Mathematisch-numerische Modellierung der Ultraschallstreuung an oberflächenverbundenen Rissen mit dem EFIT-Code

Abstract
An ultrasonic time-of-flight diffraction method for measuring stable crack growth in a three point bending specimen was analyzed by simulations of the wave field evolution in the test specimen. To calculate the actual crack length from the experimental measured time of flight of a crack tip diffracted ultrasound pulse the echo trains were successively measured during the whole bending test. The simulations deal with the generation and evolution of the ultrasound field in the specimen and with the design of the received signal. The simulations took into account the actual test geometry, the crack growth process, the blunted crack tip and the process of bending. With these simulations all individual received echoes are reproduced and interpreted. The echo, qualified for measuring the time of flight is undoubtedly the transverse wave diffracted on the crack tip. In order to optimize the test method and to increase the accuracy of measurements during the simulations Parameters like probe position, wave mode, measuring frequency and length of aperture of the probes wem separately varied. From the comparison between the simulations and the experimental measurements it can be concluded, that the developed method is weil suited for measuring stable crack growth in small specimens made from ductile material.