Guided waves in a multilayered composite and ultrasonic nondestructive evaluation

Analysis of wave propagation in a laminated composite plate with many layers is made difficult by the anisotropy of the laminae, different lay-ups, many layers and defects in the fabricated plate. A good understanding of the wave field in such a plate without defects is a prerequisite for use of ultrasonic techniques to evaluate the various defects that can substantially reduce the strength and service life of this structure. Results of modeling studies of wave propagation and scattering in a multilayered composite plate are presented. The analysis technique combines the finite element discretization through the thickness with wave form representation along the plate in order to calculate the dispersive modes of propagation in the plate. To study scattering of these waves by a matrix crack that grows into delaminations, a hybrid finite element representation of the field near the crack and the modal representation of the scattered exterior field are used. Results are presented showing the dependence of the reflection and transmission coefficients on the size of the crack with delamination which can be used to size the defect using ultrasonic techniques.