| Investigations were conducted to develop nondestructive evaluation techniques suitable for elastomer matrix composites (EMCs). Two polyurethane-based matrix systems, PPDI (paraphenylene diisocyanate) and CHDI (cyclohexane diisocyanate) reinforced with S-glass fiber, were used in the study.;The acoustic properties of EMCs, including the attenuation coefficient, echo transmittance, reflection coefficient, and phase velocity, were investigated. Predictions of wave attenuation, phase velocity and the expected waveforms of various material specifications were made using measured acoustic properties.;Ultrasonic C-scan, visual examination, x-ray radiography, and eddy current inspection were performed on specimens fabricated with simulated flaws. Among these methods, C-scan provided the most information although discernment of details was difficult because the image was degraded by the combined effect of signal distortion, signal overlap, and structural noise.;Transmitted signals based on signal reverberations between the flaw-EMC interfaces were used to extract the reflection coefficient of the interface and flaw thickness. Pulse-echo signals processed with a new time-domain deconvolution technique provided a superior capability for flaw characterization. The deconvolution method incorporated adaptive waveform prediction techniques which enable prediction of wave distortion in highly attenuating and dispersive composite media. For the intentional flaws studied, the recovered interface reflections greatly enhanced the capability to identify the type, depth, and thickness of flaws. |
