Detection of symmetric delamination using Time of Flight

A feasibility study on detection of symmetric delamination size in a quasi isotropic laminate, [0/+45/-45/90]s, using Time of Flight (ToF) of Lamb waves has been carried out through numerical modeling. Numerical simulations have been carried out using conventional Finite Element Method (FEM) on three delamination lengths of 40mm, 50mm and 60mm. In the numerical model, ply wise modeling was adopted. Delamination was modeled by de-merging the nodes at that location. Based on the interaction of the incident Lamb mode with delamination, an expression was derived, which gives the size delamination from ToF of Lamb waves. The ToFs of incident Lamb mode and mode converted Lamb mode on the transmitted side have been found from numerical simulations. These arrival times were used in the derived expression to find out the delamination size. The predicted delamination sizes were found to be matching closely with actual delamination size.