Detection of Debonding Area in Aluminium-GFRP Laminates by Electromagnetic Transducer

Abstract

Electromagnetic Acoustic Transducer (EMAT) is applied to nondestructive testing of aluminum-GFRP laminates. Because of its high specific strength, laminated FRP came to be used in place of metal materials. However, once delamination is introduced by the impact force in the out-of-plane direction, the compressive strength in the in-plane direction is greatly reduced. To improve the tolerance for impact force, fiber metal laminates (FML) have been developed. Since debonding may occur at the interface of FRP and metal sheet, nondestructive detection of the debonding is required as health monitoring of the FML. In this study, GFRP laminates were molded on aluminum sheets, and we measured the distribution of standing wave amplitude in the aluminum sheets using EMAT for shear wave. In the bonded area, the shear wave is partially transmitted to the FRP on reflection at the boundary, which makes the attenuation coefficient larger than that in the debonded area. It was found that in scanning the EMAT, the standing wave amplitude starts to change when the center of the EMAT passes the boundary between bonding and debonding areas. It was also revealed that minimum size of the debonding area that EMAT can detect is comparable to its effective area. For accurate evaluation of the debonding area, resonant frequency measurement is recommended at each point.