Guided wave feature identification for monitoring structural damage in joints between composite laminates

Composite materials are becoming a major part of aircraft and space structures. These are commonly multilayer structures, with anisotropy, that are best joined by adhesives or co-curing. Safe operation and condition based maintenance of these structures require reliable structural health monitoring. Degradation of joints is a particular concern. Ultrasonic guided waves provide strong potential for monitoring damage and degradation of joints in these types of complex structures. A thorough understanding of the ultrasonic wave mechanics of joints and transition regions is a key for designing optimal actuators and sensing systems. Finite element analysis is used to simulate guided wave propagation using excitations selected from theoretical analysis of dispersion and wave structure of the subassemblies. Features of the received guided waves are analyzed in order to identify which ones are most sensitive to joint degradation. Damage in the form of localized delaminations and disbonds are investigated. A health monitoring strategy based on frequency and wave mode tuning to introduce high shear stress at the interface to be interrogated is followed. Initial experiments on skin-stringer joints are conducted to validate the viability of the health monitoring strategy. Thus, both numerical simulations and experiments are theoretically driven.