共查询到20条相似文献,搜索用时 156 毫秒
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针对电磁超声兰姆波换能器激发的兰姆波存在多模式、频散现象和信号较弱的问题,结合铝合金板材检测背景,提出一种基于"双交点法"、"零斜率准则"和正交试验设计相结合的电磁超声兰姆波换能器多目标优化设计方法。其中,"双交点法"可有效削弱兰姆波多模式现象的影响,"零斜率准则"能够有效降低兰姆波的频散现象,而正交试验设计方法可有效提高电磁超声兰姆波信号的幅值。依据所提优化设计方法,对一个在铝板检测中常用的电磁超声兰姆波换能器的9个主要参数进行了多目标优化设计。实验表明,优化后,兰姆波信号中的多模式、频散现象得到显著抑制,而且信号幅值得到明显提升,有效改善了电磁超声兰姆波换能器的工程实用性。 相似文献
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固-液-固3层结构板中超声兰姆波的频散特性 总被引:5,自引:1,他引:4
文章采用传统矩阵方法研究固-液-固3层结构板中兰姆波的传播,数值计算结果证明了用该方法分析层状材料中的兰姆波的有效性与实用性,文章计算出的多种频散曲线对超声兰姆波的应用是有益的。 相似文献
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基于A0模式兰姆波对薄板腐蚀缺陷进行成像检测,在频率一定时,由于腐蚀造成板厚的改变将进一步影响检测兰姆波速度的变化,通过检测兰姆波波速的变化可以对板材腐蚀类缺陷进行监测.根据A0模式兰姆波的频率特征,测量发射探头与接收探头之间的兰姆波走时,结合波的实际传播路径,计算出实际检测兰姆波的速度,采用联合迭代重建技术(SIRT)对走时数据进行群速度图像重建.基于有限元数值方法,采用A0模式兰姆波对薄铝板中的腐蚀类缺陷进行模拟检测,给出了成像检测结果. 相似文献
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运用超声Lamb波对薄板钢结构进行检测,采用斜入射方式实施Lamb波的激励,并对检测信号进行模态分析。经实验发现选择合适的频率/入射角组合可实现对Lamb波模态的选择和控制,实现对检测对象的检测策略,并具有一定的工程应用价值。 相似文献
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A real-time monitoring technique for local plasticity using Lamb waves was developed. Tensile test of a thin aluminum plate with a circular hole where high stress concentration was induced was conducted to verify this technique. During the tensile test, a series of wave signals passing through the local plastic region were collected using a directional actuator/sensor set to monitor plasticity evolution. A pulse compression technique was used to process the wave signals. With the increase of tensile stress in the specimen, the amplitude changes of S0 and A0 modes were obtained and the difference of Lamb wave signals was further evaluated using a proposed signal index I calculated by wavelet analysis. Combined with the numerical stress analysis of the tensile specimen, the influence of the plasticity on the amplitudes of S0 and A0 wave modes was analyzed. As the plastic zone grows gradually, the wave amplitudes and I of S0 and A0 wave modes show their different change tendencies compared with those in elastic stage. The amplitude change is more sensitive to mild plasticity than that of I, while the change of I caused by severe plasticity is more obvious than the amplitude change. 相似文献
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Atalar A Koymen H Degertekin FL 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1992,39(6):661-667
In a conventional scanning acoustic microscope the excited leaky modes contribute significantly to the high contrast obtained in the images. However, all such modes exist simultaneously, and the interpretation of the images is not straightforward, especially in layered media. A lens geometry is proposed that can be used with acoustic microscopes to image layered solid structures. This lens can focus the acoustic waves in only one of the Lamb wave modes of the layered solid with a high efficiency. V(Z) curves obtained from this lens are more sensitive to material properties compared to that obtained from conventional lens. Measuring the return signal as a function of frequency results in another characteristic curve, V(f). The Lamb wave lens and the associated characterization methods for the layered structures are described. The results presented show that the Lamb wave lens is at least an order of magnitude more sensitive than the conventional lens and can easily differentiate between a good bond and disbond in a layered structure. 相似文献
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Wilcox PD Lowe MJ Cawley P 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2005,52(12):2370-2383
Planar coil electromagnetic acoustic transducers (EMATs) are investigated for the excitation and detection of Lamb waves in nonferromagnetic metallic wave-guides. Such EMATs are attractive for certain applications due to their omni-directional sensitivity to wave modes with predominantly in-plane surface displacement, such as the So Lamb wave mode. A model is developed that enables the modal content of the radiated Lamb wave field from a transmitting EMAT to be calculated, and the output voltage from a receiving EMAT to be predicted when a Lamb wave mode is incident on it. The predictions from this model are compared with experimental data obtained from 12 different EMATs tested on a 5-mm thick aluminum plate, and good agreement is obtained. The model then is used to analyze the different effects that contribute to the overall Lamb wave modal sensitivity of an EMAT. The relationship between coil geometry and wavelength is examined. 相似文献
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《Composites Science and Technology》2007,67(7-8):1370-1384
The propagation characteristics of Lamb waves in composites, with emphasis on group velocity and characteristic wave curves, are investigated theoretically and experimentally. In particular, the experimental study focuses on the existence of multiple higher-order Lamb wave modes that can be observed from piezoelectric sensors by the excitation of ultrasonic frequencies. Using three-dimensional (3-D) elasticity theory, the exact dispersion relations governed by transcendental equations are numerically solved for an infinite number of possible wave modes. For symmetric laminates, a robust method by imposing boundary conditions on the mid-plane and top surface is proposed to separate symmetric and anti-symmetric wave modes. A new semi-exact method is developed to calculate group velocities of Lamb waves in composites. Meanwhile, three characteristic wave curves: velocity, slowness, and wave curves are adopted to analyze the angular dependency of Lamb wave propagation. The dispersive and anisotropic behavior of Lamb waves in a two different types of symmetric laminates is studied in detail theoretically. In the experimental study, two surface-mounted piezoelectric actuators are excited either symmetric or anti-symmetric wave modes with narrowband signals, and a Gabor wavelet transform is used to extract group velocities from arrival times of Lamb wave received by a piezoelectric sensor. In comparison with the results from the theory and experiment, it is confirmed that multiple higher-order Lamb waves can be excited from piezoelectric actuators and the measured group velocities agree well with those from 3-D elasticity theory. 相似文献
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基于线性三维弹性理论和“增量变形力学”理论,采用勒让德正交多项式展开法,推导了在水平和垂直方向施加初应力时,沿纤维增强复合板的非主对称轴方向传播的声弹Lamb波的波动方程,并对波动方程进行数值求解。为了验证方法的准确性,将该文方法求解的各向同性材料的相速度频散曲线与Disperse?软件的计算结果进行比较,两者吻合良好。以单层单向纤维增强复合材料板为例,计算了无初应力状态下的波结构应力曲线,并与应力自由边界初始条件的一致性进行了比较。研究了水平和垂直方向初应力效应对Lamb波频散曲线的影响。针对声弹效应较为敏感的Lamb波A0模态,着重分析了初应力效应对波结构位移分布曲线的影响。 相似文献
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Utilization of specific Lamb wave modes with special cross-sectional wave structures is proposed for the detection of interfacial weakness between an adhesive and adherent. Such an approach is based on plate wave behavior in a three-layered medium with imperfections on the individual interfaces. Selection of appropriate modes and frequencies for adhesion weakness detection is obtained by numerical analysis of the dispersion relations and comparisons of the dispersive curves for perfect, welded and imperfect, smooth boundary conditions. The inspection parameters were evaluated by an analysis of displacement, stress, and power distributions across the three-layered asymmetric adhesive structure. Special selection criteria are proposed. Utilization of dispersive curves do not always provide expected increased sensitivity as in the cross-sectional field distribution approach. 相似文献
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Single Mode Tuning Effects on Lamb Wave Time Reversal with Piezoelectric Wafer Active Sensors for Structural Health Monitoring 总被引:2,自引:0,他引:2
Lamb wave time reversal method is a new and tempting baseline-free damage detection technique for structural health monitoring.
With this method, certain types of damage can be detected without baseline data. However, the application of this method using
piezoelectric wafer active sensors (PWAS) is complicated by the existence of at least two Lamb wave modes at any given frequency,
and by the dispersion nature of the Lamb wave modes existing in thin-wall structures. The theory of PWAS-related Lamb wave
time reversal has not yet been fully studied.
This paper addresses this problem by developing a theoretical model for the analysis of PWAS-related Lamb wave time reversal
based on the exact solutions of the Rayleigh-Lamb wave equation. The theoretical model is first used to predict the existence
of single-mode Lamb waves. Then the time reversal behavior of single-mode and two-mode Lamb waves is studied numerically.
The advantages of single-mode tuning in the application of time reversal damage detection are highlighted. The validity of
the proposed theoretical model is verified through experimental studies. In addition, a similarity metric for judging time
invariance of Lamb wave time reversal is presented. It is shown that, under certain condition, the use of PWAS-tuned single-mode
Lamb waves can greatly improve the effectiveness of the time-reversal damage detection procedure. 相似文献