Imaging delamination in composite laminates using perturbation to steady-state wavefields

Delamination in composite laminates, though barely visible, can jeopardize integrity and safety of the composite structures. Interaction of guided waves with delamination in full wavefields have been widely used to graphically characterize the delamination. Recently, steady-state wavefields (SWs) in place of transient wavefields have been used for imaging delamination. However, interaction with delamination can be largely obscured by steady-state waves and hardly observed. Addressing this problem, this study proposes a novel approach for imaging delamination using perturbation to SWs. In particular, a new concept of delamination-caused perturbation to a SW is proposed. Compared to scattered waves from delamination, it is determined by delamination only and naturally sensitive to delamination. Delamination-caused perturbation to a SW is concentrated within the delamination region and rapidly attenuates at undamaged locations. On the basis of this new concept, a delamination index (DI) is established for imaging delamination, by which the delamination can be graphically characterized. The capability of the approach is experimentally validated on composite laminates with delamination, whose SWs are acquired through laser scanning. The experimental results validate that delamination imaging can be achieved by DIs, by which the occurrence, locations, and sizes of the delamination can be graphically characterized.