A nondestructive testing method of fiber orientation by microwave

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Abstract
A nondestructive testing technique for detecting fiber orientation and fiber content in fiber reinforced composite materials such as CFRP and GFRP was devised by using 4 GHz microwave. Fiber direction, misorientation, and fiber content were detectable for unidirectional CFRP. In this apparatus the transmitted wave is divided into two cross components and their difference and/or ratio is measured, so that the sensitivity of detecting the fiber orientation is improved and the change of fiber direction is detected separately from that of the fiber content. The sensitivity of the detection for the fiber direction and misorientation was especially good in such thin CFRP samples (less than about 1 mm in thickness). This method, therefore, was found to be most useful to check the fiber orientation of intermediary materials such as prepreg rather than end constructions or products. The sensitivity of detection for GRFP was rather low in comparison with that for CFRP, because the difference of electrical property between matrix resin and glass fiber is small. Theoretical formulations and calculations for the transmission and reflection of electromagnetic waves in anisotropic layered material were performed, and good agreement with the experimental results was obtained.