Development of a fuel-powered shape memory alloy actuator system: II. Fabrication and testing

Abstract

The second part of this work discusses the fabrication and testing of a fuel-powered shape memory alloy actuator system (FPSMAAS) and its main components. Fuel (propane) is burned in a combustor and its heat is transferred to a working fluid medium, which in turn transfers the heat to the SMA element to drive its martensite-to-austenite phase transformation. For the austenite-to-martensite transformation, the heat is removed from the SMA element by a cooling fluid, from which the heat is then removed via a heat exchanger. The process of implementing the FPSMAAS consisted of three phases of increasing complexity, corresponding to three generations of the actuator system. For the final generation of the FPSMAAS, the SMA element was housed in a rectangular channel, featuring an innovative way of separating the cold from the hot fluid medium that alternately come in contact with the SMA element, in order to minimize the mixing between them. To meet our goal of miniaturization, a multi-channel combustor/heat exchanger and a micro-tube heat exchanger were developed and tested. The final actuator system was composed of pumps, solenoid valves, check valves, bellows, a micro-tube heat exchanger, a multi-channel combustor/heat exchanger and a control unit. The experimental tests of the final system resulted in 250 N force with 2.1 mm displacement and 1.0 Hz actuation frequency in closed-loop operation. The test results for the individual components as well as the final assembled actuator are compared with the results of the numerical analyses conducted in Part I and a good agreement has been demonstrated.

Aerospace applications of shape memory alloys

“…A second challenge is the low actuation efficiency. Efficiencies can reach levels in the range of 10-15 per cent [69] though in some studies they have fallen short of the idealistic Carnot predictions of ∼10 per cent [70,71]. This is often not important for commercial and military aircraft applications because engine power and waste heat are often in excess.…”

Comparative study of robotic artificial actuators and biological muscle

“…Another challenge is the low efficiency, which is approximately 10% theoretically and usually less than 5%, in practice; these values are much lower than the efficiency of biological muscle (Figure 7(a)). 108,115 Most SMA actuators are based on a spring configuration but the stress distribution is not constant over the spring cross section, which require a larger volume of material to be heated or cooled for the same output force and further reduces the actuator’s efficiency. For optimal use of the NiTi SMA, a straight wire configuration is recommended due to a greater amount of work generated from less material volume.…”

“…118,153 The high strain and stress produces a high work density of 3.4 MJ/m 3 and a high specific power of 3.6 kW/kg. 53,65,114,115 The strain rate of DEAs is 450%/s due to the charges’ quick response to an electric field. Furthermore, due to its simplicity and low modulus, this DEA is suitable for applications where mechanical compliancy and compact sizes are essential.…”

Designing shape memory alloy linear actuators: A review

“…However, tension loading produces the highest actuator efficiency and energy density for SMA actuators compared to the other types of loadings, as shown in Table 1. The actuator efficiency is based on the practical application, which is much lower than the theoretical and Carnot-cycle-based efficiencies (Humbeeck, 1999; Jackson et al, 1972; Jun et al, 2007; Mohd Jani et al, 2014). Due to the associated performance advantages, most SMA applications are designed in wire form to benefit from tension type of loading.…”