中国高铁经得起检验

高铁安不安全?从国际的发展来看,日本从1964年开始运营,已经拥有46年安全运营历史;法国1981年开始运营,拥有29年安全运营历史;德国1991年开始运营,已有19年运营历史,其中于1998年6月3日在德国慕尼黑到汉堡的高铁线上造成101死亡、88人受伤的特大安全事故。事故原因是由于

A dislocation-based solution for stress introduced by arbitrary volume expansion in cylinders

A cylindrical structure undergoing volume expansion and contraction is common in engineering practice. For example, the charging (discharging) process of axisymmetrical batteries will give rise to volume expansion (shrinkage). The nitriding process of axles for better fatigue performance also introduces volume expansion. Here, by taking the equivalence of volume expansion (or shrinkage) as continuous insertion (or distraction) of infinitesimal dislocations, we supply a framework to solve the stress field of a cylinder with arbitrary insertion (distraction) profile of materials along the radial direction. Under the assumptions that the volume expansion profile along the axis of a cylinder is uniform and the deformation is small so that the current configuration is regarded as the original, we supply analytical solutions of stress fields to several typical volume expansion or shrinkage profiles. Our analysis shows that different volume variation gives rise to either high tensile stress in the surface or hydrostatic tension in the core, and supplies distinct failure mechanisms in cylindrical batteries

Bottom-up Design of Three-Dimensional Carbon-Honeycomb with Superb Specific Strength and High Thermal Conductivity

Low-dimensional carbon allotropes, from fullerenes, carbon nanotubes, to graphene, have been broadly explored due to their outstanding and special properties. However, there exist significant challenges in retaining such properties of basic building blocks when scaling them up to three-dimensional materials and structures for many technological applications. Here we show theoretically the atomistic structure of a stable three-dimensional carbon honeycomb (C-honeycomb) structure with superb mechanical and thermal properties. A combination of sp(2) bonding in the wall and sp(3) bonding in the triple junction of C-honeycomb is the key to retain stability of C-honeycomb. The specific strength could be the best in structural carbon materials, and this strength remains at,a high level but tunable with different cell sizes. C-honeycomb is also found to have a very high thermal conductivity, for example, &gt;100 W/mK along the axis of the hexagonal cell with a density only similar to 0.4 g/cm(3). Because of the low density and high thermal conductivity, the specific thermal conductivity of C-honeycoMbs is larger than most engineering materials, including metals and high thermal conductivity semiconductors, as well as lightweight CNT arrays and graphene-based nanocomposites. Such high specific strength, high thermal conductivity, and anomalous Poisson&#39;s effect in C-honeycomb render it appealing for the use in various engineering practices.</p

A theoretical analysis of the surface dependent binding, peeling and folding of graphene on single crystal copper

The binding, peeling and folding behavior of graphene on different surfaces of single crystal copper were examined theoretically. We show that the binding energy is the highest on the Cu(111), and follows the order of Cu(111) > (100) > (110) > (112). Conventional theory is capable of capturing the dynamic process of graphene peeling seen from molecular dynamics simulations. We show that the number of graphene layers on Cu surfaces could be distinguished by performing simple peeling tests. Further investigation of the folding/unfolding of graphene on Cu surfaces shows that Cu(111) favors the growth of monolayer graphene. These observations on the interaction between graphene with single crystal Cu surfaces might provide guidelines for improving graphene fabrication

Critical Sensitivity and Trans-Scale Fluctuations in Catastrophic Rupture

Rupture in the heterogeneous crust appears to be a catastrophe transition. Catastrophic rupture sensitively depends on the details of heterogeneity and stress transfer on multiple scales. These are difficult to identify and deal with. As a result, the threshold of earthquake-like rupture presents uncertainty. This may be the root of the difficulty of earthquake prediction. Based on a coupled pattern mapping model, we represent critical sensitivity and trans-scale fluctuations associated with catastrophic rupture. Critical sensitivity means that a system may become significantly sensitive near catastrophe transition. Trans-scale fluctuations mean that the level of stress fluctuations increases strongly and the spatial scale of stress and damage fluctuations evolves from the mesoscopic heterogeneity scale to the macroscopic scale as the catastrophe regime is approached. The underlying mechanism behind critical sensitivity and trans-scale fluctuations is the coupling effect between heterogeneity and dynamical nonlinearity. Such features may provide clues for prediction of catastrophic rupture, like material failure and great earthquakes. Critical sensitivity may be the physical mechanism underlying a promising earthquake forecasting method, the load-unload response ratio (LURR)

第十八届美国理论与应用力学大会总结

1会议概况2018年6月5—9日,第18届美国理论与应用力学大会(18th U.S. National Congress of Theoretical and Applied Mechanics, USNCTAM2018)在美国芝加哥召开.本次大会由美国力学国家委员会和中国力学学会联合主办,旨在探讨和交流近四年世界范围内在理论和应用力学领域的基础研究、创新技术的最新进展,吸引了来自世界各地的近千名专家学

Some observations on the size effects in nanotwined metals and their theoretical explanation

When materials are deformed plastically via dislocations,a general finding is that samples with smaller dimensions exhibit higher strengths but with very limited amount of plasticity in tension. Here we report that one-dimensional coherent nanostructures with tilted internal twins exhibit anisotr..

固体工程科学—工程材料的应用力学理论与实践

与以往关注固体力学某一知识点如弹性、塑性、疲劳、断裂等的教程不同，本书是作者针对工程科学领域高度交的现状，面向通识化教育的需求而做出的一个尝试。本书涵括了固体变形各个知识点的力学内容，尤其对固体力学问题的物理背景、物理过程进行了深入描述，并辅以简单的工程实例，以期不同背景的读者能够容易和牢靠地掌握固体力学的核心知识。 本书的阅读和使用需要具有一定的数学知识背景，但只要具备基本的高等数学知识就可以理解、消化、吸收其中的大部分内容。 本书内容而完备，适合材料、机械、土木、化工、航空航天、工程力学等的高年级本科生、研究生、教师及相关科技人员阅读和参考。</p

梯度挛晶材料的力学行为

编者按：2016年1月16日，是力学研究所成立60周年纪念日。在1956年的这一天，由陈毅副总理亲笔签署的国务院批复文件下达，中国科学院力学研究所正式成立，钱学森先生担任首届所长。在力学所走过的一甲子年间，力学人遵循钱学森的工程科学办所思想，为推进中国的近代力学事业、为推动中国的经济国防建设，做出了重要的贡献。承蒙作者盛意，本刊在此转载魏宇杰研究员在&ldquo;庆祝中国科学院力学研究所成立60周年学术报告会&rdquo;上的报告&mdash;&mdash;梯度挛晶材料的力学行为，以飨读者。 魏宇杰 作者简介：魏宇杰，中国科学院力学研究所研究员。1997年毕业于北京大学力学系，2000年在力学研究所取得硕士学位，随后留所担任研究助理（2000．9 &ndash; 2001.8）。2001年赴美国麻省理工学院机械工程系攻读，2006年取得博士学位。2008年在美国布朗大学工程中心完成博士后学业后，在美国阿拉巴马大学机械工程系担任助理教授(2008.9 &ndash; 2010.2)。2010年2月，通过中国科学院&ldquo;百人计划&rdquo;招聘，进入力学研究所工作至今，担任研究员及非线性力学国家重点实验室副主任。其间，曾在美国科罗拉多大学伯德分校（2011.9 &ndash; 2012.5）和美国佐治亚理工学院（2014.2 &ndash; 2014.5）担任访问教授。2013年8月任中国科学院力学研究所所长特别助理，2015年任非线性力学国家重点实验室主任。其它学术兼职则有：中国力学学会第三届对外交流与合作工作委员会委员（2012.1 &ndash; 2015.12），中国力学学会第八届固体力学委员会智能材料与结构专业组副组长（2012.1 &ndash; 2015.12），《力学进展》副主编（&nbsp;2013.3 -），《Theoretical and Applied Mechanics Letters》编委（2010.1 -）。此外，还担任《Nature Materials》《Nature Communication》等20余种国际刊物的评审人<br /