基于激光测振仪的薄钢板损伤无损检测方法

基于非接触式激光测振仪的主动兰姆波检测技术,分析了薄钢板损伤的无损检测方法。试验采用单压电片激励,激光测振仪周向阵列接收的检测方式。根据兰姆波在钢板中的传播特性,绘制出相应的频散曲线,确定试验最佳激励参数,进而结合椭圆定位原理和概率成像算法,对激光测振传感器周向阵列采集到的多组信号进行损伤成像。结果表明,该无损检测方法可以有效地检测出损伤,实现损伤的二维成像定位。     

CFRP层板冲击损伤空耦超声Lamb波特征成像 ——基于时间反转损伤指数

为实现飞机碳纤维复合材料（Carbon Fiber Reinforced Plastics，CFRP）层板在役检测，采用同侧空气耦合超声兰姆波特征成像检测的方法对其缺陷进行检测。将非接触空气耦合超声传感器置于CFRP层板同侧，激发A0模态兰姆波，对其冲击损伤进行D扫描检测。引入时间反转损伤指数表征复合材料层板的冲击损伤。结合概率损伤算法，以该指数作为损伤重构成像的特征值，将不同扫描路径上的特征值数据进行融合，得到CFRP层板冲击损伤缺陷的兰姆波图像。结果表明，基于时间反转的兰姆波图像不仅能够直观地呈现损伤缺陷的位置和形状，而且能够通过避免基准信号选取和减少扫描步进次数显著提高检测效率。     

基于Lamb波的金属薄板载荷定位方法

为监测金属板件的结构健康状态,提出了一种基于Lamb波信号进行载荷位置的识别方法。首先,通过Hilbert变换提取Lamb波信号的波形包络;对不同的信号通道分别选取健康信号与差信号波包峰值和时间,通过椭圆定位法确定载荷位置。在实际应用过程中,椭圆定位的交点一般为多个交点,分析这些相交的点形成的区域,为更精确地进行载荷定位提供了有效的分析方法。初步试验结果表明:通过该方法进行分析,载荷的作用位置可以被确定在某一区域。该方法定位效果良好,可用于金属板件结构的载荷定位。     

兰姆波频率方程的数值解法

针对兰姆波频率方程求解问题,提出了以兰姆波相速度为自变量,用函数间断点划分求解区间的数值计算求解方法。通过Matlab软件对算法进行编程实现,绘制出了兰姆波在铝板和钢板中传播时的频散曲线,取得了理想的结果。该方法对兰姆波的工程应用有实际指导意义。     

兰姆波评价胶接接头内聚强度的有限元分析

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。     

用超声兰姆波探测碳纤复合材料的损伤

超声兰姆波可给航空合成构件中冲击损伤的探测提供一种有益的方法。由于叠层的各向异性导致了由分层和波传播方向所决定的兰姆波模式的波达和衰减，复合材料中兰姆波的传播是复杂的。本文采用基频对称兰姆波模式S0，研究了探测冲击损伤的各种方法。对于一种0／90和一种准各向同性的层压材料，研究了S0模式在不同的层状界面探测单一高层的能力。另外，还研究了离层党度和形状的影响。得到了S0模式兰姆波的衰减和冲击损伤程度之间的线性关系。虽然只对平面层压材料作了初步工作，但对典型航空构件冲击损伤的探测也进行了讨论。引言复合层压…     

复合材料盒段冲击损伤的成像优化

基于压电传感器的Lamb波损伤成像方法已广泛应用于复合材料结构的损伤识别与定位中,但激励传感信号在实际检测中往往会存在电磁干扰等异常扰动,从而出现漏检或者损伤的误报。针对这一问题,研究了损伤概率成像优化方法,改进了基于能量变化的损伤因子。在复合材料盒段结构的冲击损伤现场检测中,采用传统方法的概率成像算法的损伤定位精度为68%,而采用文中改进的概率成像算法的损伤定位精度为82%。     

基于波速修正和距离权值的风机叶片损伤定位成像方法

针对Lamb波被动监测方法中存在的损伤定位误差较大,检测结果不够直观、准确等问题,以风机叶片为对象,研究了复合材料结构冲击响应波速修正值标定方法和基于像素点对比度的损伤定位成像矩阵,在此基础上提出了基于波速修正值和距离权值的风机叶片损伤定位成像方法。试验结果表明:与传统的被动定位监测相比,该方法损伤定位误差小,成像位置准确。     

兰姆波表征形状记忆合金相变试验

通过求解薄板的兰姆波频散方程,绘制了NiTi形状记忆合金薄板的频散曲线,并根据频散曲线选择了对合金相变敏感的兰姆波模式。利用PZT超声探头在合金薄板中激励并接收S1及S3模式的兰姆波,测量了温度变化时兰姆波的群速度。研究结果表明,随着NiTi合金相变过程中微观组织结构的变化,兰姆波群速度明显改变,可以根据兰姆波群速度变化测量合金薄板的相变温度。     

基于强度型光纤传感技术的复合材料薄板损伤声发射定位法

声发射具有对缺陷起始和扩展探测灵敏的特点,适用于复合材料薄板损伤检测,其中定位方法的研究是关键技术之一。文章结合光纤传感技术,设计并构建了声发射检测系统,实现了复合材料薄板的损伤源定位。基于三角定位原理,进行分布式光纤传感布置,在复合材料薄板上方获取损伤信号。然后将测得的信号依次利用DaubechieslO小波和Gabor小波进行背景去噪和信号峰值提取,从而获得损伤源释放的AO模态兰姆波传播到各个传感器的精确时间。最后由到达时间依据三角损伤定位算法建立非线性方程组,通过计算即可求出损伤源位置。相比其它方法,该方法具有非接触、无需测量对象材料参数的优点,在复合材料薄板损伤检测应用中有重要意义。     

Piezoelectric Wafer Active Sensors in Lamb Wave-Based Structural Health Monitoring

Recent advancements in sensors and information technologies have resulted in new methods for structural health monitoring (SHM) of the performance and deterioration of structures. The enabling element is the piezoelectric wafer active sensor (PWAS). This paper presents an introduction to PWAS transducers and their applications in Lamb wave-based SHM. We begin by reviewing the fundamentals of piezoelectric intelligent materials. Then, the mechanism of using PWAS transducers as Lamb wave transmitters and receivers is presented. PWAS interact with the host structure through the shear-lag model. Lamb wave mode tuning can be achieved by judicious combination of PWAS dimensions, frequency value, and Lamb mode characteristics. Finally, use of PWAS Lamb wave SHM for damage detection on plate-like aluminum structures is addressed. Examples of using PWAS phased array scanning, quantitative crack detection with array imaging, and quantitative corrosion detection are given.     

Wear estimation by testing the elastic behavior of tool surface

Impedance and Lamb wave structural health monitoring (SHM) techniques are two common approaches used to successfully monitor the integrity of a variety of structures. In this paper, the feasibility of applying both methods for monitoring tool wear is investigated. Additionally, the surface response to excitation (SuRE) was investigated using spectrum analyzers an alternative to the costlier impedance method. Three approaches were used to monitor the condition of both new and artificially worn drill bits. Artificial degradation of the drill bit cutting edges was necessary to avoid any possible data contamination from accidental damage to the sensors or wiring in a harsh machining environment. The estimated magnitude characteristics found from the impedance and spectrum analyzers correctly distinguished between new and worn tools. Lamb wave characteristics were represented by the envelopes of the propagated signal. The S-transformation was then used to obtain the envelope of the harmonic component of the signal at the excitation frequency. The envelopes were nearly identical at similar tool wear levels, and envelope characteristics changed significantly when Lamb wave reflections reached the sensor from the worn cutting edges. The study indicated that each of the three approaches used successfully detected tool wear.     

基于声发射传感器阵列的风机叶片结构健康监测方法

风机叶片结构健康监测是一个迫切需要解决的问题。通过分析各种风力机叶片的损伤检测方法,结合声发射技术特点,研究了基于声发射传感器阵列的风机叶片结构健康监测方法。其中,PZT压电陶瓷传感器阵列布设于受损率较高的叶片部位,对叶片按20%最大设计载荷的增量施加载荷,结合Kaiser效应和Felicity效应,分析采集到的声发射信号,统计声发射波击数,从而判断损伤发生的区域。该方法相比于其他检测技术具有灵敏度高、定位准确和实时性好的特点,在风机叶片结构健康监测研究领域具有较大的意义。     

Application of signal processing techniques to ultrasonic testing of plates by S0 Lamb wave mode

In recent years, much attention has been paid to the use of Lamb waves for structural health monitoring. This choice is prompted by the high speed of Lamb wave inspection, although their dispersive nature can complicate the interpretation of results, especially when dealing with closely-spaced reflectors. In this paper, the objective is to improve the time resolution and signal-to-noise ratio of signals obtained from inspection of plates by the S₀ Lamb mode. The signal processing scheme used is based on deconvolution of the measured signal by Wiener filtering, followed by autoregressive spectral extrapolation. The deconvolution technique is applied to signals obtained from finite element models and also to experimentally measured signals; both sets of data are based on plates with various types of notch discontinuities. Using this technique, the separation distance between adjacent notches was estimated with high accuracy in both simulated and experimental ultrasonic signals.     

铝板结构主动Lamb波扫查合成损伤成像方法

单激励主动Lamb波板结构损伤时间反转成像方法仅对面向激励器的损伤侧敏感,在实施过程中会存在伪损伤点问题,影响对损伤的正确评估。研究提出扫查合成损伤成像方法,首先通过扫查的方法轮流选择压电元件进行激励,从多个角度实现对损伤的照射,再将扫查得到的信号进行合成成像,实现对损伤的监测。在铝板结构上的试验结果表明,该方法可有效消除监测结果的方向敏感性和伪损伤点,提高损伤成像监测结果的准确性和稳定性。     

CFRP层板低能冲击损伤的非线性超声兰姆波检测技术研究

CFRP层板中不可见冲击损伤的线性超声响应特征很弱,由此提出CFRP层板中低能量冲击损伤的非线性超声Lamb波检测方法。首先搭建非线性超声Lamb波检测平台,提出Lamb波激发方法并分析其模态构成,其次判定各模态是否满足非线性超声Lamb波检测条件,最后分析线性及非线性超声检测特征对损伤的敏感程度,提出检测不可见冲击损伤的非线性特征参数。研究结果表明,相对非线性系数对3、5 J低能量不可见冲击损伤具有较高的检测灵敏度,能够用于该类损伤的无损检测。     

Fatigue crack monitoring of riveted aluminium strap joints by Lamb wave analysis and acoustic emission measurement techniques

Statistics show that fatigue crack development comes first and foremost as a damage source in aerospace metallic structures. Currently, widespread methods are available to inspect these structures, but they are quite time-consuming, costly and require the structural system to be idle. Next, attempts to develop damage detection integrated systems are paramount for the safety and cost of such structures. This paper describes an investigation into the feasibility of using an integrated system based on Lamb waves in order to assess the integrity of riveted aluminium joints during cyclical loading. In this experimental analysis, Lamb waves are excited and received outside the joint area using piezoelectric transducers coupled onto the plates. The detected damage is cracks in joint resulting from fatigue loading. The collected signals on the piezoelectric transducers are analysed using Hilbert transform and time–frequency analysis. It is shown that the final interpretation of Lamb wave analysis may provide a means of sizing the defects and following the crack development. In addition to that, an acoustic emission system is used jointly with the Lamb wave analysis in order to discuss results and damage development. Finally, it is demonstrated that both methods can work together and the results obtained are in good agreement.     

Radome health monitoring with Lamb waves: experimental approach

With intent to ensure health monitoring of foam core sandwich structures by a system based on ultrasonic methods, the use of Lamb waves is investigated. The propagation mechanisms are analyzed and reveal leaky waves properties. Moreover, the wave sensitivity to damages induced by low-velocity impacts is tested and the feasibility to detect debonding and foam failure is evaluated.     

Higher harmonics induced in lamb wave due to partial debonding of piezoelectric wafer transducers

Piezoelectric wafer (PW) transducers used for Lamb wave actuation may get partially debonded from the host structure, because of their prolonged use, excessive voltage supply, or improper bonding onto the host structure. In this paper, higher harmonics induced in Lamb wave because of such debonding of the PW actuator are studied both experimentally and through finite element simulation. In experiments, an artificial partial debond is created while bonding the actuator patch onto a pristine aluminium plate. Lamb wave transduced by this actuator in the plate is picked up by a PW sensor which does not have any debonding. In FE simulation, Augmented Lagrangian algorithm is used to solve the contact problem at the breathing debond. Three higher harmonics are observed in the experiments and also in the FE simulation. To ensure that the generated higher harmonics correspond to Lamb wave, time–frequency analysis is carried out using Morlet wavelet transform, and the results are reported in the paper. Spectral damage index (SDI), obtained from spectral attributes of first four harmonics in experiments and simulation, is found to be decreasing with an increase in debonding area. This shows that actuator debonding introduces contact nonlinearity which induces higher harmonics in Lamb wave. Therefore, in damage detection using Lamb wave based nonlinear techniques, the higher harmonics produced may get influenced by the false higher harmonics produced by actuator debonding, leading to incorrect results, if bonding of the actuator is not taken care of properly.