Research On Bragg Fiber Grating Sensors Used In The Concrete Dynamic Strain Measurement

With the developing of science and technology,in the high tech local war,the precision control and guide weapons have so great power that they become more dangerous to the firm aim such as deep underground works.As a result,it is very important to experiment on defence engineering to increase the survival probability of the underground works.Concrete is one of the the main materials in the defence works.But it's difficult to acquire the strain inside the concrete because of the wicked circumstance in the process of constructing.As a result,it's difficult to evaluate the invade power of the weapon and the anti-invade power of the defence engineering.So it starves for techlonogy to measure the strain parameters in the concrete defence engineering. As a new sense organ,the FBG(Fiber Bragg Grating) has many strongpoints,such as a small volume,a light weight,and immune to electromagnetism.But it's difficult to demodulate the light signal and encapsulate the FBG when the dynamic strain inside the concrete is measured. Toward the military needs,the main contents include:Firstly,the feasibility of FBG which is applied to the dynamic strain measurement is analysised. Based on the light travel in FBG,this paper studies three kinds of methods applied to analysis FBG as well as how to use numerical method to study the properties of FBG.Then ,the principle of FBG applied as strain sensor is deduced.Secondly,the structure of FBG measure system is made out,a dynamic measurement system is designed to fit the characteristic of the concrete, the errors of four types of typically dynamic demodulation methods are analysed.Based on linely filter method,a high velocity demodultion system is designed,and a FBG strain sensor pakaged by expxy-resin is also designed at the same time.The important parameters such as sensitivity and return difference are researched on the equal strenght beam.Thirdly,the errors in the dynamic strain measurement is analysised by numerical method.The results show that,the errors will increase obviously if the frequency of strain wave is higher than a threshold value.According to this,the frequency range in which the FBG will work normally is calculate out.Fourthly,the FBG strain sensor and high velocity demodulation system is applied in a serial of model experiments.One of the experiments is actualized on the SHPB(Slip Hopkinson Pressure Bar) which is used to compare the abiliy of FBG with RSG(Resistance Strain Gauge) in the dynamic strain field,and the other one is actualized by TNT explosion which is used to compare the abiliy of FBG with RSG(Resistance Strain Gauge) in the real explosive circumstance.It shows that the results mesured by FBG accords well to that of RSG.Beside this,the FBG dynamic strain measuring system is able to work normally in powerful EMC(Electro Magnetic Couplement) field,so it shows a greater performance.As a conclude,the FBG strain sensor and the FBG dynamic strain measure system contained in this paper are powerful enough to be applied in the dynamic strain measurement inside concretes.This FBG sensor and measure system will greatly support the constructing and the developing of the defence engineering.