Design of Ferromagnetic Shape Memory Alloy Based Actuators
Minoru Taya, Professor and Director
Center for Intelligent Materials and Systems
Department of Mechanical Engineering
University of Washington, Box 352600
Seattle, WA 98195-2600
Email: tayam@u.washington.edu
Sponsored By:
Center for Materials Research and Analysis
UNL Academic Senate
Dept. of Engineering Mechanics
Date: Wednesday, December 4, 2002
Time: 9:30 a.m.
Place: 105 Othmer Hall
Ferromagnetic FePd alloy was proposed as a robust actuator material that can be driven by applied magnetic field at fast speed (Taya, et al, 2001). The key mechanism of actuation of FePd is “hybrid mechanism”, which is a chain reaction of applied magnetic field gradient, magnetic force, stress-induced martensite phase change from austenite. Ferromagnetic shape memory alloy (FSMA) , FePd can undergo a phase transformation, from stiff austenite to soft martensite under applied stress(s), temperature (T) or magnetic field (H), or combination of them, which requires use of three-dimensional (3D) phase transformation diagram. Three mechanisms have been proposed for actuation of an FSMA, (1) phase transformation by applied (constant) magnetic field, (2) stress-induced martensite phase transformtion (SIM), and (3) variant rearrangement of 100% martensite phase. Taya, et al (2001) proposed a hybrid mechanism, which is based on (2), but driven by applied magnetic field gradient, which induces stress field in a FSMA specimen. This hybrid mechanism is found to be the most effective in inducing large force and stroke in a FePd driven by a compact electromagnet system, a key requirement in designing compact and robust actuators. The FSMA actuators based on mechanism (1) require a huge magnetic field for phase change, as the phase boundary between martensite and austenite is often parallel to H-axis, while the FSMA actuators based on mechanism (3), such as that based on NiMnGa, are expected to provide a modest blocking stress (up to only a few MPa , as compared with 500 MPa of FePd). Based on the above hybrid mechanisms, we have designed a set of FSMA actuators, spring and membrane types. The spring type is based on polycrystalline FePd FMSA while the membrane actuator is based on FSMA composite: superlastic TiNi plate and ferromagnet Fe ring to minimize the material costs (please note that Pd is most expensive). I will talk about these few examples of FSMA actuators.
Dr. Taya obtained his BS in Engineering, University of Tokyo in 1968, and his PhD in Theoretical Applied Mechanics, Northwestern University, in 1977. He served as a Professor of Materials System, Tohoku University, Japan from 1989-1992, Royal Society Senior Research Fellow, University of Oxford in 1986, Visiting Scientist at Riso National Laboratory from 1981-1985. Currently he is Professor of Mechanical Engineering, and also Materials Science and Engineering. He is running Center for Intelligent Materials and Systems (CIMS) where a number of materials for actuators and sensors are designed and processed, they are shape memory alloys (SMA), ferromagnetic SMA (FSMA), electro-active polymers, conducting polymers and piezoelectric composites with functionally graded. The current sponsoring agencies and companies of CIMS are AFOSR, Darpa, ONR, NSF, Boeing, NEDO, Honda , Hitachi Powder metals and Toray. Current full time CIMS researchers are 3 faculty, 3 post doctors and 8 graduate student researchers.
