Study On CFRP Encapsulating Fiber Bragg Grating Sensor

There are bright development future and good commercial prospects for Fiber Bragg Grating (FBG) sensors. However, effective encapsulating should be carried out to meet the requirement of practical engineering application. Composite materials play an important role in modern engineering due to the advantages such as high specific strength, high specific modulus, convenient shaping. Smart Material and structure, which embedding function materials into composite materials, show their vigorous vitality and great importance, and have been preliminarily applied in the filed of military such as Aero-Space, naval vessel weapon, mechanical structure and civil engineering ,etc. Fiber optic sensors that encapsulating with composite material and own better compatibility with structures are always easily embedded into complex structures. In this dissertation, a novel encapsulating structure which can protect Bragg Grating effectively utilizing carbon fiber reinforced plastic (CFRP T300/648) was presented. Such encapsulating structure can be easily designed enables the sensors and matrix matching satisfactorily, thus measurement errors can be reduced and the linearity of sensor also can be improved. The technique of embedding FBG into CFRP laminates was also put forward and the measurement result which affected by different pavement direction are also investigated.The main works of this dissertation are as following:The overview about the history and development of optical fiber smart composite and its application status have been introduced; the existing problems presently are also pointed out.Having established Fiber Bragg Grating Sensor strain sensing model and temperature sensing model, which lay a theoretical basis for application research of such sensor in next chapter. Strain sensitivity and temperature sensitivity, are also deduced in respect of the naked grating of centre wavelength 1.3μm.General encapsulating methods are investigated and classified, Advantage, disadvantages and application context of those methods are also indicated. Many fabrication methods are brought forward, encapsulating principle and structures are explained in details. A novel encapsulating method utilizing carbon fiber reinforced plastic (CFRP) is presented; the technique of embedding FBG into CFRP laminates is also examined. Monitoring application is explored for FBG sensor packaged with composite in the process of composite forming and shaping. The sensors' characteristics are studied with cantilever bending test and temperature test. The influences of the encapsulation technique to the performances of FBG are also examined. There are many advantages for such encapsulating sensors: (1) Effective protection had made to the Bragg grating since packaging with high strength encapsulating materials.(2) The sensors are easily embedded into composite materials which can form Fiber smart layer because of good compatibility between the packaged sensors and composites.(3) Excellent linearity and repeatability are achieved for such sensors. (4) Temperature sensitivity is improved.