岸桥起重机随机风振疲劳可靠性分析

基于时域方法研究岸桥起重机的风振疲劳可靠性问题。采用谐波叠加法给出了符合Davenport风速谱的多维脉动风速时间历程,基于Bernoulli方程得到相应的风压时间历程,并将相应的风压荷载作用于有限元模型,采用雨流计数法处理结构关键点的应力响应。基于疲劳失效的Basquin方程、Miner线性累积损伤准则和Goodman平均应力修正方程导出疲劳累积损伤的概率模型。考虑平均风速的概率分布,提出了基于概率累积损伤机制的风振疲劳可靠度和可靠性寿命计算方法,为岸桥起重机的风振疲劳可靠性分析作了一些有益的探索和研究。     

在役钢结构吊车梁疲劳可靠性分析

基于结构可靠性理论,针对钢吊车梁的应力幅是否服从威布尔分布进行了计算验证,并对分布参数进行了讨论。对我国钢结构设计规范中的S-N曲线进行了考虑降低低应力幅的疲劳效应的双斜率形式的修正,并利用修正前后的S-N曲线的计算结果进行了分析。采用动态疲劳可靠度模型分析了表面粗糙度、残余应力、吊车竖向荷载偏心及温度对钢吊车梁的疲劳可靠度的影响规律;并提出了对钢吊车梁设计、使用和维护的参考意见。     

梁结构刚度动态非概率可靠性分析

 为了定量分析在疲劳载荷作用下梁在不同寿命期内刚度的可靠性,建立梁结构物理性能退化的精确公式就十分重要.依据疲劳载荷造成的累积损伤对材料极限应力的影响,基于材料剩余强度模型,利用材料强度与弹性模量之间的关系,推导出结构弹性模量的退化表达式,并在此基础上,提出梁弹性模量退化系数的递推表达式,推导出圆截面梁剩余抗弯刚度的表达式.在对结构可靠性分析时,概率可靠性模型和模糊可靠性模型对于原始数据信息要求较高.为了充分利用结构的不确定性信息弥补原始数据的不足,将梁的初始弹性模量及所受的疲劳载荷等看作区间变量,利用区间模型建立基于刚度退化的梁刚度动态非概率可靠性模型.最后,结合工程实例的计算表明了该方法对梁的刚度退化分析及其刚度动态可靠性分析是可行、有效和合理的.     

A new approach to the estimation of fatigue reliability at a single stress level

Based on a probabilistic model of strength-lifetime, an approach to estimating simple fatigue reliability by using first-order reliability techniques is presented. By this approach the results of life testing at two stress levels can be used directly to estimate simple fatigue reliability corresponding to any lifetime and applied stress ratio. Using the approach does not need the data of a fatigue strength staircase test which are not exact enough for describing the distribution of fatigue strength and can only be used for a specific lifetime. A numerical example is given to show the application of the approach.     

Reliability‐Based Design Optimization Considering Probabilistic Degradation Behavior

This article proposes a reliability‐based design optimization methodology by incorporating probabilistic degradation in the fatigue resistance of material. The probabilistic damage accumulation is treated as a measure of degradation in the fatigue resistance of material and modeled as nonstationary probabilistic process to capture the time‐dependent distribution parameters of damage accumulation. The proposed probabilistic damage accumulation model is then incorporated into reliability‐based design optimization model by building a dynamic reliability model inferred from the stress–strength interference model. The proposed approach facilitates to capture the dynamic degradation behavior while optimizing design variables at an early design stage to improve the overall reliability of product. The applicability of the proposed approach is demonstrated using suitable examples. Copyright © 2012 John Wiley & Sons, Ltd.     

A fatigue reliability analysis method including super long life regime

An affordable and feasible method with moderate accuracy is developed to realize fatigue reliability assessment and life prediction including super long life regime (SLLR) through series of experimental researches on a railway axle steel and real axles. A competition damage mechanism for fatigue crack initiation and growth in SLLR is revealed to fascinate an understanding on wide fatigue damage behavior and to provide a weigh and balance on material primary quality control and on-line inspection capacity. Affordable material probabilistic strength-life (S-N) curves including SLLR are presented by an extrapolation approach on a concurrent probability rule between the S-N relations in mid-long life regime and the fatigue limits with a specified life definition. And then, structural probabilistic S-N curves are deduced by considering scale-induced effect on the material curves. Random cyclic stress-strain (CSS) relations are depicted for constructing structural random stressing history. Reliability assessment and fatigue life prediction are conducted by an interference model of the applied stress deduced from the random CSS relations and the strength capacity derived from the structural probabilistic S-N curves. Availability and feasibility of the present method are indicated by a successful application on a railway axle steel.     

在役钢结构吊车梁剩余疲劳寿命的可靠寿命评估

从Miner累积损伤的定义出发,视累积损伤为随机过程,临界损伤为随机变量,基于疲劳动态可靠性理论,提出了在役钢结构吊车梁疲劳剩余寿命的可靠寿命评估方法。之后与现行《钢结构检测评定与加固技术规程》(YB9257-96)中安全期限寿命评估方法进行了分析比较,说明了安全寿命评估方法的概率意义。最后通过算例分析结果表明,提出的可靠寿命评估方法更加合理。     

Probabilistic Failure Prediction of High Strength Steel Rocket Motor Cases

In traditional deterministic analysis, uncertainties are either ignored or accounted by applying conservative assumptions. In those cases, only the mean values or nominal values are used in the analysis. Currently, the operating pressure of high strength steel rocket motor cases is predicted by arbitrarily assumed safety factor based on experience. This leads to over weight of motor cases and cost. Hence a methodology is required to predict the operating pressure more accurately by considering optimal safety factor. This paper presents the probabilistic failure assessment methodology to predict the safety factor for the specified reliability using various failure pressure prediction equations. In this study, the scatter in the yield strength, ultimate strength, and thickness of the structure is considered. Monte–Carlo simulation method is used to perform the probabilistic failure assessment. A suitable failure pressure prediction equation is identified among thirteen equations using stress–strength interference theory based on the statistical measure of the predicted and literature test failure pressure. The reliability-based safety factor is computed for the specified reliability with the use of identified failure pressure prediction equation. The safe operating pressure of steel rocket motor cases is computed for the specified reliability levels.     

A practical approach for predicting fatigue reliability under random cyclic loading

The purpose of this paper is to provide a simple approach for reliability analysis based on fatigue or overstress failure modes of mechanical components, and explain how this integrated method carries out spectral fatigue damage and failure reliability analysis. In exploring the ability to predict spectral fatigue life and assess the reliability under a specified dynamics environment, a methodology for reliability assessment and its corresponding fatigue life prediction of mechanical components using a supply-demand interference approach is developed in this paper. Since the methodology couples dynamics analysis and stochastic analysis for fatigue damage and reliability prediction, the conversion of the duty cycle history for the reliability study of an individual component is also presented. Using the proposed methodology, mechanical component reliability can be predicted according to different mission requirements. For an explanation of this methodology, a probabilistic method of deciding the relationship between the allowable stress or fatigue endurance limit and reliability is also presented.     

Probabilistic fatigue assessment for railway axles and derivation of a simple format for damage calculations

This paper describes a procedure for the determination of railway axle risk of fatigue failure under service loading for a simple fatigue assessment compliant to modern structural recommendations.After an initial review of reliability assessment under fatigue, a fully probabilistic approach is outlined, whose input data for the fatigue damage obtained with the EURAXLES project are briefly summarized. Then, a series of Montecarlo simulations was carried out in order to determine the maximum allowable stress for a given axle made of EA4T and EA1N under service conditions identified by different load spectra from the literature.Results have been obtained in terms of a safety factor for damage calculations that allows designers to adopt a simple semi-probabilistic approach for designing axles for a target reliability against fatigue. The application of this procedure to a railway axle then shows how safety factors should be have to be further increased for taking into the prospective presence of impact damages.     

ZG230-450铸钢的重构疲劳可靠性S-N曲线

给定若干概率水平的常规疲劳可靠性曲线只能做相应概率水平的疲劳设计与寿命预测,要实现任意可靠性水平的疲劳设计、寿命预测和可靠性评定,需要重构全概率疲劳可靠性S-N曲线。首先应用Monte Carlo模拟技术在可接受的误差范围重构了铁道车辆ZG230-450车轮铸钢的疲劳极限和成组法S-N数据。然后应用广义极大似然法测定了其中短寿命范围的可靠性S-N曲线。最后应用概率疲劳极限外推法获得了该材料中短和长寿命范围的合理疲劳概率S-N曲线。并进一步发展了适于车辆结构用万公里单位表征的可靠性曲线。应用该曲线可实现任意可靠性水平的疲劳可靠性设计、寿命预测和可靠性评价。     

Probabilistic modeling of threshold stress intensity factor for fatigue endurance reliability prediction

This study develops a probabilistic model for the threshold stress intensity factor range, which is a critical parameter in infinite fatigue life design under material flaws. The model is based on the proposed concept of probability of propagation in the probabilistic framework, allowing for deriving the probability density function of the threshold intensity factor range. The uncertainty in fatigue crack growth can naturally be incorporated into the resulting distribution. By further introducing the derived distribution into the Kitagawa–Takahashi diagram, the fatigue endurance reliability model can be established in a rational manner. With the first-order asymptotic approximation, the analytical form of fatigue endurance reliability index is obtained. The usefulness of the overall method is demonstrated using realistic engineering application examples.     

混凝土疲劳损伤强度可靠度置信限分析

以三参数Weibull概型为基础,结合大量C15混凝土试件的试验和某混凝土重力坝的原型观测反演结果,建立了描述高应力水平区域的混凝土在较低损伤量下低周疲劳强度的置信限分析模型,得到了具有给定置信度的疲劳强度、疲劳寿命和疲劳损伤三者间的关系曲线,NSP---g和DSP---g曲线。利用本文方法可方便地在给定置信限内计算混凝土在给定应力水平条件下的疲劳寿命、损伤量和剩余强度, 对混凝土做考虑损伤的可靠度设计,以及对已建结构进行可靠度评价。     

Fatigue reliability assessment of offshore structures

Substantial laboratory and field experience has indicated that, owing to the large number of wave stress cyles experienced by offshore steel structures, fatigue cracking should be the main consideration of structural reliability assessment. This paper presents the latest implementation of probabilistic fracture mechanics modelling for fatigue reliability analysis of the most common offshore structural component, the welded tubular joints. Coupled with the recent findings in inspection reliability, effective maintenance and integrity monitoring policies can be formulated. Examples of many practical situations have been analysed to illustrate the applications of the methodology.     

Probabilistic Fatigue Life Prediction and Structural Reliability Evaluation of Turbine Rotors Integrating an Automated Ultrasonic Inspection System

The paper presents a general method and procedure for fatigue reliability assessment integrating automated ultrasonic non-destructive inspections. The basic structure of an automated ultrasonic inspection system is presented. Fatigue reliability assessment methodology is developed using uncertainty quantification models for detection, sizing, and fatigue model parameters. The probability of detection model is based on a classical log-linear model coupling the actual flaw size with the ultrasonic inspection reported size. Using probabilistic modeling, the distribution of the actual flaw size is derived. Reliability assessment procedure using ultrasonic inspection data is suggested. A steam turbine rotor example with realistic ultrasonic inspection data is presented to demonstrate the overall method. Calculations and interpretations of assessment results based on risk recommendations for industrial applications are given.     

应变疲劳强度概率分布

利用概率论方法建立了应变疲劳强度概率分布与应变疲劳寿命概率分布之间的数学关系式，并根据应变－寿命转换关系，由已知的给定应变水平下的疲劳寿命概率分布求出给定寿命下的应变疲劳强度分布函数，便于进行可靠性分析。     

基于健康监测系统的大跨多荷载桥梁的 疲劳可靠度评估

考虑到火车、汽车与风荷载的长期作用以及多荷载的随机性,评估大跨多荷载桥梁的疲劳可靠度是一项富有挑战的任务。该研究基于健康监测系统提出了大跨多荷载悬索桥的疲劳可靠度分析框架,并应用到香港青马大桥。首先,定义了疲劳可靠度的极限状态函数,基于监测数据建立火车、汽车与风荷载的概率模型。基于概率模型和蒙特卡洛模拟方法,利用疲劳关键位置上多荷载的每日随机应力响应,估计每日应力幅m次方之和的概率分布。假设交通保持不变,可确定在给定时段内应力幅m次方之和的概率分布。最终得到桥梁不同疲劳关键位置不同时间点的疲劳失效概率。结果表明,在目前的交通状态下,青马大桥的疲劳健康状况可保持良好。     

Probabilistic fatigue crack growth analysis of spot‐welded joints

This paper presents a probabilistic fatigue crack growth life prediction methodology for spot‐welded joints under variable amplitude loading history. The loading is multi‐axial and is obtained from transient response analysis of a vehicle model using finite‐element analysis. A three‐dimensional (3D) finite element model of a simplified joint with four spot welds is developed, and the static stress analysis of this joint is performed. Then the fatigue crack inside the base material sheet is modelled as a surface crack. Probabilistic crack growth model is combined with the stress analysis result to develop a probabilistic fatigue crack growth life prediction methodology for spot welds. This new method is implemented with MSC/NASTRAN and MSC/FATIGUE and is useful for the reliability assessment of spot‐welded joints against fatigue crack growth.     

Simulation of fatigue crack growth in components with random defects

The paper presents a probabilistic method for the simulation of fatigue crack growth from crack-like defects in the combined operating and residual stress fields of an arbitrary component. The component geometry and stress distribution are taken from a standard finite element stress analysis. Number, size and location of crack-like defects are ‘drawn’ from probability distributions. The presented fatigue assessment methodology has been implemented in a newly developed finite-element post-processor, P • FAT, and is useful for the reliability assessment of fatigue critical components. General features of the finite element post-processor have been presented. Important features, such as (i) the determination of the life-controlling defect, (ii) growth of short and long cracks, (iii) fatigue strength and fatigue life distribution and (iv) probability of component fatigue failure, have been treated and discussed. Short and long crack growth measurements have been presented and used for verification of the crack growth model presented.     

Probabilistic anisomorphic constant fatigue life diagram approach for prediction of P–S–N curves for woven carbon/epoxy laminates at any stress ratio

A general engineering methodology to construct a family of anisomorphic constant fatigue life (CFL) diagrams with probability of failure as the parameter that allows efficiently predicting P–S–N curves at any stress ratios is developed and validated for a plain weave fabric carbon/epoxy laminate. Constant amplitude fatigue tests are first performed to obtain statistical samples of fatigue life at different stress levels and stress ratios, respectively. Static tensile and compressive strength data are also collected. The Kolmogorov–Smirnov and Anderson–Darling goodness-of-fit tests suggest that both two-parameter lognormal and Weibull distributions are acceptable as the distributions for the static strength and fatigue life data, respectively, at the significance level of 5%. Then, we attempt to develop a methodology for efficient construction of the anisomorphic CFL diagrams for different constant values of probability of failure. It requires the P–S–N curves for any percentile points of the distribution for the critical stress ratio. To come up with this requirement, a probabilistic scaling law is formulated. It takes account of the probability-of-failure dependence of the critical stress ratio and the stress-ratio dependence of the P–S–N curve for the critical stress ratio. Finally, the anisomorphic CFL diagrams for different constant values of probability of failure are predicted using the proposed methodology, and they are shown to be in good agreement with the experimental results. It is also demonstrated that the P–S–N curves can efficiently and accurately be predicted for the woven CFRP laminate at any stress ratios using the proposed probabilistic anisomorphic CFL diagram approach.