Determination of mode I stress intensity factor using visible mechanochromic luminescent sensing response

Rapid detection of fracture damage and structural integrity assessment are critically important for structure safety. In this study, a novel detection technique based on mechanochromic luminescent sensing film is developed to detect fracture damage. 1,1,2,2-tetrakis(4-nitrophenyl) ethylene (TPE-4N) film is coated on the surface of the compact tension (CT) specimens. The local deformation near the crack tip is converted into the visible mechanoresponsive fluorescence response under uniaxial tension. The fluorescence distribution is in good agreement with the equivalent strain distribution. After calibration the relationship between fluorescence intensity and equivalent strain using DIC method, the mode I stress intensity factor can be determined from the fluorescence intensity distribution. Compared to the ASTM E1820 standard, the errors between the experimental results and theoretical results are less than 20%, demonstrating the present method has the good accuracy. The proposed MRL-based method may provide a new idea for developing a simple and visual detection method for fracture damage in complex structures.