Buried Fiber Bragg Grating Sensor. Carbon Fiber Reinforced Composites

Fiber Optic Intelligent Structure is a multi-functional structure with recognition, analysis, judgment, action etc. It is formed through the integration of detect components, drive components, micro-processing control system and the substrate material. This structure is not only able to withstand the load, but also to perceive the change of internal and external environment, and respond by altering its physical properties or shape, so as to achieve its self-diagnosis, self-adaptive and self-healing functions. Thus, intelligent structures have a broad prospect in fields of military, civil engineering and so on.In this thesis, we select Fiber Bragg Grating as a sensing, material for carbon fiber-reinforced composite materials; embed Fiber Bragg Grating into the carbon fiber-reinforced composite materials in order to form a flexible packaging monitoring structure which is integrated with structure reinforcement and monitoring. And through experiments, we studied the structure's sensing abilities. The main contents are as follows:1. Design a structure where Fiber Bragg Grating is embedded into the carbon fiber-reinforced composite materials. Place the unidirectional carbon fiber on one end of the sheath; ensure that the reserved Carbon Weiss is outside the catheter; then penetrate the catheter through the centre with Fiber Bragg Grating, making sure that the grating is in the Carbon Weiss package outside the port and that the Carbon Weiss extends into the sheath, so the exporting and importing part of the fiber is safeguarded.2. According to the linear relationship of the strain of carbon fiber-reinforced composite material and the stress, embed Fiber Bragg Grating into the carbon fiber-reinforced composite materials; establish a correspondence between the stress variations of strain sensing model of fiber grating and offset of Bragg's wavelength; and calculate the sensing abilities of the sensors theoretically. Then, with the specific material of the structural components and its size, sensitivity of Fiber Bragg Grating is calculated as 81.4pm/Kg, theoretical resolution 0.012pm/Kg.3. Paste the carbon fiber-reinforced composite material which is implanted with Fiber Bragg Grating to the surface of uniform strength cantilever; drive Fiber Bragg Grating that is stuck to the surface of carbon fiber-reinforced composite material package to result a shift responsive to the strain by loading and unloading the uniform strength cantilever repeatedly. Experimental results show that loading sensitivity is 82.8pm/Kg, unloading sensitivity is 79.2pm/Kg and actual resolution is 0.013pm/Kg. 4. In order to work out what influence the process of strain measurement will give the overall structure, adapt an approach of independently measuring the temperature to learn the temperature sensitivity of the grating intelligent structure which is stuck to the surface of the cantilever. In the experiment, we heated the whole cantilever over and over again to change the temperature of grating intelligent structure stuck to its surface, the Bragg grating we used is 1564.5nm in center wavelength; its theoretical temperature sensitivity is 10.9pm/℃, and its temperature sensitivity was measured to be 24.7pm/℃in the experiment.