Ultrasonic stress measurement using PC based and commercial flaw detectors

The determination of the stress field inside metallic parts is one of the m ost important challenges to the designer. Although the prediction of the st ress distribution can be done by several numerical and empirical methods, t he real stress value is almost always unknown. Several destructive and nond estructive techniques have been tested to accomplish this task, including t he application of x rays, saw cut, neutron diffraction and so on, but none of them seems to have a suitable correlation between cost and applicability . Ultrasonic techniques have been used for flaw detection since the 1950s. The main application was in the identification of cracks and voids. In this work we present the application of ultrasound in the evaluation of a one-d imensional stress field using the longitudinal critically refracted waves ( L-CR). A new ultrasonic L-CR probe is presented and its performance is eval uated using PC based instrumentation. Also, the L-CR waves' sensitivity is verified using a low cost commercial flaw detector. The results show that t he technique can be applied to quantify the magnitude of the stresses in ba rs, using either the PC based or the commercial flaw detector system, as lo ng as the high sensitivity longitudinal critically refracted waves are used . (C) 2000 American Institute of Physics. [S0034-6748(00)01109-6].