The Structure Health Monitoring System Of Solid Rocket Engine Based On The Embedded Optical Fiber Sensors

The structural health monitoring technology(SHM) is used to read the structure health information of the main structure by detecting the changes of the structural response signals with and without load or by the long-term monitoring data. After quantifying and evaluating the measured signal data, the structure performance of the main structure can be determined according to the evaluation results, providing structural health distinguish basis for managers or intelligent system. At present, the SHM technology is in a booming period. SHM technology can solve the problems of real-time health monitoring of large structures and modern equipment, which avoids the major accident, life and property loss caused by the sudden structure changes. In some literature, the SHM technology is described as the technology of using the least amount of manpower to realize automatic structure, continuous monitoring and observation. Due to the effectiveness and economy of the SHM technology, it has got more and more attention from scholars and government agencies.Powder grain of solid engine is composed of gunpowder and adhesive layer.Because the process stability of the composites are relatively poor, these composite adhesive processes prone to defects and damages such as inclusions, porosity or cracks in the production, storage and transportation. The ultimate goal of this thesis is to design a portable instrument which can be used in SHM of solid engine. At present there are many kinds of sensors can be used for strain monitoring, such as the resistance strain gauge and fiber Bragg grating strain sensor and other strain sensor.However, almost all the existing sensor cannot be used for solid engine health monitoring. There are two reasons: one is the fact that the existing strain sensor is tend to bring in current to the flammable and explosive powder grain, another is that the strain range of existing sensor is too small for the limited strain range of substrate materials.It has been found that the strain of the gunpowder could be reached 24.6%. To solve this problem, an extremely large strain sensor was proposed using polymer optical fibers(POFs). Theoretical calculations show that monotonicity of the POF bending sensors can be achieved in small bending angle. However, for a bending process of small radius and large-angle range of POFs, the whispering gallery mode(WGM) and the core mode will couple at certain angles when the phase conditions are met and the radiation power will be partially reflected back into the core from the cladding-air boundary, leading to the oscillating bending loss with bending angle. The non-monotonicity of the POF bending sensors in the large angle limits POFs’ application in extreme large strain measurement. After analyzing the mechanism of the coupling between WGMs and core modes of POFs, we developed a novel method to suppress the oscillation of bending loss in a large range of bending angles by partially cutting the POFs. The bending loss of POFs designed with the new approach shows good monotonicity and linearity. Present study demonstrates a viable approach for realizing the extreme large strain measurement. We developed the test system which can effectively eliminate the influence of ambient temperature from-25°C to45°C. The test specimen was made by embedding the POF bending sensor into the viscoelastic materials. The stretch processes of the test specimen were respectively tested by a tensile testing machine and the developed application system. The results show that the POF bending sensor is useful for the strain measurement of the solid rocket engine.