Ultrasonic Inspection of GFRP Molded Plates with Distribution of Curing in the Thickness Direction

Abstract

In recent years, the deterioration of social infrastructures, such as highway piers and sewer pipes, has been a significant challenge. Therefore, on-site repair work to extend the life of aging infrastructures has attracted attention. Fiber-reinforced plastics (FRP) are widely used for repairing such structures because they are suitable for on-site molding. To verify the integrity of the repaired infrastructure, a nondestructive inspection of the cured resin is required. As the curing resin is heated from one side of the plate, there is a possibility that the curing process propagates in the thickness direction. In this study, to evaluate the curing distribution in the thickness direction by ultrasonic testing, the effect of an uncured layer on the ultrasonic propagation characteristics is investigated for GFRP-molded plates. Experimental and simulation studies reveal that for a plate with an uncured layer on one surface, quasi-surface waves that propagate mainly in the cured layer are formed. Although it is difficult to detect an uncured layer based on ultrasonic velocity, the attenuation in longitudinal waves can be used to evaluate the uncured layer thickness.