École Nationale Supérieure de
Techniques Avancées

Abstract

The use of Carbon Fiber Reinforced Polymers (CFRP) instead of metal is growing in the aerospace and automotive industries. Indeed, composites combine high strength and low weight, however, the microstructure by layers makes it easier for delaminations to appear after an impact. Plus, common techniques for damage detection in metal parts as ultrasonic or vibration analysis techniques may not work that well on CFRP. The Local Acoustic Resonance Spectroscopy (LARS) is a new method based on the coin-tapping test : the structure is hit with a hard object such as a hammer. The sound generated by the waves due to the impact is recorded by a microphone, while the excitation force is recorded by an integrated sensor on the hammer. Flaws affect the contact stiffness between the hammer and the material and a change in the impact can be detected. For this project, a CFRP sample has been studied. The objective was first to identify defects of various sizes in the plate ; then to learn the influence of each type of defects, and this way, to be able to characterize such defects during an inspection. The experiments showed that only the biggest flaws were spotted by the method, with a good detection when hitting over the exact location of the defect.