Abstract
In photoelasticity, based on the stress-optic law, the isochromatic fringe order is directly proportional to the in-plane principal stress difference. With the increase of the level of the stress difference, the extinction of component colors of an isochromatic fringe pattern follows the sequence of the increasing wavelength and repeats periodically. By integrating this periodic extinction phenomenon in photoelasticity with spectrometry, a new stress measurement method was proposed in this paper. To implement the proposed method, a calibration specimen made of the same material as the test specimen was prepared for the uniaxial tensile testing. A spectrometer was used to record the transmissivity spectrum of a point at the center of the calibration specimen under different magnitudes of tensile loading. By analyzing the spectrometry, the wavelength of each extinct component color can be individually and accurately obtained. In addition, the empirical relationship between the increasing value of wavelength of the extinct component color of the isochromatic fringe pattern and increasing value of stress difference can be established by taking average. With the established relationship obtained from the calibration specimen, the stress difference of test specimen under load can be easily and fast calculated. In contrast to the traditional photoelastic technique, there is no need to determine the refractive index and stress optic coefficient of the test specimen. A popular commercially available photoelastic material, PSM-1 was used to verify the feasibility of the proposed method. The experimental results show that the stress measured is good agreement with the actual loading stress.
