Interaction of Elastic Waves with Delaminations in CFRP Structures: A Numerical Study Using the Spectral Element Method

In many SHM applications elastic waves are used to determine the health of a structure. Especially in case of thin walled structures, guided waves have shown a high potential to detect damages or irregularities. Surface bonded or integrated piezoelectric elements excite the structure and induce elastic waves. The wave propagation at particular positions can also be sensed by piezoelectric elements. Many experiments are necessary to design an optimum sensor configuration in real SHM-applications to detect specific kind of damages. The present work discusses a typical damage type and the interaction with the elastic waves for a CFRP structure. Delamination is one of the most common failure mechanisms in laminated structures. To simulate the wave propagation and the interaction with the damage the time domain spectral element method (SEM) with 2D flat shell spectral elements is used. For materials with a symmetrical layup the result is a diagonal mass matrix. This advantage leads to a significant saving of memory and to a reduction of complexity of the time integration algorithm. Within the spectral element model the delaminated area is modelled by using separated upper and lower elements. A contact formulation is used to prevent the penetration between the separated layers. Different interaction effects of the elastic waves with the delamination will be shown by numerical studies.