Detection of sub-surface delamination based on the dynamic shear strain analysis

An analytical study about the scattering behavior of the A0-mode Lamb wave at a delamination in a quasi-isotropic composite laminated material is described. In the delamination boundary region being parallel with the free plate surface, stress-free boundary conditions are assumed. As a result of scattering on a delamination edge, transmitted wave front and reflected wave front are overlapped with each other. Therefore, the linearity between the orthogonal pair of out-of-surface shear strains is violated. Consequently, the violation of linearity arising on the boundary of defects yields the positive value of determinant of a covariance matrix which is composed of the orthogonal pair of the shear strains. In this study, the computational process in wave field near the delamination is discussed and their physical meanings are investigated through numerical experiments.