Modeling of a Shape Memory Integrated Actuator for Vibration Control of Large Space Structures

Abstract

Martin Marietta is developing a shape memory material actuator to pro vide active vibration and shape control for large, adaptive space structures. An important facet of this work is the development of analytical modeling capabilities for shape memory material behavior. These alloys exhibit a very interdependent force-length-temperature (FLT) response, which must be understood to best exploit their behavior for the efficient and timely conversion of heat into mechanical work. Also, the modal response of large, flexible space structures will be affected by the use of inherently non-linear, hysteretic shape memory actuators, and specialized control methodologies need to be developed spe cific to this application. In this work, Cory and McNichols' theory of non-equilibrium thermostatics (NET) was modified to account for the multiple quadrant (i.e., tension and compression) hysteretic behavior of shape memory alloys. Experimental results were used to provide the basis for spatial mapping of the austenite-to-martensite (AM) and mar tensite-to-austenite (MA) phase transformation boundaries, along with the relative loca tions of the 100% austenite (Z_A ) and 100% aligned martensite (Z_M ) saturation surfaces in the three-dimensional FLT material behavior domain. A Fortran subroutine, describing the shape memory material actuator, was incorporated into dynamic analyses of a simpli fied finite element model based on the Spacecraft Control Laboratory Experiment (SCOLE) structure. A slewing maneuver of 20 degrees in 12 seconds was used to study a number of cases for the shape memory actuator which utilized a biasing force (e.g., the biasing effect of a matrix in a strain-compliant shape memory composite) acting against 150 NiTi wires (0.5 mm dia. by 0.50 m in length). Temperature was used as the command variable to demonstrate active vibration control during and after the slew maneuver. Sig nificant passive damping was noted, in addition to effective active control when the actua tor's temperature was pulsed. This analytic "test bed" will provide critical insight into the design and analysis of smart, adaptive shape memory space truss tubes and actuators for vibration and shape control, as well as the vehicle by which future shape memory actuator control algorithms and methodologies can be assessed.