用能量原理推导圆轴扭转弹性变形与应力分布

关于圆轴自由扭转时横截面上的应力分布,弹塑性力学给出的弹塑性解与大量金属材料的扭转实验结果存在众多分歧。针对这一问题,通过分析材料在弹塑性变形阶段弹性变形和塑性变形对应的细观机理,根据最小变形能原理,给出了弹塑性小变形时,圆轴扭转横截面上任一点处的切应力和弹性切应变的分布规律。结果表明,圆轴扭转时小塑性变形的出现,并不影响材料的弹性性质,也不改变构件内弹性变形的分布规律,即在弹塑性小变形条件下,圆轴扭转横截面上任一点处的切应力、弹性切应变的大小仍与该点到圆心的距离成正比,亦即仍呈现出与弹性变形时相同的分布规律。     

功能梯度纯弯曲梁弹塑性问题的解析解

在小变形前提下研究了功能梯度材料纯弯曲梁的弹塑性受力变形特征.假定功能梯度材料为理想弹塑性材料,且其弹性模量与屈服强度沿梁高度方向按照指数函数变化,根据Mists屈服条件导出了纯弯曲梁的弹性极限弯矩、截面弹塑性应力以及塑性极限弯矩的解析表达式.算例分析表明功能梯度材料梁的弹塑性性能与均匀材料梁不同,材料屈服不一定首先产生于截面最大应力点,塑性变形的产生、扩展具有多种不同的模式,材料弹性模量与屈服强度沿截面高度的梯度变化对纯弯曲梁的应力分布规律及极限承载能力均有较大影响.研究结果可为功能梯度材料梁的弹塑性分析提供验证的考题,也可为简化理论的建立提供一定的依据.     

拉伸装夹改变铣削残余应力的机理研究

基于平面应变的热弹塑性理论分析了拉伸装夹加工残余应力的形成原理,建立了拉伸装夹加工的应变叠加模型,认为残余应力由加工表面的塑性应变决定,而加工表面的塑性应变是加工过程引入的塑性应变和拉伸装夹产生的初始弹性应变之和. 开展了TC4钛合金的拉伸装夹铣削试验,铣削速度从38m/min到566m/min,拉伸装夹产生的初始应变从0和3.0‰, 铣削完成后,在铣削面内与拉伸方向呈0、30、90、120度的四个方向上分别测量了残余应力.试验结果表明在四个测量方向上拉伸装夹引起的残余应力变化量和产生的初始弹性应变一是致的,验证了应变叠加模型的正确性。     

断裂力学在确定最佳自增强压力范围中的应用

自增强技术是提高超高压容器与管道疲劳强度与寿命的一种简便方法.所谓自增强,是在容器未使用之前进行超压处理,内壁形成超应变的塑性变形层,而靠近外壁的材料仍保持弹性变形.卸载后,弹性层力图回复原来尺寸而收缩,而内层不回复的塑性变形阻挡了其收缩.结果内层受到外层弹性收缩的压力而产生残余压缩应力,而弹性层则由于收缩受阻碍而产生残余拉伸应力.在工作压力下周向应力沿壁厚分布规律为:内层受拉伸应力,其峰值在内表面,外层受压缩应力.因此,自增强产生的残余应力使工作应力分布趋于均匀,从而使疲劳循环应力的平均应力值下降,超高压容器与管道的疲劳强度与寿命便提高了.     

集中荷载作用下两端固支梁的弹塑性力学解

通过结构对称性分析了两端固支超静定梁在跨中集中荷载作用下的弹塑性加载及变形过程.受力变形可分为弹性和弹塑性两个阶段,在弹塑性阶段,两固支端附近和梁中部同时产生弹塑性变形直至固支端和梁中点同时形成塑性铰而成为塑性流动机构.通过单位荷载法求出了加载过程中的位移公式,可供弹塑性力学教学和工程结构设计参考.     

基于广义位势理论的非共轴本构模型验证

基于广义位势理论提出的考虑拟弹性塑性变形的弹塑性模型,把塑性应变增量分解为满足弹性分解准则的拟弹性部分和符合传统塑性理论假设的纯塑性部分,这样得到的塑性应变增量方向不仅与应力状态有关,而且与应力增量相关,为解决土的非共轴性问题提供一种有效的方法。通过单剪试验结果及含主应力轴旋转的土体平面问题数值模拟对模型的合理性进行检验。研究结果表明:本文模型计算结果与试验结果吻合较好,且能够描述单剪试验过程中的非共轴现象;此外,与共轴模型数值模拟结果相比,本文模型能够考虑主应力轴旋转产生的土体塑性变形,计算结果更符合实际。     

基于柔度法的两端固定梁加载全过程分析

采用柔度法对两端固定粱在2个对称集中力作用下的加载全过程进行了弹塑性分析.分析结果表明,受力变形过程可分为4个阶段:弹性阶段;固定端附近产生塑性变形阶段;固定端为塑性铰而固定端附近弹塑性区卸载阶段;固定端保持为塑性铰而梁中部部分区域产生塑性变形直至形成塑性流动阶段.导出了纯弯段屈服时的曲率与弯矩的关系,给出了塑性铰处的相对转角及其引起的位移的计算方法.推导了加载各阶段的荷载、弯矩和位移计算公式,可供对超静定梁进行强度和刚度计算时参考.     

弹塑性轮盘应力场分析

一、概述 近年来日趋完善的弹塑性理论为更新传统的强度计算方法开辟了广阔的前景。一种新的指导思想是:在高应力的机械转动部件上,对具有大中心孔的圆盘和大紧度的盘轴联结采用弹塑性设计,从而利用局部塑性变形来达到结构简单,减轻重量的目的。 我们知道,轮盘处于弹性状态时,其应力与应变成正比、弹性横量E为常数。当盘内某些地方应力超过材料的弹性极限时,该部分的应力——应变不再遵循线性关系。此时按E为常数计算得到的应力分布将不再符合实际情况。实际情况是:应力超过材料弹性极限的部分将进入塑性状态,而其余部分则仍处于弹性状态。这时轮盘内既有弹性区又有塑性区,即称为弹塑性轮盘。     

基于柔度法的一次超静定刚架加载全过程分析

为了研究超静定结构的弹塑性性能,用柔度法的基本原理,对一次超静定刚架在集中荷载作用下的加载全过程进行了弹塑性分析.分析结果表明,受力变形过程可分为3个阶段:弹性阶段;固定端处截面附近产生塑性变形到形成塑性铰阶段;固定端处截面附近弹塑性区卸载到刚结点处截面形成塑性流动阶段.给出了塑性铰处的相对转角及其引起的位移的计算方法,推导了加载各阶段的荷载、弯矩和位移计算公式.     

模拟压裂作用对水泥环密封性破坏及改善研究

利用全尺寸水泥环密封性评价装置,研究了多段压裂作用下水泥环的密封完整性。分析了密封性破坏的机理;并提出了相应改善措施和评价标准。试验结果显示基浆水泥环在压裂交变应力作用下,加卸载次数较少时,水泥环密封完整性即遭到破坏;密封性失效发生在卸压阶段水泥环与套管之间的界面处。表明在套管内压高应力作用下,弹性模量较高的基浆水泥环中产生较大的应力,除了发生弹性变形还产生了塑性变形;卸载时套管弹性回缩,水泥环中塑性变形不可完全恢复而存在残余应变,导致二者在界面处的变形不协调一致而引起拉应力。随着压裂应力交变次数的增加,水泥环塑性变形不断累积,卸载后的残余变形和拉应力也随之增大。当拉应力超过界面处的胶结强度时出现微环隙,水泥环密封性破坏。采用掺入胶乳、弹性粒子等形成弹塑性水泥石,弹性模量降低并保持较高的抗压强度,压裂作用时水泥环中产生的应力相对其抗压强度较低,产生的塑性变形较小,因此提高了水泥环保持密封完整性时压裂应力交变的次数,改善了水泥环的密封性。     

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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