Diameter Shape Memory Alloy Wires Research Articles

Soft fabric muscle based on thin diameter SMA springs

This study proposes fabric muscles based on shape memory alloy (SMA) springs coiled with a thin diameter SMA wire of 80 to improve heat dissipation under natural convection and forced air cooling. A new structure and its fabrication process are developed to create soft and flexible fabric muscles capable of supplying current and withstanding high external force, using a large number of thin SMA spring bundles. A total of 250 bundles of SMA springs weighing only 3.2 g constitute the fabric muscle that can lift a 1500 times-heavier mass, where each strand behaved like a muscle fiber. The fabric muscle generates a blocking force of up to 56.54 N and a power density of 2072 W kg−1. In addition, an air-cooling structure similar to a showerhead is proposed to further improve the actuation speed of the fabric muscles and maintain the flexibility of the fabric muscles. The fabric muscle with forced air cooling is cooled 40.5% faster than that with natural cooling. Finally, the results confirm that forced cooling can drive the muscle with a cycle of 5.5 s.

A novel model-based approach for resistance estimation using rise time and sensorless position control of sub-millimetre shape memory alloy helical spring actuator

Shape memory alloy shows considerable strain during heating and cooling. This effect is due to its phase transformation with temperature. Due to this property, shape memory alloys can be deployed for physical actuation in place of conventional actuators in bio-medical and bio-mimicking robots. Sub-millimetre diameter shape memory alloy wires wound as helical springs are also used for this purpose. Due to their small size, it is difficult to use sensors for temperature or displacement measurements of shape memory alloy springs. This article attempts to demonstrate that the rise time of the current through a sub-millimetre diameter shape memory alloy helical spring is directly proportional to its displacement. To characterize the rise time–displacement hysteresis, a constant current drive with overcurrent protection is developed. The data generated are utilized to implement an open-loop sensorless control. A method to estimate the resistance from the rise time is proposed with which the temperature of the shape memory alloy during actuation can be obtained. The design avoids using an analogue-to-digital converter for the direct measurement of voltage and current for measuring the resistance variation in the shape memory alloy under actuation. This helps in the development of a new sensorless control using only the digital Input/Output pins of a microcontroller/microprocessor.

Experimental flexural behavior of SMA-FRP reinforced concrete beam

The most critical drawback in currently used steel reinforcement in reinforced concrete (RC) structures is susceptibility to accumulation of plastic deformation under excessive loads. Many concrete structures due to damaged (yielded) steel reinforcement have undergone costly repairs and replacements. This research presents a new type of shape memory alloy (SMA)-based composite reinforcement with ability to withstand high elongation while exhibiting pseudo-elastic behavior. In this study, small diameter SMA wires are embedded in thermoset resin matrix with or without additional glass fibers to develop composite reinforcement. Manufacturing technique of new proposed composite is validated using microscopy images. The proposed SMA-FRP composite square rebars are first fabricated and then embedded in small scale concrete T-beam. 3-point bending test is conducted on manufactured RC beam using a cyclic displacement controlled regime until failure. It is found that the SMA-FRP composite reinforcement is able to enhance the performance of concrete member by providing re-centering and crack closing capability.

A SMA-based actuation system for a fish robot

We design and test a shape memory alloy (SMA)-based actuation system that can be used to propel a fish robot. The actuator in the system is composed of a 0.1 mm diameter SMA wire, a 0.5 mm-thick glass/epoxy composite strip, and a fixture frame. The SMA wire is installed in a pre-bent composite strip that provides initial tension to the SMA wire. The actuator can produce a blocking force of about 200 gram force (gf) and displacement of 3.5 mm at the center of the glass/epoxy strip for an 8 V application. The bending motion of the actuator is converted into the tail-beat motion of a fish robot through a linkage system. The fish robot is evaluated by measuring the tail-beat angle, swimming speed, and thrust produced by the tail-beat motion. The tail-beat angle is about 20o, the maximum swimming speed is about 1.6 cm/s, and the measured average thrust is about 0.4 gf when the fish robot is operated at 0.9 Hz.

Enhancing the post-buckling response of a composite panel structure utilising shape memory alloy actuators – a smart structural concept

Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of a laminated panel structure. An extensive experimental and numerical programme has been conducted, of which, results will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy panel is outlined. The panel specimen features 0.3 mm diameter shape memory alloy wires embedded and partially consolidated to the host matrix at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminate. Structural finite element (FE) analysis has been employed to determine the hybrid panel's adaptive response while under the influence of the uniaxial compressive load in excess of its pseudo-critical buckling value. It is shown that, utilising the control authority generated from the small SMA actuator volume fraction employed, the out-of-plane displacement of the post-buckled laminated panel can be reduced. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.

The control of the post-buckling response in thin composite plates using smart technology

Restoration forces, associated with embedded activated pre-strained shape memory alloy wires, have successfully been employed to enhance the post-buckling behaviour of various laminated plate structures. An extensive experimental and numerical programme has been conducted, the results of which will be presented. The manufacturing methodology of the hybrid SMA/carbon/epoxy plates is outlined. Such specimens feature 0.4-mm diameter shape memory alloy wires located within tubing at desired locations. Numerical thermal analysis has been employed to predict the non-uniform temperature profile, attributed to shape memory alloy activation through resistive heating, within the laminates. Structural finite element analysis has been employed to determine the hybrid plates' adaptive response while under the influence of a uniaxial compressive load in excess of its critical buckling value. It is shown that, utilising the considerable control authority generated, even for a small actuator volume fraction, the out-of-plane displacement of the post-buckled laminates can be significantly reduced. Such displacement alleviation allows for load redistribution away from the specimens' unloaded edges. With the increase in use of composite materials within aerospace platforms, it is envisaged that the hybrid adaptive SMA/laminate configuration will extend the operational performance over conventional materials and structures, particularly when the structure is exposed to an elevated temperature.