Analysis of bonding layer quality in repair process of aircraft composite structure after impact damage

Aircraft composite structures made in autoclave prepreg technology are characterized by low porosity and high strength. Unfortunately, composite structures are susceptible to impact damage. Therefore in order to repair this type of structures, an advantageous method of structure restoration is the use of the two-step bonding method. This method relies on creating a composite patch cured in an autoclave and then bonding it into a previously prepared repair area in the repaired structure, created by removing the damaged layers. Thanks to this approach, the patch is produced in accordance with the production process of the repaired element and has similar properties including low porosity. A critical element of repair is the bonding layer between the patch and repaired structure. Difficulties in obtaining an appropriate consolidation pressure (compression) using a vacuum bag can cause local disbonding of the composite patch as well as porosity in the bonding layer. Porosity reduces the strength properties of the joint, and it also reduces its weather resistance, which may contribute to its gradual degradation. The article focuses on analysis of the influence of compression obtained by a vacuum bag on the porosity and thickness of the bonding layer. A professional line for the production of aircraft composites and a mobile system for composite repairs of aircraft structures were used to produce the samples. The computed tomography method was used to measure the porosity and thickness of the bonding layer.