共查询到18条相似文献,搜索用时 721 毫秒
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金属薄板检测中,声-超声检测方法可激发多模式的兰姆波,兰姆波能够评价金属胶接后结构质量,正确认识兰姆波传播特性与胶接接头强度的关系是有效应用该技术的基础。采用有限元模拟的方法,对金属板胶接接头中声-超声激励方式建模。将胶接接头内聚强度与兰姆波的传播模式联系起来,在0.5MHz和1MHz两种激发频率下,随着胶层内聚强度的降低,得出了对应兰姆波模式在胶接接头处内聚强度的频谱图和相对能量的变化曲线。该法能为实验研究、实际检测提供有效理论依据。 相似文献
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对兰姆波在铝合金薄板中传播的频散曲线进行了理论分析。采用任意波形信号发生器和单一传感器发射超声波,用非接触式激光测振仪、数字示波器和计算机,接收并处理超声波信号,并采取时频联合分析,运用短时傅里叶变化的方法,获得了兰姆波在三组合有不同缺陷的铝合金薄板中的传播模式。试验结果表明,超声兰姆波在无缺陷的硬铝合金薄板中传播时模式为A0,在含有空孔型的铝合金薄板传播时,没有产生新的频率成分,但是由A0模式转换成A1模式;而在含有线切割缝隙的铝合金薄板传播中,兰姆波产生了新的频率,即二次谐波,并且兰姆波的模式变成了A0和S0两种。 相似文献
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为了解防喷器内表面声发射信号的特征及传播特性,需要进行内表面的模拟试验,但常用的模拟源不能满足试验要求。为此研制出新型的模拟信号源装置,该装置使用方便、防水、密封、可控,可产生持续、稳定信号。通过对比分析,新型模拟源产生信号幅度的平均值与铅笔芯模拟源的平均值基本一样;新型模拟源的最高幅度略比铅笔芯模拟源高;新型模拟源的平面定位偏离实际位置的距离比铅笔芯模拟定位的要小,且在同一位置上各次试验定位数值间的离散度也小。从而验证了新型模拟源信号可以满足实验室研究的需要。 相似文献
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板中超声传播的几何法分析及应用 总被引:1,自引:0,他引:1
根据声-超声的发射、传播和接收模式,利用几何声学法对板中传播的超声波信号进行分析,实验证明了该方法的科学性及其在板的超声检测中的作用。 相似文献
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The acousto-ultrasonic technique has many potential applications in the NDE of composite materials. However, problems of poor reproducibility and of the sensitivity of the results to precise instrument settings have restricted its application in industry The waves employed in acousto-ultrasonics are chiefly Lamb waves which propagate in the plane of the laminate. In this paper, Lamb wave propagation in composite laminates both with and without defects is investigated both numerically and experimentally. Acousto-ultrasonic parameters based on both predicted and measured responses are calculated, and tests are carried out using a commercially available instrument. The factors which lead to the poor reproducibility of acousto-ultrasonic results are discussed and possible improvements to the technique are proposed. 相似文献
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A computer simulation technique for three-dimensional ultrasonic propagation was utilized for the visualization and investigation of ultrasonic propagation in various materials such as anisotropic solids and combined materials. The calculation technique used here is based on a finite-difference method, but uses an improved nodal calculation method following fundamental consideration of the elastic wave equations. The improvement enabled unified treatment of calculation nodes at the inside and the boundary of the solid, and offered simplicity for calculation at the boundary and applicability for combined and anisotropic materials with limitation on the applicable type of anisotropic stiffness matrix. Here, we present the applications of the calculation technique for the two-dimensional and three-dimensional ultrasonic propagation relating to nondestructive material evaluation using ultrasound, and show the usefulness and applicability for the complex ultrasonic phenomena observed in ultrasonic measurements. 相似文献
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Impact wave and damage detections using a strain-free fiber Bragg grating ultrasonic receiver 总被引:3,自引:0,他引:3
A strain-free mobile fiber Bragg grating (FBG) ultrasonic receiver is applied for the impact-related experiments of carbon fiber reinforced plastic laminates. The strain-free FBG sensor detects an impact-induced acousto-ultrasonic wave and its responses are compared with those of a piezoelectric sensor. Ultrasonic mode wavelength-related averaging effect in FBG ultrasonic sensors is also reported. The mobile FBG sensor can be useful for the acoustic characterization and the sensor placement optimization being required before construction of a built-in FBG network. Finally, the mobility of the strain-free FBG sensor head is extended to ultrasonic scanning application. Based on its high scanning spatial resolution, impact damage sizing is conducted more precisely. 相似文献
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以不同疲劳寿命的铝合金焊缝为例研究了疲劳过程中的超声波非线性效应,同时建立了非线性参数与疲劳寿命的关系曲线(S-N曲线).采用脉冲反转法对非线性超声信号进行处理.结果表明,经过脉冲反转法获得的S-N曲线与经过滤波模块获得的S-N曲线相比谐波幅值提高了一倍,所以脉冲反转法可以提高非线性超声检测法表征疲劳损伤程度能力,而S-N曲线在疲劳过程中呈先缓慢增长后快速增长,最后下降的趋势,此趋势对应了材料疲劳的3个阶段,而金相组织验证了曲线的准确性,所以通过非线性超声脉冲反转法来预测疲劳寿命是可行的. 相似文献
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基于超声波在介质中的传播理论,在当量法基础上采用超声波对激光熔覆层表层裂纹深度进行定量评价。结果表明:表层裂纹信号幅值随裂纹深度的增大而增大,当裂纹深度达到1.0 mm时,信号幅值基本保持不变。相同深度表层裂纹超声波信号幅值随检测距离增大而减小,并趋于平缓,分析认为激光熔覆层中各向异性树枝晶组织及层间界面导致声波能量衰减是引起上述结果的主要原因。结合上述研究结果,本研究对激光熔覆层组织引起的声波能量衰减进行补偿,进而实现表层裂纹深度定量评价方法的修正,在一定程度上提高了激光熔覆层表层裂纹深度的评价精度。 相似文献
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P. Muhammed Thanseer Avijit Kr. Metya S. Palit Sagar 《Journal of Materials Engineering and Performance》2017,26(6):2632-2639
Non-collinear nonlinear ultrasonic (NCNLU) wave mixing technique has been established to study the localized plastic deformation at the crack tip during fatigue. A pair of ultrasonic shear wave was mixed non-collinearly to obtain a longitudinal wave of frequency equal to the sum of the two shear wave frequencies under a resonant condition. Experiments were carried out on notched 9Cr-1Mo 3-point bend specimen during high-cycle fatigue. The variation of the NCNLU parameter with the stress accumulation at the crack tip during the fatigue crack initiation and propagation and mapping of the deformation zone around the crack tip are described in this paper. 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