基于频率变化预测玻璃纤维增强树脂复合材料层合板的剩余疲劳寿命

复合材料结构在疲劳过程中的累积损伤将导致结构刚度下降,并进一步引起结构的动态参数如频率发生衰减。因此,可以将结构疲劳状态与结构频率联系起来,基于频率预测结构的剩余疲劳寿命。本文首先基于复合材料在纵向、横向和面内剪切三个方向的疲劳特性,结合ABAQUS与Umat子程序开发了三维有限元模型模拟复合材料层合板中的疲劳损伤演变,并构建了不同疲劳状态下对应的模态分析模型,由此获得了疲劳过程中的频率衰减曲线。之后,基于疲劳过程的频率变化量训练了人工神经网络,用于预测玻璃纤维增强复合材料层合板的剩余疲劳寿命。特别地,在当前的数值模型中为每个单元分配了符合高斯正态分布的材料属性,以模拟实际情况下复合材料性能的离散性。结果表明,疲劳模型数值模拟结果与已有文献的疲劳实验数据吻合,基于频率变化量训练的人工神经网络可以成功预测玻璃纤维增强复合材料试件的剩余疲劳寿命。      

复合材料层合板冲击后压-压疲劳寿命预测方法

针对冲击后复合材料层合板, 发展了含冲击初始损伤层合板的压-压疲劳寿命预测方法。该方法基于无损单向板的力学性能和疲劳特性, 对不同铺层参数、 不同几何尺寸以及不同冲击条件下层合板的疲劳寿命进行预测。为消除人为假设冲击损伤造成的误差, 对层合板在冲击载荷及冲击后疲劳载荷作用下的破坏进行全程分析, 即把冲击后层合板的实际损伤状态直接作为疲劳分析的初始状态。同时基于逐渐损伤思想, 推导了含冲击初始损伤层合板的应力分析过程, 建立了相应的三维逐渐累积损伤模型, 开发了参数化的复合材料层合结构冲击及冲击后疲劳破坏模拟程序, 为复合材料层合结构的抗冲击设计及其疲劳损伤扩展行为研究提供了较好的技术平台。      

Fatigue life prediction for GRP subjected to variable amplitude loading

A method of predicting lifetime to failure for any glass fibre reinforced composite system subjected to a complex load–time history has been developed. The prediction first requires the generation of a model to characterize the general fatigue response of the particular composite system. Once the models are derived they can be used to predict lifetimes to failure for any load–time history using a modified Miner’s damage summation rule and rainflow analysis. Variable amplitude fatigue testing of different GRP materials, using the same load–time history, allowed a comparison to be made between predicted and actual lifetimes to failure and was useful in verifying the accuracy and robustness of the life prediction methodology employed. The results from the life prediction models for three very different GRP systems showed themselves to be accurate predictors of fatigue behaviour for the variable amplitude loading condition investigated.     

Application of continuum damage mechanics to vibration fatigue life prediction

It is pivotal to predict the multiaxial vibration fatigue life during mechanical structural dynamics design. An algorithm of the finite element method implementation for multiaxial high cycle fatigue life evaluation is proposed, on the basis of elastic evolution model of continuum damage mechanics. By considering structural dynamic characteristics, namely, resonant frequencies and mode shapes, this algorithm includes a modal analysis and harmonic analysis, which makes this different from existing fatigue life prediction methods. A 10% decrease in the resonant frequency is regarded as the failure criterion. A critical damage value was obtained, which indicates mesocrack initiation fulfilment. To validate the effectiveness of the algorithm, auto‐phase sine resonance track‐and‐dwell experiments were conducted on notched cantilever beams made of Ti‐6Al‐4V alloy. The life predictions are conservative and in good agreements with the experimental results, which are mainly distributed within a scatter band of 2. This investigation could provide technical support for structural dynamics design and the analysis of reusable spacecraft.     

Incorporation of a Probabilistic Monotonic Strain Energy Analysis to a Lifting Method

The proposed work analyzes the possibility of improving the capabilities of an energy-based fatigue life prediction method. The improvement being addressed is regarding the variation of empirical monotonic strain energy density calculations and the effects on the energy-based fatigue life prediction capability. Since the prediction method was developed from the concept that the strain energy accumulated during both monotonic failure and an entire fatigue process are equal, meaning the strain energy accumulated during monotonic failure is a physical damage quantity, it was important to understand the variation of monotonic strain energy density. The process for incorporating this variation into the prediction method explores a probabilistic, Three-Sigma analysis that is applicable for all deterministic methods of measuring experimental monotonic strain energy density. The accuracy of the probabilistic energy-based lifing method was admirably assessed by comparison with experimental fatigue life results, between 10³ and 10⁵ cycles, conducted on Titanium 6Al–4V specimens at room temperature.     

金属材料和结构的疲劳寿命预测概率模型及应用研究进展

疲劳过程的不确定性以及影响疲劳寿命的不确定性因素较多,导致疲劳寿命的分散性难以预测,在疲劳寿命预测模型中采用统计学和概率论的概念和方法是描述疲劳过程不确定性和疲劳寿命分散性的一种重要手段。本文针对疲劳寿命预测概率模型进行综述,总结和介绍了疲劳寿命经验公式和参数的随机化模型、表征疲劳寿命离散性的统计模型、基于材料微结构和疲劳物理机制的疲劳寿命预测概率模型以及研究广布疲劳损伤的概率模型,并对金属材料与结构的疲劳寿命预测方法进行了展望。     

Predicting the Fatigue Life of Different Composite Materials Using Artificial Neural Networks

Artificial Neural Networks (ANN) have been recently used in modeling the mechanical behavior of fiber-reinforced composite materials including fatigue behavior. The use of ANN in predicting fatigue failure in composites would be of great value if one could predict the failure of materials other than those used for training the network. This would allow developers of new materials to estimate in advance the fatigue properties of their material. In this work, experimental fatigue data obtained for certain fiber-reinforced composite materials is used to predict the cyclic behavior of a composite made of a different material. The effect of the neural network architecture and the training function used were also investigated. In general, ANN provided accurate fatigue life prediction for materials not used in training the network when compared to experimentally measured results.     

Continuous fatigue damage prediction of a rubber fibre composite structure using multiaxial energy‐based approach

This paper details an advanced method of continuous fatigue damage prediction of rubber fibre composite structures. A novel multiaxial energy‐based approach incorporating a mean stress correction is presented and also used to predict the fatigue life of a commercial vehicle air spring. The variations of elastic strain and complementary energies are joined to form the energy damage parameter. Material parameter α is introduced to adapt for any observed mean stress effect as well as being able to reproduce the well‐known Smith‐Watson‐Topper criterion. Since integration to calculate the energies is simplified, the approach can be employed regardless of the complexity of the thermo‐mechanical load history. Several numerical simulations and experimental tests were performed in order to obtain the required stress‐strain tensors and the corresponding fatigue lives, respectively. In simulations, the rubber material of the air spring was simulated as nonlinear elastic. The mean stress parameter α , which controls the influence of the mean stress on fatigue life, was adjusted with respect to those energy life curves obtained experimentally. The predicted fatigue life and the location of failure are in very good agreement with experimental observations.     

Fatigue properties of jointed wood composites Part II Life prediction analysis for variable amplitude loading

A method of predicting lifetime to failure for any wood composite system subjected to a complex load–time history has been developed. The prediction first requires the generation of a simple model to characterize the fatigue response of the particular composite system and a rainflow analysis breakdown of the load–time history under investigation. Once the models are derived they can be used to predict lifetimes to failure for any load–time history using a modified Palmgren–Miner damage summation rule. Variable amplitude fatigue testing of sample material using the same load–time histories allowed a comparison to be made between predicted and actual lifetimes to failure and was useful in verifying and refining the life prediction models. © 1998 Kluwer Academic Publishers     

A multi-temporal scale approach to high cycle fatigue simulation

High cycle fatigue (HCF) is a failure mechanism that dominates the life of many engineering components and structures. Time scale associated with HCF loading is a main challenge for developing a simulation based life prediction framework using conventional FEM approach. Motivated by these challenges, the extended space–time method (XTFEM) based on the time discontinuous Galerkin formulation is proposed. For HCF life prediction, XTFEM is coupled with a two-scale continuum damage mechanics model for evaluating the fatigue damage accumulation. Direct numerical simulations of HCF are performed using the proposed methodology on a notched specimen of AISI 304L steel. It is shown the total fatigue life can be accurately predicted using the proposed simulation approach based on XTFEM. The presented computational framework can be extended for predicting the service and the residual life of structural components.     

光纤光栅应变传感器监测复合材料层板疲劳过程

采用光纤光栅 (FBGs) 作为疲劳计监测了复合材料层板在等应力幅疲劳测试过程中的应变变化,该变化反映了复合材料在疲劳过程中刚度的衰减规律。试验结果验证了FBGs传感器的疲劳监测能力。FBGs不仅能够埋入复合材料中反映材料疲劳过程中的刚度衰减,而且具有良好的耐久性与稳定性,在经过高达106次循环周次后,依然保持良好的传感能力。FBGs作为一种有效的手段和工具,为复合材料服役过程中的损伤监测、寿命评估以及材料破坏失效阶段的预警提供了可能。      

单轴拉伸状态下橡胶隔振器的疲劳寿命预测研究

针对橡胶隔振器疲劳寿命预测问题,基于哑铃型橡胶材料试片的疲劳寿命试验数据,建立橡胶隔振器的疲劳寿命预测模型,进而提出橡胶隔振器疲劳寿命预测的研究方案。设计了一哑铃型橡胶试片进行拉伸疲劳试验,实测其疲劳寿命数据并以最小二乘法拟合了该试片疲劳寿命的幂函数预测模型。再通过有限元方法计算了橡胶隔振器的三种常见的疲劳寿命评价参数：对数主应变、柯西主应力和应变能密度,最后将橡胶隔振器的疲劳寿命预测值与实测值进行比对。结果发现：当疲劳失效标准静为刚度降级25%时,三种疲劳寿命评价参数均能较好地拟合成幂函数疲劳寿命预测模型,对数主应变的预测值较为接近实测值、应变能密度参数的预测值约为实测值2倍左右、柯西主应力预测寿命的可靠性验证系数均接近5,且三种疲劳损伤评价参数的疲劳寿命拟合曲线形状均较为相似。     

一种估算结构件随机疲劳寿命的新方法

提出了基于随机载荷历程频率域信息──功率谱密度函数（Ｐ．Ｓ．Ｄ）估算结构件低周疲劳寿命的一种新的计算方法。采用这种方法只要已知应力历程的功率谱密度和材料应变疲劳性能参数就可对承载结构件进行随机疲劳寿命估算。因此，对于结构设计阶段的使用寿命预估具有实际意义。最后，通过对缺口件的随机疲劳寿命估算及与试验结果比较验证了本文方法的适用性。     

An energy‐based critical fatigue life prediction method for AL6061‐T6

An energy‐based critical fatigue life prediction method is developed and analysed. The original energy‐based fatigue life prediction theory states that the number of cycles to failure is estimated by dividing the total energy accumulated during a monotonic fracture by the strain energy per cycle. Because the accuracy of this concept is heavily dependent on the cyclic behaviour of the material, a precise understanding of the strain energy behaviour throughout each failure process is necessary. Examination of the stress and strain during fatigue tests shows that the cyclic strain energy behaviour is not perfectly stable as initially presumed. It was discovered that fatigue hysteresis energy always accumulates to the same amount of energy by the end of the stable energy region, which has led to a new ‘critical energy’ material property. Characterization of strain energy throughout the fatigue process has thus improved the understanding of an energy‐based fatigue life prediction method.     

Predicting the fatigue life of offshore structures by the single-moment spectral method

The dependence of fatigue damage accumulation on power spectral density (psd) is investigated for Gaussian random processes representing stresses in offshore structures. This involves extensive computer simulation of representative stress time histories and related analyses to predict the time of fatigue failure. The recently introduced single-moment (SM) spectral method is shown to be very attractive for predicting fatigue failure. The SM method predicts the damage accumulation rate based only on a single calculation from the psd curve (a moment integral). The accuracy of the SM method and of other spectral methods is studied by comparing results with ones calculated from the much more expensive alternative of using simulated stress time histories, rainflow analysis, and Palmgren-Miner calculations.The SM method is shown to be even simpler than most spectral methods, and all spectral methods are much simpler than any method involving simulation of stress time histories. The accuracy of the SM method is shown to be quite good for a wide variety of situations. Furthermore, there are situations in which the SM method is significantly more accurate than other simple spectral methods, including the very commonly used Rayleigh approximation.It appears that the SM method may provide a valuable tool for predicting the fatigue life of offshore structures subject to complicated time histories of loading, as is required both in the design of new structures and in the reassessment of aging structures. In order to allow a proper balance between fatigue life and initial cost, there is a need for a fatigue prediction method which is both accurate and easy to apply, and the SM method appears to be adequate on both bases.     

基于概率断裂力学的老龄钢桥使用安全评估

我国交通线上存在大量老龄钢桥,这些老龄钢桥承受着日益繁重的交通荷载,其疲劳剩余寿命已受到桥梁管理部门的高度重视。为确保老龄钢桥的使用安全,避免不必要的维护与更换,建立老龄钢桥疲劳剩余寿命与使用安全评估方法十分必要。建立了反映老龄铆接钢桥疲劳破坏机理的脆断和韧断概率失效模型,给出了用于疲劳可靠性分析的极限状态方程,合理确定了随机变量的参数取值。建立了铆接钢桥构件单角钢概率疲劳破坏模型,基于MonteCarlo算法实现了铆接钢桥构件单角钢疲劳断裂失效概率的计算,编制了相应的概率断裂分析程序SAPFF。进而将铆接构件概率断裂模型应用于上海市浙江路桥的时变疲劳可靠度分析,并给出了浙江路桥概率疲劳剩余寿命评估结果与维护对策。     

Numerical calculation of bending fatigue life of thin-rim spur gears

Mechanical elements subjected to cyclic loading have to be designed against fatigue. The aim of this paper is to examine the bending fatigue life of thin-rim spur gears of truck gearboxes. The gear service life is divided into the initiation phase of the damage accumulation and the crack growth, respectively. The analysis of thin-rim gear fatigue life has been performed using the finite element method and the boundary element method. The continuum mechanics based approach is used for the prediction of the fatigue process initiation phase, where the basic fatigue parameters of the materials are taken into account. The remaining life of gear with an initial crack is evaluated using the linear-elastic fracture mechanics.     

n-Al2O3/Ni复合电刷镀层的接触疲劳行为

为研究纳米颗粒复合电刷镀层的接触疲劳行为,通过在镍盐溶液中加入纳米氧化铝(n-Al2O3)颗粒,采用电刷镀技术制备了含n-Al2O3颗粒的镍基复合镀层(n-Al2O3/Ni),采用接触疲劳试验机评价了镀态和热处理态的n-Al2O3/Ni复合镀层的抗接触疲劳性能,并与纯镍刷镀层进行了性能对比.借助SEM和TEM对复合刷镀层的组织进行了分析,探讨了复合刷镀层的接触疲劳失效过程以及纳米颗粒等对刷镀层疲劳失效过程的影响.研究表明:n-Al2O3/Ni复合镀层在镀态下的接触疲劳寿命超过100万周次,明显高于纯镍镀层;退火后n-Al2O3/Ni复合镀层接触疲劳寿命为45.9万次,为纯镍镀层的1.62倍;复合镀层的接触疲劳失效过程分为裂纹萌生、裂纹扩展和镀层断裂3个阶段;纳米颗粒在复合镀层接触疲劳失效过程中起到阻碍位错滑移的作用,从而抑制塑性变形和裂纹扩展,使复合镀层具有较高的接触疲劳寿命.