Visualization and Depth Estimation of Inner Crack in High‐Pressure Equipment Based on Organic Mechanochromic Luminescent Materials

Abstract Invisible hydrogen‐induced cracking or stress corrosion cracking easily appears in high‐pressure equipment in service. Mechanoresponsive luminogens (MRLs) can convert mechanical force into visible luminescence emission. Thus, MRL‐based detection methods to damage of structures have been paid extensive attention in recent years. However, the structural damage‐induced luminescence response and mechanism are still not fully comprehended. In this study, organic mechanochromic luminescent materials (1,1,2,2‐tetrakis (4‐nitrophenyl) ethene (TPE‐4N)) are proposed to detect the invisible inner crack in high‐pressure equipment. Because the high‐pressure equipment in service is subjected to tensile loading, the inner crack‐induced fluorescence response and mechanism under tension are investigated. The inner crack‐induced local strain concentration can be transformed into a visible green fluorescence, which can be easily observed from the outside. According to the appearance of fluorescence, the position of the inner crack can be detected. Moreover, the depth level of the inner crack can be quantitatively estimated using applied tensile loading and the ratio of fluorescent area. The investigations may provide a new idea of non‐destructive evaluation material and method for invisible damage in high‐pressure equipment.