Development of a Galfenol actuator for operation under tension

Abstract

A Galfenol-based actuator has been designed to generate output forces while operating under tensile strains, demonstrating successful long term operation with no appreciable change in performance. Two prototype actuators were manufactured and tested under quasi-static and dynamic conditions. Dynamic power requirements included a 15–16 amp DC bias and up to 25–26 amp AC (pk-pk). Two cooling fans were used to provide convection cooling of the drive coils during dynamic operation, allowing for 100% duty cycle at 300 Hz; without the use of cooling fans, 100% duty cycle operation would be limited to frequencies below 150 Hz. In quasi-static displacement mode (0.5 Hz, no applied force), the actuators were capable of outputting between 5.78 and 7.12 kN (1300–1600 lbf). While the output force decreased with applied tensile stress and operational frequency, significant forces were measured up to 0.14% (0.0014 mm mm−1) applied tensile strain using 300 Hz tones. The magnitude of the measured dynamic force output was limited by the matched stiffness between the MTS 810 load frame (140 kN mm−1 or 0.8 × 106 lbf in−1) and the prototype actuators (122.6 kN mm−1 or 0.7 × 106 lbf in−1). By connecting to stiffer loads, larger force outputs and higher tensile strains could be applied. Long term testing of the actuator at 63 Hz and alternating tensile loads of 4.45 and 22.24 kN (1000 and 5000 lbs) has continued to over one billion cycles, with no change in actuator performance. Demonstration of the Galfenol technology in this unique tensile application provides a capability that does not exist with current off-the-shelf transducer technologies.