Strain Transfer Under Complex Stress Condition And Engineering Design Of Fiber Bragg Grating

The fiber Bragg grating (FBG) strain sensor has been widely used in structural health monitoring, and the accuracy of its data plays an important role in the possibility of assessing the health status of the structure correctly. However, the measurement strain of the packaged FBG sensor and the real strain of the measured host aren't equal. The difference in material properties between the packaging layer and the measured host, the damage accumulation of the host and the structure form of the sensor can have effects on strain transfer between the fiber Bragg grating and the measured host. It's necessary to study the strain transfer mechanism of the FBG sensor based on the above situation, in order to design the sensor reasonably, reduce the test error and obtain more accurate strain field of the structure.Taking the fiber Bragg grating (FBG) strain sensor packaged by glass fiber reinforced plastics (GFRP) as the research object (GFRP-FBG strain sensor), the research is carried out on the strain transfer analysis of the embedded sensor in which elastic-plastic behavior and creep behavior of the concrete host are taken into account, the strain transfer analysis of the replaceable surfaced sensor and the design of engineering FBG strain sensors based on strain transfer theory. The main contents are as follows:(1) For the GFRP-FBG strain sensor embedded in the concrete host, on the basis of the elastic strain transfer theory, the suitable constitutive relations are selected to make strain transfer analysis in which elastic-plastic behavior and creep behavior of the concrete host are considered respectively, and the rationality of theory is verified by finite element method. Based on the strain transfer formula, the effects of the various parameters on average strain transfer coefficient are analyzed, and adverse conditions are selected as basic calculation conditions for the follow-up design of the sensor.(2) Based on the method to calculate statically indeterminate structure in the mechanics of structure, the strain transfer theory of a new replaceable surfaced GFRP-FBG sensor is analyzed, and the finite element model is established to verify the theory. On the basis of the strain transfer formula, the effects that the parameters of the support and the sensing component have on average strain transfer coefficient are analyzed, which can provide some reference for the follow-up design of the sensor.(3) Considering the two aspects of construction materials and service environment, the demand for the FBG strain sensor in civil engineering is analyzed. Based on the strain transfer theory and the demand in civil engineering, the parameter design is done for the embedded GFRP-FBG strain sensor and the replaceable surfaced GFRP-FBG strain sensor.