Crack propagation in flat panels stiffened by bonded pads

Abstract

This paper presents the results of an experimental and numerical investigation about crack growth in metallic flat panels stiffened by means of multilayered bonded pads.An experimental program was performed to assess the fatigue crack growth and the residual strength of a number of selected configurations of stiffened panels, within the framework of a collaboration between Piaggio Aero Industries (PAI) and the University of Pisa.In the paper, the test procedures and equipments used for the experimental test campaign are described and the main results of the fatigue crack growth and of the residual strength tests are reported and analysed.Finite Element analyses were performed to further investigate the crack propagation phenomena. The numerical model was validated by comparing the strains measured, at different crack lengths, by a set of strain gauges bonded on the tested panels, with those provided by FEM.Two possible scenarios are accounted for: crack propagates only in the skin, while pads remain un-cracked, or crack propagates simultaneously in the skin and in the pad layers.The values of the stress intensity factor numerically evaluated well compare with the values obtained from the experiments.