| Anchor is an important stress component in bridge system. At present the manual A-pulse ultrasonic testing is one of main conventional nondestructive testing methods for anchor. This method not only has low efficiency of testing, but also is much relied on the manual operation which is easy to cause that defects cannot be detected, and therefore the quality of anchor was threatened. Ultrasonic phased array technology has the advantage of beam deflection and focusing with intuitive image, high detection efficiency and reliable test results. This technology has been widely used in the detection of welds of steel structure, pressure vessels and so on, but less used in the detection of forging products. So based onthe experiment and analysis of influencing factors of ultrasonic phased array technology, this paper investigated the testing technology of ultrasonic phased array in bridge anchor detection.According to the structure features and testing requirements of simulating anchor, the artificial defects reference blocks with different curvatures and the probe wedges with circular arc and without circular arc were designed, and the research on the effects of phased array acoustic field with different curvature radius was carry out. Based on theoretical calculation and experimental verification, we found that there is a maximum detectable depth when using phased array angle probe to detect curved surface parts of reference blocks, and the depth is related to the curvature of work piece. the imaging of defect and gain value of A signal of defect in the reference blocks with different curvatures were compared respectively by using four different probes including plane straight probe, arc straight probe and plane angle probe, arc angle probe. The results show that arc probe has strong ability of acoustic beam focusing, and better coupling with testing surface. When the diameter of reference blocks between 100 mm and 400 mm, both the circular arc straight probe and arc angle probe show the better defect detection abi lity than plane probe.Furthermore, the influence of frequency and type of probes on defect detection was studied. And this paper analyzed the effect of the different frequency and different wedge form on the defect detection ability. Based on these result s, the optimization of ultrasonic phased array inspection for bridge anchors were carried out. It was shown that the probe with 5 MHz frequency has better sensitivity and resolution with best detection images.The influence of different defect size and different defect depth on the test results, and the influence of different defect sizes and different defect depth on ultrasonic phased array detection ability were investigated. The results show that defect detection capability improves with the increase of defect size, and defect detection ability decreases with the increase of depth of defect. Plane angle probe detection ability declines with the increase of the defect depth and the degree of its decline is associated with surface curvature; arc angle probe detection reduces with the increase of the defect depth, and the degree of decline is independent of the surface curvature.Finally, the application of ultrasonic phased array technology in the testing of bridge anchor was studied, and this paper compared testing results of different types of defects in anchor using the phased array and conventional ultrasonic testing. And the ultrasonic phased array technology shows more accurate, intuitive, and convenient to detectinternal and surface defects than conventional ultrasonic testing methods for bridge anchor. |
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