自然材料微结构的几种特征

自然材料微结构是仿生机械结构设计的灵感来源.利用激光扫描共聚焦显微镜分析了鸭子下层绒毛、水稻叶毛、松针维管束鞘、水稻侧根和松针的微结构;用扫描电镜分析了黄瓜外表皮、仙人掌表皮组织、水稻叶脉、蚊子复眼、仙人掌组织、鹌鹑蛋蛋壳、水稻根和贝壳的微结构．结合前人对其它自然材料微结构的研究,总结了自然材料的结构特征,典型微结构特征有分形结构、分级结构、多尺度结构、多孔结构、梯度结构和整合结构;并且讨论了典型生物微结构原型在仿生结构设计方面的应用．分析了自然材料微结构特征的一般性特征,即对称性和自相似性．     

通论的性能.结构和工艺：—拾贝与贝雕

本文从材料学方法论角度，对材料的性能、结构和工艺，进行普遍的讨论，并外延到广泛的物、人和事。全文分五节。第一节释题，解释题中主要概念，第二节性能，在简明地介绍材料性能的概念和分析方法后，通论了人、事、物中与性能等价的概念；第三节结构，给出材料结构及结构的普遍定义，介绍各种表述方法和稳定性；第四节工艺，讨论了生产工艺的目的，标准和稳定，自然过程的内涵，因缘、始终．原理，力学分析和结构，第五节结语，给     

科学家发现三维分层材料结构分析的方法

有关晶体材料、无定形固体、液体或气体材料的结构分析,已有一些非常成熟的方法,但对在不同长度尺度上分别具有有序和无序结构的三维分层材料,却没有较好的结构分析方法。 最新一期《自然》杂志报道,科学家开发出一种用电子显微镜直接进行结构分析的新的通用方法,该     

基于掺杂聚苯胺的核壳型电磁屏蔽/吸波复合材料研究进展EI北大核心CSCD

掺杂聚苯胺(PANI)具有合成方法简单、电导率可调、质量轻、价格低廉、性能稳定等优点,使其成为一种性能优良的本征型电导高分子。为实现日益提高的高性能电磁屏蔽/吸波材料的应用要求,需要将掺杂PANI和其他材料复合使用。核壳结构材料整合了核与壳材料的优点,通过改变核和壳的化学组成、组分和形貌,可以调控材料的性能,拓展其应用范围。文中回顾了近5年来,尤其是近3年来掺杂PANI用于核壳型电磁屏蔽/吸波材料的一系列研究工作。从材料的制备、结构、性能、屏蔽/吸波机理等方面进行了阐述,并对其发展前景进行了展望。     

仿生结构材料的研究进展

综述了贝壳珍珠层、蛛丝结构、毛竹外密内疏结构、骨骼哑铃型结构、植物的根部网状结构以及木材的年轮结构等天然生物材料的结构特征及其相应的仿生材料近年来的研究进展；展望了结构仿生材料的前景，认为应对现有生物体的结构特征与其性能的相关性进行进一步的研究，并对已经解析的结构从不同的角度构筑模型，在实际应用中寻找模型和仿生材料设计的结合点，以推动仿生材料学的发展．     

镁

焦点 由于镁合金添加材料需求向好，尽管结构材料方面的需求4年来负增长，但日本2007年镁的总需求还是达到了47435t，比2006年增长0．9％，刷新了历史记录。     

高密度硬质聚氨酯泡沫塑料的断裂特性

制备不同密度的硬质泡沫聚氨酯塑料,实验研究了材料的拉伸和冲击性能。断口的扫描电镜现察显示,材料的断裂基本上属于脆性断裂,但局部存在明显的塑性形变,这是与材料的有机大分子的特殊结构相关。材料的断裂原因在于材料中相邻泡体互通构成的结构缺陷．根据断裂力学的一般原理。确定了材料断裂韧性的预测的可行方法。并得到实验结果的验证。     

集成化MEMS工艺设计技术的研究

针对目前MEMS研究领域中普遍存在的器件设计与加工工艺脱节的问题，提出了一种集成化的MEMS工艺设计技术。即在器件设计的过程中充分考虑加工工艺的特点和制约，提高器件的工艺设计能力和效率．这种工艺设计方法以结构材料、反应材料、工艺设备和环境限制的数据库为基础，从工艺过程为结构材料和反应物之间的物理或化学反应的角度出发，提炼出了工艺设计规则；在设计过程中，结合版图尺寸和具体的工艺参数，对工艺过程中器件结构二维断面上的所有结构材料的状态和图形进行计算和记录，并以此信息为依据结合设计规则判断工艺流程的合理性，并把相应的工艺信息、材料信息等代入器件的结构分析中去，实现MEMS器件的集成化工艺和结构设计．最后三维可视化设计工具IMEE1．0实现了集成化的设计技术，并通过对一个结构比较复杂的气体传感器进行设计和制作。验证了这种集成化工艺设计技术的可行性和实用性．     

人、才、材的命运

从系统的内因(结构)和外因(环境)浅谈人、人才和材料的命运.采用静态的概念分析人、人才和材料,并讨论命、运和命运;采用动态的反馈分析,提出质变的新反馈,并示例地简介材料中的耗散结构.从哲学角度总结和强调社会系统和自然系统的相似性.     

物理所石墨烯摩尔超晶格研究取得系列进展

正最近,中国科学院物理研究所/北京凝聚态物理国家实验室(筹)纳米物理与器件实验室在《自然材料》、《自然纳米技术》、《自然物理》、《自然通讯》刊登了系列研究成果。针对石墨烯/氮化硼异质结构,他们系统研究了氮化硼基底调制下的摩尔超晶格以及相关物理现象,为石墨烯能带及电子学性质调控提供了新思路。石墨烯/氮化硼异质结构近两年来在国     

Kirigami-Design-Enabled Hydrogel Multimorphs with Application as a Multistate Switch

Morphing materials have promising applications in soft robots, intelligent devices, and so forth. Among the various design strategies, kirigami structures are recognized as a powerful tool to obtain sophisticated 3D configurations and unprecedented properties from planar designs on common materials. Here, some kirigami designs are demonstrated for programmable, multistable 3D configurations from composite hydrogel sheets. Via photolithographic polymerization, perforated composite hydrogel sheets are fabricated, in which soft and active hydrogel strips are patterned in stiff and passive hydrogel frames. When immersed in water, the gel strips buckle out of plane due to swelling mismatch. In the kirigami structures, the geometric continuity is disrupted by the introduction of cutouts, and thus the degrees of deformation freedom increases remarkably. Multiple configurations are obtained in a single composite hydrogel by controlling the buckling direction of each strip. Multitier configurations are also obtained by using a hierarchically designed kirigami structure. A multicontact switch of an electric circuit is designed by harnessing the multitier gel configurations. Furthermore, a rotation mode is realized by introducing chirality in the kirigami design. The versatile design of the kirigami structure for programmable deformations should be applicable for other intelligent materials toward promising applications in biomedical devices and flexible electronics.     

聚合物基电磁屏蔽复合材料的结构设计与性能研究进展

对近年来关于聚合物基电磁屏蔽材料的报道进行了综述.重点总结分析了不同结构(如多孔结构、隔离结构和分层结构)及其他特殊结构聚合物基电磁屏蔽材料的屏蔽效能和屏蔽机制.与均匀分布聚合物基复合材料相比,通过结构设计使填料富集,再取向并连通从而形成高效导电网络,不仅能减少填料用量,且能有效提高复合材料的电磁屏蔽性能.最后,提出了...     

储能陶粒填充石膏材料中颗粒分布分形及其对导热性能的影响

应用分形理论考察5种储能陶粒样品的粒度分布分形特征,结合灰色关联分析方法研究储能陶粒的粒度分布分形维对石膏板导热系数的影响。结果表明:各储能陶粒样品的体积累积频率和粒径与最大粒径比值的双对数值呈线形关系,相关系数均在0.95～0.98之间,强的相关表明各储能陶粒样品的粒度分布的分形结构是客观的;而且,随着温度的升高,粒度分布分形维对导热系数的影响逐渐减弱。     

石墨烯对不同形貌钴酸镍结构和电化学性能的影响

石墨烯由于其独特的空间结构和异质性,对金属氧化物的空间结构和结晶性具有非常明显的影响。目前关于石墨烯对钴酸镍(NiCo_2O_4)晶体结构和微观形貌影响的研究较少。通过改变沉淀剂体系,并用十二烷基磺酸钠(SDBS)作为表面活性剂分散石墨烯,用水热反应和煅烧法生成了一维和二维结构的NiCo_2O_4晶体和石墨烯的复合材料。利用SEM、TEM、XRD和氮气吸脱附测试对所制得的复合材料进行微观结构和形貌进行表征,采用恒流充放电、循环伏安和交流阻抗法对复合材料的电化学性能进行了研究。结果表明:石墨烯含量的增加会导致NiCo_2O_4的结晶度下降,但会提高晶体材料的比表面积,对孔隙结构的影响非常明显;石墨烯还能进一步改善复合材料的内阻,但是对电容值的贡献随石墨烯含量的增加先上升后下降。     

Fabrication of porous bioceramics with porosity gradients similar to the bimodal structure of cortical and cancellous bone

The aim of this study was to fabricate porous implant materials with graded pore structures similar to the bimodal structure of cortical and cancellous bone. Porous hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramics with interconnected porosity and controlled pore sizes required to simulate natural bone tissue morphology were fabricated by a novel technique of vacuum impregnation of reticulated polymeric foams with ceramic slip. Functionally gradient materials (FGMs) with porosity gradients were made by joining different pore per inch (ppi) foams together by either stitching or pressfitting to form templates. Post production, no defects could be seen at the interface between the two different porosity sections. The macropore sizes of the HA/TCP bioceramics were larger than 100 μm which is appropriate for bone ingrowth. A sample with a graded porous structure which is close to the human bone morphology was also developed. The two component structures were conspicuously different but joined together firmly. Four point bend testing of FGM samples showed them to have similar mechanical properties to homogeneous ceramics based on foam templates with uniform pore sizes, with no evidence of interfacial weakness. Many potential biomedical applications could be developed utilising graded porous structures. The ease of processing will make it possible to fabricate a range of complex shapes for different applications.     

Gravity wave interaction with porous structures in two-layer fluid

Oblique wave interaction with rectangular porous structures of various configurations in two-layer fluid are analyzed in finite water depth. Wave characteristics within the porous structure are analyzed based on plane wave approximation. Oblique wave scattering by a porous structure of finite width and wave trapping by a porous structure near a wall are studied under small amplitude wave theory. The effectiveness of three types of porous structures—a semi-infinite porous structure, a finite porous structure backed by a rigid wall, and a porous structure with perforated front and rigid back walls—in reflecting and dissipating wave energy are analyzed. The reflection and transmission coefficients for waves in surface and internal modes and the hydrodynamic forces on porous structures of the aforementioned configurations are computed for various physical parameters in two-layer fluid. The eigenfunction expansion method is used to deal with waves past the porous structure in two-layer fluid assuming the associated eigenvalues are distinct. An alternate procedure based on the Green’s function technique is highlighted to deal with cases where the roots of the dispersion relation in the porous medium coalesce. Long wave equations are derived and the dispersion relation is compared with that derived based on small amplitude wave theory. The present study will be of significant importance in the design of various types of coastal structures used in the marine environment for the reflection and dissipation of wave energy.     

利用木材介孔结构制备新型复合材料研究进展

综述了近年来关于木材多孔结构的新概念以及利用木材多孔结构制备新型复合材料和功能材料的新方法、新技术．重点介绍了陶瓷化木材、金属化木材的制备和应用以及以木材为多孔模板的新材料的合成。利用木材独特的多孔结构和介孔结构，设计、制备结构和功能独特的新材料是仿生材料科学和介孔材料科学一个非常值得关注的研究领域。     

抗动能多功能复合材料结构模型试验研究

根据超高速碰撞破坏原理，对抗动能多功能复合材料的结构模型进行了试验研究，并设计了数种结构模型。实验结果表明，所提出的陶瓷基复合材料迎击面加固防护层，多孔复合基体缓冲层和Kevlar/织物增强环氧树脂结构层等试验模型具有良好的抗超高速撞击功能。     

Dynamic behaviour of high strength steel parts developed through laser assisted direct metal deposition

High strength steel alloys are good candidates for many engineering applications particularly those involving high strains and impact loads. Such applications in energy absorption devices require materials that can sustain dynamic loading and remain strong under demanding conditions. But the processing cost of these alloys has been a prohibitive factor, thus re-enforcing the research on porous and cellular structures made of stainless steels. Direct metal deposition (DMD) is a process which employs the power of a CO₂ laser to melt and deposit metallic powders onto steel substrates. Such structures offer advantages of creating novel configurations only by computer control of laser “tool path”. This research investigates the mechanical behaviour of solid and porous parts with prismatic cavities under quasi-static and dynamic compressive loading. Apart from two main deficiencies of relatively large variations of properties among the test specimen and sufficiently low modulus of elasticity, the stress strain behaviour is very close to the commercial grades of stainless steel produced by rolling and forming. The energy absorption behaviour of porous specimen is also very encouraging and renders DMD as a suitable process for manufacturing of customized sandwich and graded structures that can be used as a substitution for many engineering applications such as monolithic compression plates and explosion shields.