A focused ultrasonic transducer is used for precise, step-by-step, surface ultrasonic svanuing iusgection of spot welds. Two methods for generating characteristic data matrices of ultrasonic echo signals of the spot w...A focused ultrasonic transducer is used for precise, step-by-step, surface ultrasonic svanuing iusgection of spot welds. Two methods for generating characteristic data matrices of ultrasonic echo signals of the spot welds are established. One is based on the ultrasonic echo amplitude and the other is based on frequency spectrum. Both methods generate scamping inspection data arrays and provide clear C-scan images. Based on C-scan noise reduction, the Krisch edge detection operator for edge detection-a gray window transform-reflects the shapes of the spot welds and allows quantitative determination of their size. The method based on the ultrasonic echo amplitude provides a greater quantitative detection accuracy.展开更多
The non-destructive testing of brazed joint in honeycomb structure with thin panel （ thickness ： 0. 2 mm） was studied by ultrasonic C-scan method. Samples with different types of artificial defect were designed; th...The non-destructive testing of brazed joint in honeycomb structure with thin panel （ thickness ： 0. 2 mm） was studied by ultrasonic C-scan method. Samples with different types of artificial defect were designed; the characteristic signal and the main parameters of the test were determined by the pre-experiment, and then parameters were optimized by orthogonal design, finally the optimum process was verified by a single panel sample. The multiple reflection echoes were chosen as the characteristic signal. The optimal C-scan results were achieved when the 20 MHz focus probe was used, and the pass band range for received signal were selected as 8 - 17. 5 MHz. The defects such as incomplete penetration and core damage can be detected with ultrasonic C-scan, and the detection accuracy can reach to 1 ram.展开更多
In this paper, ultrasonic C-scan test of spot welds for stainless steel has been studied. It is concluded that large scanning step length contributes to high testing efficiency, however, the low-resolution C-scan imag...In this paper, ultrasonic C-scan test of spot welds for stainless steel has been studied. It is concluded that large scanning step length contributes to high testing efficiency, however, the low-resolution C-scan image generated cannot be used to assess spot welding quality reliably. Based on bicubic image interpolation, the C-scan image in low resolution with the large step length 1 000 ~xm is subdivided and reconstructed. By this means, the C-scan image resolution is greatly enhanced and testing results obtained are satisfactory, realizing rapid assessment of spot welds. The results of rapid ultrasonic C-scan test fit the actual metallographic measured value well. Mean value of normal distribution of error statistics is O. 006 67, and the standard deviation is O. 087 11. Rapid ultrasonic C-scan test based on image interpolation is of high accuracy and excellent stability.展开更多
By means of total energy calculations within the framework of the local density approximation (LDA), the interactions between a silicon Si(001) surface and a scanning probe are investigated. The tip of the probe, comp...By means of total energy calculations within the framework of the local density approximation (LDA), the interactions between a silicon Si(001) surface and a scanning probe are investigated. The tip of the probe, comprising 4 Si atoms scans along the dimer lines above an asymmetric p(2 × 1) surface, at a distance where the chemical interaction between tip-surface is dominant and responsible for image resolution. At that distance, the tip causes the dimer to toggle when it scans above the lower atom of a dimer. The toggled dimers create an alternating pattern, where the immediately adjacent neighbours of a toggled dimer remain unchanged. After the tip has fully scanned across the p(2 × 1) surface, causes the dimers to arrange in a p(2 × 2) reconstruction, reproducing the images obtained in scanning probe experiments. Our modelling methodology includes simulations that reveal the energy input required to overcome the barrier to the onset of dimer toggling. The results show that the energy input to overcome this barrier is lower for the p(2 × 1) surface than that for the p(2 × 2) or c(4 × 2) surfaces.展开更多
通过超声水浸脉冲法对C/SiC复合材料的声阻抗进行测定,结果表明,其声阻抗介于（4.0~4.7）×106kg/m2s之间;未焊合时界面反射系数约为1,焊接良好时界面反射系数介于0.71~0.74之间。为使未焊合时界面反射信号幅度比焊接良好时至少相差...通过超声水浸脉冲法对C/SiC复合材料的声阻抗进行测定,结果表明,其声阻抗介于（4.0~4.7）×106kg/m2s之间;未焊合时界面反射系数约为1,焊接良好时界面反射系数介于0.71~0.74之间。为使未焊合时界面反射信号幅度比焊接良好时至少相差6 d B,C扫描检测时应监测二次以上界面反射信号幅度,并采用金相的方法对C扫描结果进行验证,二者一致性较好。展开更多
文摘A focused ultrasonic transducer is used for precise, step-by-step, surface ultrasonic svanuing iusgection of spot welds. Two methods for generating characteristic data matrices of ultrasonic echo signals of the spot welds are established. One is based on the ultrasonic echo amplitude and the other is based on frequency spectrum. Both methods generate scamping inspection data arrays and provide clear C-scan images. Based on C-scan noise reduction, the Krisch edge detection operator for edge detection-a gray window transform-reflects the shapes of the spot welds and allows quantitative determination of their size. The method based on the ultrasonic echo amplitude provides a greater quantitative detection accuracy.
文摘The non-destructive testing of brazed joint in honeycomb structure with thin panel （ thickness ： 0. 2 mm） was studied by ultrasonic C-scan method. Samples with different types of artificial defect were designed; the characteristic signal and the main parameters of the test were determined by the pre-experiment, and then parameters were optimized by orthogonal design, finally the optimum process was verified by a single panel sample. The multiple reflection echoes were chosen as the characteristic signal. The optimal C-scan results were achieved when the 20 MHz focus probe was used, and the pass band range for received signal were selected as 8 - 17. 5 MHz. The defects such as incomplete penetration and core damage can be detected with ultrasonic C-scan, and the detection accuracy can reach to 1 ram.
文摘In this paper, ultrasonic C-scan test of spot welds for stainless steel has been studied. It is concluded that large scanning step length contributes to high testing efficiency, however, the low-resolution C-scan image generated cannot be used to assess spot welding quality reliably. Based on bicubic image interpolation, the C-scan image in low resolution with the large step length 1 000 ~xm is subdivided and reconstructed. By this means, the C-scan image resolution is greatly enhanced and testing results obtained are satisfactory, realizing rapid assessment of spot welds. The results of rapid ultrasonic C-scan test fit the actual metallographic measured value well. Mean value of normal distribution of error statistics is O. 006 67, and the standard deviation is O. 087 11. Rapid ultrasonic C-scan test based on image interpolation is of high accuracy and excellent stability.
文摘By means of total energy calculations within the framework of the local density approximation (LDA), the interactions between a silicon Si(001) surface and a scanning probe are investigated. The tip of the probe, comprising 4 Si atoms scans along the dimer lines above an asymmetric p(2 × 1) surface, at a distance where the chemical interaction between tip-surface is dominant and responsible for image resolution. At that distance, the tip causes the dimer to toggle when it scans above the lower atom of a dimer. The toggled dimers create an alternating pattern, where the immediately adjacent neighbours of a toggled dimer remain unchanged. After the tip has fully scanned across the p(2 × 1) surface, causes the dimers to arrange in a p(2 × 2) reconstruction, reproducing the images obtained in scanning probe experiments. Our modelling methodology includes simulations that reveal the energy input required to overcome the barrier to the onset of dimer toggling. The results show that the energy input to overcome this barrier is lower for the p(2 × 1) surface than that for the p(2 × 2) or c(4 × 2) surfaces.
文摘通过超声水浸脉冲法对C/SiC复合材料的声阻抗进行测定,结果表明,其声阻抗介于（4.0~4.7）×106kg/m2s之间;未焊合时界面反射系数约为1,焊接良好时界面反射系数介于0.71~0.74之间。为使未焊合时界面反射信号幅度比焊接良好时至少相差6 d B,C扫描检测时应监测二次以上界面反射信号幅度,并采用金相的方法对C扫描结果进行验证,二者一致性较好。
