冷冻铸造技术制备仿贝壳层状结构陶瓷复合材料研究进展

贝壳珍珠层是一种天然的层状结构复合材料,类似"砖和泥"的软硬相交替的层状分级组装结构赋予其优良的力学性能。通过对贝壳的珍珠层进行仿生研究,人们已利用不同技术如冷冻铸造技术等,制备了一系列仿生高强超韧层状复合材料,并且这些材料在航空航天、军事、民用及机械工程等领域表现出广阔的应用前景。首先介绍了贝壳珍珠层的结构性能,并对其断裂机制进行了阐述;然后综合介绍了冷冻铸造技术的发展历程、作用机理、控制因素、装置设计和总体工艺流程。在此基础上,对制备仿贝壳层状结构陶瓷复合材料的表观密度、多孔陶瓷的孔隙率进行介绍,综述了多孔陶瓷的性能、陶瓷/金属层状结构复合材料以及陶瓷/聚合物层状结构复合材料的特点和应用,最后分析和总结了在研究仿贝壳层状结构陶瓷复合材料过程中出现的问题,并对该复合材料的未来发展趋势做了一定的预测。     

中国科大利用仿生方法成功合成人工珍珠母

正贝壳珍珠母是当今世界仿生材料设计研究中的热点。中国研究人员近日在美国《科学》杂志网络版上报告说,他们参照软体动物合成天然珍珠母的策略,利用完全仿生的方法制备出组分、结构和性能均与天然类似的人工珍珠母。自然界中,生命体系通常利用能大量获取的原料不断优化其微观结构,来提升其体内硬质复合材料的力学性能。而材料仿生设计研究,便是通过学习这种独特的微观结构,并结合人工合成的物质,来获得性能远远超越常规材料的     

贝壳珍珠母增韧机理研究进展

基于国内外对贝壳材料微结构研究的实验照片与力学性能的研究成果,描述了贝壳珍珠母独特的微观结构,包括无机层与有机基质层"砖-泥"式交错层叠结构、文石层波纹表面和文石表面纳米凸起与矿物桥结构等,同时也揭示了贝壳珍珠母微结构对其韧性的增强机理。对国内力学家近年来提出的微观结构"缺陷不敏感"增韧理论进行了理论阐述。     

珍珠母及其仿生复合材料力学行为的研究进展

珍珠母是由天然文石晶片和有机基质构成的一种两相生物复合材料。其中,文石晶片通过典型交错层叠方式镶嵌在连续的有机基质中,形成高度有序的分级结构,使珍珠母呈现出远优于其组份材料的力学性能。因此,受到力学、材料学和生物学领域研究学者们的广泛关注。本文首先介绍了珍珠母材料的微结构特征及其基本变形机制和力学性能,然后分别从理论分析、数值模拟和实验制备三个角度出发综述了仿珍珠母复合材料的研究进展,重点讨论了这类仿生复合材料在变形过程中的强韧化机制,并分析了结构-性能之间的关系,最后对其可能的发展方向进行了展望。      

从钢中珠光体看脆性材料强韧化仿生结构设计

叠层复合材料是人们受自然界贝壳结构的启发而设计开发的一种新型结构材料.钢中共析珠光体具有片层状结构,其实就是一种典型的叠层复合材料.介绍了珠光体和贝壳珍珠层的微结构及其力学性能特征、脆性材料强韧化结构的设计,并综述了叠层复合材料的国内外研究现状,对新型叠层复合材料的许多不足和发展趋势提出了初步的想法.     

交叠增韧仿生复合材料的研究进展

仿生设计方法为制备结构与功能一体化材料提供了重要的思路和途径,已成为各国研究的重点,贝壳的分层结构和高强韧性能仿生制造是其中较为典型的一类,据此可开发出具有优异的防护性能和抗裂纹扩展能力的层状复合材料。对层状复合材料制备工艺、界面扩散及结合强度、增韧机制、弹道防护性能的研究现状进行了简要综述,评价和总结了目前存在的问题,并对仿生制造的应用前景进行了展望,指出应加强层状复合材料变形的理论研究,进一步拓展层状复合材料的应用领域。     

室温磁电材料的制备与性能

室温下具有磁电性能的多铁性材料是近年来研究的热点,分析了室温铁磁电单相材料和复合材料的制备方法及其性能,特别是外延生长、二次烧结和无机/有机复合技术分别对单相铁磁电薄膜、颗粒弥散型以及层状铁磁电复合材料结构与性能的影响.结果表明,通过诱导晶格变形、消除体系杂相,能获得具有强室温磁电性能的单相磁电材料.通过提高磁性颗粒在复合材料中的分散程度,可以明显增强弥散型磁电复合材料的磁电性能.将磁性和铁电材料进行层状复合,选择合适的外场耦合模式,得到了高磁电耦合系数的复合材料.     

复合装甲中吸波层对材料防弹性能的影响

冲击波对复合装甲的破坏程度和方式受到一些因素的影响。采用吸波层来减弱冲击波对材料本身的破坏程度,初步研究了冲击波破坏装甲的形式和机理,并从防止冲击波振荡叠加的角度提出一些提高复合装甲防弹性能的措施。试验结果表明,使用吸波层使复合装甲的防弹性能有了明显的提高。     

舰船用轻型复合装甲研究与应用

本文论述了轻型复合装甲在舰船上的应用现状与发展趋势,阐述了轻型复合装甲材料研制的理论指导,舰用轻型复合装甲结构的一般形式以及轻型复合装甲结构装舰的工艺方法。     

仿贝壳结构壳聚糖/绢云母复合薄膜的制备和性能

采用物理共混的简易方法制备了壳聚糖/绢云母复合薄膜。场发射扫描电镜观测的结果表明,这种薄膜具有明显的取向"砖-泥"仿贝壳结构。这种独特仿生结构的形成显著地提高了壳聚糖复合薄膜的力学性能(拉伸强度和断裂伸长率),并且保持了优异的柔软弯曲性能。同时,这种复合薄膜具有良好的透明性和电绝缘性能。     

甲虫前翅结构及其仿生研究进展

综述了近年来国内外有关甲虫前翅结构与仿生应用的研究成果及其发展前景。指出前翅是以小柱为中空层的框架式结构, 其左右前翅结合部分是一种巧妙的凹凸啮合结构; 前翅内存在着网状-小柱结构, 这是一种轻量型夹芯层状三合板结构; 小柱中的纤维与上下层中的纤维是连续的, 可有效增加叠层复合材料的抗剥离强度;一些甲虫前翅的表面具有特殊的生物结构, 从而具有一些特殊的功能, 如具有减阻、集水或显色功能。结合生命科学的最新研究成果, 提出了通过基因组技术生产仿生材料的设想。      

Research Progress of Laminated Composite Ceramic Cutting Tools

The design of the lamination structure based on bionic shell pearl layer is a successful method for toughening ceramics. Lamination with strong bonding interfaces is used to improve the mechanical property and low fracture toughness of ceramic cutting tools. Based on the idea of demand–design–preparation–analysis–failure, the development and research progress of laminated ceramic tools are reviewed herein. The research status of design, interlayer diffusion reaction, residual stress, toughening mechanism, and crack propagation path of the biomimetic laminated ceramic composite tool materials is mainly introduced. The major topics of current research include the creation of material systems, the evolution of microstructure, and the assessment of macroscopic mechanical properties. The entire mechanical properties of laminated ceramic tools are significantly influenced by the multicomposition design of the ceramic material system and the optimization design of structural parameters of layer number and layer thickness ratio. However, the research on the practical cutting application of laminated ceramic tools is limited. Cutting tool wear characteristics vary between laminated and homogeneous ceramic tools. The development of useful laminated ceramic cutting tools can greatly benefit from the study on failure mechanisms of laminated ceramic tools.     

Toughening mechanisms in bioinspired multilayered materials

Outstanding mechanical properties of biological multilayered materials are strongly influenced by nanoscale features in their structure. In this study, mechanical behaviour and toughening mechanisms of abalone nacre-inspired multilayered materials are explored. In nacre''s structure, the organic matrix, pillars and the roughness of the aragonite platelets play important roles in its overall mechanical performance. A micromechanical model for multilayered biological materials is proposed to simulate their mechanical deformation and toughening mechanisms. The fundamental hypothesis of the model is the inclusion of nanoscale pillars with near theoretical strength (σ_th ~ E/30). It is also assumed that pillars and asperities confine the organic matrix to the proximity of the platelets, and, hence, increase their stiffness, since it has been previously shown that the organic matrix behaves more stiffly in the proximity of mineral platelets. The modelling results are in excellent agreement with the available experimental data for abalone nacre. The results demonstrate that the aragonite platelets, pillars and organic matrix synergistically affect the stiffness of nacre, and the pillars significantly contribute to the mechanical performance of nacre. It is also shown that the roughness induced interactions between the organic matrix and aragonite platelet, represented in the model by asperity elements, play a key role in strength and toughness of abalone nacre. The highly nonlinear behaviour of the proposed multilayered material is the result of distributed deformation in the nacre-like structure due to the existence of nano-asperities and nanopillars with near theoretical strength. Finally, tensile toughness is studied as a function of the components in the microstructure of nacre.     

层状复合陶瓷强韧化机制及其优化设计因素

层状复合是一种新型的陶瓷复合构型, 具有提高断裂韧性和强度的优异特性, 对优化陶瓷的显微结构和机械性能十分有效本文从层状复合界面结构出发, 综合评述了层状复合陶瓷的强韧化机制, 讨论基体单层强度、厚度, 界面的厚度和粘接强度等因素对断裂韧性等性能的影响, 探讨层状复合陶瓷的优化设计思路     

Microstructures of chafer cuticle and biomimetic design

Insect cuticle has high strength and high fracture-toughness. The superior material properties are closely related to the various particular microstructures in the cuticle, which has passed through natural optimization for thousands of years. In this work, a scanning electron microscope (SEM) was used for observing the various microstructures in a chafer cuticle. The observation revealed that there are several special microstructures that include helicoidal layups, round-hole-fiber arrangements and branched fibers in the cuticle. These microstructures were analyzed in order to learn more about the strength and toughness mechanisms of these microstructures. Several biomimetic composites were then designed and fabricated with special processes and moulds. Obtained biomimetic composites were tested for investigating their strength and toughness and then compared with those of conventional man-made composites. It was shown that the mechanical properties of the biomimetic composites are remarkably better than those of the corresponding conventional man-made composites.     

Biomimetic structure design — a possible approach to change the brittleness of ceramics in nature

Based on the analysis on structure of natural biomaterials, two kinds of ceramic composites with high toughness have been designed and prepared: one is fibrous monolithic Si₃N₄/BN composite imitating bamboos or trees in structure, the other is laminated Si₃N₄/BN composite imitating nacre in structure. Plastic forming methods, including extrusion and roll compaction, respectively, followed by hot-pressed sintering are used to prepare these two materials with particular structures. Both of the two composites have high values of fracture toughness and work of fracture: fracture toughness are 24 MPa m^1/2 and 28 MPa m^1/2, respectively, for fibrous monolithic and laminated Si₃N₄/BN composites, and works of fracture are both more than 4000 J/m². The load-displacement curves reveal that these two materials with biomimetic structure exhibit non-brittle feature when applied load to fracture. Through analysis on fractographs of the materials, it is revealed that high toughness comes from the synergistic toughening among multi-level toughening mechanisms in different scales: weak interfaces, whiskers and elongated grains toughening in ceramic matrix cells.     

Biological materials: Functional adaptations and bioinspired designs

Biological materials are typically multifunctional but many have evolved to optimize a chief mechanical function. These functions include impact or fracture resistance, armor and protection, sharp and cutting components, light weight for flight, or special nanomechanical/chemical extremities for reversible adhesive purposes. We illustrate these principles through examples from our own research as well as selected literature sources. We conduct this analysis connecting the structure (nano, micro, meso, and macro) to the mechanical properties important for a specific function. In particular, we address how biological systems respond and adapt to external mechanical stimuli. Biological materials can essentially be divided into mineralized and non-mineralized. In mineralized biological materials, the ceramics impart compressive strength, sharpness (cutting edges), and stiffness while the organic components impart tensile strength, toughness and ductility. Non-mineralized biological materials in general have higher tensile than compressive strength, since they are fibrous. Thus, the mineralized components operate optimally in compression and the organic components in tension. There is a trade-off between strength and toughness and the stiffness and density, with optimization. Mineralization provides load bearing capability (strength and stiffness) whereas the biopolymer constituents provide viscoelastic damping and toughness. The most important component of the nascent field of Biological Materials Science is the development of bioinspired materials and structures and understanding of the structure–property relationships across various length scales, from the macro-down to the molecular level. The most successful efforts at developing bioinspired materials that attempt to duplicate some of the outstanding properties are presented.     

金属间化合物MoSi2及其复合材料的研究和应用

金属间化合物MoSi2具有熔点高、断裂强度对温度不敏感、导电导热性能好、抗氧化等一系列的优良性质，因此作为电热元件和高温结构材料，在航空航天等高技术领域得到了广泛的应用。但是，其低温断裂韧性和高温强度较低，一般可采用不连续的颗粒、连续的晶须或纤维，也可采用固溶体合金化或第二相复合技术来提高其低温断裂韧性和高温强度。MoSi2及其复合材料因其优异性能，也可用来制备层状复合材料和梯度功能材料，还可用来制备各种耐高温保护涂层。