Based On The Critically Refracted Longitudinal Wave Cut Stress Testing Laboratory System And

As the fast developing testing technique, ultrasonic testing occupies an important position in NDT (Non-destructive Testing) domain due to its special merits and broad application. Among those ultrasonic testing techniques formed by the ultrasonic and material parameters or various relations of mechanical quantities, general stress measurements such as Bulk-wave Method and Surface-wave Method based on the acoustic elastic principle have their own flaws. This limitation closely relates to the exact type of ultrasonic, the propagation characters of which determine the measuring type of stress and accuracy.Critically Refracted Longitudinal (LCR) Wave is a complex ultrasonic formed by the incidence of longitudinal wave with the first critical angle on the interface. As a special longitudinal wave, not only does LCR wave have some traits of longitudinal wave, but also its generation principle makes the internal shear stress measurement possible from the surface of the workpiece.During the stress measurement process, the driving manner of transducer affects the character of acoustic signal directly. This article adopts both high-performance AVR MCU and DC converting circuit to generate high pressure sharp pulse and drive the ultrasonic probes, which can activate the appropriate LCR wave signal, and the circuit structure is simplified too.Acoustic elastic principle reveals the relationship between wave speed and stress, thus how to measure the propagation time accurately between known points is a key point. Concerning travel-time's little change of LCR wave caused by stress variations, Time to Digital Converter (TDC) based on the absolute transmitting delay of logic gate is employed to meet the demand of high precision measurement. In the practical application, those functional module in the system are integrated together, this can minish the size of the whole system and facilitate the adjustment.The experimental results not only reflect the approximate linear relationship between acoustic speed and applied stress fields, but also prove the feasibility of this experimental system, which provides a helpful reference for further development of the testing equipments and apparatus. At the end of this paper, a possible improving plan for this experiment is presented, which further makes the shear stress evaluation system with LCR wave better in practical.