Ultrasonic technique for the evaluation of delaminations on CFRP, GFRP, KFRP composite materials

In the present paper an ultrasonic NDI technique for the delaminations eval uation on several composite materials is described. The methodology, based on an ultrasonic test apparatus in the form of reflection, allows us to det ermine the position along the thickness and extension of delaminations on s everal CFRP, GFRP and KFRP laminates subjected to low-velocity impact test. The experiments have been performed in two distinct phases. During the firs t phase typical aerospace materials such as thermoset and thermoplastic CFR P thin laminates and sandwich were inspected, in order to validate the ultr asonic NDI system and the original test methodology. Then, in the second phase, tests have been performed on glass fiber and pol yester resin systems, where the fiber was in the form of woven fabric or wo ven roving, and Kevlar and polyester resin system, where the Kevlar is in t he form of woven fabric. All the specimens are made by RTM technology and t he thickness are comprised between 5 and 6 mm. Moreover, the NDI analysis w as performed using two different probes (5 and 15 MHz), in order to evaluat e the importance of the probe frequency for the reliable evaluation of dela minations on composite materials. The results show the NDI system capabilities in terms of damage detection, location and evaluation. (C) 2000 Elsevier Science Ltd. All rights reserved .