Study of Wave Propagation in Damaged Composite Material Laminates

The characteristics of carbon fiber composites have enabled these materials to be accepted as replacements for metal parts in industry. However, due to their unsymmetrical material properties, carbon fiber composites are susceptible to damage, such as a delamination, which can cause premature failure in the structure. This has resulted in the need for nondestructive testing methods that can provide quick, reliable results so that these parts can be tested while in service. In this study, an approach was examined that involved a pencil lead break to excite multiple wave modes in a composite plate in an effort to identify key characteristics based on the wavespeed and frequency. These characteristics were then compared to models based on boundary conditions to generate dispersion curves using the transfer matrix method for whole composite plates that were either undamaged or damaged. To first test this approach, experiments were performed on multilayer isotropic plates and then on a composite plate. The results for all cases showed that modes could be excited by the pencil lead break in the undamaged region of the plates that were not theoretical possible in a delaminated region. Also modes that were specific to the delaminated region were excited and this allowed for a clear comparison between the two regions. This approach could be placed into practice to provide routine testing to detect delamination for in-service, carbon fiber composite parts.