Analytical approach for modal characteristics of honeycomb sandwich beams with multiple debond

An analytical formulation for the evaluation of vibration characteristics of sandwich beams with multiple debond at the interface between the carbon fiber reinforced plastic (CFRP) face sheets and honeycomb core is obtained and verified through test. The well-known split theory is modified considering the core stiffness of sandwich beam model and accordingly the equations of motion are set up for both the undebonded and the debond regions to solve the Eigenvalue problem. Honeycomb sandwich beams with aluminium as well as quasi-isotropic carbon epoxy laminate face sheets of same thickness and core height are fabricated and tested. In the case of cantilever beam with single debond, the region of validity of the analytical solution for natural frequencies and mode shapes are found to be within a debond size of 12% of the beam length for sandwich beams with either CFRP or aluminium skin. Studies on multiple debond reveal that a single long debond can result in significant reduction in the frequencies of the beam than multiple debond of comparable length located along the same axial direction compared to intact beam.