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激光超声技术能够在材料表面形成超声波,是实现材料缺陷无损检测的重要环节。借助Abaqus有限元分析工具,基于激光超声热弹机制建立了轴对称铝板的表面缺陷模型,模拟了激光激发产生的表面波在材料中的传播特性及其与铝板缺陷的相互作用过程。数值模拟实验表明,铝板表面缺陷的分布深度值越大,反射波越强,并且当缺陷深度达到一定程度时,反射波的幅值趋于稳定;但缺陷的分布宽度对于反射波的影响则十分有限。所得结论为基于激光超声的材料缺陷的定量检测及识别提供有效的理论依据。 相似文献
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激光超声无损检测技术 总被引:1,自引:0,他引:1
传统的无损检测方法具有一定的局限性,例如:在高温高压、高湿、有毒等某些恶劣检测环境中,或被测工件具有放射性或腐蚀性,以及被测工件具有较快的运动速度时,已不能完全满足要求。因此,人们一直都在努力寻找适合于上述情况的无损检测方法。这里介绍一种激光超声检测技术,它是利用激光脉冲激发超声从而实现无损检测的一种方法,已逐渐成为材料无损检测的一种重要手段。本文详细介绍了激光超声的检测原理及应用,并指出目前尚存在的问题及解决措施。激光超声的激发原理激光超声是指用脉冲激光在介质中所产生的超声波或利用激光来产生超声这一物理过程。激光可以在固体中产生超声,也可以在气体和液体中产生超声。 相似文献
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激光激发超声波为评价材料近表面弹性性质提供了有效的手段. 考虑到由于冲击硬化、表面热处理、表面氧化等引起的金属材料近表面层弹性性质的变化,建立了一种激光在基底上的梯度材料中激发超声波的理论模型. 用有限元方法模拟了热弹条件下脉冲激光作用于材料上表面激发出的超声波及其传播过程,研究了近表面层离散的层数对超声波的产生和传播的影响,并分别讨论了表面层“变硬”和“变软”两种情况下声表面波的模式变化及用二维傅里叶变换得到各模式的色散曲线. 为进一步研究近表面层的弹性性质建立合理的计算模型及材料性质的反演提供了理论依
关键词:
超声波
有限元法
近表面弹性性质
色散 相似文献
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通过对材料点、线、面等几类不同缺陷的电子结构和声子激发研究的回顾,特别是对它们的声子激发及其局域振动模式分析,给出了材料缺陷导致的材料局域振动模式的微观图像;分析了多原子分子所具有的高频局域振动态以及采用超声或激光方法激发获得长寿命局域振动的基本原理;提出了一种能够利用耦合共振原理进行材料缺陷局域原子结构非接触调整的方法 相似文献
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激光超声的原理及其在固体中的应用 总被引:5,自引:0,他引:5
激光超声是指脉冲激光所产生的脉冲超声。激光超声是较新的产生超声的方法。它的主要特色是,可以遥发遥收,这样就有可能在高温、有危险辐射等恶劣环境下以及在样品运动的生产线上进行超声检测。皮秒级和飞秒级的激光所激发的超声近来又用来研究固体中电子和声子的相互作用。文章介绍了固体中激光超声的声学性能及两种产生机理:热弹机理和电子机理。 相似文献
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Z. Shi J.-M. Yang T. Fan D. Zhang R. Wu 《Applied Physics A: Materials Science & Processing》2000,71(2):203-209
We investigated the YAG laser-generated ultrasonic wave in a solid with an array of rectilinear sources in the melting regime. By adapting the melting rectilinear sources, a 31.2 gain factor of amplitude of the excited ultrasound can be obtained for the aluminum (Al) sample in comparison with the ultrasound generated by rectilinear sources in the thermoelastic regime. In the melting regime, the sample surface remains undamaged during the inspection. Calculations and experimental results show that the array characteristics and the detection point will decide the increase of amplitude, center frequency, bandwidth, and directivity pattern of the narrow-band ultrasound signals generated by a melting-source array. Through our research, the array of melting sources is proved to be a useful tool to enhance the generation efficiency and detection sensitivity in nondestructive inspection. 相似文献
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Most of the factors limiting the extensive application of laser-based ultrasonic for nondestructive evaluation of surface
breaking crack are its poor sensitivity, low efficiency relative to conventional contact ultrasonic methods and limit on the
dimension of the cracks. For this reason, a new technique that multiplepulse narrow-band ultrasound generated by laser arrays
has been proposed. It is found that crack detection dependent on spectrum of narrow-band ultrasound generated by laser arrays
can be operated with low amplitude requirements. In this paper, the narrow-band ultrasound generated by pulse laser arrays
interacting with surface breaking cracks has been simulated in detail by the finite element method (FEM) according to the
thermoelastic theory. The pulsed array lasers were assumed to be transient heat source, and the surface acoustic wave (SAW)
which propagating on the top of the plate was computed based on thermoelastic theory. Then the frequency spectrums of both
reflected waves by crack and transmission ones through crack were compared with the direct waves. Results demonstrate that
multiple-frequency components of the narrow-band ultrasound were varied with change of the depth of surface breaking cracks
significantly, which provides the possibility for precise evaluation of surface breaking cracks. 相似文献
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An aluminium hemicylindrical sample has been irradiated with an array of laser lines, with each line acting as a source of acoustic waves. Detection of the generated ultrasonic waves was performed using both a wide-band stabilized Michelson interferometer and a 20 MHz piezoelectric transducer. Experimental and theoretical results are presented which reveal that the use of a spatially modulated laser source produces significant narrow-banding of the detected ultrasound, compared with a single point or single line source case. Additionally, for a given line spacing, ultrasound of a particular frequency can be directed. Owing to the nature of the acoustic signals generated by each individual array element, superposition of several signals does not result in any energy directivity similar to that encountered in phase electromagnetic array antennas. While time or frequency feature enhancement may be obtained in a desired direction, in most cases the far field energy directivity pattern is simply the incoherent sum of the energy directivity of each array element. 相似文献
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An optical method of generating narrowband Lamb waves is presented. It is carried out with a laser line array in a thermoelastic regime implemented by the Michelson interference technique, where the formed array element spacing can be flexibly and conveniently changed to achieve selective mode excitation. In order to simulate the displacement response generated by this array, its intensity distribution function is presented to build a theoretical analysis model and to derive the integral representation of the displacement response. The experimental device and measuring system are built to generate and detect the Lamb waves on a steel plate. Numerical calculation results of narrowband Lamb wave displacement signals based on the theoretical model show good agreement with experimental results. 相似文献
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We carried out an experimental investigation of the frequency regime of generation of a holographic distributed feedback (DF) dye laser. We show that the convection induced in liquid by heating-up a solution in the excitation zone ensures self-pumping of the solution through this zone that is sufficient for stable operation of the laser in the regime of frequently repeating pulses without forced circulation of the solution through the cuvette. It is found that the main condition for the operation of a DF-laser in this regime is the sharp focusing of pumping radiation, which ensures transverse dimensions of the generation zone of less than 1 mm. In experiments, we produced stable generation of a holographic DF dye laser in the regime of self-pumping of a solution with a pulse repetition rate of up to 1 kHz with an efficiency of 10% and a spectral line width of 0.01 nm. 相似文献
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Extremely intense laser field that makes nonlinear quantum vacuum can be generated by coherent superposition of multiple lasers in circular configuration that incorporates optical fibers synchronization scheme and piecewise mirrors in circular array operating below typical damage threshold. Coherent amplification and large laser beams can produce intensity reaching nonlinear quantum vacuum regime. The effects of phase jitter and envelope timing of the pulses due to imperfect synchronization are simulated and analyzed for both linear and circularly polarized pulses. We obtain simple analytical expressions that well describe the envelope jitter and phase jitter. Several practical aspects are discussed, including implications of scaling the laser dimension and pulse duration, with possibility for giant laser facility. 相似文献
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This work investigates the impact of the background turbulence generated by randomly placed cylinders on the vortex shedding regime and the mechanisms associated to vorticity fluxes. The goals are achieved by exploring velocity databases acquired with a two-dimensional particle image velocimetry system in two types of turbulent flow experiments: flow around a single infinite cylinder and flow within random array of infinite cylinders. Formation lengths, power spectral density functions and vortex distributions are employed to discuss the vortex shedding regime. The effects of background turbulence and vorticity cancellation, due to opposite sign vorticity, on the vorticity fluxes are discussed. The results show that the background turbulence reduces the formation length and consequently increase the shedding frequency. The stronger decay of longitudinal vorticity flux in denser arrays is not accompanied by an increase of the lateral flux of vorticity. Furthermore, it was concluded that the decay of longitudinal vorticity flux is mainly caused by the vorticity cancellation due to the vorticity of opposite sign of close downstream cylinders. 相似文献