Structural Morphing using Piezoelectric Modulation of Joint Friction

An innovative approach to morphing/reconfiguration in flexible structures through friction control in joints is proposed and theoretically explored in this study. The customary method of morphing structures through embedded actuators suffers from the fact that actuators have limited authority and high density, and that the presence of integrated/ embedded actuation devices results in stress concentrations in the substrate. As opposed to using induced elastic strain to cause morphing in elastic structures, the concept presented utilizes piezoelectric control of friction for locking/unlocking in structural joints, and sensors for sensing the structural vibration state in conjunction with naturally occurring or excitation vibration energy, to morph the structure under control. The applications of this concept are not limited to morphing alone but in a broader sense, encompass fields of reconfigurable and fault/damage tolerant structures, having characteristics typically desirable in space structures such as deployable antenna reflectors and space cranes. The proof of this concept is theoretically demonstrated using a single flexible beam (n=1) free at one end and connected to a semi-active revolute joint at the other. Based upon the commanded state of the joint, the beam can switch between a cantilevered and a pinned-free configuration, respectively. The beam is to be reconfigured to a desired azimuth angle in the least time by providing an initial excitation and controlling joint locking and unlocking timing in an optimal manner. The control actions for the timely locking and unlocking of the semi-active joint are determined analytically and verified numerically by using a finite element model simulation using DYMORE. A design of a semi-active joint model capable of providing the desired locking/unlocking action is proposed.