模拟混凝土破坏过程的微裂纹模型及其应用

提出了一种适用于定量模拟混凝土材料的微细观裂纹数值模型.该模型可用于模拟和分析材料破坏的全过程,包括砂浆/粗骨料界面上初始微裂纹的扩展、微裂纹的聚合、宏观主裂纹的形成与扩展及最终破裂的全过程.作为分析实例,对4组不同配比的16种混凝土拉伸试样进行了破坏过程仿真分析.结果表明,利用该数值模型可揭示混凝土常见的拉伸破坏模式与机理;骨料体积增加时,混凝土的延展性有增大趋势,强度则呈现减小趋势,这与已有文献中混凝土拉伸实验结果相符.该数值模型直接从失效机理出发,建立了定量描述含微细观裂纹的准脆性材料破坏过程的新方法,可望为该类材料/结构的失效控制或安全设计提供参考.     

工程结构损伤的两个重要科学问题--分布式损伤和尺度效应

工程结构的失效起始于底层,即从材料中的孤立的空洞成核开始,形成微裂纹,发展为宏观裂纹,直至整个结构破坏,因此分布式损伤和尺度效应在工程结构损伤问题中显得十分重要,本文简要介绍了一种处理分布式损伤（微损伤）的方法－“统计细观损伤力学”,以及其于该方法讨论了分布式损伤的演化规律,对于跨尺度失效问题的尺寸效应,通过分析应力波引起的损伤问题（存在2个反映尺度效应的Deborah数）,指出各类尺度耦合的机理和特征是关键点。     

岩石宏细观弹塑性损伤破坏对比研究

为了考虑岩石内细观局部塑性变形,基于应变空间理论导出岩石弹塑性损伤增量本构方程,提出了在计算程序中用破坏单元网格消去法清晰模拟裂纹扩展的方法,解决了有限元模拟裂纹的难题,分别从宏观尺度和细观尺度研究了岩石Ⅰ型裂纹弹塑性损伤破坏问题.对比分析表明,宏观尺度研究Ⅰ型裂纹扩展符合断裂力学理论分析;细观尺度研究岩石破坏过程能深入解释细观破坏机理,岩石宏观破坏直接与其内部的细观损伤破坏有关;三维数值模拟破坏过程比二维破坏更为复杂;大理岩偏三点弯曲梁弹塑性损伤破坏数值模拟得到的结果与试验结果较为吻合,验证了新建细观尺度模型模拟岩石破坏问题的合理性.     

岩石宏细观弹塑性损伤破坏对比研究

为了考虑岩石内细观局部塑性变形,基于应变空间理论导出岩石弹塑性损伤增量本构方程,提出了在计算程序中用破坏单元网格消去法清晰模拟裂纹扩展的方法,解决了有限元模拟裂纹的难题,分别从宏观尺度和细观尺度研究了岩石I型裂纹弹塑性损伤破坏问题。对比分析表明,宏观尺度研究I型裂纹扩展符合断裂力学理论分析;细观尺度研究岩石破坏过程能深入解释细观破坏机理,岩石宏观破坏直接与其内部的细观损伤破坏有关;三维数值模拟破坏过程比二维破坏更为复杂;大理岩偏三点弯曲梁弹塑性损伤破坏数值模拟得到的结果与试验结果较为吻合,验证了新建细观尺度模型模拟岩石破坏问题的合理性。     

TB5钛合金板试件疲劳破坏过程的宏微观跨尺度数值模拟

为了研究TB5钛合金板试件从微观初始缺陷到宏观疲劳断裂全过程中的跨尺度数值模拟问题,以约束应力表征材料的疲劳损伤度,以约束应力区裂纹模型描述材料从微观到宏观的疲劳破坏过程,以应变能密度因子作为宏微观跨尺度疲劳裂纹扩张的控制参量,发展了一种宏微观跨尺度疲劳破坏过程的数值模拟方法。在该模型中,可通过疲劳源处材料初始缺陷大小和3个尺度效应函数来表征材料微观因素对疲劳破坏过程的影响。对TB5钛合金光滑板试件(应力集中系数Kt=1)和含切口板试件(Kt=3)进行了数值模拟计算,结果表明,计算S-N曲线与试验S-N曲线能够精准吻合。通过考虑微观效应,其疲劳寿命试验数据的离散性也可由模型计算结果得以体现。     

描述微裂纹成核与扩展的疲劳损伤多尺度模型及其应用

利用多尺度模拟的方法建立了针对疲劳损伤累积过程中微裂纹成核与扩展阶段的疲劳损伤多尺度模型,对模型的有效性进行了实验验证,并将其应用于变幅疲劳载荷下某装甲车传动轴的疲劳寿命评估中.研究结果表明,所提模型能同时预测宏观尺度疲劳损伤与细观尺度微裂纹的成核与扩展率,利用该模型所预测的宏观疲劳损伤值与实验所测值相符.该模型既能合理地描述宏观尺度下不同应力水平的疲劳损伤演化过程,又能综合反映细观尺度下微裂纹的成核与扩展行为.利用这种多尺度疲劳损伤模型可以预测结构在疲劳微裂纹成核与扩展阶段所消耗的疲劳寿命,为各类结构疲劳损伤累积过程评估和准确进行寿命预测提供了一种新途径.     

强冲击荷载作用下混凝土材料动态力学特性及本构模型

基于连续损伤力学理论、统计细观理论和Perzyna黏塑性本构方程, 构造了一个塑性与损伤相耦合的本构模型来描述混凝土材料在强冲击载荷作用下的应力-应变响应特性. 在该模型中假设: 1) 宏观上混凝土材料是一个均匀连续体, 而从细观分析其内部则包含了大量随机分布的微裂纹和微空洞等损伤缺陷; 2) 混凝土材料的损伤演化是由其内部拉伸应力作用下微裂纹扩展的累积而引起的, 导致了材料强度和刚度的弱化; 3) 随着微空洞的塌陷, 混凝土材料内部产生了不可恢复的塑性变形, 体积模量也相应增加, 将这一过程看作是微空洞损伤的演化发展; 4) 微裂纹和微空洞损伤之间不发生相互作用; 5) 当裂纹扩展累积到一定程度时, 混凝土材料发生粉碎性破坏. 利用实验结果确定模型所需参数, 并将利用该模型得到的模拟曲线与实验测试曲线进行比较, 结果表明两者较一致.     

基于RPIM的混凝土“拉-压”组合破坏模型

为了避免传统裂缝扩展模型中断裂韧度KIC的尺寸效应和定步长方法对模拟裂纹扩展过程的影响,针对混凝土宏观裂缝的应变尺度,提出"最大周向拉应变"裂纹扩展判据.结合混凝土的压碎破坏准则,建立混凝土"拉-压"组合破坏模型,并对三点弯曲简支粱的破坏过程进行模拟.     

含弧形裂隙花岗岩裂纹扩展特征PFC模拟

为了研究非直裂隙对岩石强度及破裂特征的影响,对含弧形裂隙岩样进行单轴压缩模拟,探讨弧形裂隙几何参数对试样宏细观力学行为的影响规律。首先,利用颗粒流程序(PFC)构建花岗岩试样数值模型,通过与完整和含单直裂隙试样室内试验结果进行比较,标定1组能够反映花岗岩力学特性的细观参数。在此基础上,对含不同裂隙倾角α和裂隙长短轴比γ的弧形裂隙试样进行单轴压缩模拟。研究结果表明：1)含弧形裂隙试样的峰值强度和弹性模量随着α增大而增大。当α=0°和45°时,试样的峰值强度和弹性模量随着γ的增大而增大;当α=90°时,试样的峰值强度和弹性模量随着γ的增大而减小。2)含弧形裂隙试样主要发生拉伸破坏,初始裂纹在裂隙尖端萌生,随着α增加,试样的破坏程度逐渐增大;γ主要影响裂纹类型、数量和萌生位置。3)首先在弧形裂隙尖端出现应力集中,初始裂纹产生后在裂纹尖端附近出现应力集中,微裂纹逐渐聚集、连通形成宏观裂纹,宏观裂纹的不断扩展导致试样破坏。     

基于随机骨料模型的混凝土塑性损伤耦合力学性能研究

为了探讨混凝土塑性损伤耦合力学性能,基于随机骨料模型和塑性损伤耦合模型,研究了骨料质量分数和加载速率对混凝土宏观力学性能的影响。通过几何模型及本构模型确定其参数,再利用数值模拟软件进行分析得出结论。研究结果表明:随着荷载增大,裂纹走向趋于复杂,局部裂纹扩展逐渐形成贯穿裂纹最终导致混凝土失效。骨料的存在改变了砂浆受力性能,骨料质量分数的增加提高了砂浆的强度,同时,高骨料质量分数也改变了混凝土的破坏模式。随着加载速率的减小,混凝土强度降低。     

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.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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     

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