Nuclear Magnetic Resonance Nondestructive Evaluation of Composite Materials

Nuclear magnetic resonance (NMR) was studied for use in the nondestructive evaluation of composite materials, with particular emphasis on NMR imaging. NMR parameters of potential use for generating images showing high contrast between acceptable and unacceptable regions of composites were measured for typical organic matrix materials. The attenuating effects of carbon fibers were measured and relationships were developed to compute the conditions necessary to obtain images of carbon-fiber composites. NMR images of aerospace composites containing poly(aryl-ether-ether-ketone) (PEEK) and epoxy resins were obtained using solid state 13C techniques. The contrast mechanism used for these images was the composites. NMR images of hydrogen in PEEK were also obtained using multiple-pulse techniques to reduce dipolar broadening. Selective pulses were used to obtain images of the spatial variations in the crystalline content of PEEK. The results of these experiments were used to assess the feasibility of using NMR for nondestructive evaluation of composite materials.