Sizing of delamination using time-of-flight of the fundamental symmetric Lamb modes

In this study, a procedure is devised, using the fundamental symmetric Lamb mode (S-o) to estimate the size of an impactinduced delamination at the bottom interface of a composite laminate, which has been subjected to a low-velocity impact. When S-o mode incidents at the edge of delamination, it propagates independently in 0 degrees layer and the rest of layers. Based on the propagation of S-o mode in the delaminated region, an expression is derived, which can estimate the size of interface delamination using measured arrival times or Time-of-Flight (ToF) of S-o modes. Numerical simulations were carried out on glass/epoxy (GFRP) cross-ply laminates ([0/90(2)](s)) to confirm the derived expression and eventually it was validated through experiments carried out on [0/90/0] GFRP laminates. Moreover, the minimum detectable size of delamination through the proposed method was estimated analytically and verified through numerical simulations.