Development of Smart Pultruded Composite Materials with Embedded Fiber Bragg Gratings for In-Situ Strain Monitoring

Abstract

The major benefits of using composite materials as civil engineering structures are high strength, lightweight, high corrosion resistance, high formability and tailoring. Adding functionalities into composite materials, resulting in so-called smart structures, is a promising alternative to conventional methods for structural health monitoring. A large smart composite platform (20m x 3.5m) was built in september 2012 (DECID2 project). All sub-structures of the platform are made by pultrusion which is a manufacturing process for producing reinforced composite structural shapes of continuous lengths with constant cross-sections. Two composite girders (I-beam cross section) are used to support small composite beams on which precast composite deck have been assembled. The monitoring of this structure is based on Fiber Bragg Gratings (FBG) which are used as strain and temperature sensors. This kind of sensor exhibits numerous advantages such as small size, relative lightness, an immunity to electromagnetic interference, geometrical flexibility and so on. In our project, FBG sensors are embedded in composite girders during fabrication. The embedment of optical fiber sensors in pultruded composite materials was one of the key- technical challenges. The ingress and egress of optical fiber from a composite component made by pultrusion are real issues which are difficult to solve. Indeed, ingress and egress of optical fiber must be enough robust for the successful, cost-effective development of embedded sensor technology. In our project, we have developed and tested a miniaturized connector which can be embedded in composite component during pultrusion process. This connector can withstand the harsh conditions (high temperature and shear stresses) of the pultrusion process. We will also discuss the mechanical performance of optical fiber sensors while embedded in pultruded materials. Quasi-static and fatigue mechanical tests have been performed on composite specimens. The results show that embedded FBG sensors could monitor strain with a good precision although a slightly decrease of fatigue performance of smart composite specimens was noticed.