Residual Stress Measurement By Ultrasonic Method Based On Displacement Differential Method

Welding residual stress is one of the important parameters in evaluating reliability of welded structures. It will be the vital significance, if we can test residual stresses non-destructively. Comparison of destructive and non-destructive method of welding residual stress measurement, ultrasonic method has a great potential in application.In order to decrease the measured area and increase resolution of gradient stress field, we bring into forward a new method which is called displacement differential method to test residual stress. The basic theory of displacement differential method was mentioned and the formulas of testing residual stress by displacement differential method were also verified. Then two routes of displacement differential method were put into forward in this research.Furthermore, a laboratory system for displacement differential method was set up to test residual stress. The probe mounting clamp was designed to realize the precise movement between transceiver probes. Then the stability tests were conducted and a right distance between transceiver probes was selected. This paper calibrated the nominal acoustoelasticity coefficient of different distances between transceiver probes and a fitting equation of nominal acoustoelasticity coefficient and distance between transceiver probes was built.After that, we created two different gradient stress fields that we have known. The gradient stress fields were measured repeatedly, demonstrating the reliability and accuracy of the displacement differential method system. The sound path reduced to 5mm and this method increased resolution of gradient stress field.In the last of the paper, the residual stresses of aluminum alloy were measured by the displacement differential method system. To validate the reliability and accuracy of results measured by displacement differential method, a hole-drilling technique was used to determine the residual stress in the sample. The verification results shows that the residual stresses measured by hole-drilling technique were good agreements with the results by displacement differential method. Then the welding residual stress of high-speed train body structure was measured by displacement differential method system. It is very important to optimize the technology of welding and evaluate the security of the train.