Detection and Quantification of a Disbonded Aluminum Honeycomb Panel Using Nonlinear Superharmonic Frequencies

Abstract

Damage in composite materials is challenging to detect because of complex behavior. Using nonlinear analytical techniques, the behavior of a disbond in an aluminum honeycomb material is illuminated. By analyzing the superharmonic frequencies under sinusoidal excitation, quadratic stiffness was seen in a disbonded panel and tracked as the damage area increased. A cubic nonlinearity was also observed, but only when the damaged area was larger. It is hypothesized that the quadratic nonlinearity is due to the change in face sheet stiffness as the top sheet vibrates off and into the honeycomb core. The cubic nonlinearity is not as easily explained due to the changes in response amplitude not following the analytical approximations. The lack of a nonlinear backbone curve indicates that the cubic nonlinearity is not related to stiffness but most likely damping. The elastic behavior of the epoxy adhesive under high strains and geometric constraints is thought to contribute to the cubic nonlinearity. More work into understanding the relationship between the epoxy viscoelastic behavior and the panel response is necessary.