The impact of finite-stiffness bonding on the sensing effectiveness of piezoelectric patches

Abstract

This note assesses the impact of the quality of the bonding layer on the sensing capability of plane piezoelectric patches. The bonding layer between the piezoelectric material and the main structure is assumed to be elastic, having a finite stiffness and considerable thickness as compared to the thickness of the piezoelectric sensor. The equations governing the mechanical equilibrium are simplified by assuming a pure shear stress state in the bonding film. The equilibrium equations are derived, the associated functional is obtained and, subsequently, the finite-element method is employed to solve the problem in two dimensions. The displacements found are those occurring on the contact surface between the bonding film and the piezoelectric sensor. The numerical solution obtained in terms of displacements allows the calculation of the effective voltage 'observed' by the piezoelectric sensor. This investigation addresses shear lag effects and shows that end-bonding must be carefully assessed in order to enhance the quality of the sensing output.