Damage monitoring of composite laminates using ultrasonics

Damage characterization of composites is usually conducted through their acoustic behavior. As damage is being accumulated, this behavior is anticipated to change. Different damage mechanisms are active during loading. These mechanisms are acting in different time scales of the service life and are interdependent. Loading of cross-ply laminates leads to the accumulation of matrix cracking, delamination between successive plies and fiber rupture at the final stage of loading. The acoustic activity of damage may be correlated to the source damage mechanisms. Additionally, damage accumulation has been reported to strongly affect the wave propagation characteristics of the material. In the case of cross ply laminates, an increase of pulse velocity and transmission occurs as the top stiff layer becomes progressively isolated from the rest of the material due to matrix cracking and delaminations. As loading continues, the accumulation of longitudinal fibre breaks becomes dominant causing an eventual decrease of transmission before the failure of the specimens. The present work aims to evaluate the efficiency of ultrasonics as a methodology for structural health monitoring.