Luminance Distribution and Stress Analysis at the Stress Concentration using Mechanoluminescence

Currently, there are about 700,000 bridges in Japan. However, about 20[%] of these have been over 50 years old, and aging such as fatigue cracks and corrosion is considered serious. Therefore, it is important to grasp the deterioration situation on-site as soon as possible. One method is non-destructive inspection. But there are drawbacks such as high skill required for inspectors and inspection only within a narrow range. Accordingly, we focus on a material called ML and aim to develop a new non-destructive inspection technology that can be inspected for simpler and wider than the conventional method. ML has the property that the stress concentration part emits light when mechanical external force is applied in the phosphorescent state. The purpose of this study is to verify whether the luminance distribution and Finite Element Method (FEM) have a high correlation even when the stress distribution is complicated by multiple defects. Tensile test was performed by applying ML to a test pieces with three and five holes damaged. In comparison with the maximum principal stress, the distribution was similar. In comparison with the equivalent stress, the distribution was close to more than the maximum principal stress between the two test pieces. Therefore, it is considered that the equivalent stress is more appropriate than the maximum principal stress as a comparison object.