一种复合材料层合板故障诊断的频响—广义模态能量法

复合材料故障诊断问题日益受到人们的重视。利用振动理论和实验技术进行故障诊断是一种很有吸引力和值得探索的方法。本文提出了一种复合材料层合板损伤的频响一能量诊断新方法,此方法选取对故障比较敏感,又能反映结构动力特性的频响函数作为诊断故障的参数,并引入阻尼耗散能计算本文定义的无损板在各阶模态下广义模态能量的分布,通过理论推导和计算得到了损伤前后频响函数在各阶共振峰处的变化,与无损板在给定模态下各单位的模态能量贡献之间的联系。从而得到一种分析小损伤位置和范围的新方法。此方法的一个重要结论是:在小损伤的前提下,对于同一单元或同一区域各阶广义模态能量贡献之间的比值,同假设这一单元或区域有损伤而得到的各阶频响函数在无损板峰值处的变化率之比基本相等。文中提供了能量贡献分布图等,可供分析之用。算例与实验的结果表明,本文提供的方法是有效,可行的。     

复合材料层合板故障诊断的一种新方法

本文计算了无损板在给定模态下各单元的能量,求得每个单元对该阶模态下全板能量的贡献,并通过模态实验得到损伤前后各阶固频的变化.分析发现两者之间存在着内在联系,从而得到一种分析小损伤位置和范围的新方法.     

基于VMD及广义分形维数矩阵的滚动轴承故障诊断

提出基于变分模态分解及广义分形维数矩阵的滚动轴承故障诊断方法。对信号进行变分模态分解得到若干模态函数,根据不同权重因子计算得到每个模态函数的广义分形维数序列,排列构成广义分形维数矩阵,最后通过分析待测信号和各样本信号的广义分形维数矩阵的相关系数判断故障状态。实验结果表明该方法能精确、稳定提取故障特征,区分不同状态的信号。     

基于EMD和Teager能量算子的轴承故障诊断研究

提出了一种基于EMD和Teager能量算子的齿轮箱轴承故障诊断的新方法,该方法综合利用了经验模态分解和Teager能量算子分析技术.首先利用经验模态分解方法,将振动信号分解成不同特征时间尺度的单分量固有模态函数,然后用Teager能量算子计算各固有模态函数的瞬时幅值,最后对感兴趣固有模态函数瞬时幅值的包络谱进行分析,就可识别齿轮箱轴承的故障部位和类型.齿轮箱轴承故障振动实验信号的研究结果表明:该方法能有效地识别轴承的故障.     

Hilbert-Huang变换在行星齿轮箱故障诊断中的应用

提出了一种基于Hilbert-Huang变换的行星齿轮箱轴承故障诊断的新方法,叙述了该方法的基本原理.测量了行星齿轮箱轴承的故障振动信号,并用经验模态分解方法将振动信号分解成不同特征时间尺度的固有模态函数,然后对固有模态函数进行边际谱和能量谱分析,就可识别齿轮箱轴承的故障部位和类型.齿轮箱轴承故障振动实验信号的研究结果表明:该方法能有效地识别轴承的故障.     

基于EEMD降噪和1.5维能量谱的滚动轴承故障诊断研究

将1.5维谱分析和Teager能量算子相结合,提出了1.5维能量谱的分析方法,并针对滚动轴承故障诊断问题,从提高故障信号信噪比的角度出发,提出基于EEMD降噪和1.5维能量谱的故障诊断新方法。该方法首先对故障信号进行聚合经验模态分解(Ensemble Empirical Mode Decomposition,EEMD)运算,得到一组本征模态函数(Intrinsic Mode Function,IMF)分量后运用相关系数-峭度准则对其进行筛选,并利用筛选出的IMF分量重构信号,最后计算重构信号的1.5维能量谱,从而获得轴承故障特征频率信息。利用该方法对滚动轴承内圈故障的模拟数据以及实测数据分别进行分析,诊断结果令人满意。     

基于能量泛函的开口矩形板自由振动特性分析

基于能量泛函方法,建立了开口矩形板自由振动分析模型。计算了开口矩形板的固有频率和振型函数。在处理开口问题时,利用对称性和反对称性只研究四分之一块板,并将其分割成三个区域,通过位移连续条件建立区域之间的联系,并用梁函数模拟位移场,最终得到整体能量泛函。对其变分后得到广义特征值矩阵方程,求解方程可以求出各阶固有频率。结果对比表明本文方法的准确性,为在方案设计阶段快速分析开口矩形板振动及其相关问题提供了理论基础。     

基于能量聚集性的轴承复合故障诊断

轴承复合故障类型多样,且部分故障的特征频率相近噪声污染严重。采用经验模态分解(EMD)的方法,在强噪声背景下会引起相近频率故障成分的无法识别,同时也难以提取微弱的故障信号。由此,提出一种基于能量聚集性的轴承复合故障诊断方法。首先借助离散余弦变换(DCT)的频域能量聚集性和奇异值分解(SVD)的时域能量聚集性,对轴承复合故障信号进行预处理,实现降噪并分离频率相近的微弱故障信号。然后对分离出来的不同故障信号进行经验模态分解,去除伪分量,对剩余的本征模态函数进行频谱分析。最后,根据本征模态函数的频谱诊断故障。仿真信号和实测轴承故障诊断信号分析表明,与直接使用EMD进行轴承复合故障诊断相比,该方法能够在强背景噪声下准确分离频率相近的微弱故障分量,改善复合故障诊断的准确性。     

受单点横向非定常约束梁的响应分析

为研究梁上任意一点受横向非定常约束的稳态响应问题。提出直接使用第一类拉格朗日方程与欧拉-伯努利梁理论建立梁的动力学方程,从而可以使用简单边界下梁的模态函数表示约束作用于任一位置时的梁的响应;以约束为谐波函数为例推导了梁响应的解析表达式,并通过算例验证了该方法的正确性。研究结果表明:受单点横向非定常约束梁的共振频率与非定常约束作用点的位置相关;共振时各阶模态频响会同时达到峰值,模态频响曲线呈现多峰值特征;而在各阶主频附近,对应阶模态响应没有明显的峰值,而其余阶模态响应会达到极小值;利用求解响应峰值频率比计算公式,得到非定常约束作用位置与梁动态响应峰值和极小值之间关系的解曲线;对解曲线的分析表明:当非定常位移约束作用在模态函数零点位置时,模态频响曲线会发生峰值与极小值合并的现象。     

基于子结构能量的点阵结构损伤诊断方法研究

提出了二阶子结构能量法以检测点阵结构损伤，称为SOSEM (second order substructure energy method)。对于复杂点阵板，在已知损伤位置条件下，该方法只需结构中存在“缺陷”构件的模态信息，就可以准确地得到构件损伤程度，而传统基于模态分析的方法必需整体结构完全的模态信息，新方法提高了检测效率，对实现快速（实时）点阵结构损伤检测具有重要的应用价值。为了验证本文方法的有效性，以点阵板为例，采用数值方法分析了几种典型损伤情况，结果表明，该方法能够准确地检测出点阵结构中一个或多个单元的损伤。     

Local Damage Detection with the Global Fitting Method Using Operating Deflection Shape Data

The present study extends the previous vibration based damage detection method (Yoon et al. in J. Nondestruct. Eval., 2008) by using Operating Deflection Shape (ODS) derived from experimental Frequency Response Function (FRF) data to detect the locations and extent of damage in steel beams, composite beams and plate-like structures. The present method requires to use FRF data obtained only from the damaged structure based on an assumption that the undamaged structure is homogeneous and smooth. The procedure uses the Global Fitting Method (GFM) that fits a smooth and analytic ODS to the measured ODS. Both the analytic and measured ODS are differentiated twice to yield the Curvature Operating Shapes (COS). The Structural Irregularity Index (SII) at each grid point on the structures is the difference between the analytic and measured COS. The procedure is repeated for each frequency in the FRF. Then, SII are averaged over the selected frequencies to obtain the frequency-averaged SII, which are statistically treated to locate damage.     

Damage in MMCs using the GMC: theoretical formulation

In this work the incorporation of damage in the material behavior is investigated. Damage is incorporated into the generalized cells model (GMC), and applied to metal-matrix composites (MMCs). The local incremental damage model of Voyiadjis and Park is used here in order to account for damage in each subcell separately. The resulting micromechanical analysis establishes elasto-plastic constitutive equations that govern the overall behavior of the damaged composite. The elasto-plastic constitutive model is first derived in the undamaged configuration for each constituent of the metal-matrix composite. The plasticity model used here is based on the existence of a yield surface and flow rule. The relationships are then transformed for each constituent to the damaged configuration by applying the local incremental constituent damage tensors. The overall damaged quantities are then obtained by applying the local damage concentration factors obtained by employing the rate of displacement and traction continuity conditions at the interface between subcells and between neighboring repeating cells in the generalized cells model. Examples are solved numerically in order to explore the physical interpretation of the proposed theory for a unit cell composite element.     

基于频响函数虚部的板结构损伤检测方法研究

仅利用损伤后的板结构频率响应函数虚部,建立二维板结构的损伤定位指标, 避免了由于建立未损伤有限元计算模型所引起的损伤检测误差。提出了一种基于测量点平均互相干性的加权格式,以减小测量系统误差对检测效果的影响。数值算例详细对比了模态振型指标、均匀载荷面指标和频率响应函数虚部指标对板结构损伤定位效果。最后,通过一多损伤薄板结构的损伤检测实验,验证了该指标具有良好的损伤敏感性和抗噪声能力。对于实际工程中的薄板结构损伤定位研究具有一定的意义。     

Vibration analysis of laminated composite plates with damage using the perturbation method

The present work focuses on vibration characteristics of damaged laminated composite plates. Damage is considered as a local reduction of anisotropic plate stiffness, and three damage factors (representing the damage severity, damage anisotropy, and damage location/area, respectively) are defined to describe damage status in the laminated composite plates. The analytical solutions are obtained by the perturbation method. A numerical analysis is conducted on the vibration of damaged laminated composited plates, and the effect of damage factors on the vibration characteristics is discussed. Results indicate that three damage factors have different influences on the vibration characteristics. Also, the modal curvatures and strain energy show higher damage sensitivity than the natural frequencies and displacement mode shapes. The perturbation-based vibration analysis developed in this study can be used to effectively evaluate the effect of damage on the vibration behavior of anisotropic plates and potentially identify the damage in the laminated plates.     

基于CMSE理论和小生境遗传算法的结构多损伤检测方法研究

本文提供了一种基于交叉模态应变能简称CMSE（cross modal strain energy）和小生境遗传算法的结构多损伤位置和严重程度的有效检测方法。交叉模态应变能方法可以使用完好结构和损伤结构的任意一阶模态信息，并且可以使用极少量（例如只用一阶测量模态）的测量信息。不仅与传统的模态应变能方法相比有了很大的改进，而且对实际检测过程中的信息测量降低了要求。在损伤位置的检测中引入了小生境遗传算法，降低了计算量，提高了检测效率，有利于大型复杂结构的损伤位置检测。复合材料机翼盒段算例结果表明，CMSE方法与小生境遗传算法相结合是检测结构多损伤的有效方法之一。     

Modal parameter identification and vibration based damage detection of a multiple cracked cantilever beam

This paper presents a detailed investigation on the modal parameter identification and vibration based damage detection of a multiple cracked cantilever beam with hollow circular cross-section. To consider multiple crack effects, a cantilever beam including cracks is considered for six damage scenarios. Finite element models are constituted in ANSYS software for numerical solutions. The results are validated by experimental measurements. Ambient vibration tests are performed to extract the dynamic characteristics using Enhanced Frequency Domain Decomposition (EFDD) and Stochastic Subspace Identification (SSI) methods. Calculated and measured natural frequencies and mode shapes for undamaged and damaged beams are compared with each other. Automated model updating is carried out using the modal sensitivity method based on Bayesian parameter estimation to minimize the differences for damage detection. In addition, modal assurance criterion (MAC) and coordinated modal assurance criterion (COMAC) factors are obtained from the mode shapes and two set of measurements to establish the correlation between the measured and calculated values for damage location identification.     

Damage detection by the topology design formulation using modal parameters

The feasibility of using the topology design method for structural damage identification is investigated for the first time. The finite element model of an undamaged structure and some point‐frequency response functions of a damaged structure are assumed to be available. To carry out the feasibility study, the topology optimization formulation suitable for structural damage detection is newly set up, where both resonances and anti‐resonances are used as the damage indication modal parameters. An idea to progressively reduce the candidate damaged elements is also developed to improve the accuracy and efficiency of the proposed method. Copyright © 2006 John Wiley & Sons, Ltd.     

A study on low velocity impact damage evaluation and repair technique of small aircraft composite structure

Composite structures are very prone to damage at fairly modest levels of impact energy due to foreign object damages. A repair technique using external patch is recognized as an effective method to recover the damaged structures during service life. This work is focusing on the impact damage evaluation and the external patch repair techniques of the aircraft composite structure. The impact damages of composite laminates of the carbon/epoxy UD laminate and the carbon/epoxy fabric face sheets-honeycomb core sandwich laminate are simulated by the drop-weight type impact test equipment. The damaged specimens are repaired using the external patch repair method after removing the damaged area. The compressive strength test and analysis results of the repaired impact damaged specimens are compared with the compressive strength test and analysis results of the undamaged specimens and the impact damaged specimens. Finally, the strength recovery capability after repairing is investigated.