Stress Sensing With Fluorescent Or Fiber Optic Method

Stress plays an important role in the mechanical and optical properties ofmaterials, and then the measurement of stress and strain attracts more and moreattention. For different application and in different environment, there are a variety ofsensing system, measurement methods, data analysis and calculation method for thetest of stress or strain. This thesis compares several stress test methods, studies thefluorescent spectrum under pressure, and monitors residual stress by refractive indexmeasuring. The former is applicable for stress monitoring of coating or surfaces, andthe latter can be used for deep stress measurement of material.（1） Rare earth fluorescence piezo-spectroscopy effect measuring stress is basedon the regulation of nephelauxetic effect. The theory is that the coordination of rareearth ion atomic energy is proportional to the reciprocal lattice constant and the roleof rare earth materials under stress when the change of lattice constant isproportional to the stress variation, thus, we can measure the energy levels of rareearth ions in the center of gravity position offset for fluorescent light-emittingmaterials by the size of the stress. This paper design a set of fluorescence spectrumtest pressure stress system, respectively selecting YAG: Ce³⁺as5d-4f energy leveltransition and Y₂O₃: Er, Yb as4f-4f energy level transition of two kinds of rare earthmaterials as test samples, by measuring the level of center of gravity moving to getthe samples information by stress, and fitting with the tested results, the Linearsensing equation:E0=18107.667-8.762σ。（2）Refractive index is the inherent physical properties of a material, it is equal tothe square root of the relative dielectric constant of the material, which react thepolarization phenomenon of material compared with dielectric constant. Whenmaterial under strain, the lattice space between atomic will shrink or swell and evenappear non-uniform shrinkage, at this point, the internal polarization degree ofmaterial will change, affecting the material refractive index change. Therefore, wecan through the refractive index to test the size of the internal stress in the material.The paper designed a set of refractive index of real-time monitoring system thatbased on the Fresnel principle, monitoring the one light curing process and heattreatment process of epoxy resin adhesive, observing the refractive index changescorrespond to residual stress release. When it produces thermal expansion and contraction, the refractive index of the fiber-optic sensing system for measuring therefractive index of the data material volume data is a good match with epoxy resinLorentz-Lorenz relations, indicating that the refractive index measurement caninstead of TMA （Thermal Mechanical Analysis） in some material Analysisapplications...