考虑疲劳本构随机性的结构应力疲劳可靠性分析方法

提出考虑疲劳本构关系随机性的结构应力疲劳可靠性分析方法。视循环本构模型的材料常数为相关随机变量,考虑存活概率和置信度2个概率测度,与疲劳试验有机结合,应用极大似然原理建立随机疲劳本构的概率模型。随机疲劳强度即概率S－N关系也用2个概率测度下表征,并考虑从中短到长寿命阶段的可能工程实践范围。基于载荷史服从疲劳本构关系产生随机应力载荷、给定寿命时概率S－N关系揭示结构强度分布的观点,建立随机应力载荷—强度干涉可靠性分析模型,可实现任意概率水平的可靠性寿命预测和可靠度评定。中国铁路货车RD2型车轴的可靠性寿命预测和可靠性评定,说明了方法的有效性。     

应变疲劳可靠性理论与方法的新进展

介绍概率应变疲劳试验法、评价模型和损伤随机演化机制方面的新进展。突破经典极大似然法在参考试验载荷之外的单试样限制，提出新的广义极大似然疲劳试验法。新发现随机循环应力—应变响应现象并建立其概率模型。新发展概率疲劳应变一寿命模型。概率模型参数由称为广义极大似然法的方法确定，在整体数据层面综合考虑数据分散性规律与样本量对概率评价的影响。考虑随机应力—应变关系反映“随机应变载荷”、随机应变—寿命关系揭示材料的“应变强度”，提出随机应变载荷—强度干涉恒幅可靠性模型，与Keciguliu的递推法结合可进行变幅和应变载荷谱下的可靠性分析，形成了应变疲劳可靠性理论和方法的新体系。进一步根据有效短裂纹准则，揭示疲劳性能随机及演化性的本质原因源于主导有效短裂纹萌生区域及其裂尖区域微观结构扩展条件的差异及演化性；随机疲劳裂纹扩展、应变—寿命和应力—应变关系是3个关联的随机疲劳关系；疲劳损伤是一个由初始混沌状态，到独立无关的随机状态，然后到史相关随机状态的演化过程。     

Transient dynamics in structures with non-homogeneous uncertainties induced by complex joints

This paper deals with numerical models for the prediction of the transient dynamical response induced by shocks upon structures with complex joints and shows experimental comparisons. The usual numerical methods for analysing such structures in the low- and medium-frequency ranges consist in using reduced matrix models constructed with the elastic modes. The contribution of the higher modes is very sensitive to the model errors and to the data errors. In this paper, a non-parametric probabilistic method is applied to construct the random matrix model allowing model errors and data errors to be taken into account. The paper presents an extension of the non-parametric method for the case of non-homogeneous model errors through the structure. A dynamic substructuring method is then used and the non-parametric probabilistic model of random uncertainties is used in each substructure with its own level of uncertainties. This approach is applied to a dynamical system made of two plates attached by a complex joint. Experiments have been performed and are used to validate the probabilistic predictive model.     

钳式盘形制动器的多目标可靠性优化设计

在基本随机变量的概率特性已知的情况下，采用随机摄动技术和Hooke—Jeeves直接搜索优化方法对钳式盘形制动器进行多目标可靠性优化设计，并通过计算机程序直接实现，迅速准确地得到了钳式盘形制动器的可靠性优化设计信息。     

机构运动精度可靠性分析方法的研究

通过直接对机构独立运动方程组全微分，建立了以矩阵运算形式表达的机构运动（包括位移、速度和加速度）精度概率分析的一般模型。在概率分析的基础上，引入机构运动精度可靠性的概念，将机构运动精度可靠性定义为机构输出误差落在最大允许误差范围内的概率。提出了机构运动精度可靠性分析的随机过程方法和随机变量方法     

压力容器受低周疲劳裂纹萌生寿命的可靠性分析

由于压力容器构件的不确定因素,造成了构件局部应力应变响应和疲劳寿命具有随机性。通过将循环迟滞回线,应变寿命曲线表示为概率曲线,并考虑累积损伤的随机性,反映了构件的不确定性。使用Taylor多项式计算局部应力应变的均值和方差,并求出构件疲劳萌生寿命的均值和方差。计算了一定可靠性下的疲劳萌生寿命,得出在一定使用寿命时,结构的可靠度曲线。算例表明,它在疲劳寿命的可靠性估计中的应用及其工程意义。     

Estimation of the life of machine parts in block loading

The life of machine parts is checked with a probabilistic analysis in the case of random external loading approximated by block loading taking into account various models of material damage. The effect of the loading background and a number of physicomechanical characteristics on damage accumulation are investigated. Accumulation of fatigue damage of the material is noted to have a significant influence on reduction of the endurance limit. The results can be useful for prediction of reliability and durability of machine parts exposed to random external loading.     

改进的概率疲劳极限测定方法

提出了利用升降试验法数据测定概率疲劳极限的3种改进方法。揭示了现有常规法存在不能合理反映疲劳极限的随机性和预测误差较大的缺陷。依据可能的3种试验数据形式,改进方法以疲劳极限附近具有“概率Basquin局部S-N关系”为基础,将疲劳极限视为给定疲劳寿命的条件随机变量,其统计特征通过配对试样的随机疲劳寿命来揭示。应用于车辆LZ50车轴钢概率疲劳极限的测定,验证了改进方法的有效性。     

区间参数桁架结构动力特征值分析的概率处理

将不确定桁架结构中的区间参数用随机变量来表示,对获得的广义区间特征值方程的求解方法进行了研究,提出了一种简洁的算法。此方法假定各区间参量在允许取值区间内为具有熵最大的矩形分布,各随机变量在所定义区域内均匀分布并假设它们彼此独立,将区间特征值方程的求解采用概率理论来处理,再利用随机因子算法,来确定结构动力特征值边界,并与用随机正态分布变量描述的区间求解做了比较。通过实际工程算例对本文方法的有效性进行了验证,并与其他算法进行了比较。     

随机载荷下疲劳寿命的估算

复杂随机载荷下疲劳寿命的评估，一直是工程上所关心的问题之一。在设计阶段，通常难以确定详细的应力历程，因而也无从进行循环计数和累计损伤。本文基于传统的疲劳设计思想和概率分析方法，综合考虑平均应力的影响和疲劳寿命固有的分散性，研究了宽带随机载荷作用下疲劳寿命的估算问题     

Discrete Algorithms for Solving Two Continuous Problems of Random

A combinatorial-discrete approach to solving continuous probabilistic problems arising in the analysis of random point structures is proposed. It is based on replacement of computational schemes based on calculations of cumbersome multidimensional integral expressions by schemes that do not require the use of the apparatus of differential and integral calculus. Another distinctive feature of the study is the systematic use of the generalized Catalan numbers from the multidimensional extension of the classical Catalan sequence for ranking random mutually dependent sequences.     

Probabilistic Analysis of Lateral Wheel–Rail Forces

Russian Engineering Research - In probabilistic analysis of lateral wheel–rail forces, the wheel–rail interaction is assumed to involve a modified useful process and a random process of...     

基于随机有限元法的燃气轮机对称支承板机座强度可靠性分析

由于尺寸和实验成本所限,重型燃汽轮机周期性对称支承板机座的的可靠性分析主要依据可靠性仿真。热通道进口温度、进口流速和进口压力是影响燃气轮机切向支撑板机座的主要随机变量。文中运用有限元软件和蒙特卡洛法相结合的随机有限元法,随机产生120组左右的初始变量,以每一组变量为初始值对支承板机座进行流固耦合分析得到温度场分布,再进行稳态热分析得到热应力分布,提取每一组的最大应力值,并对最大应力的概率分布进行曲线拟合,得到最大应力的概率分布函数。根据应力—强度干涉模型,对切向支承机座极限热应力区域进行了可靠度计算,为大型燃气轮机的可靠性分析提供了参考。     

Calculating the reliability of shafts with probability and possibility variables in the limiting-state model

A new approach is proposed in calculating the reliability of shafts in any mechanical systems. In this approach, the basic parameters in the mathematical model of the limiting state are a combination of random and fuzzy variables, when probabilistic and statistical methods cannot be used for reliability calculation.     

Robust mechanism synthesis with random and interval variables

Robust mechanism synthesis minimizes the impact of uncertainties on the mechanism performance. It has traditionally been performed by either a probabilistic approach or a worst case approach. Both approaches treat uncertainty as either random variables or interval variables. In reality, uncertainty can be a mixture of both. In this paper, methods are developed for robustness assessment and robust mechanism synthesis when random and interval variables are involved. Monte Carlo simulation is used to perform robustness assessment under an optimization framework for mechanism synthesis.     

Errorless readout of random discrete-point fields

A closed analytical relation required to describe the reliability of readout of a random discrete-point field by integrators with two threshold levels is rigorously proved. The corresponding probabilistic problem is solved with the use of two nonstandard tricks: first, codes are developed for performing analytical computations on a computer; second, a new notion of ??three-dimensional generalized Catalan numbers?? is introduced and successfully applied.     

An alternate formulation of mean value for random geometric figures*

In contrast to the traditional technique of averaging functionals of a random geometric figure, it is possible to consider an averaging process which treats the figure as a whole. The result in probabilistic terminology is an expectation, which is itself a figure. Theoretical foundations and various instances are presented in an informal survey.     

表面粗糙度对扩散连接孔隙闭合时间的影响

为考察实际连接表面粗糙度分布的随机性对扩散连接孔隙闭合的影响，把由表面粗糙度决定的接触界面的孔隙高度和半径视为随机变量。在原有确定性模型的基础上考虑了粗糙度孔隙的概率分布，建立了扩散连接孔隙闭合的概率模型。采用蒙特卡罗模拟和数值积分方法，计算了不同扩散连接时间下孔隙闭合的概率大小，并进行了参数敏感性分析，讨论了蠕变指数和孔隙半径对孔隙闭合时间的影响规律。