Damage detection and vibration control in smart plates: Towards multifunctional smart structures

This paper demonstrates the concept of sensitivity enhancing control (SEC) to aid in damage detection in smart structures through both experimental an d simulation evaluation. Methods of implementing state estimate feedback us ing point measurements of strain along the structure are described, and an initial proof-of-concept laboratory experiment demonstrating enhancement of modal frequency shifts due to tip mass damage in a cantilevered beam is re ported. Simulation results focus on applying state feedback control to fini te-element models of a cantilevered structure with slot, through-surface cr ack, or surface crack damage. The simulation analysis ascertains the abilit y to enhance sensitivity of modal frequency shifts due to realistic damage cases that are difficult to evaluate experimentally. The simulation also as certains the potential for using the same sensors and actuators for impleme nting both sensitivity enhancing control laws and vibration damping control laws that are insensitive to damage. In the control model with which SEC l aws are designed, damage consists of simple reductions in thickness over a small area of the structure. Finite-element models to which control laws ar e applied are developed using commercial software (ABAQUS(TM)) that more ac curately models stiffness damage by releasing element connections or by usi ng line spring elements to model fatigue cracks. Experimental results show that enhancement in sensitivity of modal frequencies to damage can be achie ved using a single piezoceramic actuator and multiple piezoelectric strain sensors along the beam. Simulation results indicate that feedback control l aws can be designed for either sensitivity enhancement or vibration suppres sion using identical hardware, providing for multifunctional smart structur es. In addition, analysis demonstrates that commercial finite-element softw are is useful for model-based simulation of damaged controlled structures.