螺栓松动损伤的亚谐波共振识别方法

螺栓松动将导致结构完整性的破坏,螺栓连接状态的实时有效监测和评估具有重大意义。提出了一种基于亚谐波共振分析的螺栓松动识别方法。针对螺栓连接结构简化的单自由度非线性模型,采用多尺度方法分析了亚谐波共振现象,定性模拟了螺栓松动损伤亚谐波激励条件。以铝梁螺栓搭接结构为实验对象,利用粘贴在铝梁表面的压电作动/传感单元,采用不同频率的激励信号作用在作动片上,传感片接收响应信号,对其进行频谱分析,通过提取响应频谱中的亚谐波成分进行螺栓松动损伤识别。仿真与实验结果表明,亚谐波产生所需激励频率在两倍固有频率附近,使用亚谐波检测方法能有效识别螺栓松动。     

载荷影响下的机电阻抗协整结构损伤识别方法

高频机电阻抗(electromechanical impedance,简称EMI)方法利用粘贴在结构表面的压电传感器(piezoelectric transducer,简称PZT)进行主动激励,通过连续监测和分析PZT机电导纳信号的变化评估结构的健康状态;然而EMI方法容易受到环境工况变化的影响,导致结构损伤的误报。针对此问题,采用时间序列协整方法处理及消除结构工作载荷对阻抗谱特征信号的影响。该方法是基于结构动荷载作用下PZT阻抗谱导纳信号的非平稳特征,将动荷载影响下的阻抗谱非平稳时间序列经线性组合变换成平稳时间序列,根据得到的协整余量序列有效判断结构的健康状态。为验证该方法的有效性,开展了动应力影响下铝梁结构的螺栓松动损伤识别实验。结果表明,协整消除了动态应力对EMI方法的影响,当铝梁内存在持续变化的应力时,仍可以准确识别螺栓松动。机电阻抗协整方法能够消除结构健康监测中荷载作用的影响,及时准确地进行结构损伤识别。     

载荷影响下的机电阻抗协整结构损伤识别方法

高频机电阻抗(electromechanical impedance, 简称EMI)方法利用粘贴在结构表面的压电传感器(piezoelectric transducer, 简称PZT)进行主动激励，通过连续监测和分析PZT机电导纳信号的变化评估结构的健康状态；然而EMI方法容易受到环境工况变化的影响，导致结构损伤的误报。针对此问题，采用时间序列协整方法处理及消除结构工作载荷对阻抗谱特征信号的影响。该方法是基于结构动荷载作用下PZT阻抗谱导纳信号的非平稳特征，将动荷载影响下的阻抗谱非平稳时间序列经线性组合变换成平稳时间序列，根据得到的协整余量序列有效判断结构的健康状态。为验证该方法的有效性，开展了动应力影响下铝梁结构的螺栓松动损伤识别实验。结果表明，协整消除了动态应力对EMI方法的影响，当铝梁内存在持续变化的应力时，仍可以准确识别螺栓松动。机电阻抗协整方法能够消除结构健康监测中荷载作用的影响，及时准确地进行结构损伤识别。     

压电阻抗技术用于智能螺栓的实验研究

针对工程结构中的螺栓连接件易松动的问题,进行了基于压电阻抗技术(EMI)的螺栓松动监测实验。实验将锆钛酸铅压电陶瓷材料(PZT)直接粘贴在螺栓和螺母上,通过万能试验机对螺栓施加不同的拉力来模拟螺栓预紧力的变化,采用精密阻抗分析仪提取不同螺栓和螺母上压电材料的导纳信号,引入基于电导纳的均方根偏差(RMSD)损伤指标,建立螺栓松动程度和预紧力之间的对应关系。试验结果表明,不同型号的螺栓和螺母上安装的压电材料都可以感知预紧力的变化;得到了损伤指标(RMSD)和预紧力之间的定量对应关系;通过分析损伤指标和预紧力之间的关系可得到螺栓的松动情况,并且可直接定位松动的螺栓。研究表明基于压电阻抗技术的智能螺栓(智能螺母)可以实现松动自检测。     

基于结构界面波能损耗的螺栓联接结构健康监测

针对工程实际中的螺栓松动问题,基于压电陶瓷片激发的超声波通过粗糙接触界面后的能量损耗变化与螺栓预紧力的关系,提出了一种螺栓联接结构压电主动式健康监测的方法。通过有限元法模拟了超声波通过螺栓联接界面的传播过程,分析了超声波通过联接界面后的波能损耗变化,并进行实验验证。结果表明:随着预紧力的增加,超声波通过联接界面后的波能损耗减小,波能损耗与预紧力呈单调变化关系。利用该性质监测螺栓联接松动具有很好的应用前景。     

温变工况下的EMI螺栓松动损伤识别

环境温度变化易引起机电阻抗方法(EMI)结构健康监测的损伤误报,以螺栓组连接的铝板为对象,分别进行了温度对导纳信号的影响实验及温变工况下的螺栓松动损伤识别实验,采用平均绝对偏差与相关系数偏差量化表征导纳信号改变程度,利用信号互相关迭代算法分段补偿温度影响。结果表明,温度变化引起导纳信号的水平偏移,且偏移量随频率与温差的增加而增大,引起损伤指标变化,影响螺栓连接状态判定。通过迭代算法进行温度补偿后,极大程度消除了温度影响,有效提高了螺栓松动损伤识别的敏感程度,避免温度变化引起损伤误报。     

基于非线性超声调制方法的损伤识别与定位

在结构健康监测技术中,非线性弹性波谱方法具有对结构微小变化敏感的特性,能够有效地对裂纹等非线性损伤进行识别。笔者针对采用两个持续激励的普通非线性弹性波谱方法不能定位损伤的问题,提出了一种能够识别并且定位铝板中疲劳裂纹的非线性超声调制方法。该方法通过识别脉冲与高频超声波之间的调制现象来进行损伤检测。实验中,压电阵列粘贴于疲劳裂纹铝板表面,汉宁窗调制的正弦脉冲激励和正弦持续激励同时施加在压电阵列上。通过采集不同的作动传感路径的响应,利用短时傅里叶变换对响应进行频域分析,构造损伤指数量化损伤程度,对疲劳裂纹进行识别和定位。实验结果表明,所提出的方法可以成功地检测并定位疲劳裂纹损伤。     

导弹支撑座连接螺栓松动故障诊断的实验研究

针对某导弹支撑座在环境激励下易引发连接螺栓松动这一具体问题,在支撑座模型结构的宽带随机振动实验的基础上,探讨了实验中的问题,根据支撑座连接螺栓在不同预紧力情况下的结构稳态响应信号,分析了信号功率谱特征的差异,提出了相应的谱矩松动故障特征的提取方法。分析结果表明,谱矩因子的降低作为该结构连接螺栓松动的诊断特征是可行的。     

压电阻抗解耦技术在螺栓联接状态监测中的应用

针对螺栓联接状态监测问题,提出了基于压电阻抗解耦技术的螺栓松动监测技术。建立相应的实验装置,检测螺栓在不同预紧力下的导纳信号,将所采集的压电导纳信号,剔除导纳信号的被动部分后对所得到的导纳信号主动部分采用阻抗解耦算法,获得新的测点结构阻抗信息。以解耦得到的测点结构阻抗信号的实部定义了RMSD(Root Mean Square Deviation均方根偏差)损伤指标,识别螺栓联接状态(表现为螺栓轴向预紧力变化)。试验表明:导纳实部损伤指标能反映螺栓的联接状态;将解耦得到的机械阻抗实部作为监测螺栓联接状态的指标,较之常用的直接采用导纳信号实部定义的RMSD损伤指标,该方法所得的损伤指标明显提高,能更加有效的识别螺栓联接状态。     

基于压电阻抗频率变化的螺栓松动检测技术

针对螺栓松动问题,提出基于压电阻抗频率变化的螺栓松动监测方法。在螺栓头部安装压电材料,采用材料试验机拉伸螺栓来精确模拟螺栓所受预紧力;研究了洁净环境和油污环境中,压电材料导纳谱中的峰值频率随螺栓预紧力的变化。结果表明：随着螺栓预紧力的增大,压电导纳谱中的峰值频率降低,且两者间具有较好的线性关系;油污对测试影响较小。     

Contact and non-contact approaches in load monitoring applications using surface response to excitation method

Surface response to excitation (SuRE) method is a low-cost alternative to electromechanical impedance based structural health monitoring (SHM) technique. The SuRE method uses one piezoelectric transducer to excite the surface of a structure with a sweep sine wave. Piezoelectric sensors or scanning laser vibrometer can be used to monitor the dynamic response of structure.In this study, the performance of the SuRE method was evaluated with the conventional piezoelectric elements and scanning laser vibrometer used as contact and non-contact sensors, respectively, for monitoring the presence of loads on the surface. In order to determine the accuracy and reliability of both monitoring approaches in detecting changes in level of applied load, three different experimental setups were studied. Response of a system in the presence of a single ​load applying and multiple loads applying and its performance in detecting tightness in a nut and bolt system were investigated. The spectrum of the dynamic response is collected at the optimal operating condition. Any significant change of the spectral characteristics may indicate defects, improper loading or loose fasteners. The performance of the SuRE method using contact and non-contact sensors indicated that both variations of the method could be successfully used in load monitoring applications.     

Modeling of EMI response of damaged Mindlin–Herrmann rod

To ensure high sensitivity to incipient damages, electromechanical impedance (EMI) is measured at high frequencies for damage detection. In the working high-frequency range, very high vibration modes, of the order of the thousandth mode or higher, of a structural member are likely to be activated. This imposes a great difficulty on the accurate modeling of EMI response of a structure. In this paper, the reverberation matrix method (RMM) is adopted to study the dynamics of a Mindlin–Herrmann rod with surface piezoelectric patches. The rod is inhomogeneous along the axial direction so that damage-induced reduction of cross-section or Young's modulus could be easily incorporated in the model. A piecewise-homogeneous rod model is subsequently introduced to approximate the inhomogeneous rod, along with a shear lag model of interfacial bonding between the lead zirconate titanate (PZT) patches and the host rod. An analytical expression for the electric impedance (or admittance) of the coupled model of PZT patch-bonding layer-host rod system is derived. Comparison with other established results is presented. Parametric investigations are also performed to show the dynamic properties of the coupled smart structural system. The analysis in this paper provides necessary theoretical basis for damage detection of rod via the EMI signatures.     

基于阻抗技术的压电元件自损伤检测-

为了保证结构健康监测系统的有效运行,基于压电阻抗技术原理,提出了一种压电传感、驱动元件自损伤检测方法.通过研究压电元件等效电容值(压电元件导纳虚部数值)的变化,判别压电元件是否破损及其与主体结构之间是否剥离,并在悬臂梁结构上进行压电元件自损伤检测试验.结果表明,相比压电元件完好的情况,各频率下压电元件电纳值随脱粘部分面积的增加而上升,随破裂部分面积的增加而下降,并且损伤程度和等效电容变化量成比例关系,与理论分析结果吻合较好.     

Time-domain analysis of piezoelectric impedance-based structural health monitoring using multilevel wavelet decomposition

A new approach to analyze the response from a piezoelectric wafer in an impedance-based structural health monitoring (SHM) method is proposed. It is shown that the time-domain response of a piezoceramic wafer provides information on the electromechanical impedance (EMI) variation when a monitored structure is damaged. Practical analysis was carried out using wavelet transform in two different levels. This approach simplifies EMI based SHM and the results show that it is more sensitive to damage than methods based on impedance measurements in the frequency domain. The efficiency of this new approach is demonstrated through experiments using an aluminum plate. The piezoelectric wafer was excited using a chirp signal and its response was analyzed using both frequency response functions (FRF) and the proposed method. The results confirm that this new approach is more sensitive to detect damage than FRF based methods.     

复合材料板Chirp激励的Lamb波成像技术研究

作为一种快速、高效的无损检测方法,Lamb波技术在结构健康监测领域具有巨大的应用潜力并受到广泛关注。采用线性宽带Chirp信号作为激励信号,替代传统的窄带Tone burst信号。响应信号经过后处理可以解调出其带宽范围内任意中心频率的等效Tone burst响应信号。优化设计一种压电传感器,能够在低频段激励和接收纯净的A0模态。由于A0模态对板中缺陷非常敏感,使信号更便于分析。将这种传感器按照稀疏阵列的形式布置于准各向同性复合材料板上,对模拟缺陷进行检测。通过实验所得Chirp信号的检测数据解调出多个中心频率下的响应信号,结合椭圆成像技术和数据融合方法进行缺陷成像,实现了板中缺陷定位,并且多个频率下响应信号融合后的成像结果具有更高的分辨率、对比度和定位精度。     

非对称智能减振板优化设计

通过分析非对称智能板的导纳值,实现了智能板压电片的优化设计。由于压电分流阻尼电路中能量的消耗是导纳值的函数,因此用导纳值来评价智能板的减振效果。用模态分析得到智能板的振型和固有频率,再通过谐响应分析求得智能板的导纳值。针对3个非对称模态,采用子问题的优化方法,优化设计压电片的位置,使其减振效果达到最佳。     

Damage identification in skeletal structures using the virtual distortion method in frequency domain

The paper is a continuation of research on the application of a structural reanalysis method—the virtual distortion method—to structural health monitoring. The first approach, formulated previously in the time domain, suffered from a considerable numerical cost. In order to reduce it, this paper presents an alternative approach, formulated in the frequency domain thanks to the assumption of using harmonic excitation (quasi-static problem). The hardware devices supposed to collect structural responses are piezoelectric patch sensors. The software tool for damage identification solves a nonlinear least squares optimization problem by employing analytically derived sensitivities. Strains are the analyzed quantities, contributing to the objective function. Considerations are restricted to skeletal structures and a simplified dynamic problem with no damping. Effectiveness of the frequency-domain identification is demonstrated in numerical examples. Experimental verification is envisaged.     

Mechanical impedance-based technique for steel structural corrosion damage detection

The electromechanical impedance (EMI) technique has gained acceptance for structural health monitoring, due to its merits of model-free, high frequency detection and fast response features. This paper presents an innovative mechanical impedance-based technique to monitor the development of corrosion damage on steel structure, which is different from the traditional admittance (inverse of impedance)-based EMI technique. Firstly, structural mechanical impedance (SMI) which directly manifests the structural properties is theoretically deprived. Secondly, by measuring the raw admittance signature, the sensitivity of SMI is investigated in the experiment of steel structural corrosion damage conducted within 117 days. Finally, the corrosion damage quantification is also discussed by calculating the root mean square deviation (RMSD) index. The results indicate that structural mechanical impedance is sensitive to corrosion damage but the detecting range is limited. The real part of SMI can be adopted for an effective indicator of steel structural corrosion damage. The proposed technique is found to be effective in steel structural corrosion damage detection.