Electron beam welding （EBW） is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. It is a complex high-temperature metallurgical process, and the quality of...Electron beam welding （EBW） is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. It is a complex high-temperature metallurgical process, and the quality of welding may deteriorate because of defects caused by improper welding parameters, especially in the EBW of thickened aluminum alloy plate. Ultrasonic phased array（UPA） technology has been applied more widely in the field of nondestructive testing because of its ability of effectively controlling the shape and direction of the emitted ultrasonic beam. In present research, a specimen with EBW seam on thickened aluminum plate was tested with a linear array ultrasonic phased array probe, and a large number of B-scan images of the weld were acquired by electronic scanning in probe combined with the mechanical scanning of the probe along the weld direction. This large number of B-scan images were stacked to construct the volume data, with which the 3D image of the weld discontinuities were reconstructed, and the 3D visualization was realized. More details about weld discontinuities＇ spatial distribution and orientation were revealed, and this approach also made the results of non-destructive ultrasonic testing more easily to understand.展开更多
In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization ...In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization of ultrasonic D-scan image,clutter wave suppression and de-noising were presented firstly.Then,the image is processed by binaryzation using KSW 2 D entropy based on image segmentation method.The results showed that,the global threshold based segmentation method was somewhat ineffective for D-scan image because of under-segmentation.Especially,when the image is big in size,small targets which are composed by a small amount of pixels are often undetected.Whereas,local threshold based image segmentation method is effective in recognizing small defects because it takes local image character into account.展开更多
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,...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.展开更多
According to the principle of synchronous demodulation, the modulation informa- tion in the output signal of vibro-acoustic modulation test was investigated and the nonlinear interaction of sound and vibration with th...According to the principle of synchronous demodulation, the modulation informa- tion in the output signal of vibro-acoustic modulation test was investigated and the nonlinear interaction of sound and vibration with the crack interface in a metallic rod was analyzed. A swept signal excitation was used to obtain a proper high frequency parameter in the test of alu- minum rod samples with different sizes of cracks and the modulation information in the output signal was analyzed. It was found that the ultrasound wave in the structure can be separated into two parts. One is the wave which passes through the crack interface modulated by the low frequency vibration, and other wave has no any changes. The nonlinear modulation model was modified and a quantitative method for crack detection was proposed. It is demonstrated by comparing with the ultrasonic C-scanning that this method can be used to estimate the fatigue crack size in the metallic rod.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51575134 and 51175113)
文摘Electron beam welding （EBW） is a fusion welding process in which a beam of high-velocity electrons is applied to two materials to be joined. It is a complex high-temperature metallurgical process, and the quality of welding may deteriorate because of defects caused by improper welding parameters, especially in the EBW of thickened aluminum alloy plate. Ultrasonic phased array（UPA） technology has been applied more widely in the field of nondestructive testing because of its ability of effectively controlling the shape and direction of the emitted ultrasonic beam. In present research, a specimen with EBW seam on thickened aluminum plate was tested with a linear array ultrasonic phased array probe, and a large number of B-scan images of the weld were acquired by electronic scanning in probe combined with the mechanical scanning of the probe along the weld direction. This large number of B-scan images were stacked to construct the volume data, with which the 3D image of the weld discontinuities were reconstructed, and the 3D visualization was realized. More details about weld discontinuities＇ spatial distribution and orientation were revealed, and this approach also made the results of non-destructive ultrasonic testing more easily to understand.
基金supported by the National Nature Science Foundation of China(51375002,51005056)。
文摘In order to improve the work efficiency of non-destructive testing(NDT)and the reliability of NDT results,an automatic method to detect defects in the ultrasonic image was researched.According to the characterization of ultrasonic D-scan image,clutter wave suppression and de-noising were presented firstly.Then,the image is processed by binaryzation using KSW 2 D entropy based on image segmentation method.The results showed that,the global threshold based segmentation method was somewhat ineffective for D-scan image because of under-segmentation.Especially,when the image is big in size,small targets which are composed by a small amount of pixels are often undetected.Whereas,local threshold based image segmentation method is effective in recognizing small defects because it takes local image character into account.
基金supported by the National Natural Science Foundation of China(50775054,10774158)supported by the International Joint Research Program of China(2007DFR70070).
文摘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.
基金supported by the National Natural Science Foundation of China(51575134,51175113,51105033,51205083)
文摘According to the principle of synchronous demodulation, the modulation informa- tion in the output signal of vibro-acoustic modulation test was investigated and the nonlinear interaction of sound and vibration with the crack interface in a metallic rod was analyzed. A swept signal excitation was used to obtain a proper high frequency parameter in the test of alu- minum rod samples with different sizes of cracks and the modulation information in the output signal was analyzed. It was found that the ultrasound wave in the structure can be separated into two parts. One is the wave which passes through the crack interface modulated by the low frequency vibration, and other wave has no any changes. The nonlinear modulation model was modified and a quantitative method for crack detection was proposed. It is demonstrated by comparing with the ultrasonic C-scanning that this method can be used to estimate the fatigue crack size in the metallic rod.
