Di Jepang, Amerika, German, dan negara maju lainnya sedang meneliti "keajaiban" bahan polimers yang disebut nitinol. Bahan itu kelak akan digunakan sebagai actuator diberbagai bidang. Mulai dari kepentingan industri manufaktur sampai pada untuk membantu orang cacat bahkan untuk robotic.

Untuk penjelasan lebih lanjut dapat dicari di google dengan kata kunci "Nitinol" atau "electroactive polymers".

Nah, apakah di Indonesia sudah ada penelitian seperti ini?. Atau bangsa kita tetap jadi bangsa yang menunggu hasil penelitian orang lain lalu menjiplak atau membelinya dengan harapan dapat komisi dan korupsi?. Seperti halnya minyak, oknum pertamina lebih baik beli minyak jadi ketimbang memproduksinya sendiri, karena bisa dapat komisi dan dikorupsi. .

..polimer sintetik kayak kevlar sama mylar aja sulit dibikin dinegara ini...apalagi nitinol

 Oh gitu yah. Nasib emang tinggal dinegara tertinggal.

..bukannya malas nge googling nih, tetapi bisa ngga Mat dilllom menulis dikit pengertian nitinol agar forum ini jadi lebih keren...

HERMALLY ACTIVATED SHAPE MEMORY ALLOYS (SMA)

Over a century after Joule's discovery of the equivalence of energy and heat the shape memory effect was reported by Chang and Read [5]. They observed that an alloy of gold and copper returns to the same shape if heated after deformation. The same effect was later discovered in Indium-Titanium alloys by Basinski and Christian [1], and Nickel-Titanium alloys by Buehler, Gilfrich and Wiley [4]. These researchers used the term "Shape Memory Effect" (SMA) to describe the phenomena. Of all the SMAs, Nickel Titanium (NiTi) alloys (better known as Nitinol) are the most extensively studied [7]. NiTi fibers and springs have often been studied and used as artificial muscles [3,8,10,13-14] because of their relative nontoxicity, reasonable cost and an electrical resistivity that easily lends itself to Joule heating (passing of an electrical current to generate heat).

Mechanism: Martensitic transformations are at the heart of the shape memory effect as shown by Otsuka and Shimizu [16]. Martensitic transformations were discovered by the metallurgist Adolf Martens in steels [17]. It was found that the transformation from the high-temperature, body-centered cubic lattice austenitic phase to the low temperature, face-centered tetragonal lattice takes place without atomic diffusion. Martensitic transformations are phase changes that occur as a displacitive, lattice-distortive, first order diffusionless athermal transformations. In NiTi alloys with a surplus of nickel or with nickel partly replaced with a third element, a two stage martensitic transformation may occur. The intermediate phase has a rhombohedral crystal structure.

TABLE IX
THERMAL SHAPE MEMORY ALLOYS [11,12,15,20]
Property   Min.   Typ.   Max.
Strain (%)       5   8
Stress (MPa)           200
Work Density (kJ/m3)       1,000   10,000
Strain Rate (%/s)       300   
Power (W/kg)       1,000   >50,000
Life (cycles)
at an amplitude strain of:   300
~5%       107
~0.5%
Efficiency (%)           <5
Modulus (GPa)   20       83
Tensile Strength (MPa)       1,000   
Density (kg/m3)       6,450   
Applied Potential (V)   4       
Conductivity (S/m)       1,250   1,425
Cost (US$/kg)       300   
In most NiTi alloys the shape memory effect is only observed when an external stress is applied. In the martensitic phase the alloy has a twinned martensite that can be easily deformed as it de-twins. As it is heated it returns to its parent austenitic phase, which is a highly ordered state, and the alloy retrieves a well defined high-temperature shape.

NiTi alloys may also exhibit a two-way shape memory effect (TWSM) first observed by Delaey et al. in 1975 and by which the alloy will exhibit the shape memory effect without an external stress [6]. In the two-way shape memory effect NiTi alloys also have a "remembered" state at low temperature as well as all the intermediate shapes between the high temperature and low temperature. The origin of TWSM is stress-biased martensite and it can only be obtained by special conditioning involving thermo-mechanical treatment.

The contraction time of NiTi is governed by the speed at which the martensitic to austenitic phase transformation occurs and hence by the electrical power when electrical Joule heating is used. By using very large current pulses this contraction time can be reduced to several milliseconds [13]. The NiTi contraction and expansion cycles are mainly limited by the time required for NiTi to cool and return to its lower temperature shape. The cooling time is governed by thermal diffusion and convection. Factors such as heat capacity and latent heat involved in the phase transformation between the austenitic and martensitic phases must be considered when designing an actuator. Use of water cooling and nucleate boiling can dramatically reduce cooling time, enabling millisecond response times [13].

Features [1-17]: Shape memory alloys can exert very large forces per unit area (exceeding 200 MPa), operate at very high strain rates (300%/s) and undergo relatively large deformations (> 5% for poly-crystalline NiTi fibers). The peak energy density (107 J×m-3) and power per unit mass (50 kW×kg-1) of these actuators is unmatched.

Limitations: SMAs have several characteristics that impede their use as muscle-like actuators. One of them is the difficulty of controlling the length of NiTi fibers as they undergo a phase transformation. The change in length is observed over a narrow temperature range and a significant hysteresis is observed between the martensitic to austenitic and austenitic to martensitic phases. The phase transformation temperatures vary more or less linearly with stress and the cycling characteristics also change if only partial transformations occur. All of these factors must be modeled appropriately when NiTi fibers are used in a servo-actuator.

NiTi actuators also have a limited cycle life. At very large strains their shape memory effect degrades significantly, from millions of cycles at 0.5% strains to a few hundred cycles at strains of 5% [7] depending on the alloy and conditioning. Their usage is also limited by the low efficiency of NiTi fibers in converting electrical energy to mechanical work which is found to be 5% in the best case (including recovery of energy from heat, [15]) and is usually much lower.

Materials: Nickel titanium shape memory alloys are commercially available from several sources including Shape Memory Applications Inc. http://www.sma-inc.com/.

Applications: NiTi wires, tubes and components are widely used in medical applications due to their super-elasticity, a property related to the memory effect. Little use is made of the actuation properties.

[1] Basinski, Z.S. and Christian, T. Acta Metallurgica, 1954, 2, 101.
[2] Bergamasco, M. Salsedo, F. and Dario, P. A linear SMA motor as direct-drive robotic actuator. 1989 IEEE International Conference on Robotics and Automation, May, 1989, Scottsdale, Arizona, 618-623.
[3] Bergamasco, M. Salsedo, F. and Dario, P. Shape memory alloy micro-motors for direct-drive activation of dexterous artificial hands. Sensors and Actuators, 1989, 17, 115-119.
[4] Buehler, W.J., Gilfrich, J. and Wiley, K. Journal of Applied Physics, 1963, 34, 1465.
[5] Chang, L.C. and Read, T.A. Transactions of the American Institute of Mechanical Engineers, 1951, 189, 47.
[6] Delaey, L., Thienel, J. Shape Memory Effects in Alloys, Jeff Perkins (Ed), Plenum, 1975, New York, 341-350.
[7] Funakubo, H. (ed.) Shape Memory Alloys. Gordon and Breach: New York, 1987.
[8] Hirose, S., Ikuta, K. and Umetani, Y. A new design method of servo-actuators based on the shape memory effect, in Theory and Practice of Robots and Manipulators, Proceedings of RoManSy'84, the 5th CISM-IFToMM Symposium, Hermes Publishing, 1985, 339-349.
[9] Hirose S., Ikuta, K. and Sato, K. Development of a shape memory alloy actuator. Improvement of output performance by the introduction of a s-mechanism. Advanced Robotics, 1989, 3, 89-108.
[10] Homma, D., Miwa, Y. and Iguchi, N. Micro robots and micro mechanisms using shape memory alloy. The 3rd Toyota Conference Integrated Micro Motion Systems: Micromachining, Control and Application. Nissin, Aichi, Japan, October, 1989, 22, 1-21.
[11] Hunter, I.W. Novel Actuators For Use in Robotics And Tele-Robotics, US Office of Naval Research Report, 1990, 88p, NTIS.
[12] Hunter, I.W., Lafontaine, S. and Hollerbach, J.M. Artificial muscle prototype for use in robotic and prosthetic limbs. Proceedings of the 16th Canadian Medical and Biological Engineering Conference, 1990, 16, 35-36.
[13] Hunter, I.W., Lafontaine, S., Hollerbach, J.M. and Hunter, P.J. Fast reversible NiTi fibers for use in microrobotics. Proceedings IEEE Micro Electro Mechanical Systems, 1991, 2, 166-170.
[14] Ikuta, K. Micro/miniature shape memory alloy actuator. Proceedings IEEE Micro Electro Mechanical Systems, 1990, 3, 2156-2161.
[15] McCormick, P.G., On the practical efficiency of shape memory engines, Scipta Metallugica 1987 21, 99-101.
[16] Otsuka, K. and Shimizu, K. Scripta Metallurgica, 1970, 4, 469.
[17] Van Humbeeck, J., Chandrasekaran, M. and Delaey, L. Shape memory alloys: materials in action. Endeavour, New Series, 1991a, 15(4), 147-154.
[18] I. Hunter & S. Lafontaine, "A comparison of muscle with artificial actuators", Technical Digest IEEE Solid State Sensors & Actuators Workshop, 1992, pp. 178-185.

This material is based on Artificial Muscle Technology: Physical Principles and Naval Prospects by John D. Madden, Nathan Vandesteeg, Patrick A. Anquetil, Peter G. Madden, Arash Takshi, Rachel Z. Pytel, Serge R. Lafontaine, Paul A. Wieringa and Ian W. Hunter in the IEEE Journal of Oceanic Engineering, Vol. 29, No. 3, p. 706, July 2004.