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应用超声端点反射法测量薄壁工件中缺陷高度时,需要深入研究检测信号的产生机理、检测信号与缺陷的对应关系、缺陷信号的识别等。采用有限元计算方法,对测量薄壁(6 mm)工件中未焊透高度的超声端点反射法进行了数值分析。通过构造合适的有限元模型,计算得到了超声波与未焊透缺陷相互作用的散射声场,对源于缺陷上端与底部的反射回波的产生、传播过程以及含有不同高度未焊透的薄板工件的检测回波信号进行对比分析。结果表明:超声端点反射法用于薄壁工件中未焊透高度测量时,可同时得到缺陷的上端与底部反射回波,且两回波在检测得到的A扫描信号中具有一定声程差,其值与未焊透的高度呈线性关系;此外,为得到更易于识别的缺陷上端反射回波,超声检测探头可进行小幅度的位置变动。在此基础上,对平板未焊透模拟试样进行了实际超声检测试验,试验结果与有限元分析结果具有良好的吻合性。
When using ultrasonic endpoint reflection method to measure the height of defects in thin-walled workpieces, it is necessary to study the mechanism of detection signal, the correspondence between signal and defect, the identification of defect signal and so on. The finite element method was used to analyze the ultrasonic endpoint reflection method for measuring the impervious height of thin-walled (6 mm) workpieces. By constructing a suitable finite element model, the scattering sound field interacting with the impervious defect is calculated. The generation and propagation of reflected echoes from the top and bottom of the defect, Test echo signal for comparative analysis. The results show that when the ultrasonic endpoint reflection method is used to measure the impermeability of thin-walled workpieces, the top and bottom reflected echoes of the defects can be obtained at the same time, and the two echoes have a certain acoustic path difference in the detected A-scan signal. Its value is linear with the impermeable height; in addition, to provide easier-to-recognize top-reflected echoes of defects, the ultrasonic probe can be used for small amplitude changes. On this basis, the actual ultrasonic testing of the unsplit slab was carried out. The experimental results are in good agreement with the results of finite element analysis.