考虑应力梯度及附加强化的多轴疲劳寿命预测

以多轴缺口件为研究对象,考虑应力梯度和非比例附加强化对疲劳寿命的影响,建立一种适用于多轴缺口件的疲劳寿命预估模型.首先,以最大剪切应变幅作为损伤参量,借助坐标变换原理确定临界面位置,研究了裂纹萌生和扩展的物理机制;其次,利用有限元方法获得临界面上非均匀应力场,提取特定路径上的应力分布并进行归一化处理,给出多轴加载时的等效应力梯度因子;最后,考虑相位差的影响提出一种新的非比例附加强化因子,基于Manson-Coffin方程提出了一种多轴疲劳寿命预测方法.将本文模型、Smith-Watson-Toper(SWT)模型和Manson-Coffin方程的计算结果与实验寿命进行对比,结果表明本文方法的预测精度高于SWT模型和MansonCoffin方程.     

新型风机增速箱输出轴优化设计及寿命预估

以新型风机增速箱输出轴为研究对象,对输出轴进行设计、校验,然后对实心结构空心优化,模拟实际工况,进行有限元分析,结果表明空心轴满足强度要求,验证了空心优化的合理性。在此基础上考虑低幅载荷强化与软化的双重作用,提出了一种修正的寿命预估模型,利用新模型对输出轴进行寿命预估,与设计寿命相差5.22%左右,具有较高的预估精度,而且计算简单,能够弥补现有模型忽略低幅载荷循环特性的缺陷。该研究方法对轴类零件的优化设计及寿命预估具有一定的指导意义。     

基于有限单元法的裂纹梁结构疲劳寿命预测模型

为了准确预测裂纹梁结构的疲劳寿命,提出一种裂纹梁结构的振动与疲劳裂纹扩展耦合分析方法。首先,基于有限单元法建立裂纹梁结构的动力学模型;然后,根据裂纹梁单元的特点,推导裂纹梁单元的应力强度因子表达式,在此基础上应用Walker方程建立疲劳裂纹扩展增量计算式,再基于振动响应与裂纹扩展循环同步分析法,计算疲劳裂纹扩展寿命;基于该疲劳寿命预测模型,分析激振频率、激振力幅值和应力比对裂纹梁疲劳寿命的影响;最后,对裂纹梁进行疲劳试验,将试验测量结果与模型计算结果进行比较,验证所提出模型的准确性。研究结果表明:提出的疲劳寿命预测模型较好地表征了疲劳裂纹扩展寿命与其结构参数之间的内在关系,反映了振动对裂纹梁结构疲劳寿命的影响;随着激振频率接近固有频率,裂纹扩展速率增大,裂纹梁的疲劳寿命明显降低;随着激振力幅值增大,裂纹梁的应力强度因子幅增大,疲劳裂纹扩展寿命降低;随着应力比增加,裂纹梁的疲劳寿命显著提高。     

柔性结构疲劳寿命的预测方法

讨论柔性构架结构疲劳寿命的预测方法,建立刚柔耦合多体动力学模型,计算结构危险点的动载荷时间历程;利用有限元准静态分析法,获得应力影响因子;利用模态分析技术获得结构固有频率和模态振型,确定结构的危险点位置.基于危险应力分布的动载荷历程,结合材料特性曲线以及线性损伤理论,进行标准时域的柔性结构应力应变的循环计数,损伤预测和寿命估计.应用该方法对构架结构进行疲劳寿命预测,结果表明,该预测方法预测精度有效,可以有效提高结构耐久性设计质量.     

CFRP加固裂纹钢板的疲劳寿命及加固参数研究

钢结构在运行一段时间后,其母材或焊缝附近易产生裂纹,因此需要对裂纹进行修复以延长使用寿命.文中研究了碳纤维增强复合材料(CFRP)加固裂纹钢板的疲劳寿命及加固参数.首先采用粘结力理论,建立CFRP加固裂纹钢板的有限元模型,计算得到裂纹尖端的应力强度因子;然后进行4组对比疲劳试验,利用试验数据和Paris公式计算材料常数C和n,将计算的应力强度因子代入Paris公式预测试件的疲劳寿命;最后利用有限元模型对CFRP加固的刚度、长度、宽度等加固参数进行了研究.结果表明:根据有限元模型计算的应力强度因子幅和Paris公式可以准确预测CFRP加固裂纹钢板的疲劳寿命;CFRP加固可以减小裂纹尖端的应力强度因子,有效提高裂纹钢板的疲劳寿命.     

基于ANSYS的恒幅载荷下桥式起重机疲劳寿命模拟

针对评估桥式起重机金属结构疲劳寿命的问题,以桥式起重机受力分析为基础,借助ANSYS软件的相互作用积分法,结合恒幅载荷下裂纹扩展寿命的理论,对箱型梁腹板跨中部位的腹板——下翼缘板处的裂纹进行分析,拟合出应力循环次数与裂纹尺寸的关系,得出恒幅载荷下桥式起重机的疲劳裂纹扩展寿命。同时,归纳桥式起重机疲劳寿命计算的影响因素及其试验推荐值。结果表明,循环次数与裂纹尺寸之间的关系符合疲劳裂纹扩展的客观规律。     

无干涉铆接搭接结构的多裂纹扩展预测方法

建立了含有广布损伤(MSD)裂纹的无干涉铆接搭接结构三维有限元模型,求解裂纹尖端左右两侧的应力强度因子,并提出了等效应力强度因子的概念。以Paris公式为基础,结合改进的载荷循环叠加方法、塑性区连通准则,并考虑MSD裂纹扩展中的相关性,建立了等幅谱下MSD裂纹扩展预测模型。计算结果与试验结果表明,使用该方法预测的3种开裂模式下的寿命值误差均在7%以内;对搭接结构进行分析不能简化为二维模型;MSD裂纹扩展寿命与结构开裂模式有关,结构中共存的裂纹越多其裂纹扩展寿命越短。     

钢箱梁疲劳裂纹气动冲击法维修效果评估

以实桥疲劳裂纹为研究对象,从应力和应力强度因子角度评估气动冲击维修方法的现场实施效果.对维修前后疲劳裂纹尖端附近的应力分别进行24 h数据采集,并采用雨流计数法,探讨裂纹尖端应力幅的变化规律.结合应力强度因子测试理论,对比研究裂纹尖端应力强度因子幅的变化规律.研究结果表明:本测点疲劳裂纹为典型的Ⅰ-Ⅱ复合型裂纹,维修后疲劳裂纹尖端张拉和剪切应力幅均得到有效降低,改善了裂纹尖端受力条件.高应力强度因子幅的循环次数显著降低,表明气动冲击维修技术对于制约复合型裂纹扩展具有良好效果.     

恒幅循环荷载作用下FRP加固桥梁疲劳寿命预测

在线性渐进叠加假定的基础上,理论推导了三点弯曲荷载下FRP加固桥梁应力强度因子的计算公式,并结合FRP加固桥梁疲劳裂纹扩展试验,分析了FRP加固梁裂纹的扩展行为,验证了裂缝口张开位移CMOD的经验公式可用于计算标准三点弯曲梁的裂缝口张开位移,进而计算断裂模型中梁的临界有效裂缝长度.利用线弹性断裂力学中应力强度因子对疲劳裂纹扩展进行定量描述,进而对FRP加固桥梁的疲劳寿命进行预估算研究.     

三维裂纹体的断裂分析

采用等参奇性边界单元法求解了三维裂纹体的复合型应力强度因子，并采用Ｆｏｒｍａｎ模型，模拟了三维裂纹体疲劳断裂过程，预估了在等幅和变幅载荷作用下的三维裂纹体的疲劳寿命。文中给出了两个数值算例，其计算值与试验结果比较表明，提出的方法与程序可满足工程分析要求。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with