Fatigue crack detection of steel truss bridge by using mechanoluminescent sensor

Recently, innovative mechanoluminescent (ML) particles have been made available, each of which repeatedly emits light in response to small stresses that are applied, such as deformation, friction, or impact. When dispersedly coated on a structure, each particle acts as a sensitive mechanical sensor, while the two-dimensional emission pattern of the whole assembly reflects the dynamical stress distribution inside the structure and the mechanical information around the crack and defect. From results of the application of a ML sensing technique to an aged bridge with fatigue crack and diagonal failure, we successfully measured the stress concentration at the tip of the crack and the crack mouth opening displacement in a dynamical loading test with a heavy vehicle (over 25 t). Such cracks went undetected and hence were unexpected by conventional inspection methods. We also succeeded in distinguishing the influence between before and after diagonal failure from the ML intensity and pattern.