Study Of The Ultrasonic Scattering Detection Method For Thin Planar Welds

As a crucial part in welding structure, the quality of the welds has direct influence on the performance,reliability and service life of welding members. The ultrasonic time of flight diffraction(TOFD) method is considered as a postscript to the conventional ultrasonic testing techniques and has been widely used in real application of evaluating welds. However, the limitation of TOFD is the existence of certain dead zone nearby scanning surface. Especially in detecting thin planar welds, this sort of problem is more serious. The purpose of this study is to research new method used in thin planar welds in view of ultrasonic scattering characteristics.This paper first reviews the ultrasonic TOFD methods, then analyses the reasons of dead zone and means to improve the measurement accuracy nearby surface in thin planar welds. In addition, the nondestructive testing improvement based on diffraction/scattering waves recent years is introduced.Moreover, this paper focus on different scattering laws of side-drilled hole and crack under incident longitudinal and shear waves, including mode conversion, propagate behaviors, energy intensity as well as angular distributions. When incident waves meet discontinuity, the reflected waves energy distribution is in accord with the results of acoustic intensity reflectance by MATLAB. Furthermore, as longitudinal waves are incident to discontinuity, it performs high-intensity scattered head waves. On the other side, as shear waves obliquely incidence with greater than third critical angle, advancing reflect waves are produced at the discontinuity. The whole scattering characteristics in acoustic field above mentioned are simulated and analyzed by WAVE2000.Following this, in light of the scattering characteristics of discontinuity under incident longitudinal and shear waves, this study presents evaluation methods named STSR(Shear-Transmit-Shear-Receive) and LTLR(Longitudinal-Transmit –Longitudinal-Receive). STSR method means the scattered shear waves generated by straight probe are received by shear probe. Similarly, LTLR method presents the scattered longitudinal waves generated by the transverse wave angle beam probes are received vertically by straight probe.Finally, considering STSR and LTLR methods are hardly affected by lateral waves and bottom waves, this paper further proposes evaluation methods based on the scattering laws and then carries out testing experiment on 9mm thick specimen. The result shows that it can detect the subsurface notch tip which is 1mm in depth and 0.2mm in width successfully by scattered head wave when using STSR method. The error between measured values and actual one is less than 0.2mm. It is feasible to detect the notch which is 2mm in depth by reflected shear wave. According to the A-scan signals of the experiment on same specimen, LTLR method possessing similar evaluate ability for the notch in 9mm thick specimen is also confirmed. Besides, the experiment used manual photoelectric locating system combing with different scan methods is performed. The 2D-graphs and all data mentioned in this paper verified both two methods can be contributed to improving the limitation of dead zone nearby surface in thin planar welds in views of ultrasonic scattered waves.