MULTISCALE MECHANICS OF BIOLOGICAL AND BIOLOGICALLY INSPIRED MATERIALS AND STRUCTURES

The world of natural materials and structures provides an abundance of applications in which mechanics is a critical issue for our understanding of functional material properties. In particular, the mechanical properties of biological materials and structures play an important role in virtually all physiological processes and at all scales, from the molecular and nanoscale to the macroscale, linking research fields as diverse as genetics to structural mechanics in an approach referred to as materiomics. Example cases that illustrate the importance of mechanics in biology include mechanical support provided by materials like bone, the facilitation of locomotion capabilities by muscle and tendon, or the protection against environmental impact by materials as the skin or armors. In this article we review recent progress and case studies, relevant for a variety of applications that range from medicine to civil engineering. We demonstrate the importance of fundamental mechanistic insight at multiple time- and length-scales to arrive at a systematic understanding of materials and structures in biology, in the context of both physiological and disease states and for the development of de novo biomaterials. Three particularly intriguing issues that will be discussed here include： First, the capacity of biological systems to turn weakness to strength through the utilization of multiple structural levels within the universality-diversity paradigm. Second, material breakdown in extreme and disease conditions. And third, we review an example where the hierarchical design paradigm found in natural protein materials has been applied in the development of a novel hiomaterial based on amyloid protein.     

MICROMECHANICS OF MACROELECTRONICS

The advent of flat-panel displays has opened the era of macroelectronics. Enthusiasm is gathering to develop macroelectronics as a platform for many technologies, ranging from paper-like displays to thin-film solar cells, technologies that aim to address the essential societal needs for easily accessible information, renewable energy, and sustainable environment. The widespread use of these large structures will depend on their ruggedness, portability and low cost, attributes that will come from new material choices and new manufacturing processes. For example, thin-film devices on thin polymer substrates lend themselves to roll-to-roll fabrication, and impart flexibility to the products. These large structures will have diverse architectures, hybrid materials, and small features; their mechanical behavior during manufacturing and use poses significant challenges to the creation of the new technologies. This paper describes ongoing work in the emerging field of research - the mechanics of macroelectronics, with emphasis on the mechanical behavior at the scale of individual features, and over a long time.     

Preface

<正>Micromechanics aims mainly at establishing the quantitative relation between the macroscopic mechanical behavior and the microstructure of heterogeneous materials.It provides an efficient tool for understanding the deformations and strength of materials,and for the design of new materials as well.The basic idea of micromechanics dates back to some pioneer works of continuum mechanics,in which a matter with     

NANOSCALE PROCESS ENGINEERING

The research of nanoscale process engineering (NPE) is based on the interdisciplinary nature of nanoscale science and technology. It mainly deals with transformation of materials and energy into nanostructured materials and nanodevices, and synergizes the multidisciplinary convergence between materials science and technology, biotechnology, and information technology. The core technologies of NPE concern all aspects of nanodevice construction and operation, such as manufacture of nanomaterials “by design“, concepts and design of nanoarchitectures, and manufacture and control of customizable nanodevices. Two main targets of NPE at present are focused on nanoscale manufacture and concept design of nanodevices. The research progress of nanoscale manufacturing processes focused on creating nanostructures and assembling them into nanosystems and larger scale architectures has built the interdiscipline of NPE. The concepts and design of smart, multi-functional, environmentally compatible and customizable nanodevice prototypes built from the nanostructured systems of nanocrystalline, nanoporous and microemulsion systems are most challenging tasks of NPE. The development of NPE may also impel us to consider the curriculum and educational reform of chemical engineering in universities.     

Assessing mixing characteristics of particle-mixing and granulation devices

The mixing of particulates such as powders is an important process in many industries including pharmaceuticals, plastics, household products （such as detergents） and food processing. The quality of products depends on the degree of mixing of their constituent materials which in turn depends on both geometric design and operating conditions. Unfortunately, due to lack of understanding of the interaction between mixer geometry and the granular material, limited progress has been made in optimizing mixer design. The discrete element method （DEM） is a computational technique that allows particle systems to be simulated and mixing to be predicted. Simulation is an effective way of acquiring information on the performance of different mixers that is difficult and/or expensive to obtain using traditional experimental approaches. Here we demonstrate how DEM can be used to unravel flow dynamics and assess mixing in several different types of devices. These devices used for mixing and/or granulation of particulates, are classified broadly as gravity controlled, bladed and high shear. We also explore the role of particle shape in mixing performance and use DEM to test whether Froude number scaling is suitable for predicting scale performance of rotating mixers.     

PERSPECTIVES IN MECHANICS OF HETEROGENEOUS SOLIDS

The Microand Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives,trends,and directions in mechanics of heterogeneous materials in January 2010.The international journal,Acta Mechanica Solida Sinica,is devoted to all fields of solid mechanics and relevant disciplines in science,technology,and engineering,with a balanced coverage on analytical,experimental,numerical and applied investigations.On the occasion of the 30 th anniversary of Acta Mechanica Solida Sinica,its editor-in-chief,Professor Q.S.Zheng invited some of the forum participants to review the state-of-the-art of mechanics of heterogeneous solids,with a particular emphasis on the recent research development results of Chinese scientists.Their reviews are organized into five research areas as reported in different sections of this paper.§I firstly brings in focus on microand nano-mechanics,with regards to several selective topics,including multiscale coupled models and computational methods,nanocrystal superlattices,surface effects,micromechanical damage mechanics,and microstructural evolution of metals and shape memory alloys.§II shows discussions on multifield coupled mechanical phenomena,e.g.,multi-fields actuations of liquid crystal polymer networks,mechanical behavior of materials under radiations,and micromechanics of heterogeneous materials.In §III,we mainly address the multiscale mechanics of biological nanocomposites,biological adhesive surface mechanics,wetting and dewetting phenomena on microstructured solid surfaces.The phononic crystals and manipulation of elastic waves were elaborated in §IV.Finally,we conclude with a series of perspectives on solid mechanics.This review will set a primary goal of future science research and engineering application on solid mechanics with the effort of social and economic development.     

Handbook of Fluidization,Mooson Kwauk,Hongzhong Li （Eds.）.

Fluidization is an important process technology and is ubiquitously present in the process industry. The phenomena of fluidization also represent one of the most fascinating fluid-particle interactive behaviors in nature that are manifested by complex, intertwining science and engineering principles. Even though it is a centuries old practice, pursuit of the fundamental understanding of fluidization has its origins in the 1940s. Since the 1960s, fluidization has been a vibrant field for fluid mechanics, particle mechanics, as well as modeling and computation. From the historical perspective, Professor Mooson Kwauk and Professor Richard Wilhelm＇s 1948 article ＂Fluidization of Solid Particles,＂ is proved to be a pioneering work that sets a stage for subsequent fundamental studies in the characteristics of fluidization. As the field has evolved over the last six decades, Professor Kwauk has been a leader of fluidization research in China and the world,     

DETERMINATION OF INTERNAL STRAIN IN 3-D BRAIDED COMPOSITES USING OPTIC FIBER STRAIN SENSORS

A reliable understanding of the properties of 3-D braided composites is of primary importance for proper utilization of these materials. A new method is introduced to study the mechanical performance of braided composite materials using embedded optic fiber sensors. Experimental research is performed to devise a method of incorporating optic fibers into a 3-D braided composite structure. The efficacy of this new testing method is evaluated on two counts. First, the optical performance of optic fibers is studied before and after incorporated into 3-D braided composites, as well as after completion of the manufacturing process for 3-D braided composites, to validate the ability of the optic fiber to survive the manufacturing process. On the other hand, the influence of incorporated optic fiber on the original braided composite is also researched by tension and compression experiments. Second, two kinds of optic fiber sensors are co-embedded into 3-D braided composites to evaluate their respective ability     

GIBBS-APPELL’S EQUATIONS OF VARIABLE MASS NONLINEAR NONHOLONOMIC MECHANICAL SYSTEMS

In this paper,the Gibbs-Appell’s equations of motion are extended to the most generalvariable mass nonholonomic mechanical systems.Then the Gibbs-Appell’s equations ofmotion in terms of generalized coordinates or quasi-coordinates and an integral variationalprinciple of variable mass nonlinear nonholonomic mechanical systems are obtained.Finally,an example is given.     

疲劳热像法研究综述

能量方法是疲劳研究的重要方法, 新兴的红外热像技术则是实现这一方法的重要手段. 红外热像法作为一种无损、实时及非接触的测试技术, 已被广泛地应用于疲劳研究中. 近年来, 提出了一些用于快速确定材料及构件疲劳极限的热像法, 并得到了很好地开发与推广. 文中介绍了疲劳热像法的兴起、发展与深入研究, 讨论了该领域出现的主要问题及当前的研究热点, 并展望了疲劳热像法的研究前景.     

The role of mechanics in biological and biologically inspired materials

In the development of new materials, researchers have recently turned to nature for inspiration and assistance. A special emphasis has been placed on understanding the development of biological materials from the traditional correlation of structure to property, as well as correlating structure to functionality. The natural evolution of structure in biological materials is guided by the interaction between these materials and their environment. What is most notable about natural materials is the way in which the structure is able to adapt at a wide range of length scales. Much of the interaction that biological materials experience occurs through mechanical contact. Therefore, to develop biologically inspired materials it is necessary to quantify the mechanical behavior of and mechanical influences on biological structures with the intention of defining the natural structure-property-functionality relationship for these materials. In particular, the role mechanics has assumed in understanding biological materials, and the biologically inspired materials developed from this knowledge, will be clarified. The following will serve to elucidate on this role: the helical structure of fibrous tissue, the multi-scale structure of wood, and the biologically inspired optimal structure of functionally graded materials.     

石墨烯力学性能研究进展

石墨烯是近年来发现的由单层碳原子通过共价键结合而成的具有规则六方对称的理想二维晶体, 是继富勒烯和碳纳米管之后的又一种新型低维碳材料. 由于具有非凡的电学、热学和力学性能以及广阔的应用前景, 石墨烯被认为是具有战略意义的新材料, 近年来迅速成为材料科学和凝聚态物理等领域最为活跃的研究前沿. 本文简要介绍了研究石墨烯力学性能的实验测试、数值模拟和理论分析方法, 重点综述了石墨烯力学性能的最新研究进展, 主要包括二维石墨烯的不平整性和稳定性, 石墨烯的杨氏模量、强度等基本力学性能参数的预测, 石墨烯力学性能的温度相关性和应变率相关性、原子尺度缺陷和掺杂等对力学性能的影响以及石墨烯在纳米增强复合材料和微纳电子器件等领域的应用, 最后对石墨烯材料与结构的力学研究进行了展望.      

二维材料实验力学综述

以石墨烯为代表的二维材料因其原子级厚度、独特物理性质,成为近年来物理、化学、材料交叉学科的研究热点,在合成制备、结构表征、应用开发等方面的研究工作表明其在微纳机电系统、光电器件与功能复合材料领域有广泛且重要的应用前景。然而,由于二维材料结构与尺度的独特性,在其基本物性的理解方面仍存在许多未解决的问题,尤其是力学性能的表征,面临着诸多挑战。本文综述了二维材料本征力学性质和界面力学行为的微纳测试与表征技术的最新进展,例如纳米压痕技术、微孔鼓泡法等,并详细探讨了影响二维材料力学性能及行为的主要因素,分析了其微观尺度下的作用机制,以期通过物理或化学手段实现力学性能的调控。     

THE REASONABLE DESIGN OF BEAM SECTION

本文针对梁的截面设计,展示了随时代变迁其发展历程,并结合工艺与材料讨论了梁截面设计思路,可为材料力学教师与学生全面认识与理解弯曲梁的合理设计提供课堂教学补充材料。     

数据驱动梯度结构材料弹塑性本构

梯度结构材料因其优异的力学性能被广泛应用于工程结构中。本文整合塑性理论和人工神经网络技术,发展了一种构建梯度结构材料弹塑性本构模型的新方法。该方法基于梯度结构材料不同位置的微结构,构建不同代表性体积单元,进而生成应力应变数据,应用生成的数据训练人工神经网络,建立基于神经网络的材料本构模型。应用该方法,本文开展了针对实际工程结构件的计算,算例结果表明,该方法可快速计算梯度功能复合材料在循环载荷反向载荷状态下的宏观响应,且较为准确。该方法为模拟含复杂梯度结构材料的结构件弹塑性力学响应提供了新的工具。     

利用摩擦纳米发电机的流体能量俘获研究新进展

环境中的流体 (包括气体和液体) 动能是十分丰富且重要的清洁能源之一, 流体能量可通过不同的能量俘获技术 (电磁发电技术、压电能量俘获技术) 被转化为电能并供人们使用. 自2012年王中林研究团队发明摩擦纳米发电机 (triboelectric nanogenerator, TENG) 以来, TENG已成为了最重要的能量, 俘获技术之一, 并应用于流体能量俘获研究中. 论文综述了当前用于流体能量俘获的摩擦纳米发电机 (fluidic energy harvesting TENG, FEH-TENG) 的研究现状. 介绍了 FEH-TENG 中摩擦电材料之间的电荷转移原理以及基本的工作模式. 在气流动能俘获方面, 流致振动 (如涡激振动、驰振、颤振和尾流驰振等)是一种有效的将流体动力转化为机械能的物理机制, 基于该机制, 总结了FEH-TENG在风能和流致振动能量俘获中的研究进展以及各类能量俘获结构. 液体动能俘获方面总结了 FEH-TENG 在波浪和雨滴能量俘获中的研究进展. 介绍了基于 FEH-TENG的混合能量俘获系统和摩擦电材料优化在提升FEH-TENG流体能量俘获效率方面的研究. 接着介绍了FEH-TENG在不同领域中的应用. 最后讨论了目前 FEH-TENG 在流体能量俘获中存在的问题并提出了一些展望. 论文工作有助于推动FEH-TENG在流体能量俘获领域的发展以及促进相关研究人员对该领域的认识.      

STRUCTURE AND THERMODYNAMICS OF GRANULAR MATERIALS

颗粒介质由大量离散的粗颗粒聚集而成,如自然界中的粗砂和碎屑堆积体等. 在工程实践中,人们依据经验和实验数据建立了许多模型,虽然可以满意地描述某些力学现象,但是对颗粒介质力学性质全貌的认识以及颗粒介质物理本质的理解仍远远不够. 颗粒介质长程无序、短程有序的结构和复杂的能量转化过程,注定了其独特的力学性质. 该文综述了颗粒介质结构探测和表征技术、热力学理论和固态-流态转变方面的新进展,特别介绍了清华大学近5 年来开展的颗粒介质结构模型化方法和双颗粒温度热力学理论. 最后,提出了开展结构分析-热力学理论的联合研究思路,以期更加深入认识颗粒介质的力学特性,探究颗粒介质的热力学根源,改善现有唯象研究现状.     

电流变液和电流变效应

电流变液是一种极有发展前景的新颖材料，通常由不导电的母液和均匀散布在其中的电介质微粒组成。对于外加电场的变化，它的力学性能可以作出迅速的响应，因而在工业上极具应用前景。本文将就电流变液的研究进行综述，涉及的内容有：电流变效应的机理、电流变液材料及其力学性能、应用和展望．