Effect of debonding on natural frequencies and frequency response functions of honeycomb sandwich beams

The natural frequencies of honeycomb sandwich beams having debonding or delamination embedded between the face-layer laminates and the honeycomb core are studied herein. A theoretical analysis of the effect of the extent of debonding on the flexural stiffness and on the natural frequency is compared with experimental observations. In this analysis the free vibration of the delaminated sandwich beams is studied using the split sandwich beam model, and the equations of motion are set up for the undelaminated region of the sandwich beam and the delaminated region of the laminated beams. Finally, changes in the peaks and valleys of the frequency response functions (FRFs) due to delamination are examined. By using the modal parameter identification method [H.Y. Kim, W. Hwang, Compos. Struct., 2001 (in press)], the extent of delamination of the sandwich beams can be identified in terms of the natural frequencies and damping ratios of the debonded beams. Vibration testing was conducted on honeycomb sandwich beams with carbon/epoxy laminated composite faces and Nomex-aramid honeycomb core. Agreement between the predictions of the model and experimental results is good.