Delamination on Impacted Natural Fibers Composite Materials by Means of a New Ultrasonic Method

摘要

The purpose of the present paper is to describe the effectiveness of an ultrasonic N.D.T. system in form of reflection (pulse-echo) for the detection of delaminations on composite laminates. For this study very low-cost composite materials has been considered such as Jute based systems, that have been subjected to transversal impact loads at low-velocity. The specimens were subjected to impact tests at several impact energy levels, to obtain an internal damage mostly in form of delaminated areas. All the specimens were subjected to N.D.T. ultrasonic inspections before the impact, in order to evaluate the delaminations produced by the poor fabrication process (molding by vacuum bag) and after the impact, in order to evaluate the extention of the damage and it's localization along the thickness. For the purpose a new technique, described with details on this paper, has been pointed out by the authors for such laminates. Owing the high attenuation of the materials, the DAC electronic function (software) and a 5 MHz frequence probe have been utilized.