【百家大讲堂】第89期：化学-力学：固体力学和化学交叉学科中的挑战

　　讲座题目：化学-力学：固体力学和化学交叉学科中的挑战

                            Chemo-Mechanics: Challenges at the Intersection of Solid Mechanics and Chemistry

　　主 讲 人：Robert M. McMeeking

         美国国家工程院院士，美国加州大学圣芭芭拉分校材料与机械工程系特聘教授，德国萨尔布吕莱布尼茨新材料研究所外籍研究员

  主 持 人：方岱宁院士

　　时   间：2018年8月31日 8:30

　　地   点：中关村校区 7号楼报告厅

　　主办单位：研究生院、先进结构技术研究院

　　报名方式：扫描下方二维码

　【主讲人简介】

  Robert M. McMeeking，加州大学圣芭芭拉分校材料与机械工程系特聘教授，美国国家工程院院士，德国萨尔布吕莱布尼茨新材料研究所外籍研究员。1972年在苏格兰格拉斯哥大学以一级荣誉获得理科学士学位，并于1976年在布朗大学James R. Rice教授指导下获得固体力学博士学位。他在斯坦福大学任职2年，担任代理助理教授，随后担任伊利诺伊香槟分校理论与应用力学系助理教授和副教授。1985年加入加州大学圣芭芭拉分校（UCSB）担任材料与机械工程系教授，并于1992-1995年以及1999-2003年担任机械工程系主任。McMeeking发表了250多篇科学论文，涉及塑性，断裂力学，计算方法，冰川学，坚韧陶瓷，复合材料，材料加工，粉末固结和​​烧结，铁电体，微观结构演变，纳米摩擦学，驱动结构，结构爆炸和碎片保护，水下爆炸冲击流体结构相互作用，细胞及其细胞骨架的力学，锂离子电池和燃料电池。 1998年，当选为美国机械工程学会会员，并于2002年被科学信息研究所评为材料科学与工程领域的高度引用研究员。2005年当选美国国家工程院院士，并于2006年和2013年两次获得洪堡高级科学家奖，2007年获得布朗大学布朗工程校友奖。2014年当选为英国皇家学院院士和爱丁堡皇家学会会员，并获得2014年工程科学学会William Prager奖章和美国机械工程师学会2014年Timoshenko奖章。

    Robert M. McMeeking is Distinguished Professor of Mechanical Engineering at the University of California, Santa Barbara, and is an External Member of the Leibniz Institute for New Materials, Saarbruecken, Germany.  He earned a B.Sc. (with 1st Class Honours) at the University of Glasgow, Scotland in 1972, and in 1976 he completed his Ph.D. in solid mechanics at Brown University under the supervision of Professor James R. Rice.  He spent 2 years at Stanford University as Acting Assistant Professor, and then was appointed Assistant Professor, and subsequently Associate Professor, at the University of Illinois at Urbana-Champaign, in the Theoretical and Applied Mechanics Department.  McMeeking moved to the University of California, Santa Barbara (UCSB) in 1985 as Professor of Materials and of Mechanical Engineering.  He was Chair of the Department of Mechanical Engineering 1992-1995 and again during 1999-2003.  He has published over 250 scientific papers on such subjects as plasticity, fracture mechanics, computational methods, glaciology, tough ceramics, composite materials, materials processing, powder consolidation and sintering, ferroelectrics, microstructural evolution, nanotribology, actuating structures, blast and fragment protection of structures, fluid structure interactions arising from underwater blast waves, the mechanics of the cell and its cytoskeleton, lithium-ion batteries and fuel-cells.  In 1998 he was advanced to Fellow grade in the American Society of Mechanical Engineers and in 2002 was recognized by the Institute for Scientific Information as a Highly Cited Researcher in the fields of Materials Science and Engineering.  McMeeking was elected to the U.S. National Academy of Engineering in 2005, and held a Humboldt Award for Senior Scientists in 2006 and again in 2013.  He was given the Brown Engineering Alumni Medal by Brown University in 2007, and elected Fellow of the U.K. Royal Academy of Engineering in 2012.  In 2014 he was also elected Fellow of the Royal Society of Edinburgh and received both the 2014 William Prager Medal of the Society of Engineering Science and the 2014 Timoshenko Medal of the American Society of Mechanical Engineers.  McMeeking was Editor of the Journal of Applied Mechanics for the term 2002-2012. 

【讲座摘要】

      化学-力学是一个古老的工程学科，至少可以追溯到唐代中国火药的发明。蒸汽机和内燃机的出现更增加了该主题的工程重要性，当然，材料的机械性质从根本上来说也是它们的化学问题。但随着相关领域的进一步发展，又出现了许多新的问题，且在这些问题中固体力学和化学的交叉起着至关重要的作用。因而，必须要将固体力学与化学相关的重要性引入到研究问题中。要做到这一点，必须考虑系统的能量构成，以及不同类型的能量在热力学中可以发挥的相对重要的作用。例如，汽油的比能量远大于通常与材料的弹性变形相关的应变能密度。因此，固体力学和化学发挥同等重要作用的主题有些特殊，人们必须将注意力集中在这些特殊领域，以应对固体力学与化学交叉的挑战。本次报告将讨论从各种相关领域抽取出的化学-力学交叉问题。一个问题是在氧化环境中的中间温度下SiC/SiC复合材料的应力破裂问题，这是一系列内部化学和热机械过程导致过早的局部纤维断裂的结果。通过建立的模型首次解释了为什么这种失效机理在中等温度下普遍存在而在低温和高温下不存在。固体力学在化学中发挥重要作用的另一个主题是锂离子电池，其中力学作用会影响离子传输、氧化还原反应等电化学过程的速率。在生物细胞力学中，同样存在许多应力和力影响细胞生物化学，细胞信号传导和细胞对环境响应行为的现象。此外，在凝胶和弹性体中，化学和固体力学之间的相互作用会影响材料的状态及其力学性质。

   Chemo-Mechanics is an old subject in engineering, dating back at least as far as the invention of gunpowder in China during the Tang dynasty.  Steam and internal combustion engines increased the engineering importance of the subject, and, of course, the nature of the mechanical properties of materials is fundamentally an issue of their chemistry.  But the area has grown, and today there are a large number of additional topics where the intersection of solid mechanics and chemistry is of importance.  Nevertheless, the importance of solid mechanics in relation to chemistry must be put in context.  To do this, one must consider the energy content of systems, and the relative importance of the roles that different types of energy can play in thermodynamics.  For example, the specific energy content of gasoline is vastly greater than the strain energy density typically associated with elastic deformation of materials.  Therefore, the topics in which both solid mechanics and chemistry play equally important roles are somewhat special, and one has to focus one’s attention on these special areas to address the challenges that lie at the intersection of solid mechanics and chemistry.

 This talk will address a few such areas drawn from a variety of subjects.  One area is stress rupture of SiC/SiC composites at intermediate temperatures in oxidizing environments, which is the result of a series of internal chemical and thermomechanical processes that lead to premature, localized fiber fracture.  The model developed has, for the first time, explained why this failure mechanism is prevalent at intermediate temperatures but not at low and high temperatures.  Another topic where solid mechanics plays a significant role in the chemistry is the subject of lithium-ion batteries, where mechanical work can bias the rates of electro-chemical processes that are involved in ion transport and redox reactions.  In biological cell mechanics there are many phenomena where mechanical stress and forces affect the cell biochemistry, cell signaling and cell behavior in response to its environment.  Additionally, in gels and elastomers interactions between chemistry and solid mechanics influence the state of the material and its mechanical properties.