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The AERoBOND and AERoBOND+ technologies are composite resin materials design innovations that enable new methods for composites joining and manufacturing. The resins are formulated with carefully selected off-set stoichiometries to delay/control the cure such that initial curing of individual components can be followed separately by joining/curing of components together. The ability to delay and control the co-cure joining step provides ease of manufacturing of multi-part composite structures, without compromising joint integrity. There are significant cost savings associated with eliminating fasteners and joint surface preparation steps. To date, the focus of the NASA development effort has been on novel epoxy-based prepreg formulations though other types of thermosets could be considered as well. The AERoBOND+ innovation provides an added adhesive layer to the AERoBOND joint design to improve the ability to join composite surfaces when these surfaces are less tightly matched. Conventional adhesives, e.g., film, paste, etc., are employed. By including an adhesive between the offset stoichiometric prepreg plies, the adhesive can fill the gaps between the bonding surfaces while maintaining reflowable AERoBOND layer interfaces. Since all interfaces are reflowable, they are much more tolerant of surface contamination, thereby mitigating a primary challenge for conventional adhesive bonding.

NASA's Method of Evaluating Adhesive Bond Strength is an accurate, robust, quantitative, and nondestructive bond strength measurement method that meets an immediate need in composite manufacturing. Even with careful control of the bonding procedure, destructive testing has shown that bonded joint strength shows substantial variation. Prior art in the field is insensitive to weak interfacial bonding, which leads to poor service life and potential catastrophic failure. Using NASA's method, phase measurements are acquired at a single frequency and then swept to obtain measurements at other frequencies. Narrowband filtering removes extraneous frequencies, which allows for much lower phase measurement uncertainty than other methods. Digital sine wave generation allows for better phase measurement resolution. The resultant system is a phase-based ultrasonic measurement tool for interrogating bonded joints and detecting weak adhesion with superior sensitivity than the state of the art. This new method models adhesive interfaces as a distributed spring system, where the interfacial stiffness constants of the joint can be determined from the zero- crossing frequency of the phase response and the "sharpness" or slope of the phase response. Previous theoretical research has shown that a linear correlation exists between interfacial stiffness constants and mechanically-measured interfacial bond strength. As such, the ultrasonic phase measurement method identifies intermediate bond strengths, rather than simply detecting good or bad bonds. This technique verifies bond quality in metal and composite joint systems, including those commonly found in aerospace, automotive, and many other transportation and infrastructure designs. The demonstrated ultrasonic phase method is applicable to a variety of bonding material systems.