between the sheath and the wire. For these types of yarns, the sheath somehow restricts the movement of the wire during the actuation test. The restriction occurs because as the wire is tried to coil up upon actuation, it pulls the sheath together with it. As the wire is loosely gripped, the sheath tends to buckle and contract and this results in some restriction to the movement of the wire as the sheath achieves its maximum contraction. Samples that are spun at other delivery speeds produces tighter sheath/wire yarn structure. The tight interaction results in higher internal gripping force of SMA FSY (for S1 S6 yarns, internal grip force is 81, 153, 119, 102, 90 and 72 respectively). The sheath can easily move with the wire while actuation takes place. With the exception of Sample S2 (lowest delivery speed), it can be said that as the delivery speed increases, the internal grip (force) of the sheath material to the core decreases. This is in agreement with results reported by Das et al. 9. The time of actuation is reflected in the output power generated to lift the load. As can be seen in Fig. 6, the wire (W) shows the highest output power in comparison with the SMA FSY yarns. The SMA FSY actuates slowly than the wire due to some restrictions given by the loose sheath fibres, as explained above. The SMA FSY is not able to maximise its power for lifting in comparison with the reference wire and hence resulting in lower output power. It is also found that there are not much significant differences in terms of the actuation capabilities at different voltage supply. The SMA actuator wire is successfully spun using the DREF 3000 spinning system where the wire is correctly positioned at the central axis position of the Fig. 6 Relationship between output power and spinning parameters
SHORT COMMUNICATIONS 197 yarn and totally covered by the sheath material. As the delivery speed increases, the work done by the yarns also increases as a result of less internal friction between the sheath and the SMA wire. Meanwhile, the output power of actuation of the SMA FSY yarns is lower than the actuation of the wire itself, due to restriction of the wire movement by the sheath material. Acknowledgement The authors thankfully acknowledge the support from Nordin Technologies Sdn. Bhd., Malaysia, for providing access to the DREF 3000 friction spinning machine. Thanks are also due to the Ministry of Higher Education, Malaysia, for funding the project under the Fundamental Research Grant Scheme (FRGS). References 1 Costin-Sebastian Z & Christian U, Sci Bull, 2 (2010) 68. 2 Nespoli A, Besseghini S, Pittaccio S, Villa E & Viscuso S, Sensors Actuators, A158 (2010) 149. 3 Marius-Mihai C & Nica V, Physics Adv Materials Winter School, (2008). 4 Casati R, Passaretti F & Tuissi A, Procedia Eng, 10 (2011) 3423. 5 Bailleul G & Boussu F, AUTEX Res J, 2 (2002) 1. 6 Vasile S, Ciesielska-Wrobel I L & Githaiga J, Fibres Text Eastern, 89 (19) (2011) 41. 7 Vasile S, Grabowska K E, Ciesielska-Wrobel I L & Githaiga J, Fibres Text Eastern, 78 (18) (2010) 64. 8 YvonneY F & Vili C, Text Res J, 77 (2007) 290. 9 Das A, Ishtiaque S M & Yadav P, Text Res J, 74 (2004) 134.