Modeling of Subsurface Damage in Sandwich Composites Using Measured Localized Nonlinearities

Abstract

Composite materials are being used more frequently in commercial and military aircraft structures. Many nondestructive techniques have been developed to inspect composite materials for subsurface damage; however, many of these existing inspection techniques aim to detect either linear changes in the material properties of the composite or geometrical changes in the material to determine the presence of damage. Subsurface damage in a sandwich composite panel is tested using a scanning laser vibrometer, and nonlinear vibration response properties are identified in the forced frequency response of the composite panel. The nonlinear behavior identified in the composite panel is applied to a homogeneous, isotropic beam model such that the forced frequency response of localized damage in the beam resembles the behavior measured in the sandwich composite panel. Stiffness and damping nonlinearities induced locally in the analytical model are used to show that multi-amplitude frequency response functions may be used as a means of detecting nonlinear behavior attributed to composite damage in a composite material. The results of the analytical model show that the nonlinear behavior due to damage displays a global behavior in an analysis of the frequency response of the system and is able to be identified locally when consideration of the linear system dynamics are taken into account.