基于L_(1)范数振动传递率的梁构件损伤识别研究EI北大核心CSCD

基于传递率函数在频域给定结构各测点输出响应间的函数关系而无需测量结构输入荷载信息的特点,提出了L_(1)范数归一化传递率函数结构损伤识别方法。首先,对加速度响应数据频域分析构建传递率函数矩阵,通过主成分分析法实现传递率频域特征的降维,提取与梁结构损伤特征高度相关的特征,以不同状态下的主成分有无发生偏离为依据来判断结构是否发生了损伤;其次,结构如果发生损伤,其损伤前后的传递率函数会发生变化;最后,将传递率函数进行L_(1)范数归一化,构建L_(1)范数归一化传递率函数损伤指标。数值仿真和试验结果表明,该方法可有效识别结构不同的损伤位置及程度,识别精度高,具有一定的噪声鲁棒性。     

磁导率检测技术对430不锈钢构件检测的最优激励频率设计研究

磁导率检测技术是一种可高精度评价铁磁构件整体或部分区域应力集中、疲劳损伤状况的无损检测方法。依据磁导率检测原理,以430铁素体不锈钢试件为研究对象,研究激励电压幅值、激励线圈匝数、检测线圈匝数及外加拉应力对检测传感器最优激励频率的影响。研究发现,最优检测频率随激励线圈匝数的增加而减小;最优检测频率与外加拉应力有关,当外加拉应力超出试件的弹性变形阶段时,最优频率随拉应力的增大而增大;最优检测频率不随激励电压幅值、检测线圈匝数的变化而变化,但随着激励电压幅值、检测线圈匝数的增加,检测灵敏度升高。该研究结论可为灵敏传感器的设计提供参考。     

相位角加载条件下2A12铝合金多轴疲劳失效行为

采用SDN100/1000电液伺服拉扭复合疲劳试验机对2A12铝合金进行不同相位角加载条件下多轴疲劳试验研究,通过加载循环曲线和微观断口形貌分析失效机理,对不同损伤累积模型的预测效果进行评价,修正Manson损伤曲线模型以期达到更好的预测效果。结果表明:单级加载条件下,随相位角正弦值的增加疲劳寿命线性递减,当相位角为0°时,轴向硬化、软化交替出现,切向出现循环硬化,90°加载下轴向和切向单独作用效果明显;两级累积路径下,随一级加载周次的增加多轴疲劳寿命延长,0°加载阶段轴向和切向都出现循环硬化现象,两种路径下断口都呈现出多裂纹源特征,在裂纹源区附近观察到台阶状形貌,扩展区存在大量划痕和鳞片状花样;修正后的Manson损伤曲线模型预测误差均在15%以内。     

考虑加载路径影响的改进Park-Ang损伤模型

合理准确地评价结构和构件在地震作用下的损伤程度是地震工程研究领域中的重要课题。Park-Ang损伤模型具有良好的试验基础,近似考虑了首次超越和塑性累积损伤综合作用的破坏机理,在地震工程研究领域应用广泛。该文针对Park-Ang损伤模型不能考虑加载路径的影响、单调加载时损伤指标大于1等问题,根据低周疲劳理论和Miner准则,结合国内外相关试验结果,提出了能考虑加载路径影响的改进模型。利用Kunnath完成的尺寸和配筋构造完全相同仅加载路径不同的系列试验的结果对改进模型进行了验证。结果表明,改进模型能比较准确地评价加载位移幅值较小时试件产生的低周疲劳损伤破坏,且对于不同的加载路径,改进模型减小了构件破坏时损伤指标的离散性,提高了损伤评估的准确性。     

Lamb波的交叉递归分析在金属板损伤量化中的应用EI北大核心CSCD

针对金属板疲劳损伤演变的非线性动力学特性,提出了基于Lamb波交叉递归分析的疲劳裂纹量化检测方法。该方法首先从结构动力学角度采用交叉递归图分析了损伤信号与无损信号在相空间中的非线性相关性,并在此基础上采用了交叉递归量化分析(cross-recurrence quantification analysis, CRQA)特征对Lamb波信号中的裂纹损伤进行表征。接着,结合CRQA特征的状态相关性、单调性、鲁棒性及特征间的关联性进行特征的优化选择,采用支持向量描述模型对优选特征进行了融合,构建了金属板疲劳损伤的统一量化指数。最后,采用铝板随机裂纹仿真试验与铝板弯折试验对该研究提出方法进行了验证。结果表明,基于Lamb波交叉递归分析的损伤评估方法突破了Lamb波的多模态性、散射性、损伤波包的微弱性造成的损伤特征提取困难的问题,不仅能够对金属板疲劳损伤进行有效的量化评估,还具有较好的噪声鲁棒性,在复杂结构疲劳损伤检测与评估领域具有较好的应用前景。     

基于条件随机场的钢箱梁正交异性板疲劳微裂纹检测

钢箱梁正交异性板在桥梁建设中应用广泛,对此类结构疲劳损伤进行无损检测并发现病害特征,有利于及时的进行现场维修加固。该文使用高倍数显微相机进行疲劳微裂纹的检测,提出基于条件随机场(CRFs)的金属疲劳微裂纹检测算法,该方法使用单个像素的表观特征来进行裂纹判别,同时也考虑其他像素标注值间的影响,从而很好地抑制离散噪音点。通过多种表观特征和机器学习方式自动识别出区分性最强的特征从而加以选择使用。实验结果表明,基于CRFs模型的裂纹检测方法对于试件6～16万次的图像裂纹宽度测量与人工测量值非常接近,这为钢箱梁正交异性板疲劳损伤快速检测提供可靠的分析手段。     

两列同向共线纵波混叠的数值研究

针对大型复杂装备的早期微弱疲劳损伤进行识别和评估这一亟待解决的问题,基于高阶弹性模量分析的非线性超声无损检测方法由于对疲劳导致的微观结构改变具有敏感性而在近年引起关注。针对两列同向共线纵波混叠的情形,运用高分辨率的半离散中心差分方法,对波束混叠法这一新型非线性超声无损检测方法在评价材料早期疲劳损伤的应用开展了数值研究。通过对谐振波成分的传播特性的分析可见,差频与和频谐振波成分可以同时在两个相互垂直的方向上产生和扩展,而其中剪切方向产生的差频谐振波成分能够随材料非线性系数而单调递增,从而可以对材料非线性进行准确测量,进一步为波束混叠法在材料早期微弱疲劳损伤损伤检测中的应用提供有效的方法和依据。     

金属磁记忆检测技术定量评估构件疲劳损伤研究

对18CrNi4A钢缺口试件在三级应力水平下进行疲劳试验和磁记忆信号检测,研究金属磁记忆信号在疲劳过程中的变化规律和磁记忆检测技术对构件疲劳损伤的定量估评.结果表明:在稳定循环阶段,磁信号随疲劳循环周次增加无显著改变,疲劳裂纹萌生后,磁信号逐渐增加,并在断裂后发生激变;磁信号特征参量Kmax,Hp(y)max,Hp(y)min和Hp(y)sub值与应力水平和疲劳损伤程度存在强烈的相关性,特征参量绝对值随应力水平或疲劳损伤程度的增加而逐渐增加;磁信号特征参量Kmax平均值法可较准确地定量评估构件疲劳损伤,该方法判据为:当m(m=Kmax/KAVmax)＞1,试件存在严重的疲劳损伤.     

基于劲度模量分析的橡胶沥青混合料疲劳寿命研究

变幅加载下沥青的疲劳损伤累积具有明显的非线性特征,传统的Miner’s线性疲劳损伤累积准则无法表征不同变幅加载次序下沥青的非线性疲劳损伤累积(NLFDA)。该研究旨在建立考虑加载次序影响的NLFDA模型,准确表征加载次序对沥青疲劳损伤累积的影响。通过开展应力控制的沥青恒幅加载疲劳试验,采用耗散伪应变能(DPSE)表征沥青疲劳损伤,分析恒幅加载下沥青的疲劳损伤累积规律;采用低-高和高-低两种加载次序,开展应力控制的沥青变幅加载疲劳试验,分析变幅加载下沥青的疲劳损伤累积规律;基于损伤等效准则,建立考虑加载次序影响的NLFDA模型,分析加载次序对疲劳损伤累积的影响。结果表明：应力控制模式下的沥青疲劳损伤,呈先缓慢后急剧的非线性增加演化趋势;恒幅加载下沥青疲劳损伤服从Miner’s准则发生线性累积,且累积寿命分数等于1;变幅加载下沥青疲劳损伤不服从Miner’s准则而发生非线性累积。低-高和高-低变幅加载次序下,沥青累积疲劳寿命随一级寿命分数的增大而分别增加和减小,累积寿命分数分别大于1和小于1;建立的NLFDA模型可克服Miner’s准则缺陷,并较为准确地表征加载次序对沥青疲劳损伤累积的影响。

     

疲劳损伤磁性无损评估技术研究现状及发展前景

磁性无损检测技术是评估铁磁材料疲劳损伤以及重要结构件可靠性的重要检测手段。针对铁磁材料的疲劳损伤,介绍了几种典型的磁性无损检测技术,如磁巴克豪森噪声(MBN)、磁声发射(MAE)、漏磁(MFL)和金属磁记忆(MMM)等,对其产生机理及应用特点进行了概述;对几种磁性检测技术在疲劳损伤评估领域的研究现状以及取得的主要研究成果进行了综述;最后指出几种技术尚存的问题和进一步的研究方向,并对其发展前景进行预测。     

Effect of the loading frequency on fatigue properties of JIS S15C low carbon steel and some discussions based on micro-plasticity behavior

Ultrasonic testing method has been often used to investigate fatigue properties of various metallic materials. Since ultrasonic fatigue tests are conducted at a very high loading frequency, they are particularly convenient for fatigue tests in the very high cycle regime. Indeed, ultrasonic fatigue method allows us to conduct fatigue tests up to 10⁹–10¹⁰ cycles in a definite period. However, due to the huge gap of loading frequency between ultrasonic testing method (around 20 kHz) and usual testing method (most of the cases in the range 1–100 Hz), the frequency effect on the fatigue property is still unclear. Low carbon steel is one of typical metallic materials to provide a significant discrepancy between fatigue strengths obtained under ultrasonic testing frequency and under usual testing frequency range.Thus, by preparing a lot of specimens of JIS S15C low carbon steel (0.15% C), fatigue tests were carried out in a wide range of the loading frequency. The frequency effect on the S–N property was first examined and a useful procedure was proposed to obtain a common S–N property normalized by the lower yield stress. In addition, micro-plasticity behavior such as the stress–strain hysteresis loop and the local misorientation were also measured and the frequency effect on the fatigue property was discussed.     

Nondestructive Testing and Prediction of Remaining Fatigue Life of Metals

A nondestructive testing method is presented for the prediction of the remaining fatigue life (RFL) of metals with prior fatigue damage subjected to tension-compression fatigue load. It is shown that the slope of temperature rise obtained from a short-time excitation fatigue test is a good candidate to assess the present state of fatigue damage in the material. Three series of uniaxial tension-compression normal fatigue tests are carried out with two different materials under different loading conditions to characterize their fatigue behavior. Eight validation tests are performed under different loading conditions to evaluate the RFL prediction capability of the proposed method. Results show that the proposed method has good potential for predicting RFL of metallic specimens.     

利用非线性表面波评价材料疲劳损伤

采用非线性Rayleigh表面波检测方法,实现了不同疲劳阶段下钢试样拉伸和腐蚀疲劳损伤的测试与评价;基于楔块\换能器激发与接收声波方式,搭建非线性Rayleigh波检测系统,测量了不同激励水平下基波幅值平方与二次谐波幅值间的线性关系以及Rayleigh表面波二次谐波的累积效应;分别在拉伸载荷和腐蚀疲劳载荷下,采集非线性时域信号并进行频谱分析,测量声学非线性系数在不同疲劳阶段下变化趋势,并分析不同疲劳载荷对钢试样声学非线性系数的影响。实验结果表明:超声非线性系数与疲劳周期数呈单调递增关系,可以用声学非线性系数来表征材料的表面疲劳损伤程度;相比较周期性拉伸疲劳损伤,腐蚀疲劳试样的声学非线性系数会增大,是由于腐蚀环境会加重实验中钢试样的疲劳损伤程度。研究成果可为疲劳损伤无损检测与评价提供一定的指导意义。     

An experimental approach to estimate damage and remaining life of metals under uniaxial fatigue loading

An experimental procedure to estimate damage evolution and remaining fatigue life of metals associated with fatigue loading is presented. Experimental phase involves uniaxial tension–compression fatigue tests performed with solid API 5L X52 and tubular carbon steel 1018 specimens subjected to both constant and variable amplitude loading. A correlation between the so-called damage parameter and the thermal response of a material at different damage levels is proposed. Results demonstrate that the correlation can estimate damage evolution with reasonable accuracy in both constant and variable amplitude fatigue processes. It is shown that under the conditions tested the evolution of damage parameter with respect to the normalized fatigue life is independent of the load amplitude, load ratio, loading sequence, material properties, and specimen geometry. The proposed correlation and the relationship between the damage parameter and the normalized fatigue life are employed to develop a non-destructive method to predict the remaining fatigue life of metallic specimens with prior fatigue damage. The method is applied to both constant and variable amplitude loading and the predicted results are found to be in good agreement with those obtained from the experiments.     

Frequency-Domain Laser Ultrasound (FDLU) Non-destructive Evaluation of Stress–Strain Behavior in an Aluminum Alloy

The evaluation of the stress–strain state of metallic materials is an important problem in the field of non-destructive testing (NDT). Prolonged cyclic loading or overloading will lead to permanent changes of material strength in an inconspicuous manner that poses threat to the safety of structures, components and products. This research focuses on gauging the mechanical strength of metallic alloys through the application of frequency-domain laser ultrasound (FDLU) based on a continuous-wave diode laser source. The goal is to develop industrial NDT procedures for fatigue monitoring in metallic substrates and coatings so that the technique can be used for mechanical strength assessment. A small-scale, non-commercial rig was fabricated to hold the sample and conduct tensile FDLU testing in parallel with an adhesive strain gauge affixed on the tested sample for independent measurement of the applied stress. Harmonic modulation and lock-in detection were used to investigate the LU signal sensitivity to the stress–strain state of ordinary aluminum alloy samples. A 1 MHz focused piezoelectric transducer was used to detect the LU signal. During the tensile procedure, both amplitude and phase signals exhibited good repeatability and sensitivity to the increasing stress–strain within the elastic regime. Signals beyond the elastic limit also revealed significant change patterns.     

Recent developments in ultrasonic fatigue

The recently increased interest in very high cycle fatigue properties of materials has led to extended use and further development of the ultrasonic fatigue testing technique. Specimens are stimulated to resonance vibrations at ultrasonic frequency, where the high frequency allows collecting lifetime data of up to 10¹⁰ cycles and measuring crack propagation rates down to 10^?12 m per cycle within reasonable testing times. New capabilities and methods of ultrasonic testing and outstanding results obtained since the year 1999 are reviewed. Ultrasonic tests at load ratios other than R = ?1, variable amplitude tests, cyclic torsion tests and methods for in situ observation of fatigue damage are described. Advances in testing at very high temperatures or in corrosive environments and experiments with other than bulk metallic materials are summarized. Fundamental studies with copper and duplex steel became possible and allowed new insights into the process of very high cycle fatigue damage. Higher cyclic strength of mild steels measured at ultrasonic frequency because of plastic strain rate effects are described. High‐strength steels and high‐alloy steels are less prone to frequency influences. Environmental effects that can lead to prolonged lifetimes in some aluminium alloys and possible frequency effects in titanium and nickel and their alloys are reviewed.     

Non-linear ultrasonic evaluation of damaged concrete based on higher order harmonic generation

Non-linear ultrasonic testing, based on higher order harmonic generation, is a true mean for nondestructive evaluation of concrete allowing damage detection at early stages of damage. Using conventional non-destructive testing methods like pulse echo, velocity and impact echo for evaluation of such damages is difficult because poor sensitivity of these methods to early damage occurrence. In this paper an experimental investigation of 18 cubic concrete specimens, caste with three different water–cement ratios, using non-linear ultrasonic technique is presented. The specimens were ultrasonically evaluated both in damaged and undamaged conditions. The specimens were damaged progressively by loading them under compression in several steps up to their ultimate load bearing capacity. At the end of each loading step ultrasonic evaluation was performed and time domain waveforms were recorded at different power levels. Frequency spectra were prepared by performing Fast Fourier Transformation of the recorded time domain waveforms. The frequency spectra were used to obtain the first three harmonic amplitudes. The captured harmonic amplitudes were used to calculate the second and third harmonic ratios. Comparison of the harmonic ratios has shown the extraordinary sensitivity of the non-linear ultrasonic method, used in this study, to early damage detection. It was also observed that this sensitivity further increases as water cement ratio increases.     

Nonlinear Elastic Wave Spectroscopy (NEWS) Techniques to Discern Material Damage, Part II: Single-Mode Nonlinear Resonance Acoustic Spectroscopy

The presence of mesoscopic features and damage in quasi-brittle materials causes significant second-order and nonlinear effects on the acoustic wave propagation characteristics. In order to quantify the influence of such micro-inhomogeneities, a new and promising tool for nondestructive material testing has been developed and applied in the field of damage detection. The technique focuses on the acoustic nonlinear (i.e., amplitude-dependent) response of one of the material's resonance modes when driven at relatively small wave amplitudes. The method is termed single-mode nonlinear resonance acoustic spectroscopy (SIMONRAS). The behavior of damaged materials is manifested by amplitude dependent resonance frequency shifts, harmonic generation, and nonlinear attenuation. We illustrate the method by experiments on artificial slate tiles used in roofing construction. The sensitivity of this method to discern material damage is far greater than that of linear acoustic methods.     

基于电阻变化的3D C/SiC复合材料疲劳损伤演化

为了研究三维碳纤维编织体增强碳化硅陶瓷基复合材料(3D C/SiC)在疲劳过程中的损伤演化并建立其电阻变化率(ΔR/R₀)随疲劳周次变化的模型, 对其进行了应力比为0.1、 频率为20 Hz、 最大疲劳应力为250、 255、 260 MPa的拉-拉疲劳试验, 通过电阻增量仪器测量了连续3D C/SiC在疲劳中的电阻变化率。实验结果表明, ΔR/R₀除首次循环降低外, 随着疲劳周次的增加呈缓慢增加、 台阶式增加和急剧增加3个阶段。根据损伤力学理论, 以ΔR/R₀为损伤参量, 得到了ΔR/R₀随疲劳周次变化的模型, 该模型结果与实验结果吻合较好。      

Accelerated fatigue testing method

A method for accelerated fatigue testing of materials, based on a cumulative damage rule, is developed and examined. The method is based on monotonically increasing the stress amplitude with the number of cycles, until failure. When the initial stress amplitude is above the endurance limit, two tests are needed to determine the S/N curve; another test, with an initial stress amplitude below the endurance limit, is needed to determine the fatigue endurance limit. It is shown how to choose the right loading rate and starting level. This method minimizes the number of tests needed for the determination of the fatigue strength endurance limit, and also shortens these tests by reducing the number of cycles, (as each test ends with specimen failure).