Shape memory materials

Demonstrator of an actuator moving the flap of the horizontal stabiliser for SW-4 helicopter

The most important element of the actuator – tape with NiTi wires

Control over work of the nitinol actuator from a PC

Device for rewinding and annealing (training) of nitinol wires

Project of a twisting actuator based on shape memory wires

The goal of the project was managing an enormous technical potential carried by alloys with shape memory, through: basic studies on the materials themselves, creation of new, innovative applications of such allows and creating a self-sustained network of companies based on knowledge, which will take care in the future of development of new applications of these unusual materials.

Research and modeling

Basic research on shape memory materials included physical basics of the phenomenon itself, mathematical modelling of the phase transition process (responsible for the shape memory effect) and creation of empiric models for semi-products made of nitinol (wires, tapes, sheets), which allow predicting how elements or structures made of them will behave.

Manufacturing and quality control

One of the most convenient forms of nitinol are thin wires. They are manufactured by repeated drawing of thick, cast rods. In order for the wire to obtain the designed functionality, it must be subjected to so called  "training" – a special thermal processing cycle. For more complex functionalities, the training should be non-uniform - different at different wire parts. A device designed especially for this purpose by SKA Polska can not only automatically "train" large amounts of the wire (with diameter from 0.15 to 2 mm), but also, after using a specific head, to check its quality and identify segments which meet the given criteria.

Applications

Below we present some of nitinol applications created by the participants of the project:

• Use of a nitinol energy dissipating feature allowed to create a motorbike helmet, which being much lighter than the classic composite helmets , meets all safety norms.
• Surgical stent made of a cylindrical nitinol structure uses the superelasticity effect. Compressed to a very small diameter, it is very easily introduced to the vein, where it expands, making it passable.
• Another example is a nitiniol wire with a two-way action  – woven into the fabric, it enabled to create a family of filters, which are self-cleaning thanks to appropriate vibrations.
• A special composite on  a nitinol-based fabric was used for construction of professional skies , which are characterised by high vibration damping.
• An orthopaedic rehabilitation band is initially relatively loose. After putting on - under the influence of bodily heat - it compresses.  The effect is reversible and compression characteristics may be adjusted individually to a patient.
• A very interesting example of using a shape memory alloy is a pseudoplastic tape, which is a main component of a two-way actuator. It has been experimentally used as an actuator of a trimmer in a horizontal stabilizer of Polish SW-4 helicopter. Proper design of the tape was required, so it takes into account load characteristics of the trimmer and appropriate convection conditions. A non-trivial task was also to design the control system. Besides the superior (position related) feedback loop, inferior feedback loop has been taken into account - resulting from resistance characteristics of the wire, supported by a mathematical model of a phase transition between martensite and austenite. A functional model of such an actuator has been designed and manufactured thanks to cooperation of  SKA Polska and PZL Świdnik companies.