Interface Waves for Detecting Defects in Bonded Hybrid Joints

Damage nucleation and growth can be complex in hybrid bonded structures composed of metals and laminated composites. There are limited reliable analytical and empirical methods to evaluate the bond integrity of such structures and to quantify the state of bonding in hybrid joints. Depending on the geometry and accessibility to hybrid joint sections, ultrasonic Nondestructive Testing (NDT) techniques are available for inspection of these structures. The interfacial damages at the bondline of structural joints represent challenging detection tasks for traditional ultrasonic nondestructive inspection (NDI) methods such as the pulse–echo method. This work investigates a method for bonded joint inspection that uses interface guided ultrasonic waves propagating along the bondline of these hybrid joints. An analysis, based on the use of finite element models for hybrid structures, is conducted to examine the use of interface waves to detect common defects found at or in the vicinity of interfaces of hybrid isotropic-anisotropic structures. Both cohesive and adhesive damage in a bonded joint are examined. Several damage scenarios are numerically studied and the guided wave time of flight (TOF) is shown to be sensitive to the size and location of interfacial damages. The results of this study suggest that interface guided waves can be used for integrity assessment and damage detection in hybrid structures.