Identification of the effect of debonding on the linear and nonlinear effective damping of an adhesive joint

In this paper, inverse-eigen sensitivity identification technique is used to investigate the effect of damage on the effective damping of a viscoelastic adhesive, in both linear and nonlinear regions of adhesive behavior. The modal parameters derived from the measured linear and nonlinear Frequency Response Functions (FRF) of the bonded structure are used in identification process. Experimental FRFs are employed to identify linear and nonlinear bending and shear modes which are then used for identifying of damping coefficient at different frequencies. The nonlinear FRFs are measured using the Optimum Equivalent Linear System (OELS) concept. The results indicate that the damping of the adhesive decreases with frequency. Also, debonding damage has a decreasing effect on damping of adhesive, both in linear and nonlinear regions, and with increasing the damage percentage the reduction becomes more significant. Results also show that the linear and nonlinear effective damping are different and hence depend on both amplitude of response and the mode shapes involved.