Abstract
A new technique using Lamb wave is proposed to detect uncured region in GFRP laminates nondestructively. Polymer based composites play an increasingly important role in the field of civil engineering in recent years. For example, laminated sheets consisting of thermoplastic layer, organic fabric sheets and SMC (sheet molding compound) are used to rehabilitate aged sewerage pipes. The cylindrical laminate is inserted in the pipe, and is inflated and cured by steam blowing to create close-fit pipe. This CIPP (cured in place pipe) is one of several trenchless rehabilitation methods to repair aged pipes. In this study, ultrasonic Lamb wave is applied to the detection of uncured region in a laminated composite plate. Oblique incidence method in which ultrasonic waves are launched by the transducer inclined at a selected angle is applied to excite specific mode of Lamb waves in the laminate. Wheel type probes are used to improve inspection efficiency. Beside wave attenuation, AU parameters which are derived from power spectrum of a broadband signal are introduced. It is found that application of AU parameters leads to the improvement of the detectability of uncured region.
