Research on Response of Ultrasonics to Closed Cracks and Nondestructive Evaluation

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1.In order to establish a high accuracy and high speed sampling method by using an automatic two dimensional scanning for an amplitude of echo from crack, water and an ultrasonic equipment were used as medium for ultrasonic wave propagation and sampling of wave date. The data was installed in a digital oscilloscope which has a high sampling speed.2.An evaluation equation which was simplified from a theoretical equation of a closed crack was derived. The evaluation method and a program of a computer to get a length of crack and a relative insensitivity of crack closure was shown by analyzing an inverse problem using the simplified evaluation equation.3.In a quest to develop an improved detection and signal processing scheme, a new experimental study of a single probe ultrasonic technique concerning a beam angle has been conducted in an attempt to achieve better characteristic response of ultrasonics.4.A high sensitive and automatic sampling system applied for crack echo data with oblique angle was developed from the automatic system using normal incident ultrasonics.5.The relation between the oblique angle of ultrasonic incident beam and the reflection of the wave and also mode conversion were examined experimentally. The possibility of a nondestructive evaluation by ultrasonics with oblique angle was shown.6.Two simulated small cracks extremely narrow width, 0.1 mm-wide slit, having depths of 1 and 3mm, wer evaluated by using oblique incident ultrasonics. The method can be applied for an evaluation of small cracks.