Investigation of fatigue crack in stainless steel using a mobile fiber Bragg grating ultrasonic sensor

A mobile fiber Bragg grating (FBG) sensor was applied to detect a closed fatigue crack in 18Cr–8Ni stainless steel by ultrasonic pitch–catch method. Response to ultrasound that crossed fatigue crack showed a time delay compared with the reference response in intact area. Conventional piezoelectric sensors were applied to the similar experiment and the response signal was compared with that detected with the FBG sensor. Experimental results showed that FBG sensors could determine the location of crack tip more precisely than piezoelectric sensors.