Study On Luminescent Photoelastic Coating Method

Luminescent photoelastic coating (LPC) method is a relatively new measurement technique to provide the full-field in-plane maximum shear strain and the principal strain directions on the surfaces of the test structures. In order to overcome the shortcoming of low signal-to-noise ratio in signal detection faced in its practical applications, the improved LPC configuration and test method are proposed. In this dissertation, the principal works on the improved LPC prepared by Epoxy resin, Dibutyl phthalate (DBP), Diethylenetriamine (DETA) and Rhodamine B (RhB) are listed as follow:Theoretical analysis and experimental verification of the new single-layer LPC. The intensity formula for the new LPC was derived. Fluorescence emission spectra of both the new LPC and the original LPC were measured using fluorescence spectrophotometer. The results show that the new LPC could remarkably improve signal-to-noise ratio with increasing emission intensities. Furthermore, the emission spectra of the new LPC with the same thickness but different weight ratios of luminescent dyes show that both an appropriate concentration of luminescent dyes and an emission wavelength adopted to capture intensity images in LPC method are of real significance in effectively improving signal intensities.The theoretical research and experimental verification of the LPC thickness measurement method. In order to correct the influence of coating thickness nonuniformity resulted from spray-on or brush-on coating on accurate strain measurements, a non-contact coating thickness measurement method based on establishing linear calibration curve between the thickness and luminescent signal intensity of test coating is proposed. The experimental results show that the linear calibration curve between LPC intensity and its thickness can be given by selecting an appropriate concentration of luminescent dye added in LPC, and the correlation coefficient of this linear calibration curve is to more than0.999.The theoretical studies and experimental measurement of the LPC refractive index. According to the amplitude theoretical analysis of the emission light exiting the coating along the same path as the incident excitation light, a new measurement method of the LPC refractive index based on optical Fresnel response of the coating is proposed. The refractive index of the new LPC was measured and can be used to calculate the non-strain related optical Fresnel response for principal strain separation by oblique incidence technique.Propose the oblique-incidence method for principal strain separation in the LPC. The value of the principal strain difference can be obtained by the normal incidence in LPC. To obtain two separate principal strain components in LPC method, a theoretical model of strain separation by oblique incidence with a new LPC only containing luminescent dyes is presented. Considering the non-strain related refraction effect included in the total optical response at oblique incidence, the theoretical analysis of getting the strain related optical response from the total optical response used to separate principal strains is given. The optimal angle of incidence for the oblique incidence method was determined from the signal-to-noise ratio curve.