Experimental and numerical studies of stepped-scarf circular repairs in composite sandwich panels

This paper investigates the static mechanical performance of bonded circular repairs on sandwich panels made with carbon-epoxy composite skins and a Nomex core. First, the mechanical behaviour of pristine, open-hole and repaired sandwich panels under edgewise compressive loading is studied. Next, pristine and repaired sandwich beams are tested under four-point bending with the circular repair loaded in tension. Then, finite element analyses are performed to predict the strength of the repaired sandwich panel. The adhesive film was considered as an elastic-plastic material with a shear failure criterion. The honeycomb core is assumed to behave as a linear elastic material while for the composite skins, a progressive damage model for woven fabric composites is used to predict the skin behavior until rupture. The good agreement between stiffness and strength levels obtained for both experimental measurements and finite element predictions, for pristine, open-hole and repaired sandwich panels, indicates that an effective analysis tool for the mechanical behavior of the repaired panels has been set-up.