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

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.