Research On Whole Life Health Monitoring Of Composites Structure Based On Fiber Optic Sensing Technology

Advanced composite structure has been applied broadly in aerospace. In order to avoid structure being destroyed and reduce cost of maintenance, structure health monitoring has been an effect method. Good compatibility with composite, excellent ability of anti-interference and corrosion resistant and acting light as signal which make fibre optic sensors be applied to act as embedding sensors into composite to monitor the structure in real-time.This paper built a whole life system of structure health monitoring with fibre optical sensors for composite manufacture and service process for the goal of improving products percent of pass and reducing cost of maintenance. Studies as follows have been developed.1. Quality of manufacture has been upgraded by the information of viscosity which decides the best pressure-applied moment for the process of composites cure. Chemo-rheological equation of HD03 epoxy resin was acquired by constant temperature experiment and data fitting. When FBG sensors were embedded into T300/HD03 composites, temperature evolution could be monitored during cure. Substituting temperature form monitoring into the chemo-rheological equation, real-time viscosity number can be calculated from which a suitable pressure-applied moment can be choosed. Influences to thickness of laminate, residual strain and strain variation of cure have been compared under different pressure-applied moment and the viscosity range for best pressure-applied moment has been acquired. By means of embedding FBG sensors monitoring temperature, viscosity number can be transferred from temperature to choose best pressure-applied moment which can effectively control pressurization moment and complete closed-loop control of composite manufacture. Qualities of composites are improved and monitoring of composites manufacture process is realized.2. Experimental data was provided for different materials in common use by FBG sensor-based monitoring common cure of composites and aluminum plate and deformation process under temperature load. FBG sensors were embedded to monitor the cure of filament wound unidirectional laminate and the strain between composite and aluminum plate. Due to different mechanical property of composite and aluminum, the inner and interface of composite is different during the cure and in the final time of cure detachment arises and some quantity of heat deliveries. Embedding a FBG into composites and stick two FBGs on the surface of composite, under the temperature course, the strains of the three interfaces were monitored. The results of monitoring and numerical simulation were compared. The different properties under different temperature of the glue have great influence on the results of composite surface monitoring. The embedding ability of FBG sensors provides a tool to monitor the interface between different materials and the data from monitoring improves the safety of integral structure.3. By the finite element software analyzing on composite pressure vessel, failure mechanism of pressure vessel was disclosed and the law of monitoring sensors placement was provided. A finite element model of composite pressure vessel has been built by ANSYS finite element software. In the model, angle of winding and variation thickness of dome was same as the true manufacture and accuracy of the model has been verified by monitoring the strain and the deformation. Strain was measured by strain gauges and helix direction of the cylinder was selected as deformation of the whole cylinder which was monitored by SMARTape sensor. It was realized the comparison between forecasting value and monitoring value by the path function of ANSYS. The forecasting value and the monitoring value matches good. On the base of this model, according to Hashin failure criterion and maximum stress criterion, course of damage analysis was proceed and bursting pressure was predicted. By building finite element model to analyze the structure and through experiments to verify, analyzing base was provided for health monitoring.4. A kind of interference fibre optic sensors has been developed and together with FBG sensors real-time health monitoring of reusable composite structure can be realized. Base for whole life health monitoring of aircraft important parts can be built. A fibre optic sensor was developed for composite structure under long distance monitoring based on Michelson's interferometer. Tension response of the sensor was verified by micro-move device whose deformation was concordance with the reading of demodulation. Monitoring damage ability of the sensor and characters of temperature response were tested. A local and global composite pressure vessel monitoring system was built by FBG sensors and interferometer sensors for point and whole strain of structure. Property of low temperature and hydrostatic pressure was monitored and the results of monitoring were compared with that of ANSYS and strain gauges which showed good concordance. The bursting process of composite vessel was also monitored from which the ability of finding structure damage was verified. The study of composite pressure vessel monitoring will push other composite structure of aircraft whole life health monitoring forward.