Experimental and Numerical Study of the Effect of Debonding Defect in Composite Patch Repairs on Composite Plate

Composite patches are generally used in different fields to repair damage in metal structures and even in composites. The effectiveness of the repair is directly related to a good preparation of the surface and a good choice of the suitable adhesive for the plate and the patch. However, the bonding surface presents defects in most cases (impurity, cavity, air bubble, poor adhesion, etc.). These defects and under mechanical stress can be a source of initiation of damage in the adhesive layer which will cause poor load transfer from the damaged area to the patch and consequently the detachment of the patch. In this study, an experimental work followed by a numerical analysis was carried out to analyze the effect of debonding on the effectiveness of a composite patch repair. The damage is an artificial debonding located in the adhesive layer and which was simulated by inserting Teflon strips of different sizes between the composite laminate and the adhesive layer. The effects of the repair technique used, single or double patch, the adhesive properties, the length and the dimensions of the patch as well as the position of the adhesive debonding have been highlighted on the variation of the rigidity of the repaired structure. The results show clearly that the performance of the composite patch on improving the strength of the damaged plate depends not only on the mechanical properties of the adhesive and the length of the patch, but also on the position and the debonded zone in the adhesive layer especially if the debonding area is located in the vicinity of the damaged area where the load transfer will be minimal and therefore poor resistance of the repaired plate. The convergence ratio between the experimental and numerical study varies from 5 to 10%.