Initial Exploration On The Reliability Of Phased Array Ultrasonic Testing And Numerical Simulation Of POD

The reliability of nondestructive testing system is affected by many factors. It is value of research that which is the most important factor and how these factors influence the testing results. Phased array ultrasonic technology has been widely used in industrial field since1990s due to its good acoustic beam accessibility, high detection efficiency and real-time imaging. PAUT system has various parameters and the setting up is complex, so the reliability of PAUT has received more and more attention. In this paper, the reliability of PAUT was studied by both experiment and simulation. The evaluation index of reliability is probability of detection (POD) and probability of sizing (POS). The main work is as follows:(1) PAUT was conducted on a55mm-thick steel block. The bottom notches with the height from1mm to10mm and the skew angle within the range90°±9°was detected. The probability of detection was estimated and compared with that obtained from simulation. Size of the defect that will be detected with a probability90%was2.56mm in experiment, while it was2.66mm in simulation. It indicated the accuracy of POD estimation.(2) Through the experiment and simulation, POD and POS curves of phased array probes with different frequencies and different element sizes were compared. When the frequency of the probes were2.25,5,7.5MHz, size of the defect that will be detected with a probability’90%were2.66,5.55,14.91mm respectively, and size of the defect that will be sized with a accuracy100%were6.9,3.9,3.8mm respectively; When the element width increases, for2.25MHz and5MHz probes, size of the defect that will be detected with a probability90%were2.75,3.22mm respectively, and size of the defect that will be sized with a accuracy100%were4.8,4.0mm respectively.(3) With numerical method, for side drilled holes in stainless steel, the influence on test results of the attenuation coefficient, structure noise was studied. The results showed:as attenuation coefficient of0,0.05,0.10dB/mm, size of the defect that will be detected with a probability90%were1.19,3.13,4.86mm respectively; For different structural noise, there is a big difference between POD curves, When the signal-to-noise ratio is11.1dB and6.2dB, size of the defect that will be detected with a probability90%were1.43mm and2.74mm respectively.(4) Four different shapes of defects were simulated:rectangle, semi-elliptical, cylinder, sphere. The imaging characteristic and the amplitude changing rule of the four type embedded defects were compared. Furthermore. the POD curves of planar defects are estimated. The results showed:size of the defect that will be detected with a probability90%of the rectangle and semi-elliptical bottom defects were2.16mm and2.66mm respectively. The bottom notches with orientation in55mm thick carbon steel block were simulated and analyzed. The estimation of POD was carried out when the standard deviation of skew angle and tilt angle changes within the range of1°-5°. The results showed:notch skew angle had a greater influence on POD curves than tilt angle.