共查询到19条相似文献,搜索用时 218 毫秒
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超声检测过程的数值模拟 总被引:14,自引:2,他引:12
简要评述超声检测过程的数值模拟,探讨超声波声场的模拟、超声波和缺陷的相互作用、换能器-缺陷检测系统、超声波在材料和构件中的传播路径、探头设计和超声检测可靠性等。 相似文献
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Linearly polarized ultrasonic shear waves constitute a privileged tool for investigation in the field of mechanical behavior of materials and metallic structures as well as for the determination of acoustical properties of porous materials. These waves are often generated by a piezoelectric plate vibrating in a direction perpendicular to its thickness. However, this way of production presents some difficulties to obtain a perfectly linear polarization. To palliate to this inconvenience, shear waves can be generated by the mode-conversion of a longitudinal wave.This paper deals with the principle and some applications of two types of mode conversion transducers which permit transmitting and receiving shear waves obtained by reflection mode-conversion. These transducers are made up with straight ultrasonic probes coupled, by contact, to acoustic delay lines (or relays) of different geometry. The first type of transducer uses an acoustic relay or delay line of big length. When it is buried in a recipient containing dry sand, it permits the detection of external mechanical disturbances as vibrations and transient shocks. The second type of transducer, for which the delay line has a reduced length, is used for the detection of material anisotropy and for the study of the polarization direction of conventional normal incidence shear wave transducers. 相似文献
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The amplitude of an ultrasonic signal generated by electromagnetic acoustic transducers (EMATs) is typically low when compared to those generated by contacting transducers, which restricts the application of EMATs in the fields of nondestructive testing and nondestructive evaluation. The transmission process of a surface wave EMAT is studied, based on a previously established 3-D model, with the aim of enhancing the amplitude of ultrasonic waves generated by the EMAT. The effect of changing various EMAT parameters on the surface wave is investigated, by utilizing the orthogonal test method. Results indicate that after optimization, the signal amplitude of the EMAT has increased by 25.2%. 相似文献
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Ultrasonic surface wave propagation and interaction with surface defects on rail track head 总被引:1,自引:0,他引:1
Electromagnetic acoustic transducers (EMATs) are non-contact ultrasonic transducers capable of generating wide band ultrasonic surface waves on metallic samples. A lab-based laser-EMAT system has been developed to observe the ultrasonic surface wave propagation and interaction with surface breaking defects on the sample rail head surface. A wide band EMAT generating surface waves with a frequency content between approximately 50 and 500 kHz is used to propagate ultrasonic waves on the surface of a rail head down the length of the sample. A stabilised Michelson interferometer is used to measure the out-of-plane displacement of the surface wave. A complete picture of the ultrasonic surface wave on the sample surface over time is reconstructed using this technique, with exceptionally high spatial and temporal resolution. Despite the curvature of the rail head, the ultrasonic surface wave propagating down the rail is found to have similar properties to Rayleigh waves by direct comparison to those observed on flat samples using the same technique. 相似文献
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H.D.Chen Y.W.Wang J.Xue 《金属学报(英文版)》2004,17(1):38-42
A computer simulation technique for ultrasonic propagation is utilized for the simulation of ultrasonic nondestructive testing (NDT).In this paper,one goal of the simulation is to compute ultrasonic field radiated by arbitrary transducers into pieces under examination.The other simulates a testing experiment.The simulation approach is based on the model for the computation of the ultrasonic field in isotropic media radiated from actual NDT transducers.After the field is known, remaining to be modeled is the interaction between this field and the scatters (defect) and the echo structure. The model of beam-defect interaction is based on the Kirchhoff‘s diffraction approximations theory applied to elastodynamics.We assumed that the incident wave fronts on the defect are plane in the case of a focused immersed transducer and material is isotropic and homogeneous.The simulating results demonstrate that the model in ultrasonic NDT of welds is practical in further research and useful in optimizing testing configurations. 相似文献
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An ultrasonic method for either independent or simultaneous determination of stress and texture is discussed. Quantitative
differentiation between stress and texture during simultaneous measurements can be made. The method is useful for unidirectionally
rolled, extruded, or cast material, and the validity of the method has been experimentally verified by extensive tests on
rolled materials. Electromagnetic acoustic transducers (EMAT’s) have been used, and these allow measurements during processing.
In principle the method is applicable to non-conducting materials if piezoelectric or ferroelectric transducers are used,
but since they are contracting and EMAT’s are noncontacting, the constraints are more severe. 相似文献
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A real-time ultrasonic imager operating at a frequency of 3.5 MHz to test composites in immersion has been developed. It is based on linear array transducers and provides either B-scan or transmission images of composite plates of a few centimeters thickness. The electronic scanning has a pitch of 1.25 mm and an amplitude of 80 mm, and the electronic focusing as well as the acoustic lens on the arrays are set to work at a depth of 40 mm in water. Tests made on composite and plastic plates of 5 to 17 mm thickness show that the system allows the detection of different types of defects and that the interpretation of the ultrasonic signals can be performed on line. 相似文献
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The main disadvantage of electromagnetic acoustic transducers (EMATs) is their inefficiency in generating ultrasound. A new design of Rayleigh-wave EMAT is proposed with improved ultrasonic generation efficiency on non-ferromagnetic materials. The new EMAT's magnet is narrower than the meander-line coil used in the transducer and the coil itself has an uneven distribution of conductors. The principle of the new design is informed by finite element simulations, which show that the EMAT generates Rayleigh waves more efficiently by taking advantage of both horizontal and vertical magnetic fields of the magnet simultaneously. Experimental measurements verify that the maximum amplitude of the ultrasonic signal generated by the new design of EMAT working under a pulse-echo configuration has been enhanced by 90%, when compared to conventional designs. 相似文献
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Characterization of stress corrosion cracking in carbon steel using nonlinear Rayleigh surface waves
This research uses nonlinear Rayleigh surface waves to characterize stress corrosion cracking (SCC) damage in carbon steel. Cold rolled carbon steel is widely used for buried fuel pipelines; the environment surrounding these pipelines creates a mildly corrosive environment, which, in combination with an applied stress, can cause SCC. To ensure the safe operation of these structures, it is crucial that damage due to SCC be detected before their structural integrity is reduced by large cracks. In the early stages of SCC, microstructural changes such as dislocation formation and microcrack initiation occur, which have shown to considerably increase the acoustic nonlinearity of a material. These microstructural changes distort and generate higher harmonics in an initially monochromatic ultrasonic wave. This research considers four different levels of SCC induced in four separate 1018 steel specimens, a material which has a similar susceptibility to SCC as steel used for buried fuel pipelines. Then nonlinear ultrasonic measurements are performed before and after the SCC damage is induced. Nonlinear Rayleigh surface waves are utilized to detect the SCC damage that is concentrated near the material surface. The amplitudes of the fundamental and second harmonic waves are measured with contact wedge transducers at varying propagation distances to obtain the acoustic nonlinearity of the specimens as a function of SCC damage. The results show an increase in the measured acoustic nonlinearity in the early stages of SCC, indicating the feasibility of using this nonlinear ultrasonic method to detect the initiation of SCC in carbon steels. 相似文献