Detection of Voids and Inhomogeneities in Fiber Glass Reinforced Plastics by Microwave and beta-Ray Backscatter Techniques

摘要

Microwaves were used as a means of detecting voids and inhomogeneities in fiber glass reinforced plastics. A number of experiments that were designed to empirically establish the limits of detectability of various types of defects are described. Based on the results of the investigation, it is possible to detect a 1/8-inch-diameter hole in a 1/4-inch-thick panel of fiber glass reinforced plastic with X-band microwaves. However, several factors such as sensitivity of the signal amplitude to defect location, test-piece position, geometry, and homogeneity make interpretation of results difficult. Beta-ray backscatter measurements are potentially useful as a means of detecting local variations in glass-to-resin ratio. The contribution of fillers as a third constituent in the composite system must, however, be considered in establishing a relation between backscattering and glass-to-resin ratios. (Author)