Real Time Strength Verification of Bonded Composites

The elimination of fasteners to join two composite components together and reliance on adhesive bonds in a bonded structures is becoming an important factor in the design and development of adhesively bonded composite structures for the Air Forces’ next generation of fighter and bomber.  It is also an important factor in the application of composite patch repairs at the depots as part of a sustainment operation to extend the operational life of aircraft.  Present process control emphasizes surface preparation as the primary means of controlling quality and bond strength.  To date, thermographic inspection is the only means, aside from visual inspection, that is used to judge the quality of adhesively bonded structures and repair patch installations. Laser Bond Inspection (LBI) offers new opportunities for the characterization of adhesive bond strength that are absent from traditional NDT techniques (Ultrasonic Inspection).  LBI can be used to validate the integrity of adhesive bonds during the manufacturing process by identifying weak bonded repairs and to detect the presence of “kissing bonds.”  The implementation of the LBI method is to verify the adhesive bonding process is under control during manufacturing and the bond meets the intended design requirements.  The current LBI inspection head available for the LBI system can inspect confined and easily accessible bonded structures such as wing skins bonded to a spar or stringer.  The objective is to design an inspection head that can be used to conduct inspection in confined locations.  The size of the inspection head is partially dictated by the detection instrument that is built into it to detect and record the characteristics of the returning stress wave. This SBIR Phase I proposal is focused on demonstrating a new detection instrument to detect the characteristics of the returning stress wave to replace the existing instrument that is large and bulky Photo Doppler Velocimeter to support the LBI tools an inspection head concept that is capable of inspecting bond joints during initial manufacturing and to support current and future depot level sustainment The investments made by Industry and Government to generate data and build the various LBI system components to conduct this inspection process will be leveraged to support this proposed Phase I for maturation and implementation for the inspection of bonded composite to demonstrate the effectiveness of the new detection instrument.