一种新的多轴疲劳损伤参量

基于临界面法提出一种与加载路径无关的多轴疲劳损伤参量，该参量考虑临界损伤平面上的最大剪切应变和法向应变程两个参数，并利用Ｖｏｎ Ｍｉｓｅｓ准则将两参数合成一个等效损伤在量，结果表明，本文所提出的多轴疲劳损伤参量既可用于多轴比例循环加载，也可用在非比例加载条件下，用其预测多轴疲劳寿命，误差约在１．５个因子之内。     

多轴载荷下GH4169合金疲劳寿命预测

基于多轴疲劳临界损伤面原理,在对GH4169合金薄壁圆管和缺口试件的高温疲劳特性及有限元应力-应变关系进行分析的基础上,通过引入三轴因子FT,应用von-Mises准则提出了一个能够适用于GH4169合金不同应力状态的多轴疲劳损伤参量.新的损伤参量考虑了临界面上最大剪应变和法向应变对多轴疲劳损伤的不同以及应力状态对多轴疲劳寿命的影响.该多轴疲劳损伤参量不含有经验常数,便于工程应用.利用新的多轴疲劳损伤参量,结合Manson-Coffin方程,建立了新的多轴疲劳寿命预测模型.预测结果表明,该模型较准确地预测了GH4169合金薄壁圆管和缺口试件的高温多轴疲劳寿命.     

基于临界面损伤参量的金属材料多轴疲劳寿命预测

对最大剪切应变幅模型、KBM模型、FS模型和MKBM模型4种广泛讨论的临界面模型进行了对比分析,统计了8种金属材料圆管薄壁型试件在173个应变加载工况下的多轴疲劳试验数据,验证了这4种临界面模型对金属材料多轴疲劳寿命的预测能力,讨论了基于临界面损伤参量进行多轴疲劳损伤评估和寿命预测时仍需关注的几个主要问题.研究结果表明:最大剪切应变幅模型和KBM模型能较好地适用于多轴比例加载条件下的疲劳寿命预测,而对多轴非比例疲劳寿命的预测结果一般偏于危险估计;FS模型和MKBM模型在损伤控制参量中引入了一个临界面上的最大法向正应力参数来反映材料的非比例附加强化效应对多轴疲劳损伤的影响,显著提高了对多轴非比例疲劳寿命的预测能力.     

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.     

高温多轴比例与非比例循环加载下疲劳寿命预测

利用薄壁圆管和缺口试样,在MTS 809电液伺服材料试验系统上对GH4169合金的高温多轴疲劳特性进行了实验研究. 实验采用对称轴向和扭转应变控制、比例与非比例循环加载,轴向与扭转应变的相位差分别为0°,45°,90°. 通过对薄壁圆管和缺口试样的高温多轴疲劳寿命特性分析,基于临界面方法提出了一个的多轴疲劳寿命预测模型,在考虑临界面上最大剪应变和正应变对多轴疲劳损伤贡献的同时,还引入了应力状态对多轴疲劳寿命的影响因素. 应用新模型对GH4169合金高温多轴疲劳寿命进行预测结果表明,该模型对于缺口试样和薄壁圆管的高温多轴疲劳寿命估算具有较高的准确性.     

复合材料层压板疲劳寿命预测方法

测定了碳纤维／树脂基T300／QY8911复合材料的3组典型单轴循环应力下的S-N曲线．基于试验数据，建立了多轴循环应力作用下单向板的寿命模型，并通过整合平面应力分析、失效分析和材料性质退化模块模拟多向层压板的疲劳失效过程．这种方法试图基于单向板在确定应力比下的疲劳试验结果，预测同种材料体系的任意铺层形式的多向层压板在复杂循环应力作用下的疲劳寿命．对于以分层破坏为主控因素的层压板，基于层间应力的计算结果，用计算面内累计损伤的方法计算分层损伤，层压板的寿命等于分层扩展寿命和分层后子层板剩余寿命之和．考虑分层扩展后，层压板的寿命预测结果得到明显改善．     

多轴疲劳寿命预测及验证

以薄壁管试件为研究对象,分析了拉扭联合加载作用下的多轴疲劳应变变化特性·根据多轴疲劳临界平面法原理,以临界平面上最大剪应变幅、正应变幅以及表征材料总体损伤水平的非比例度为参数建立多轴疲劳损伤参量,结合MansonCoffin方程建立了多轴疲劳寿命预测模型·该模型考虑了材料总体损伤程度·模型中表征材料总体损伤的非比例度是加载参数的函数,与多轴疲劳应变变化特性密切相关·试验验证,预测寿命误差因子小于15·     

考虑应力集中的吊车梁多轴疲劳寿命预测

钢结构吊车梁在工业建筑中被广泛应用,应力集中的存在导致几何不连续位置在复杂应力下服役.借助有限元法分析吊车梁应力-应变状态,确定危险点位置,并提取应力、应变分量;以应变能密度作为损伤参量并以最大平面为临界面,基于能量准则建立临界面位置数值计算方法,结合有限元结果给出吊车梁临界面位置;考虑吊车梁在非对称载荷下服役,借助Goodman方程进行平均应力修正,并结合Q355D钢近似S-N曲线计算疲劳寿命.该方法考虑了应力集中处多轴应力对疲劳损伤的影响,可以为复杂应力下几何不连续钢构件的疲劳寿命评估提供新方法.     

考虑应力梯度的多轴缺口件疲劳寿命预测方法

以缺口附近疲劳损伤影响区的场强为损伤参量,结合Manson-Coffin方程提出一种多轴比例加载下缺口件疲劳寿命预估方法.首先,借助坐标变换矩阵定义应变能密度最大的平面为临界面,克服了传统能量法作为标量难以描述裂纹萌生和扩展方向的不足.其次,利用有限元软件分析临界面上等效应力分布规律,拟合距离危险点5 mm内等效应力分布函数,通过求相对应力梯度函数的驻点确定疲劳损伤影响区的大小,以疲劳损伤影响区的场强作为疲劳损伤参量对Q345钢多轴缺口件进行寿命预估.最后,将利用该方法、局部应力应变法的预估寿命与试验寿命进行对比,结果表明:两种方法预估寿命的误差都在2倍因子以内,但由于该方法考虑了应力梯度效应,预估精度要优于局部应力应变法.     

面-面接触铝合金紧固件微动疲劳寿命预测方法研究

针对具有面-面接触特征的铝合金紧固件,根据其接触特点,建立有限元模型计算了其应力场分布。考虑接触面高轴应力梯度的力学响应,用接触面应力三维度的概念来反映微动疲劳多轴应力状态。考虑损伤和弹塑性势能的耦合,从热力学第二定律出发,基于损伤力学本构方程,推导出基于热力学耗散势函数的耦合损伤演化模型。结合实验参数,得到预测铝合金紧固件微动疲劳寿命的方法。寿命预测结果与实验值进行对比,误差分散在25%范围内。     

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     

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     

Journal of Donghua University ( English Edition) Contents of Volume 31

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