Bond Quality Determination Using Nuclear Magnetic Resonance NDE Techniques

At the present, a major barrier to the optimum utilization of adhesive bonding as a joining method in primary structures is the inability of NDE techniques to determine bond quality, and thus structural integrity. Methods that have been used to investigate bond quality include sonics, ultrasonics, holography, radiography, thermography, acoustic emission, and nuclear magnetic resonance (NMR). Since bonds degrade chemically and since, with the exception of NMR, none of these methods are sensitive to chemical degradation, it is not surprising that previous efforts at bond quality NDE have been less than successful. However, NMR is not only sensitive to chemical degradation, it is also sensitive to the presence of moisture, which is a leading cause of bond failure. Quantum Magnetics has recently shown that NMR can be used to detect heat damage, moisture, and surface cracks in the carbon/epoxy composite materials common in aerospace applications. Quantum Magnetics has also shown that NMR information can be obtained from adhesives located in close proximity to steel plates, which are ferromagnetic and produce considerable field distortion. As a result of these recent developments, NMR technology has now reached the point where it is both realistic and attractive to consider its application to the NDE of adhesive bond quality.