| In this paper, the relation between the surface wave propagation speed and the surface stress of material is studied in theory. A formula for calculating the stress based on the surface wave acoustoelasticity is optimized. Furthermore,The relation between the surface wave propagation time and the surface stress is presented, and the surface stress is detected by surface wave nondestructive technique.The detection system is consist of MODEL 5800 ultrasonic pulser/receiver, TDS5000 B digital oscillograph, personal computer, surface wave transducer and signal sample device. The biggest sample frequency is 5GHz.A pair of surface wave sensors with 5MHz in frequency is well prepared for the research.The ultrasonic signal is pretreated by band-pass filter, the flying-time difference between two ultrasonic echoes is recognized by application of a digital correlation method. The time difference between two surface waves is successfully identified by the method. The reliability and accuracy of the Correlation Method is validated through a simulation program. Moreover The influence of different sample frequency and length of the window on the identification accuracy are discussed. And that,The interpolation technique is applied to increase the precision of time difference detection. By processing the surface wave signals sampled in different stress level, the ultrasonic signal time difference can be automatic detected.Finally the curve of the relationship between surface wave propagation time difference and the stress in A3 steel, aluminium and organic glass are obtained respectively. The acoustoelasticity coefficient is obtained by experiment. The speed varieties of the surface wave introduced by the roughness and flatness of a specimen are carefully analyzed, and the methods for resolving the problem are verified by the experiment. In the end the uniaxial stress detection is successful realized, and the primarystress separate method is applied to detect the biaxial stress problem. |
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