Fiber Bragg Grating Sensor Durability And Impact Dynamics Response Analysis

With China’s space industry’s continuous development and innovation,China’s position in the space field is gradually rising,and the frequency of launching spacecraft is increasing year by year.As the power source of spacecraft,the stable operation of an aerospace engine guarantees the safe operation of spacecraft.The external structure of the aero-engine is faced with the high-speed or low-speed impact of foreign objects,and the internal is faced with the danger of hydrogen leakage,which puts forward a greater demand for sensors that can safely and real-time monitor the inside and outside of the aero-engine.In this paper,based on the finite element platform,the process of forming a hydrogen-sensitive film on the surface of fiber grating and the process of ball impact on the surface of the test plate are numerically simulated.The numerical simulation results are verified by hydrogen sensitivity test,durability test,and ball drop test,and the best coating process parameters and sensor arrangement scheme are obtained.The contents are summarized as follows:(1)In order to solve the problem of low durability of fiber Bragg grating hydrogen sensor,based on numerical simulation,the birth and death element method is used to simulate the process of forming a hydrogen sensitive film on the surface of the gate area by coating technology.The influence of coating process parameters on the residual stress on the surface of the film-gate area was explored,and the optimal coating process parameters were obtained.The sensor’s hydrogen sensitivity and durability tests are carried out based on the optimal process parameters.The test results are close to the numerical simulation results.The optimal coating process parameters are obtained: the hydrogen sensitive film of 200 nm thickness,the film formation rate of 62.5 μm/ s,and the number of three layers of hydrogen sensitive thin film.The optimal test range of the fiber grating hydrogen sensor prepared according to these process parameters is 0.5%～1% hydrogen concentration.It provides a new idea and experimental basis for improving the durability of the sensor in the future.(2)Aiming at the problem of health monitoring of outer surface structure of aerospace engine,the impact of small ball on the surface of test plate is dynamically simulated based on numerical simulation,and the influence of different impact intensity and impact angle on the real strain value of test plate surface is explored.The results show that the maximum value of the real strain on the surface of the test plate hit by the ball appears at the impact point.The real strain value on the surface of the test plate decreases gradually with the measuring point away from the impact point.The circle form decreases with the center of the impact point and the distance from the impact point as the radius.The real strain value of the test plate surface increases with the impact strength and the impact angle,but the angle factor has little influence on the real strain value of the test plate surface.(3)Based on the numerical simulation results,a strain sensor is installed on the aluminum plate’s surface,and the small ball’s impact test is carried out by using the drop test-bed.The accuracy of the strain sensor is tested by changing the diameter and material of the ball and the angle between the aluminum plate and the base of the test-bed.The experimental results are close to the numerical simulation results.The empirical formula between impact point strain,impact load,and impact angle is obtained by numerical fitting.The impact force and impact angle of aluminum plate can be quickly judged by the data measured by the sensor system.It provides a reference basis for the health monitoring of the surface structure of aerospace engines.