Methodology for Design of an Active Rigidity Joint

Abstract

Active control of composite structures has primarily focused on vibration control and other small-scale deformations. For use in morphing aircraft structures, a composite ``smart joint'' is proposed, employing both shape memory alloy and shape memory polymer to replace a conventional rotary actuator. This joint functions as a discrete member capable of both actuation and structural rigidity in user programmable states, with large-scale tip deflections on the order of 10—20% camber. A strain energy model is used to prescribe joint deflection in terms of thermally varying material properties across the thickness of the joint, allowing the designer of a morphing system to select electrical power input and element composition as based on deflection, response speed, and load capacity. This model discretizes the transformation into a multiple step shape change maneuver using the tri-phase process to determine deflection both when heated and when set into its cooled state. Comparison with a finite element model confirms thermodynamics analysis as well as deflection accurate within 2% of analytically predicted behavior.