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

In the present paper an ultrasonic NDI technique for the delaminations evaluation on several composite materials is described. The methodology, based on an ultrasonic test apparatus in the form of reflection, allows us to determine the position along the thickness and extension of delaminations on several CFRP, GFRP and KFRP laminates subjected to low-velocity impact test. The experiments have been performed in two distinct phases. During the first phase typical aerospace materials such as thermoset and thermoplastic CFRP thin laminates and sandwich were inspected, in order to validate the ultrasonic NDI system and the original test methodology. Then, in the second phase, tests have been performed on glass fiber and polyester resin systems, where the fiber was in the form of woven fabric or woven roving, and Kevlar and polyester resin system, where the Kevlar is in the form of woven fabric. All the specimens are made by RTM technology and the thickness are comprised between 5 and 6 mm. Moreover, the NDI analysis was performed using two different probes (5 and 15 MHz), in order to evaluate the importance of the probe frequency for the reliable evaluation of delaminations 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.