Non-Destructive Evaluation of Carbon Fiber Composite Reinforcement Content

Abstract

The use of light-weight, high-strength composite materials in motors, generators, and energy storage devices has become common as a means to maximize energy density. To ensure reliability, non-destructive and destructive evaluation techniques have been employed to measure the mechanical properties of fabricated components. In carbon fiber-reinforced, polymer matrix composites, mechanical strength is primarily derived from the fiber volume fraction. Due to the lack of a nondestructive method, common techniques for fiber volume determination are currently destructive. In this investigation, a non-destructive method for the measurement of the fiber volume fraction of carbon fiber-reinforced, polymer matrix composites has been developed using cold neutron prompt gamma activation analysis (PGAA). Fiber volume determination is accomplished in this technique by measuring and comparing the carbon and hydrogen content in a given sample (or samples). PGAA is a nuclear analytical technique performed by exposing a sample to neutron radiation. PGAA measurements are non-destructive and can be performed without chemical preparation of the sample. Fiber volumes of several composite coupons have been determined relative to standard samples of known fiber volume and measurements are in good agreement with values predicted by acid digestion tests. Fiber volume measurement using PGAA can potentially be applied to any composite material where the contents of the matrix and reinforcement differ. The technique can also be spatially sensitive, with resolution limited by the dimensions of the neutron beam that is used.