Development of scanning stress measurement method using laser photoelasticity

We have developed an optical equipment that possesses high detection sensitivity for measuring the small optical retardation induced by small stress by means of laser photoelasticity. A He-Ne laser is used as a light source to measure small stress in transparent materials. We explain the theory and process of the measurement of optical retardation in the materials. The magnitudes of principal stress difference and the directions of the principal stress are obtained simultaneously and quantitatively using our equipment. To evaluate the validity of the measurement results of the equipment, the stress distribution of a pulled rectangular glass plate with notches at both sides is measured using the equipment. The experimental results of stress distribution agree well with the analytical results of FEM. The stress distribution can be determined quickly by using the equipment and scanning stress distribution measurement has been realized.