不同取向贝壳材料力学性能的压痕法研究

天然生物材料的组织结构特征及其与性能间的关系研究对于材料的仿生设计有重要意义.利用压痕法压研究了贝壳材料的硬度,断裂韧性及脆性指标,并结合SEM技术研究了贝壳珍珠层压痕形貌,探讨了珍珠层的增韧机制.结果表明,无论是珍珠层和还是柱状晶生长纹对其性能影响较小,珍珠层在平行于片层方向上与垂直于片层方向的性能差别较大,珍珠层明显的各向异性主要来自于其独特的组织特征.珍珠层其成分和独特的微观结构特点决定了其在应力场中是一种能量耗散结构,裂纹在扩展过程中,裂纹偏转,有机物桥联,纤维拔出等多种增韧机制在协同作用于材料韧性.     

高韧性复相陶瓷材料的仿生结构设计、制备与力学性能

从天然生物材料 (竹、木、贝壳等 )结构出发 ,提出了高韧性复相陶瓷材料仿生结构设计新思路及设计的基本要点 .针对仿贝壳珍珠层结构特征 ,采用轧膜或流延成型工艺 ,成功制备出仿贝壳珍珠层结构特征的Si3 N4 /BN层状陶瓷材料 .通过对该材料的结构参数和几何参数进行优化设计 ,可获得优异的力学性能 :断裂韧性在 2 0～ 2 8MPa·m1/ 2 ,断裂功高于 40 0 0J/m2 ,同时抗弯强度可保持在 5 0 0～ 70 0MPa .并分析了该材料具有高韧性的原因 ,提出了仿生结构陶瓷材料的增韧机制     

珍珠母堆垛微结构的力学性能和热稳定性

一直以来,软体动物贝壳内的珍珠母因为其由文石片和片间有机基质薄层堆垛而成的微结构及其卓越的力学行为而广受关注,但对贝壳珍珠母的多级结构,尤其是其中的两级有机基质结构的力学功能研究甚少.本文通过机械载荷和温度载荷组合来研究皱纹盘鲍（Haliotis Discus Hannai）贝壳内的珍珠母的结构和力学特性关联.发现文石片层间的有机基质的热解有效降低了珍珠母堆垛微结构的强度和韧性,并在250℃时使珍珠母的层叠堆垛结构完全崩溃,此时有机基质的热解量约为1.7wt%,仅为有机基质总量的40%.而力学性能试验比较发现,珍珠母堆垛微结构的热稳定远低于其基本组成单元——文石片纳米复合结构.另外,尽管有机基质薄层的黏着作用对珍珠母的力学性能具有积极意义,但珍珠母微结构本身的逐层交错堆垛设计机制是影响其刚度的决定性因素.     

珍珠层中的蛋白质及其与碳酸钙相互作用研究进展

近年来对珍珠层中蛋白质及蛋白质对碳酸钙结晶控制作用的研究得出珍珠层中含各种各样的功能蛋白质，不同种类动物形成的珍珠层中所含的主要蛋白质种类不同，它们各自独有自己的结构和功能，蛋白质对珍珠层中无机相的成核、结晶、形貌等的控制作用明显存在，但是，目前体外的仿生矿化实验不能复制珍珠层中无机相的形貌，这种控制作用的详细机理仍不清楚，人们对其认识还处于初步的阶段。     

仿生材料设计与制备的研究进展

自然界中一些生物体的优异结构和特性给人类在不断制造和更新新型材料的过程中带来灵感和启发．根据这些生物体的优秀特征综述仿生材料的主要设计思想和方法，重点分析目前一些典型仿生材料如仿生复合材料、仿生陶瓷材料、仿生纳米材料和仿生涂层材料等设计和制备研究的新进展和存在的困难，并提出一些新的材料设计思想方法和制备的模型，对仿生材料的设计和研究等均具有指导意义，最后则展望了仿生材料的发展前景．     

A general strategy for nanocrystal synthesis

New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Organometallic and other organic solution phase synthetic routes have enabled the synthesis of functional inorganic quantum dots or nanocrystals. These nanomaterials form the building blocks for new bottom-up approaches to materials assembly for a range of uses; such materials also receive attention because of their intrinsic size-dependent properties and resulting applications. Here we report a unified approach to the synthesis of a large variety of nanocrystals with different chemistries and properties and with low dispersity; these include noble metal, magnetic/dielectric, semiconducting, rare-earth fluorescent, biomedical, organic optoelectronic semiconducting and conducting polymer nanoparticles. This strategy is based on a general phase transfer and separation mechanism occurring at the interfaces of the liquid, solid and solution phases present during the synthesis. We believe our methodology provides a simple and convenient route to a variety of building blocks for assembling materials with novel structure and function in nanotechnology.     

石墨烯/聚合物纳米复合材料研究进展

 石墨烯是由单层碳原子通过共价键结合形成的二维片层状结构,是一种新型碳类纳米材料,具有优异的力学、电学和热学等性能,被认为是一种非常有前景的材料,近年来广泛用于改性各种聚合物。本文回顾了石墨烯/聚合物纳米复合材料的制备方法、性能和应用现状;综述了石墨烯/聚合物纳米复合材料的强度、刚度、韧性、电学和热学等性能的研究进展。主要内容包括石墨烯改性聚合物常见的3种制备方法(溶液共混、熔融共混和原位聚合)及其对石墨烯在聚合物基体中分散性的影响,石墨烯/聚合物纳米复合材料力学性能变化规律与作用机理,石墨烯微观结构等因素对材料热学性能以及导电阈值的影响等;讨论了石墨烯/聚合物纳米复合材料的潜在应用和面临的挑战和机遇,并展望了其低成本产业化的发展前景。     

复相陶瓷材料力学性能的仿真预测

建立了预测复相陶瓷力学性能的回归分析模型和人工神经网络模型，预测值民试验结果较为相符，模型可加快新材料的开发过程。分析了两种模型的利弊及适用条件，在实际就用中应加以选择使用。     

纳米复相陶瓷刀具性能研究

纳米复相陶瓷刀具材料的研究成功有望从根本上解决陶瓷材料的脆性问题,比起传统陶瓷刀具材料,它具有更高的抗弯强度、断裂韧性等力学性能。本文介绍纳米复相陶瓷的增韧补强机理;对研制高性能纳米陶瓷刀具材料需考虑的主要因素进行了探讨。     

Nonlinear material behaviour of spider silk yields robust webs

Natural materials are renowned for exquisite designs that optimize function, as illustrated by the elasticity of blood vessels, the toughness of bone and the protection offered by nacre. Particularly intriguing are spider silks, with studies having explored properties ranging from their protein sequence to the geometry of a web. This material system, highly adapted to meet a spider's many needs, has superior mechanical properties. In spite of much research into the molecular design underpinning the outstanding performance of silk fibres, and into the mechanical characteristics of web-like structures, it remains unknown how the mechanical characteristics of spider silk contribute to the integrity and performance of a spider web. Here we report web deformation experiments and simulations that identify the nonlinear response of silk threads to stress--involving softening at a yield point and substantial stiffening at large strain until failure--as being crucial to localize load-induced deformation and resulting in mechanically robust spider webs. Control simulations confirmed that a nonlinear stress response results in superior resistance to structural defects in the web compared to linear elastic or elastic-plastic (softening) material behaviour. We also show that under distributed loads, such as those exerted by wind, the stiff behaviour of silk under small deformation, before the yield point, is essential in maintaining the web's structural integrity. The superior performance of silk in webs is therefore not due merely to its exceptional ultimate strength and strain, but arises from the nonlinear response of silk threads to strain and their geometrical arrangement in a web.     

非均相沉淀法制备PLZT富锆陶瓷及其电击穿性能研究*

PZT95/5型铁电陶瓷的抗电击穿强度对材料的实际应用至关重要,实际应用中PZT95/5型铁电陶瓷较低的抗电击穿强度限制了它的应用;选择了PZT95/5型铁电陶瓷材料为研究对象,以提高材料的抗电击穿强度为目的,从材料的制备工艺、材料的微观结构的优化以及电击穿性能等方面,探索提高PZT95/5型铁电陶瓷抗电击穿强度的途径;采用了传统固相法、非均相沉淀法制备出了不同微观结构和性能的PZT95/5型铁电陶瓷;研究表明,采用非均相沉淀法制备了PZT95/5型铁电陶瓷,其介电、压电、铁电性能和抗电击穿性能都优于传统固相法所制备陶瓷的性能;根据弱点导致电击穿的理论,采用韦布尔分布表征和研究了所制备的PZT95/5型铁电陶瓷的电击穿性能。     

微组装纳米多层材料的力学性能研究

为研究探索新材料,采用离子束溅射沉积的方法制备了子层厚度为纳米量级的陶瓷／金属以及陶瓷／高分子多层膜。对这些纳米多层膜的结构和硬度、韧性行为进行了研究。发现纳米多层膜的硬度行为强烈地依赖于材料系统,在某些系统中出现了超硬度效应,而在某些系统则没有这一现象。纳米多层膜的韧性比单相的陶瓷材料有明显提高。硬度、韧性等力学行为与多层结构的组分比例、调制波长等参数有关。研究表明纳米多层结构是获取具有优良力学性能新材料的有效途径。     

表面活性剂制备ZTM陶瓷的作用机制

用高分子表面活性剂取代无乙醇作分散剂制备ＺＴＭ陶瓷，研究了制备方式对陶瓷烧结性和力学性能的影响。分析了不同粉体的粒度及其分布并采用Ｘ－射线衍射分析计算出各试样的氧化锆含量。研究发现分别以ＰＥＧ、无水乙醇作分散剂制备的试样具有相近的力学性能，为优化工艺、改善性能提供了条件。     

Biomimetic fabrication and characterization of an artificial rice leaf surface with anisotropic wetting

In nature,rice leaves exhibit special anisotropic sliding capabilities.Although researchers have succeeded in fabricating artificial rice leaf structures and realizing the wettability function of the leaf surface,these methods used to date are complex and do not allow the fabrication of surfaces with large area.Herein,we adopted a simple technology—two steps soft transfer to fabricate biomimetic rice leaf.The fabricated surface well reproduced the structures of the rice leaf surface and exhibited a static superhydrophobic property similar to that of the real rice leaf surface.In terms of its dynamic wettability,it clearly exhibited an anisotropic sliding property.Systematic measurements showed that the sliding angles parallel and perpendicular with the vein direction were 25° and 40°,respectively.The method was simple and reliable,without the need for expensive instruments and complex technologies,which could be used for the rapid fabrication of large-area artificial rice leaf surfaces.We believe that the artificial rice leaf surface fabricated by this method has great potential applications in biomimetic functional surfaces,microfluidics,and so on.     

DNA-based self-assembly of chiral plasmonic nanostructures with tailored optical response

Matter structured on a length scale comparable to or smaller than the wavelength of light can exhibit unusual optical properties. Particularly promising components for such materials are metal nanostructures, where structural alterations provide a straightforward means of tailoring their surface plasmon resonances and hence their interaction with light. But the top-down fabrication of plasmonic materials with controlled optical responses in the visible spectral range remains challenging, because lithographic methods are limited in resolution and in their ability to generate genuinely three-dimensional architectures. Molecular self-assembly provides an alternative bottom-up fabrication route not restricted by these limitations, and DNA- and peptide-directed assembly have proved to be viable methods for the controlled arrangement of metal nanoparticles in complex and also chiral geometries. Here we show that DNA origami enables the high-yield production of plasmonic structures that contain nanoparticles arranged in nanometre-scale helices. We find, in agreement with theoretical predictions, that the structures in solution exhibit defined circular dichroism and optical rotatory dispersion effects at visible wavelengths that originate from the collective plasmon-plasmon interactions of the nanoparticles positioned with an accuracy better than two nanometres. Circular dichroism effects in the visible part of the spectrum have been achieved by exploiting the chiral morphology of organic molecules and the plasmonic properties of nanoparticles, or even without precise control over the spatial configuration of the nanoparticles. In contrast, the optical response of our nanoparticle assemblies is rationally designed and tunable in handedness, colour and intensity-in accordance with our theoretical model.     

Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al2O3/BN dental ceramics

3Y-TZP/3wt％ Al2O3 powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12wt％ showed the best processability, but had diminished mechanical properties (such as fracture toughness and bending strength). The ceramic with a BN content of 9wt％ showed better processability than those with 3wt％ and 6wt％ BN. However, the fracture toughness was affected by the addition of 9wt％ BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In con-trast, the ceramics with a BN content of 3wt％ or 6wt％ fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.     

Structural basis for the fracture toughness of the shell of the conch Strombus gigas

Natural composite materials are renowned for their mechanical strength and toughness: despite being highly mineralized, with the organic component constituting not more than a few per cent of the composite material, the fracture toughness exceeds that of single crystals of the pure mineral by two to three orders of magnitude. The judicious placement of the organic matrix, relative to the mineral phase, and the hierarchical structural architecture extending over several distinct length scales both play crucial roles in the mechanical response of natural composites to external loads. Here we use transmission electron microscopy studies and beam bending experiments to show that the resistance of the shell of the conch Strombus gigas to catastrophic fracture can be understood quantitatively by invoking two energy-dissipating mechanisms: multiple microcracking in the outer layers at low mechanical loads, and crack bridging in the shell's tougher middle layers at higher loads. Both mechanisms are intimately associated with the so-called crossed lamellar microarchitecture of the shell, which provides for 'channel' cracking in the outer layers and uncracked structural features that bridge crack surfaces, thereby significantly increasing the work of fracture, and hence the toughness, of the material. Despite a high mineral content of about 99% (by volume) of aragonite, the shell of Strombus gigas can thus be considered a 'ceramic plywood' and can guide the biomimetic design of tough, lightweight structures.     

Effects of BN content on the mechanical properties of nanocrystalline 3Y-TZP/Al_2O_3/BN dental ceramics

3 Y-TZP/3 wt% Al_2O_3 powder was coated with varying amounts of BN using the urea and borate reaction sintering method, and then multiphase ceramics were prepared by hot pressing sintering. The micro-topography and the compositional analysis of synthesized ceramics were conducted through scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A mechanical tester was used to analyze the Vickers hardness, fracture toughness, and bending strength of the synthesized ceramics. The results showed that the ceramic with a BN content of 12 wt% showed the best processability, but had diminished mechanical properties(such as fracture toughness and bending strength). The ceramic with a BN content of 9 wt% showed better processability than those with 3 wt% and 6 wt% BN. However, the fracture toughness was affected by the addition of 9 wt% BN, making this ceramic only usable as a base material for a three-unit fixed bridge. In contrast, the ceramics with a BN content of 3 wt% or 6 wt% fulfilled the criteria for use in multi-unit restoration, but their low processability made them unsuitable for milling after sintering.     

珍珠层作为骨修复材料的研究进展简

寻找和研制理想的骨修复材料一直是生物材料研究的热点之一。珍珠层作为生物骨替代材料,其优势在于含有具有诱导成骨作用的有机成分、合适的降解性能以及与人骨组织接近的力学性能。本文综述了珍珠层的结构、无机成分、有机成分、细胞相容性和生物降解性,这些研究结果表明,珍珠层具有很好的生物相容性。同时还分析了珍珠层作为骨修复材料存在的问题,展望了珍珠层作为骨修复材料应用的前景。     

Observation of rare-earth segregation in silicon nitride ceramics at subnanometre dimensions

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, central to the design of high-performance Si3N4 ceramics, has been sought for many years. Here we show direct images of dopant atoms (La) within the nanometre-scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La for the crystalline surfaces, which is essential for forming elongated grains and a toughened microstructure. Whereas principles of micrometre-scale structural design are currently used to improve the mechanical properties of ceramics, this work represents a step towards the atomic-level structural engineering required for the next generation of ceramics.