Vibration of debonded laminated fibre composite sandwich beams

Abstract

A new generation composite sandwich made up of glass fibre reinforced polymer skins and lightweight but high strength core material has been developed in Australia. A structural composite beam can be manufactured by gluing a number of these sandwiches. The presence of unbonded areas in the glue line due to manufacturing faults or deterioration in bond in some of the originally fully bonded areas due to aging is a possibility in a FRP structure consisting of glue-laminated fibre composite sandwich beams. The presence of no bonding in some areas of the glue line may cause changes to the vibration parameters, such as natural frequencies and mode shapes, of the beam. In particular, unbonded areas could reduce the natural frequency and if the reduced natural frequency is close to the working frequency of the beam, resonance could happen. Therefore, it is imperative to make accurate predictions of changes in natural frequencies in such beams. This paper presents a numerical investigation into changes in natural frequency due to various amounts of debonding along the glue line in a laminated fibre composite sandwich beam. The numerical analysis is carried out using beam and link elements (rigid links and master slave links) in Strand7 finite element software package. The accuracy of the numerical solution is verified by comparing present results with bench mark solutions reported in the literature. Variation of the natural vibration frequencies with delamination length in a composite beam constructed from four layers of sandwich plates is presented.