Composite-Bonded Joint Strength Evaluation

This is a proposal to develop the technology to measure bond strength. The approach is to use a novel ultrasonic transducer that is capable of generating pulse amplitudes that produce strains just below the required bond strength. If the bond survives the pulse it is considered good. Previous work by others has shown the feasibility of this approach, however the equipment that was used requires a vacuum chamber and has other limitations that make it impractical for production or repair inspection. Piezoelectrics are incapable of generating ultrasonic pulses of sufficient amplitude and bandwidth for this application. The new approach sends an extended signal from a piezoelectric into a "broadband resonator". By selecting the correct input signal all frequency components arrive at the output in phase at some later time to produce the pulse. A portable, battery powered system could be developed to handle a wide range of material thickness with hand-held transducers spanning a broad range of center frequencies. The experimental plan is to fabricate specimens containing bonds of various strengths by changing the bond material characteristics, subject the bonds to pulses just below the bond strength, note any failures, then test the strength of any intact specimens with destructive tests.