Ultrasonic condition monitoring of composite structures using a low-profile acoustic source and an embedded optical fiber sensor

TLDR: In this article, a structural monitoring system for composite structures using material compatible sensors is presented, which uses acoustic and ultrasonic Lamb wave propagation through carbon and glass fiber reinforced panels, and the interaction of the Lamb wave with different defects in these materials is monitored.

Abstract: The purpose of this paper is to provide a concise introduction to the developments and recent findings of a BRITE-EURAM program of work (BRE2.CT94-0990 , Structurally Integrated System for the comprehensive evaluation of COmposites). The aim of the program has been to develop an acoustic/ultrasonic based structural monitoring system for composite structures using material compatible sensors. Since plate-like structures have been investigated, it has been a requirement to utilise the propagation of ultrasonic Lamb waves through the sample materials. Preliminary investigations utilised conventional piezo-electric sources coupled to the sample via perspex wedges. The Lamb waves generated by these sources were monitored using either a fully embedded or surface mounted optical fibre sensors. The system was tested with a variety of different carbon and glass fibre reinforced panels, and the interaction of the Lamb waves with different defects in these materials was monitored. Conventional signal processing allowed the location of defects such as impact damage sites, delaminations and holes. Subsequent investigations have endeavoured to refine the system. This paper reports the development of advanced wavelet based signal processing techniques to enhance defect visibility, the optical connectorisation of composite panels, and the development of flexible low profile acoustic sources for efficient Lamb wave generation.