Organic mechanochromic luminescence‐based visualization of fatigue damage and life prediction of aluminum to steel resistance spot welds

Abstract Dissimilar material joined structures are increasingly used in the automotive industry to reduce weight in the vehicle body structure for better fuel economy. Therefore, it is necessary to reveal the fatigue damage and develop the fatigue life prediction method of dissimilar material joined structures. Unlike conventional detection methods, mechanoresponsive luminogen‐based method can directly visualize stress distribution and fatigue crack growth. An organic mechanochromic luminescence material (TPE‐4N) is therefore used to detect the fatigue damage of coach peel Al‐steel resistance spot welds. The fatigue crack initiation and propagation are detected as visible green fluorescence under ultraviolet excitation. The results show that the fluorescence intensity increases linearly in the early stage of fatigue cycles while grows much faster in the specimen with lower fatigue life. A new fatigue life prediction method has been developed based on the response of fluorescence intensity. Highlights Fatigue damage of resistance spot welds is detected by mechanochromic luminescence. Fatigue crack evolution is converted into real‐time and visible fluorescence emission. A fatigue life prediction method is proposed based on the fluorescence response.