The quest for stiff,strong and tough hybrid materials: an exhaustive exploration

How to arrange soft materials with strong but brittle reinforcements to achieve attractive combinations of stiffness, strength and toughness is an ongoing and fascinating question in engineering and biological materials science. Recent advances in topology optimization and bioinspiration have brought interesting answers to this question, but they provide only small windows into the vast design space associated with this problem. Here, we take a more global approach in which we assess the mechanical performance of thousands of possible microstructures. This exhaustive exploration gives a global picture of structure–property relationships and guarantees that global optima can be found. Landscapes of optimum solutions for different combinations of desired properties can also be created, revealing the robustness of each of the solutions. Interestingly, while some of the major hybrid designs used in engineering are absent from the set of solutions, the microstructures emerging from this process are reminiscent of materials, such as bone, nacre or spider silk.     

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.     

天然和仿生柔性生物结构的设计

自然界中生物材料表现出的力学性能与其结构设计形式紧密相关。柔性生物材料多为多级结构设计,其独特的功能梯度特征使其具备优异的变形能力及良好的断裂韧性。本文借鉴工程结构设计基本单元的思想提出柔性结构仿生元素理念,根据几何形态将结构仿生元素分为：线元素、梁元素、柱元素、板壳元素、薄膜元素及组合元素。根据系统论的观点建立仿生柔性结构设计体系,归纳总结出柔性仿生结构的设计准则,并基于鱼鳞梯度结构设计新型仿生功能梯度板。通过有限元的方法对功能梯度板归一化自然频率进行分析。结果表明,类鱼鳞功能梯度板具有柔韧性及刚度软化特性。阐述了仿生柔性结构的设计方法,包括模仿设计、组合设计及选择匹配设计。     

天然铠甲高效防护的材料学机理

总结了天然铠甲材料的三种共性组织结构特征及其内在强韧化机理,归纳出三种典型的生物力学效应,包括梯度结构取向效应、原位结构再取向效应和多级\"缝合\"界面效应,并提出了相应的仿生材料结构优化设计原则.生物力学理论的完善和多种仿生结构的综合应用,有利于使用新型仿生材料更好地解决实际工程问题.     

聚乳酸接枝多糖类生物仿生材料的研究进展

聚乳酸与多糖都是生物可降解、生物相容性材料,将聚乳酸的力学性能优越性和多糖的生物学优越性能综合利用起来,设计生物仿生材料是一种制备生物医用材料的新手段。文中综合讨论了聚乳酸与多糖接枝改性的最新研究进展,同时对于这类生物仿生材料目前存在的问题以及前景进行了评估。