Fracture Mechanics Analysis Model for Functionally Graded Materials with Arbitrarily Distributed Properties

Functionally Graded Materials (FGMs) have been developed as super-resistant materials for propulsion systems and airframe of space-planes in order to decrease thermal stresses and to increase the effect of protection from heat. It has been experimentally observed that surface cracking in FGMs is the most common failure mode of a metal-ceramic FGM when it is subjected to a thermal shock. Therefore, it is very important to consider the thermally induced fracture behaviors of FGMs. In this paper, a functionally graded material strip containing an embedded or a surface crack perpendicular to its boundaries is considered. The graded region is treated as a large number of single layers, with each layer being homogeneous material. The problem is reduced to an integral equation and is solved numerically. Unlike most of the existing researches, which considered only certain assumed material distributions, the method developed in this paper can be used to investigate functionally graded materials with arbitrarily varied material properties.     

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。     

梯度热电材料的研究进展

热电材料梯度化是在保证各组分单一材料的热电性能的基础上,拓宽其应用温度范围,使各组分材料都能工作在最佳温区,以确保热电材料在一定的工作温度范围内具有较高的ZT值,保证其高的热电转换效率.介绍了热电材料的研究基础及其梯度化设计,对梯度热电材料在国内外的研究进展进行了综述并对未来的研究趋势进行了展望.     

Non-Local Theory Solution for an Anti-Plane Shear Permeable Crack in Functionally Graded Piezoelectric Materials

In this paper, the non-local theory solution of a Griffith crack in functionally graded piezoelectric materials under the anti-plane shear loading is obtained for the permeable electric boundary conditions, in which the material properties vary exponentially with coordinate parallel to the crack. The present problem can be solved by using the Fourier transform and the technique of dual integral equation, in which the unknown variable is the jump of displacement across the crack surfaces, not the dislocation density function. To solve the dual integral equations, the jump of the displacement across the crack surfaces is directly expanded in a series of Jacobi polynomials. From the solution of the present paper, it is found that no stress and electric displacement singularities are present near the crack tips. The stress fields are finite near the crack tips, thus allows us to use the maximum stress as a fracture criterion. The finite stresses and the electric displacements at the crack tips depend on the crack length, the functionally graded parameter and the lattice parameter of the materials, respectively. On the other hand, the angular variations of the strain energy density function are examined to associate their stationary value with locations of possible fracture initiation.     

Multiscale Toughening Mechanisms in Biological Materials and Bioinspired Designs

Biological materials found in Nature such as nacre and bone are well recognized as light‐weight, strong, and tough structural materials. The remarkable toughness and damage tolerance of such biological materials are conferred through hierarchical assembly of their multiscale (i.e., atomic‐ to macroscale) architectures and components. Herein, the toughening mechanisms of different organisms at multilength scales are identified and summarized: macromolecular deformation, chemical bond breakage, and biomineral crystal imperfections at the atomic scale; biopolymer fibril reconfiguration/deformation and biomineral nanoparticle/nanoplatelet/nanorod translation, and crack reorientation at the nanoscale; crack deflection and twisting by characteristic features such as tubules and lamellae at the microscale; and structure and morphology optimization at the macroscale. In addition, the actual loading conditions of the natural organisms are different, leading to energy dissipation occurring at different time scales. These toughening mechanisms are further illustrated by comparing the experimental results with computational modeling. Modeling methods at different length and time scales are reviewed. Examples of biomimetic designs that realize the multiscale toughening mechanisms in engineering materials are introduced. Indeed, there is still plenty of room mimicking the strong and tough biological designs at the multilength and time scale in Nature.     

Flourishing Bioinspired Antifogging Materials with Superwettability: Progresses and Challenges

Antifogging (AF) structure materials found in nature have great potential for enabling novel and emerging products and technologies to facilitate the daily life of human societies, attracting enormous research interests owing to their potential applications in display devices, traffics, agricultural greenhouse, food packaging, solar products, and other fields. The outstanding performance of biological AF surfaces encourages the rapid development and wide application of new AF materials. In fact, AF properties are inextricably associated with their surface superwettability. Generally, the superwettability of AF materials depends on a combination of their surface geometrical structures and surface chemical compositions. To explore their general design principles, recent progresses in the investigation of bioinspired AF materials are summarized herein. Recent developments of the mechanism, fabrication, and applications of bioinspired AF materials with superwettability are also a focus. This includes information on constructing superwetting AF materials based on designing the topographical structure and regulating the surface chemical composition. Finally, the remaining challenges and promising breakthroughs in this field are also briefly discussed.     

功能梯度材料

介绍了功能梯度材料的提出，开发流程，研究现状，对于当前功能梯度材料的设计过程，制备方法，性能评价方法和实验手段进行了详细叙述，提出了功能梯度材料应进一步发展的方向。     

Unidirectional Wetting Properties on Multi‐Bioinspired Magnetocontrollable Slippery Microcilia

Here, a smart fluid‐controlled surface is designed, via the rational integration of the unique properties of three natural examples, i.e., the unidirectional wetting behaviors of butterfly's wing, liquid‐infused “slippery” surface of the pitcher plant, and the motile microcilia of micro‐organisms. Anisotropic wettability, lubricated surfaces, and magnetoresponsive microstructures are assembled into one unified system. The as‐prepared surface covered by tilted microcilia achieves significant unidirectional droplet adhesion and sliding. Regulating by external magnet field, the directionality of ferromagnetic microcilia can be synergistically switched, which facilitates a continuous and omnidirectional‐controllable water delivery. This work opens an avenue for applications of anisotropic wetting surfaces, such as complex‐flow distribution and liquid delivery, and extend the design approach of multi‐bioinspiration integration.     

Bioinspired Interfacial Materials with Enhanced Drop Mobility: From Fundamentals to Multifunctional Applications

The development of bioinspired interfacial materials with enhanced drop mobility that mimic the innate functionalities of nature will have a significant impact on the energy, environment and global healthcare. Despite extensive progress, state of the art interfacial materials have not reached the level of maturity sufficient for industrial applications in terms of scalability, stability, and reliability. These are complicated by their operating environments and lack of facile approaches to control the local structural texture and chemical composition at multiple length scales. The recent advances in the fundamental understanding are reviewed, as well as practical applications of bioinspired interfacial materials, with an emphasis on the drop bouncing and coalescence‐induced jumping behaviors. Perspectives on how to catalyze new discoveries and to foster technological adoption to move this exciting area forward are also suggested.     

Analysis of Functionally Graded Magneto-Electro-Elastic Composites Using Hybrid/Mixed Finite Elements and Node-Wise Material Properties

A new class of hybrid/mixed finite elements, denoted "HMFEM-C", has been developed for modeling magneto-electro-elastic (MEE) materials. These elements are based on assuming independent strain-fields, electric and magnetic fields, and collocating them with the strain-fields, electric and magnetic fields derived from the primal variables (mechanical displacements, electric and magnetic potentials) at some cleverly chosen points inside each element. The newly developed elements show significantly higher accuracy than the primal elements for the electric, magnetic as well as the mechanical variables. HMFEM-C is invariant through the use of the element-fixed local orthogonal base vectors, and is stable since it is not derived from a multi-field variational principle; hence it completely avoids LBB conditions that govern the stability of hybrid/mixed elements. In this paper, node-wise material properties are used in order to better simulate the spatial material grading of the functionally graded materials (FGM). A computer code was developed, validated and used to calculate the three magnetoelectric (ME) voltage coefficients for piezoelectric-piezomagnetic (PE-PM) composites, namely, the out-of-plane, transverse and in-plane ME voltage coefficients. The effects of the piezoelectric phase volume fraction as well as the mechanical boundary conditions and loadings on the ME voltage coefficients are investigated. Also, the effects of grading functions in PE-PM composites with functionally graded layers, as well as single-layered functionally graded magneto-electro-elastic materials, on the three ME voltage coefficients are presented.     

功能梯度材料的制备与应用进展

功能梯度材料(FGM)是由日本人首先提出的一种新型复合材料,从提出后到现在已经得到了深入的研究和广泛的应用.阐述了功能梯度材料的概念及其产生背景,重点评述了功能梯度材料各种制备技术的原理和特点,以及国内外在应用方面取得的各种成果,探讨了功能梯度材料的发展方向.     

Bioinspired Synthesis of Monolithic and Layered Aerogels

Aerogels are the least dense and most porous materials known to man, with potential applications from lightweight superinsulators to smart energy materials. To date their use has been seriously hampered by their synthesis methods, which are laborious and expensive. Taking inspiration from the life cycle of the damselfly, a novel ambient pressure‐drying approach is demonstrated in which instead of employing low‐surface‐tension organic solvents to prevent pore collapse during drying, sodium bicarbonate solution is used to generate pore‐supporting carbon dioxide in situ, significantly reducing energy, time, and cost in aerogel production. The generic applicability of this readily scalable new approach is demonstrated through the production of granules, monoliths, and layered solids with a number of precursor materials.     

梯度热电材料的优化设计及研究进展

将2种不同的单体材料连接起来,制备成梯度结构热电材料(FGTM),不仅能扩大材料的应用温区,而且能极大地提高材料的热电转换效率.介绍了梯度热电材料优化设计的理论基础及方法,综述了梯度热电材料的研究进展及应用前景.     

仿生超疏水表面的发展及其应用研究进展

受自然界荷叶 “出淤泥而不染”的启发, 超疏水现象引起了研究者广泛的关注, 并成功制备了人工超疏水表面。本文对典型的仿生超疏水材料进行梳理, 并针对近期研究成果进行了综述, 对超疏水涂层的诸多制备方法作了优缺点总结和评述, 概述了超疏水涂层在自清洁、防覆冰、耐腐蚀和油水分离领域的应用研究现状, 尤其对超疏水防覆冰的机理及实现方式作了总结分析, 剖析了现阶段超疏水研究过程中面临的挑战, 展望了未来的发展趋势, 希望为超疏水涂层在工程领域的应用研究提供参考。     

Nano/Micro‐Manufacturing of Bioinspired Materials: a Review of Methods to Mimic Natural Structures

Through billions of years of evolution and natural selection, biological systems have developed strategies to achieve advantageous unification between structure and bulk properties. The discovery of these fascinating properties and phenomena has triggered increasing interest in identifying characteristics of biological materials, through modern characterization and modeling techniques. In an effort to produce better engineered materials, scientists and engineers have developed new methods and approaches to construct artificial advanced materials that resemble natural architecture and function. A brief review of typical naturally occurring materials is presented here, with a focus on chemical composition, nano‐structure, and architecture. The critical mechanisms underlying their properties are summarized, with a particular emphasis on the role of material architecture. A review of recent progress on the nano/micro‐manufacturing of bio‐inspired hybrid materials is then presented in detail. In this case, the focus is on nacre and bone‐inspired structural materials, petals and gecko foot‐inspired adhesive films, lotus and mosquito eye inspired superhydrophobic materials, brittlestar and Morpho butterfly‐inspired photonic structured coatings. Finally, some applications, current challenges and future directions with regard to manufacturing bio‐inspired hybrid materials are provided.