随机振动疲劳寿命评估频域法模型适用性研究

为了研究频域法中的应力幅值概率密度函数(Probability Density Function,PDF)模型在随机振动疲劳寿命评估过程中的适用性，首先介绍常用的5种频域法模型，接着设置由不同谱宽系数、中心频率和功率谱密度(Power Spectral Density,PSD)谱值组合的限带白噪声应力功率谱。在此基础上利用傅里叶逆变换得到对应的时域信号，并将频域法模型计算得到的应力幅值概率密度函数与模拟的时域信号经过雨流循环计数得到的结果进行对比，评估各种频域模型的适用性和精度。结果表明，在整个带宽范围内，ZhaoBaker模型和Dirlik模型都有较高的准确性和适用性，Weibull模型在模拟小谱宽系数(ε<0.15)的单峰谱和谱宽系数大于0.6的宽带PSD时拥有不错的精度；频域模型的精度误差都随中心频率和谱值的增加有不同程度的下降。     

一种新的非高斯随机振动疲劳寿命估计方法

构造了非高斯修正系数的多项式响应面模型,提出了一种基于高斯近似的非高斯随机振动疲劳寿命估计方法。采用Winterstein传递函数法将非高斯随机应力转化成高斯随机应力,并联合雨流计数和Miner损伤准则分别估算两种随机应力下的累计损伤和谱矩,对多个样本进行最小二乘拟合之后构建一个关于应力谱矩和非高斯修正系数的多项式响应面模型。利用高斯近似法估算非高斯随机振动疲劳损伤量,并与经过雨流计数和Miner损伤准则估算的非高斯随机过程下疲劳损伤对比,结果表明:高斯近似法具有较好的精度。     

变流器穿墙套管安装板在随机载荷下的振动疲劳寿命分析

以动车组中变流器穿墙套管安装板为研究对象,建立其在实际工况下的等效有限元模型,并通过模态测试得到模态参数校验修正的有限元模型,保证模型的合理性.然后采用IEC61373—2010标准中的加速度功率谱作为激励载荷,根据频域随机疲劳理论,利用有限元分析软件ANSYS和n Code Design Life对穿墙套管安装板进行...     

基于应力概率密度和功率谱密度法的随机声疲劳寿命预估方法研究

针对航空发动机燃烧室火焰筒结构的声疲劳问题,研究了一种用于随机载荷下结构疲劳寿命预估的有效方法。首先,对薄壁结构在随机载荷作用下的Von Mises应力过程的概率分布作了研究,给出了应力峰值概率密度函数的表达式。基于Miner线性理论,提出了基于应力概率密度和功率谱密度法的随机声疲劳寿命预估方法,并建立了疲劳寿命预估模型。以某型航空发动机燃烧室火焰筒结构为例,在采用耦合的有限元和边界元方法计算出随机声疲劳应力基础上,应用所建立的模型进行了疲劳寿命估算,并对计算结果进行了宽带修正。结果表明,该方法对航空薄壁结构随机疲劳寿命分析具有实用性。     

基于规范反应谱的全非平稳地震动过程模拟

在经典的两类演变功率谱模型基础上,建议了另两类全非平稳地震动过程的演变功率谱模型。为生成与规范反应谱一致的全非平稳地震动时程,将地震动加速度过程分解为两个独立的随机过程,其一为已知演变功率谱的全非平稳地震动过程,其二为修正的非平稳地震动过程。对于第一个随机过程,应用非平稳过程模拟的谱表示-随机函数方法,即可生成代表性时程集合及其平均反应谱。对于第二个随机过程,其演变功率谱是由调制函数和功率谱密度函数组成,而功率谱密度函数则由第一个随机过程的平均反应谱与规范反应谱的拟合误差计算得到。通过对第二个随机过程演变功率谱的修正,可使合成后的全非平稳地震动过程的平均反应谱与规范反应谱拟合一致。最后,算例验证了此方法的有效性和实用性。     

基于小波变换的拖拉机PTO载荷加速编辑方法

拖拉机动力输出轴(power take-off, PTO)的作业载荷中无损伤或小损伤载荷占据大量比例,在耐久性试验中会导致试验时间过长,经济性变差,将这些载荷剔除可以得到加速载荷谱。以40马力拖拉机为研究对象,采用Daubechies小波对拖拉机PTO实测载荷信号分解并重构高频小波系数得高频小波分量,在总伪损伤保持基本一致的前提下,选取合适的阈值并结合包络线损伤判别方法,从原始载荷信号中提取损伤较大的载荷片段并拼接成加速载荷谱,分别得到压缩比为42.0%、49.8%、61.7%、62.4%、81.9%的加速载荷谱。基于频域、幅值域、统计参数和疲劳损伤等理论验证所编制加速载荷谱的正确性,以及与原始载荷谱的相似度。结果表明,加速载荷谱与原始载荷谱在伪损伤基本一致的前提下,频域、幅值域分布曲线保持相似,最值、均方根值、峰度系数等参数误差均在5%以内,对零部件造成的损伤效果也基本一致。证明该加速方法适用于拖拉机零部件加速载荷谱编制,并为农机领域加速载荷谱的编制提供参考依据。     

基于小波变换的非平稳脉动风时变功率谱估计方法研究

为揭示非平稳随机脉动风的时频特性,基于小波变换原理推导了时变功率谱的时间、频率和幅值与小波变换系数的关系,建立了非平稳随机脉动风时变功率谱估计的小波函数加权和法,并采用模拟非平稳脉动风和实测台风过程对理论推导结果进行了验证。研究结果表明：非平稳随机过程在某一时刻的不同尺度小波变换系数是一个以此非平稳随机过程的调制函数与小波函数的乘积为调制函数的非平稳随机过程的傅里叶变换,非平稳随机过程的时变功率谱等于不同尺度和不同时移的小波函数模平方的加权和,小波函数加权和法计算的非平稳随机脉动风的时变功率谱与理论结果具有良好的一致性。小波函数加权和法可有效地估计非平稳随机脉动风的时变功率谱,估计的时变功率谱可为进一步理解强(台)风的随机脉动特性奠定基础。     

一种多轴向随机激励下结构疲劳寿命分析方法

提出了一种多轴向随机激励下结构疲劳寿命估计的频域分析方法。首先,对结构进行频响分析,得到在基础加速度激励下的应力频响函数矩阵,通过随机振动分析,得到结构应力的功率谱密度矩阵;其次,采用等效的Von Mises应力功率谱密度将多轴应力问题转化为单轴应力问题;最后,利用单轴应力疲劳寿命估计的频域分析方法对结构疲劳寿命进行估计。对一典型构件在多轴向随机激励下的疲劳寿命进行了计算,并与实验结果进行了对比。另外,对构件在多轴向同时激励与单轴分别激励的疲劳损伤结果进行了对比分析,表明多轴向同时振动具有明显的多轴效应,因此进行多轴向振动疲劳研究十分必要。     

一种基于白噪声响应的随机载荷谱识别方法

基于频域内随机振动响应与载荷的关系,根据对结构控制点随机振动响应谱的预设,提出一种新的随机载荷谱简便识别方法。首先计算结构在白噪声载荷谱下,结构控制点处的响应功率谱,即系统的频响函数;然后将控制点的期望输出响应谱与控制点在白噪声载荷谱下的响应谱相比,进而得到相应的随机载荷谱。应用上述方法,借助于有限元仿真软件在设定控制点输出加速度响应谱为梯形谱的条件下,对某典型舱段结构进行基础加速度载荷谱逆向识别与正向检验,证明方法的有效性与准确性。     

国产轿车后轴强化路耐久性断裂试验研究

为研究国产某型轿车试验场强化路可靠性试验阶段出现的后轴断裂问题,采集断裂部位附近的应变载荷谱,应用Neuber法则和循环应力-应变滞回环曲线方程,将名义应变历程转换为断裂位置的局部应力-应变响应,根据Manson-Coffin模型修正平均应力对疲劳损伤的影响,在INFIELD软件中编程计算断裂裂纹处的损伤。利用电磁激振器对后轴与车身进行振动模态扫频,识别后轴振动频率与强化路激励频率及车身振动频率关系。试验结果表明,裂纹处的疲劳损伤主要集中在搓板路面,搓板路强迫振动激励频率为24.07Hz时,后轴振动模态频率与搓板路激励频率较接近而引发共振,致使后轴因高应力集中产生较大应变和疲劳损伤发生振动疲劳断裂。     

Accelerated Random Vibration Testing of Transport Packaging System Based on Acceleration PSD

Transport packaging of products is a complex structural system, having a variety of modes for vibration damage failure under the action of random vibration in logistics. In order to evaluate the packaging performance effectively, the accelerated random vibration testing becomes one of important tools. This paper develops a more general and practical method for accelerated random vibration testing of transport packaging in the framework of linear random vibration of discrete packaged product. The suggested method is based on the response acceleration power spectral density (PSD) of component which is easy to measure, and suitable for the different fatigue models more than Basquin fatigue model. It is confirmed by the experiments of a packaged desk computer that exerted two types of acceleration PSDs. Copyright © 2017 John Wiley & Sons, Ltd.     

Using computer techniques for vibration damage estimation under stochastic loading using the Monte Carlo Method for aerospace applications

The main focus of this article is a review of legacy methods for vibration damage estimation under stochastic loading and extending research made by Dirlik and Bendat using two combined methods: FEM and Monte Carlo simulation, for which we used Python programming for aerospace applications. For some aircraft, regulated by the RTCA international aviation standard DO-160G (Environmental Conditions and Test Procedures for Airborne Equipment), stochastic loading is defined as one of the requirements. This article will focus on the stochastic loading impact on the fatigue life assessment made on a dummy sample, and frequency and time domain damage estimation shall be considered in parallel to compare both results. Additionally, dummy PSD responses shall be defined in the frequency domain for signal statistical parameters research. The article introduces Rainflow Cycle Counting methods in the frequency domain for procedures used commercially in aerospace applications. The first method introduced and developed further is the Dirlik method of Rainflow Cycle Counting in the frequency domain, which is the most popular method in commercial use. The second technique introduced and developed further was established by Bendat — the Narrow Band Method. The new empirical equation presented in this paper is the modification of the Narrow Band Method fitted for general use (narrow band, wide band, and white noise signals). A new approach for the integration of spectral moments is introduced in this paper, allowing for an accurate evaluation of the signal statistic parameters in the frequency domain for use in the modified Dirlik and Narrow Band methods. Research results also revealed new phenomena not researched by Dirlik, such as high vibration damage variation from stochastic loading, which depends on the frequency resolution (the block size used in Inverse Fourier Transformation). This discovery will be the subject of further study. Research results presented in this paper will also be utilised to combine stochastic and deterministic loading scenarios for military helicopters, as well as fighter aircraft, and will be the subject of further research.     

A damage gradient model for fatigue life prediction of notched metallic structures under multiaxial random vibrations

In the present paper, a damage gradient model combing the damage concept with the theory of critical distance (TCD) is established to estimate the fatigue lives of notched metallic structures under multiaxial random vibrations. Firstly, a kind of notched metallic structure is designed, and the biaxial random vibration fatigue tests of the notched metallic structures are carried out under different correlation coefficients and phase differences between two vibration axes. Then, the fatigue lives of the notched metallic structures are evaluated utilizing the proposed model with the numerical simulations. Finally, the proposed model is validated by the experiment results of the biaxial random vibration fatigue tests. The comparison results demonstrate that the proposed model can provide fatigue life estimation with high accuracy.     

Energy-based time derivative damage accumulation model under uniaxial and multiaxial random loadings

A new fatigue life prediction method using the energy-based approach under uniaxial and multiaxial random loadings is proposed. The uniqueness of the proposed model is based on a time-derivative damage accumulation unlike classical cycle-based damage accumulation models. Thus, damage under arbitrary random loading can be directly obtained using time-domain integration without cycle counting. First, a brief review of existing models is given focusing on their applicability to uniaxial/multiaxial, constant/random, and high cycle fatigue/low cycle fatigue loading regimes. Next, formulation of time-derivative damage model is discussed in detail under uniaxial random loadings. Then, an equivalent energy concept for general multiaxial loading conditions is used to convert the random multiaxial loading to an equivalent random uniaxial loading, where the time-derivative damage model can be used. Finally, the proposed model is validated with extensive experimental data from open literature and in-house testing under various constant and random spectrum loadings.     

疲劳振动对瓦楞纸板承载能力与缓冲性能的影响

对瓦楞纸板进行疲劳振动试验,测定分析振动次数、加速度对瓦楞纸板承载能力、缓冲性能的影响,并与未经振动材料进行比较.结果表明,随着振动次数、振动加速度的增加,瓦楞纸板剩余屈服应力减小,缓冲系数增大,其中在小应力阶段缓冲系数变化不大,在大应力阶段,缓冲系数显著增大.进行频率20Hz、加速度为2.0g、80000次振动试验后,瓦楞纸板承载能力下降了38.88%,静态应力0.012MPa下的缓冲系数增大了46.37%.缓冲包装设计时,应考虑疲劳效应对瓦楞纸板衬垫缓冲性能的影响,以确保实现预期缓冲包装的要求.     

Random fatigue life prediction of carbon fibre-reinforced composite laminate based on hybrid time-frequency domain method

To evaluate fatigue life of composite laminate with hole under random loading, a random fatigue life prediction model is established by hybrid time-frequency domain method in this paper. Firstly, dynamic response of composite laminate is obtained from FE model in frequency domain. Secondly, root mean square of stress of six stress components of critical damage point in frequency domain are transferred to stresses in time domain. At last, 3D Tsai–Hill static failure criterion is adopted to convert the multiaxial stress into the uniaxial equivalent stress. Fatigue life is predicted by equivalent stress fatigue life code. The method is validated with the random vibration fatigue test of carbon fibre-reinforced composite laminate. Numerical results are compared with random fatigue experiments which show good agreement with numerical results.     

疲劳振动效应对瓦楞纸板承载能力与缓冲性能的影响

瓦楞纸板作为产品运输包装的承载与缓冲基础材料,其使用过程中的性能保持性至关重要。运输振动将引起纸板疲劳破损,导致其相应性能的变化。对单瓦楞纸板进行加速度为0.5－2.0g、振动频率为20Hz的疲劳振动试验;进行瓦楞纸板的准静态压缩、跌落冲击试验,测定其承载能力与冲击加速度。结果表明,随着振动次数、振动强度的增加,纸板的承载能力、剩余屈服应力显著降低,缓冲性能下降。在此基础上,基于瓦楞纸板冲击试验数据,分析不同振动次数对瓦楞纸板的冲击最大加速度和缓冲系数的影响,获得了瓦楞纸板冲击最大加速度—静应力—振动次数、缓冲系数—最大应力—振动次数三维关系。研究表明瓦楞纸板存在疲劳破坏效应,研究结果为瓦楞纸板的疲劳缓冲包装设计提供技术依据     

剩余强度模型对瓦楞纸板疲劳振动的分析研究

对瓦楞纸板进行疲劳振动试验,测定分析振动次数、加速度对瓦楞纸板塑性变形、承载能力的影响,并与未经振动材料进行比较.基于疲劳累积损伤理论中的剩余强度模型,提出瓦楞纸板疲劳振动后剩余承载能力衰减模型.疲劳加载后瓦楞纸板的剩余承载能力,不仅与载荷的循环数有关,还与疲劳加载的加速度峰值和频率有关.拟合了振动频率20Hz、加速度2.0g振动试验后,瓦楞纸板的剩余承载能力与振动次数之间的关系曲线.结果表明,随着振动次数和振动加速度的增加,瓦楞纸板剩余屈服应力减小,经过80000次振动后,其承载能力下降了38.88%.为了确保实现预期包装效果,在进行包装设计时,应考虑到瓦楞纸板的疲劳性能.     

Comparative study of multiaxial fatigue damage models for ductile structural steels and brittle materials

Fatigue damage prediction under a general multiaxial service loading consists of three main steps: multiaxial cycle counting, damage evaluation for an identified cycle (or reversal), and damage accumulations. The accuracy of fatigue life predictions depends on all the above steps. This paper reviews the evolutions of various multiaxial fatigue damage models, a comparative study is conducted about the physical basis, the computational efficiency, and the application range of the approaches. Based on the comparative studies, a new procedure is proposed to evaluate fatigue damage under general multiaxial random loading, which uses the Wang and Brown´s multiaxial cycle counting method for identifying cycles (or reversals), the modified procedure of the minimum circumscribed ellipse (MCE) approach for fatigue damage evaluation for an identified cycle (or reversal), and the Miner´s linear damage law for fatigue damage accumulations. By comparisons of the predicted life results with experimental results and with other approaches, it is shown that the proposed procedure is very efficient and suitable for computer aided structural optimization against fatigue.     

Frequency based fatigue analysis and temperature effect

This paper proposes a temperature modified Dirlik method to estimate the high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from a power spectral analysis. Besides, the methodology for combining the frequency based fatigue analysis with the temperature effect is represented. This approach is based on a new definition of loading as a random Gaussian process. The fatigue damage estimation of the high pressure die-cast aluminium alloy AlSi₉Cu₃ is investigated at elevated temperatures. Finally, numerical simulations on the known power spectral densities with different shapes at different temperatures are performed in order to establish proper dependence between the temperature modified Dirlik method, the rainflow cycle counting, the linear cumulative fatigue damage and the spectral bandwidth parameters. The proposed method enables computationally fast fatigue damage estimation for the random loadings and the temperature histories.