Abstract: This paper regards metal /composite materials structure with debonding as a research object,the finite element method is used to study the influence of composite thickness on the natural frequencies,modal shapes,flexibility matrix to detect structure debonding defects. The results show that: As the thickness increases,the rate of change of the natural frequencies, the modal shape of debonding region and the flexibility matrix of debonding region all appear a increasing and then decreasing trend,when the thickness of composite materials is 5mm,the rate of them are the maximum; On different composite thickness conditon,the flexibility matrix used to detect small area debonding is feasible. The results of this paper provides theoretical guidance for experimental detecting the debonding defects of solid rocket motor nozzle structure based on the modal method in next step.

Key words: debonding, finite element method, natural frequency, modal shape, flexibility matrix, nondestructive testing