Interface Waves in Hybrid Metal-Composite Structures

Damage nucleation and growth can be complex in hybrid structures composed of layers of metal and laminated composites. Presently there are limited reliable damage growth analytical and empirical methods to evaluate the bond integrity of such structures and to quantify the state of bonding in such joints. Depending on the geometry and accessibility of hybrid joints, ultrasonic nondestructive testing (NDT) techniques are available for inspection of these structures. However there are some limitations for the usage of typical bulk or guided waves to quantify the integrity of bondline in hybrid structures. This work suggests the use of specific forms of ultrasonic guided waves that propagate along the bondline of these hybrid structures. This study is dedicated to modeling of interface guided waves for the purpose of disbond crack damage assessment. The nature of interface waves is discussed and the numerical simulation based on the material properties and geometries of hybrid interfaces as well as composite stacking sequence is verified. A finite element model of a hybrid structure with isotropic and anisotropic multilayer composites is constructed. The behavior of interface guided waves influenced by disbond cracks at free edges of hybrid bonded joints is numerically studied. The propagation characteristics of interface waves is shown to be sensitive to the size of disbond cracks. The velocity of interface waves is shown to have an inverse relation to the disbond damage size. Results show the speed is also a function of the interfacing ply orientation at the bondline. These results suggest that interface waves can be used to monitor the condition of bonded joints in hybrid structures.