In order to obtain good understanding of complicated beam propagation behaviors in nickel-based alloy weldments , ray tracing simulation is established to predict the ultrasonic beam path in a special welded structure of dissimilar steels. Also experimental examinations are carried out to measure the ultrasonic beam paths in the weldment. Then comparisons of the modeling predictions with experimental results are presented to reveal the complicated beam propagation behaviors.
A nonparaxial multi-Gaussian beam model based on the rectangular aperture is proposed in order to overcome the limitation of paraxial Gaussian beam model which losing accuracy in off-axis beam fields. With the method, acoustical field generated by an ultrasonic linear phased array transducer is calculated and compared with the corresponding field obtained by Rayleigh-Sommerfeld integral, paraxial multi-Gaussian beam model, and Fraunhoffer approximation method. Simulation examples show that nonparaxial multi-Gaussian beam model is not limited by the paraxial approximation condition and can predict efficiently and accurately the acoustical field radiated by a linear phased array transducer over a wide range of steering angles.
为了定量检测厚壁焊接结构中的缺陷,对基于USB接口的便携式超声衍射时差法(TOFD,time of flight diffraction)的缺陷检测及定位系统进行了研究.为了便于缺陷的定量及定性识别,引入了信号互相关算法,实现了检测图像的校正.利用该检测系统进行了锅炉压力容器焊缝的检测.结果表明,该系统所获得的D扫描图像清晰、直观、易分辨,同时较准确地确定了缺陷位置,信号互相关算法很好地解决了检测图像不连贯的现象.
Ultrasonic inspections on nickel-based alloy weldments meets some difficulties due to the curvilinear propagating paths will appear in both anisotropic and inhomogeneons welded joints. Thus, it is difficult to determine the exact location of flaws using the traditional ultrasonic testing method which is based on the assumption that the sound beam will propagate in straight lines. In order to overcome this problem, we provide a new model-based inspection approach to locate the flaws in the nickel-based alloy weldments. Furthermore, some experimental examinations are carried out to compare the locating accuracy between the traditional and the modeled-based approach. It shows that the provided model-based inspection method is more accurate than the traditional method in inspection of the nickel-based alloy weldments.
针对常规的超声反射波法检测结果记录性差、可靠性低等技术缺点,采用超声衍射时差(time of flight diffraction,TOFD)法对厚壁(≥20mm)紫铜焊缝缺陷进行检测研究.通过对紫铜材料声学特性的分析,为超声波换能器的选取提供了依据;通过人工缺陷检测,测试了系统的检测灵敏度及精度,并确定了能更全面地反映焊缝中缺陷分布情况的检测工艺;采用超声TOFD法对紫铜焊缝进行了检测,并通过破坏性试验对无损检测结果进行了验证.结果表明,通过采用合理的检测工艺,超声TOFD法能够有效识别紫铜焊缝中裂纹类危险性缺陷.
