Jean Chazelas

Damage detection in woven-composite materials using embedded fiber-optic sensors

This paper presents our preliminary results on the use of fiber optic sensors for impact detection on Kevlar-epoxy panels. Interfero-polarimetric measurements have been performed by using two different kinds of polarization-maintaining optical fibers. The sensitivity of the fibers to internal process stresses and to external impact stresses is discussed with respect to the coating nature. The effect of an over-coating on the fiber sensitivity is also reported. Impact-induced delaminations have been observed and the optical response has been adjusted by using an appropriate over-coating.

Microwave subcarrier optical fiber strain sensor

At present, there is an acute need for techniques in monitoring civil engineering structures, and optical fiber sensors are acknowledged to be amongst the best candidates. For more than ten years, interferometric optical fiber sensors have been widely investigated and now provide a rich extended basis for measuring strains experienced by structural elements. However, because of their periodic response, those sensors need extending measuring techniques to fulfill civil engineering requirements. Amongst different methods, Thomson-CSF and the University of Strathclyde have recently employed a microwave subcarrier system [1]. A specific sensor dedication to the arena of large civil engineering structures has been designed and tested.

Optical fiber sensors for monitoring of structures (OSMOS)

Optical fiber sensors for monitoring of structures (OSMOS) is a European collaborative research project which has, over the past three years, embraced a number of technological issues related to the problem of structural monitoring in the civil engineering and aerospace industries. A key technical objective of the program was the measurement of temperature and strain using a single sensor length. A laboratory prototype using the differential sensitivities of polarimeters based on the fundamental, LP01 mode and the first higher order LP11 mode of polarization maintaining fiber demonstrated parameter recovery to within 2 C and 5 (mu) (epsilon) . A receiver enabling quasi-distributed measurements to be made with a linear spatial resolution of 70 cm using white light polarimetry was assembled. White light polarimetry was also used in conjunction with pressure sensitive fiber to detect impact damage on a composite radome structure. Impacts of 5 Joules in magnitude were detected with a spatial resolution of around 1 cm. Microwave radio frequency subcarrier measurement techniques were used to develop the engineering processes necessary to integrate optical sensors into civil engineering structures for simulated applications trials. This enabled issues such as stress transfer, mechanical bonding and sensor protection to be addressed. For the aerospace industry, embedding of optical fiber sensors remains an important issue. Here we developed techniques for embedding connectorized fibers such that the component could be machine finished after curing, an important feature of the manufacturing process.

Introduction to the BRITE-EURAM II OSMOS project

This paper describes the framework and objectives of the OSMOS (Optical fiber Sensing system for MOnitoring of Structures) project. OSMOS is a CEC funded BRITE project with the aim of demonstrating the industrial feasibility of manufacturing optical fiber smart structures for Civil Aeronautics and Civil Engineering. The sensor concepts and associated technological issues to be addressed are presented in connection with the specific applications investigated in the framework of this project.