摘要:
针对常规超声TOFD(time of flight diffraction,衍射时差)法存在超声衍射声场能量低、检测回波信号弱的问题,提出一种线聚焦超声TOFD焊接缺陷识别方法. 基于几何声学理论,根据所需主轴声线折射角度及聚焦深度,设计线聚焦超声TOFD法所用的声楔块. 通过铝合金板人工缺陷试件的检测,研究线聚焦法的检测灵敏度;通过铝合金板搅拌摩擦焊试件的检测,验证线聚焦法的有效性. 结果表明,和常规方法相比较,相同测试条件下线聚焦超声TOFD法的检测灵敏度更高,采集的图像具有更好的对比度,同时能较好地保持图像边缘. 所提新方法在改善缺陷分辨力、提高缺陷检出率及降低漏检等方面具有很好的使用价值.
Abstract:
Defect signals collected using conventional TOFD (time of flight diffraction) ultrasonic method is often weak in amplitude because of the low energy of diffracted sound field. In order to improve the testing sensitivity, a new ultrasonic TOFD detection method using line-focusing probe is put forward. Based on geometrical acoustics theory, a line-focusing wedge was designed according to the desired refraction angle of the spindle acoustic field and the focus depth. Through the testing of an aluminum alloy block containing artificial defects, the sensitivity of the proposed method was studied. Through the testing of several friction stir welded aluminum alloy pieces, the advantage of the proposed method was verified. The result shows that the testing sensitivity of the line-focusing ultrasound TOFD method is higher than the conventional method. In the collected D-scan image using the proposed method, the contrast between the defect and background image is sharp, and the image edge can also be kept well. The new method has the advantages in the improvement of defect resolution and the increase of defect detection rate, as well as the reduction of residual error rate, which contribute to a great application prospect.
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