Develop a Tool to Measure Bonded Joint Strength for Primary Load Bearing Aircraft Structures

To reduce weight and improve fuel efficiency, composites are being adhesively bonded into integral structural elements of aircraft at an accelerating rate. Once a bonded structure is assembled, there is no conventional NDI method available to assure that bond strength is adequate for service. The presence of weak regions in bonds can lead to disastrous failure of the structure under flight loads. Laser Bond Inspection (LBI) offers a practical solution to locating weak regions in laminate-adhesive bonds in aircraft structures. It is a local proof-testing method that applies a well-controlled dynamic stress to the composite structure, and senses the failure of weak adhesive bonds in response to the stress. The controlled stressing of the composite material has no effect on the material or bond if it is not damaged, defective, or substandard. In order for LBI to be widely applicable, however, advanced technology needs to be developed to inspect thick multilayer composite structures (0.5-1.0 inch thick), bonded structure with non-parallel surfaces (e.g., tapered flange to skin composite), and mixed material joints (e.g., metal-to-composite). The innovative aspect of the proposed SBIR Phase I program is to perform key experiments to demonstrate new LBI technical approaches to these difficult inspection problems.