Nondestructive Evaluation of Hygrothermal Effects on Fiber-Reinforced Plastic Laminates

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Abstract
Ultrasonic tests were performed on glass-, carbon-, and Kevlar®-fiber-reinforced plastic laminates that had been exposed to varying hygrothermal ambient conditions. Results reveal similar trends between ultrasonic attenuation measurements and the degree of material degradation as reflected by laminate strength characteristics. A slow decrease in attenuation with almost no degradation was found to be common in all laminates exposed to cold water immersion. Hot water immersion seems to affect significantly glass-fiber-reinforced and Kevlar-fiber-reinforced plastic laminates, which exhibited an increase in attenuation with exposure time. Such a trend is attributable to the degradation process found to be significant in glass-fiber-reinforced plastics and almost nonexistent in the carbon-fiber-reinforced plastic systems.