基于LiToSim平台的疲劳寿命评估LtsFatigue软件开发及应用

针对结构的疲劳问题,考虑随机载荷作用,在自主开发的LiToSim平台基础上,嵌入结构疲劳分析数值计算程序。基于LiToSim平台开发LtsFatigue疲劳软件,运用时域疲劳算法,通过雨流计数法对应力时程曲线处理并计算结构疲劳寿命;引入频域疲劳算法,基于应力响应功率谱根据应力循环分布估算疲劳寿命;通过齿轮算例进行疲劳分析,与商业软件对比,验证了LtsFatigue定制化疲劳软件时域法、频域法的计算精度,同时,频域算法有效提高了计算效率,凸显了LtsFatigue软件的优势。基于LiToSim平台的LtsFatigue定制化疲劳软件开发,对大型复杂结构的疲劳仿真具有重要的应用价值。     

危岩主控结构面疲劳断裂寿命计算方法

危岩的破坏机理和安全性受控于危岩主控结构面．通过计算危岩主控结构面在自重、裂隙水压力及地震力作用下的Ⅰ型及Ⅱ型应力强度因子,建立了主控结构面临界长度计算方法;把主控结构面内的裂隙水压力视作交变荷载,通过计算其对主控结构面应力强度因子的贡献,遵循P-M准则运用Paris疲劳方程建立了处于临界状态条件下主控结构面的疲劳断裂寿命计算方法,并通过疲劳断裂试验确定了三峡库区万州地区典型长石石英砂岩的疲劳系数C值和m值．     

用概率断裂力学方法预测管状接头的疲劳寿命

本文研究了Ｔ型管状接头在面内和面外弯曲循环载荷作用下的疲劳强度问题，通过将材料常数和初始裂纹尺寸作为随机变量，采用ＭｏｎＣａｒｌｏ模拟方法对疲劳寿命进行了统计分析．同时，对计算结果进行了线性回归，并与实验结果作了比较。     

机床疲劳载荷的统计分析和概率设计

本文对复杂的机床传动系统的动力特性和疲劳载荷进行统计分析，对传动件的疲劳寿命也视为概率分布状态，在探讨载荷与疲劳寿命的分布规律基础上，提出了机床传动件概率设计的理论公式，用这种新的设计方法可以预测传动件的可靠度或疲劳寿命。     

核电厂稳压器波动管热震荡应力评估研究

典型的管道分析会对所有预期的热载荷进行评估,研究表明核电厂稳压器波动管会经受非预期的并伴随热分层现象产生的热震荡载荷。利用理论分析方法推导出便于求解的半解析公式,并对其进行了工程实例验证,从而验证推导的半解析公式的正确性。同时采用半解析公式评估了核电厂典型的稳压器波动管在热分层温差不同时热震荡载荷导致管道内壁产生的局部峰值应力,并根据ASME规范评估了稳压器波动管热震荡应力对管道疲劳的影响。研究结果表明,核电厂在升温或停堆期间热震荡载荷对波动管的疲劳使用系数影响较小;在核电厂长时间的正常运行期间,当稳压器波动管横截面垂直方向的温差达到临界值时,热震荡载荷对波动管的疲劳使用系数影响非常显著。     

正交各向异性圆柱体在轴压作用下的应力场

基于材料体积不可压假设,对轴向压缩作用下圆柱试件在加载面内的环向和径向应力分布进行理论分析,计算结果表明:当试件材料本构为正交各向异性时,环向和径向应力分布为半径的幂函数形式;试件材料为横观各向同性时,环向和径向应力为半径的二次函数.在圆柱试件轴线上环向和径向应力相等,且均具有最大值;试件圆周边界上径向应力为0,环向应力具有极小值.通过最大拉伸应变破坏理论对试件环向应变进行分析,获得了产生环向拉伸破坏时的临界轴向载荷;并采用Hill-蔡强度理论对试件圆周边界上计算得到的应力参量进行描述,得到了轴压作用下圆柱试件的Hill-蔡强度理论表达式,其不仅取决于轴向应力和试件材料的基本力学性能,还与试件轴向变形的应变率及应变率随时间的变化率相关.     

PCB焊点热循环失效分析和改进设计

针对PCB（印制电路板）焊点在高低温热循环下的失效,建立了传统结构的三维模型和在芯片边角下加锡块的改进设计模型,通过实验测得FR-4的弹性模量和热膨胀系数,用ANSYS计算了PCB在高低温循环下的应力应变,并用修正的Coffin-Manson经验方程计算了焊点的热循环寿命。结果表明,通过在芯片边角下加锡块,PCB焊点的最大等效塑性应变显著降低,其热疲劳寿命得到明显提高.     

A Study on the Fatigue Life of the Laser Additive Manufactured Metallic Material北大核心CSCD

随着军用飞机上越来越多的结构件使用增材制造（AM）技术成形,对增材制造材料和结构疲劳特性的研究就变得十分迫切.为了研究激光增材制造（选区激光熔化成形,SLM）铝合金以及钛合金的疲劳寿命特性,设计了一系列带各种结构细节的模拟试验件,进行常幅谱和随机谱下的试验,统计分析了各组试验的基本可靠性寿命,并得到了可靠度安全寿命曲线.断口分析发现铝合金试验件缺陷较多,存在混合失效特征,而钛合金试验件疲劳分散性较锻件大.     

K型管状接头随机疲劳强度和裂纹扩展规律的研究

分析了K型焊接管状接头受轴向和面外弯曲载荷作用下的随机疲劳问题。通过将焊趾处的表面裂纹的初始尺寸和材料常数作为随机变量处理,并计及焊缝的影响,共产生500个随机样本,最终得到裂纹扩展寿命和裂纹形状变化影响的统计计算结果,并与有关实验数据比较,给予了回归分析。同时,也考察了裂纹扩展规律。     

反应堆顶电缆托架及电缆桥结构力学分析

电缆托架及电缆桥结构位于反应堆堆顶抗震支承环上方,主要是将堆顶所有的电源电缆和测量电缆引到指定的土建接口。采用ANSYS软件的BEAM188单元建立了该复杂结构的分析模型,并基于ANSYS的瞬态分析功能(ANTYPE,TRANS)中的模态叠加法进行地震非线性时程分析,叠加结构的自重载荷,得到了结构在单元坐标系中的载荷(轴力Fx,剪力Fy、Fz和扭矩Mx以及弯矩My、Mz),并直接利用这6个载荷分量计算得到的结构应力,最终开展应力校核。结果表明,反应堆压力容器堆顶结构的应力强度满足抗震要求。     

A Probabilistic Model of the Fatigue Life of Composite Materials for Fatigue-Curve Approximations

A simple mathematical model for the fatigue life of composite materials in which the basic load is taken up by parallel rigid components (fiber strands) is offered. Based on the Markov chain theory, the model allows us to obtain an S-type curve for the growth of internal stresses and to calculate the relationship between the parameters of static strength distribution and the S-N fatigue curve (Wholer curve). The model is too simple and does not provide a numerical coincidence with experimental fatigue-test data, but, when used with additional parameters, it agrees with experiments and can be applied to the model of nonlinear regression in describing the fatigue curve and its variation as the parameters of static strength change.     

Buckling of an annular plate under tensile point loading

In this paper, we address the stability of an elastic thin annular plate stretched by two point loads that are located on the outer boundary. A roller support is considered on the outer boundary while the inner edge of the plate is free. Muskhelishvili’s theory of complex potentials has been applied to obtain a solution of the plane problem in the form of a power series. The buckling problem has been solved using the Rayleigh–Ritz method, based on the energy criterion. The critical Euler force and the respective buckling mode have been computed. Dependence between the critical force and the relative orifice size has been illustrated. Analysis of the results has shown that a symmetric buckling mode takes place for a sufficiently large hole, with the greatest deflection observed around the hole along the force line. However, an antisymmetric buckling mode occurs for relatively small holes, with the greatest deflection being along a line that is orthogonal to the force line.     

广义疲劳等寿命曲线与二维疲劳极限概率分布

基于传统等寿命曲线,提出了广义疲劳等寿命Sa-Sm曲线概念,并找出该曲线的普遍表达式;根据相关系数优化法建立了该表达式的参数估计公式,并给出了具有可靠度p的广义疲劳等寿命P-Sa-Sm曲线公式;以广义P-Sa-Sm曲线为基础,导出了二维疲劳极限概率分布;进行了3组不同应力均值下的LY11CZ铝合金材料的二维配对升降法试验,试验结果验证了广义疲劳等寿命Sa-Sm曲线的合理性和算法的拟合精度.     

Statistical analysis of progressive stress accelerated life test for the product of two-parameter Laplace BS fatigue life distribution under inverse power law model

Based on the product of two-parameter Laplace Birnbaum-Saunders fatigue life distribution, its failure distribution mode is theoretically derived under the progressive stress accelerated life test with inverse power law model, and then three-parameter generalized Laplace Birnbaum-Saunders fatigue life distribution is introduced. The basic properties of three-parameter generalized Laplace Birnbaum-Saunders fatigue life distribution are analyzed, and the image characteristics of its density function, failure rate function and average failure rate function are investigated. Meanwhile, the point estimate method is given for three parameters, and then the point estimates of parameters are obtained for the product of two-parameter Laplace Birnbaum-Saunders fatigue life distribution under the progressive stress accelerated life test with inverse power law model. In addition, the practical example and simulation examples are illustrated to show the feasibility of the proposed method.     

Optimal design of multi-purpose beam-columns

The paper deals with the optimal design of an elastic pinended member of given volume that is to serve as a beam for a part of its design life and as a column for the rest. The optimal design can be interpreted in two ways. Firstly, it is the design that has the maximum Euler buckling load in column action, subject to a prescribed maximum deflection as a beam. Secondly, it is the design that has the least deflection as a beam under a midspan concentrated load, subject to a minimum permissible Euler buckling load in column action. The effectiveness of the optimal design is judged by comparing it with a prismatic bar of the same volume.     

一个用于低周疲劳寿命预测的损伤函数

选择循环塑性应变能作为损伤变量,建立了它的瞬态响应数字模型,采用损伤力学分析方法,导出了计及循环相关的非线性疲劳损伤函数,得到了用于低周疲劳寿命预测的数学公式。利用该损伤函数预测的低周疲劳寿命与试验结果符合较好。