香螺壳体的结构特征分析

本文以我国黄渤海地区的香螺为对象,研究了其结构及组织形态特征.研究表明:香螺壳体主要由方解石构成,其次为具有正交晶系结构的文石.香螺壳体的纵截面由外层的柱状晶粒结构层,中间的交错纹片结构层和内层的柱状结构层组成.外层和中间层主要由方解石组成,内层由方解石和文石构成.显微硬度测试结果表明:香螺壳体的硬度从外层到内层是逐渐增加的,说明内层的致密度比中层和外层的高.     

Structural characterization and mechanical behavior of a bivalve shell (Saxidomus purpuratus)

The structure and mechanical behavior of Saxidomus purpuratus bivalve shell were investigated. XRD results show that the only form of calcium carbonate present in the shell is aragonite. The inner and middle layers have a cross-lamellar structure, while the outer layer has porosity and does not have tiles, but instead has ‘blocky’ regions. The hardness of middle and inner layer are close in both plane view and cross section, but the hardness of outer layer is significantly less, especially in the plane view. The compressive strengths with loading along the three orientations were established and significant differences were found. The Weibull strength at 50% of the probability of failure varies between 59 and 148 MPa and is dependent on the loading orientation and in condition of shell (dry vs. hydrated). These differences are interpreted in terms of the anisotropic structure and coarser structure of the external layer.     

香螺壳的结构和微观力学性能

测量产自黄/渤海海域的香螺贝壳的硬度和弹性模量,研究了贝壳的结构与性能之间的关系.结果表明,香螺贝壳主要由方解石和文石两种矿物镶嵌在有机质中构成,方解石结构为不均匀的柱状晶,文石结构为多级超微的交错纹状结构,其中第三级结构为10-80 nm的纳米级纤维.文石的力学性能优于方解石的性能.贝壳类复合材料的压痕效应主要源于裂纹扩展,而微观裂纹扩展与晶体类型以及晶体结构的排列方式是密切相关的.方解石裂纹形状曲折、不规则且沿着方解石层的边界扩展,抗裂纹扩展能力较差;而文石压痕周围平直清晰,裂纹沿着其二级结构界面扩展,性能较好.     

不同参数下的单、双层圆柱壳体速度场研究

研究圆柱壳体表面速度场的重构：疗法对潜艇水下辐射噪声的预报具有重要的意义。采用了分区段重构轻外壳速度场的思想，在此基础上建立无限流体中的有限长单、双层加肋圆柱壳模型，分析了壳体表面速度场随不同结构参数的变化规律，并对单、双层圆柱壳体，以及双层圆柱壳体内、外壳的振动响应性能作了一定的比较。得到了单区段壳体长度的选取、模型刚度特性以及不同频段内壳体间耦合作用等对壳体速度场的影响，为研究潜艇轻外壳速度场重构方法提供了理论依据。     

Preparation of multilayered organic-inorganic hybrid core-shell particles by stepwise surface formation

This paper introduces a stepwise formation method for micro-sized, multilayered core-shell particles comprising an inorganic core, organic inner shell, and inorganic outer shell. A silica core was coated with a polystyrene seed layer, followed by surface seed polymerization with styrene, to afford the inner shell. These particles were then coated with a silica outer shell by a surface sol-gel reaction with tetraethoxysilane. The versatility of this combined surface seed polymerization and sol-gel method is emphasized by the precise control achieved over particle diameter as well as shell thickness and count. Moreover, the organic inner shell can be readily eliminated to afford a single-core-containing micro-capsular structure.     

离心铸造Mg2Si 和Si 自生增强锌基复合材料的组织与性能

采用热模金属型工艺, 离心铸造Zn-27Al-9.8Mg-5.2Si 和Zn-27Al-6.3Mg-3.7Si 合金, 获得了内层聚集大量块状初生Mg₂Si 、少量初生Si, 中层不含初生Mg₂Si 和初生Si, 外层含有初生Mg- Si 和初生Si 的自生锌基复合材料。离心铸造Zn-27Al-3.2Mg-1.8Si 合金, 获得了不含初生Mg₂Si 和初生Si 的单层材料。考察了复合材料的组织形貌, 检测了复合材料的硬度和耐磨性, 分析了复合材料的断裂模式。结果表明: 复合材料的内层因聚集大量的初生Mg₂Si 和初生Si 具有较高的硬度和较优的耐磨性。复合材料的断裂方式为脆性断裂, 含共晶Mg₂Si 和共晶Si 的中层在断裂中比含块状初生Mg₂Si 和初生Si 的内层经历了更多的塑性变形。      

离心铸造过共晶Al-Si 合金自生表面复合材料

采用热模金属型工艺, 离心铸造过共晶Al-Si 合金, 获得了外层或外层和内层富集初晶Si, 其余部分为共晶组织构成的自生表面复合材料。分析了复合材料的形成过程, 考察了复合材料的组织、硬度和耐磨性。     

离心铸造Al-16wt%Si合金自生梯度复合材料

本文作者通过改变离心铸造的转速,获得了内层有较多初晶Si其余部分为共晶组织或初晶Si由外向内偏析的Al-16wt%Si合金自生梯度复合材料。分析了复合材料的形成过程,考察了复合材料的组织、硬度、耐磨性和物相结构。     

鲍鱼壳的结构和力学性能

以皱纹盘鲍鱼壳为对象,研究了其结构与力学性能之间的关系.研究表明,鲍鱼壳主要由方解石和文石构成,且外层为方解石,内层为文石.鲍鱼壳的力学性能随其加热温度的升高而明显降低,密度也呈现同样的变化,说明鲍鱼壳中所含有的少量有机质随着加热温度的升高而减少,致使鲍鱼的力学性能明显下降.     

Mechanical properties of laminated bamboo strips from Gigantochloa Scortechinii/polyester composites

In this study, the mechanical properties of culm fiber composites with various thicknesses from the inner through the outer layer of bamboo strips were investigated. This study utilized a specific type of bamboo species named Gigantochloa Scortechinii (Buluh Semantan), which was collected from the Bukit Larang village in Melaka, Malaysia. In these experiments, unsaturated polyester (UP) and bamboo fiber (BF) strips were prepared through the hand lay-up technique using 3 mm thick aluminum mould. The composite bamboo strips were prepared in 1.5–2.5 mm thicknesses. The weight of the inner, middle and outer bamboo parts varied from a minimum of 0.742 g to a maximum of 2.600 g. The specimens were then characterized using several techniques including tensile, flexural, hardness, and impact tests. The results indicated that the properties of the middle part of the bamboo strips improve as the bamboo strip thickness increases due to the incorporation of unsaturated polyesters. However, the hardness properties increase for the outer layer of the laminate. These findings suggest that bamboo strips, based on unsaturated polyesters, yield excellent mechanical properties and are a viable alternative to composite-based reinforcing fibers.     

Motorcyclist helmet composite outer shell characterisation and modelling

In this study a new finite element model of composite outer shell of motorcyclist helmet is proposed, by modelling each layer of the composite material that builds the laminated structure of the outer shell of the helmet. Elastic and rupture properties of the laminate are taken into account for developing the finite element (FE) model and are extracted experimentally. A coupled experimental–numerical method combined with experimental modal analysis on beam samples is used to obtain the elastic characteristics of each layer of the outer shell. The rupture properties for each layer are extracted by experimental impact tests. The FE model of the outer shell is then validated with experimental data for elastic and rupture behaviour.     

Hierarchical multiscale structure–property relationships of the red-bellied woodpecker (Melanerpes carolinus) beak

We experimentally studied beaks of the red-bellied woodpecker to elucidate the hierarchical multiscale structure–property relationships. At the macroscale, the beak comprises three structural layers: an outer rhamphotheca layer (keratin sheath), a middle foam layer and an inner bony layer. The area fraction of each layer changes along the length of the beak giving rise to a varying constitutive behaviour similar to functionally graded materials. At the microscale, the rhamphotheca comprises keratin scales that are placed in an overlapping pattern; the middle foam layer has a porous structure; and the bony layer has a big centre cavity. At the nanoscale, a wavy gap between the keratin scales similar to a suture line was evidenced in the rhamphotheca; the middle foam layer joins two dissimilar materials; and mineralized collagen fibres were revealed in the inner bony layer. The nano- and micro-indentation tests revealed that the hardness (associated with the strength, modulus and stiffness) of the rhamphotheca layer (approx. 470 MPa for nano and approx. 320 MPa for micro) was two to three times less than that of the bony layer (approx. 1200 MPa for nano and approx. 630 MPa for micro). When compared to other birds (chicken, finch and toucan), the woodpecker''s beak has more elongated keratin scales that can slide over each other thus admitting dissipation via shearing; has much less porosity in the bony layer thus strengthening the beak and focusing the stress wave; and has a wavy suture that admits local shearing at the nanoscale. The analysis of the woodpeckers'' beaks provides some understanding of biological structural materials'' mechanisms for energy absorption.     

Iridescent colors on seashells: an optical and structural investigation of Helcion pruinosus

Many animal species display exceptionally bright iridescent coloration caused by interference or diffraction from a periodic surface microstructure. Although many mollusks are colored, only few utilize such a form of structural coloration. We are not referring to the well-known pearly appearance that is due to the nacreous layer found on the inner surfaces of most shells, but to small brightly colored spots on the outer surface. The Helcion pruinosus is one such example. We show by optical measurements and scanning electron microscopy (SEM) that coloration in this shell is indeed of a structural nature based on thin-film interference from a layered quarter-wave stack tilted by approximately 24 degrees with respect to the outer surface. The microstructure is embedded in the transparent top layer of the shell approximately 50 microm below the surface. By comparing the SEM and optical measurements, we were able to establish that the layered structure is made from a birefringent material (crystalline aragonite) giving slightly different spectral peaks for S- and P-type reflections.     

Synthesis and characterization of ZnO/MgZnO heterostructure nanorods by simple two-step evaporation

ZnO-core/MgZnO-shell heterostructure nanorods with high aspect ratio were synthesized using a two-step thermal evaporation procedure, in which the core and the shell layers were formed separately at different temperatures. Microstructural characterization revealed a position dependence of the crystal structure and composition in the shell layer. The shell layer in the upper region consisted of MgO with quantum dot-like structure having cubic phases embedded in an amorphous oxide layer, while a Mg(0.35)Zn(0.65)O shell layer with a self-assembled superlattice structure of triple periodicity was formed in the middle region.     

Antipulverization Electrode Based on Low‐Carbon Triple‐Shelled Superstructures for Lithium‐Ion Batteries

The realization of antipulverization electrode structures, especially using low‐carbon‐content anode materials, is crucial for developing high‐energy and long‐life lithium‐ion batteries (LIBs); however, this technology remains challenging. This study shows that SnO₂ triple‐shelled hollow superstructures (TSHSs) with a low carbon content (4.83%) constructed by layer‐by‐layer assembly of various nanostructure units can withstand a huge volume expansion of ≈231.8% and deliver a high reversible capacity of 1099 mAh g^?1 even after 1450 cycles. These values represent the best comprehensive performance in SnO₂‐based anodes to date. Mechanics simulations and in situ transmission electron microscopy suggest that the TSHSs enable a self‐synergistic structure‐preservation behavior upon lithiation/delithiation, protecting the superstructures from collapse and guaranteeing the electrode structural integrity during long‐term cycling. Specifically, the outer shells during lithiation processes are fully lithiated, preventing the overlithiation and the collapse of the inner shells; in turn, in delithiation processes, the underlithiated inner shells work as robust cores to support the huge volume contraction of the outer shells; meanwhile, the middle shells with abundant pores offer sufficient space to accommodate the volume change from the outer shell during both lithiation and delithiation. This study opens a new avenue in the development of high‐performance LIBs for practical energy applications.     

Scanning electron microscopic structure of the prismatic layer in the Bivalvia

The shell structure of the Bivalvia has been observed with the use of optical and electron microscopes since the early 1900’s. The prismatic structure is one of the more attractive shell structures in bivalved mollusks. This structure is composed of the aggregation of polygonal prisms arranged densely. Each prism is made of small calcite crystallites arranged perpendicular to a growth shell surface. Organic materials, named organic sheaths, accumulate around prisms and stain well with heamatoxylin-eosin. The Bivalvia, which make prismatic structures, are divided into two groups. One group has the inner shell layer made up of a nacreous structure, and the other has the inner shell layer made up of a foliated structure. The aragonite prismatic layer and the prismatic layer are closely related to each other, as is the aragonite prismatic layer to the composite prismatic one.     

Scanning electron microscopic structure of the prismatic layer in the Bivalvia

The shell structure of the Bivalvia has been observed with the use of optical and electron microscopes since the early 1900’s. The prismatic structure is one of the more attractive shell structures in bivalved mollusks. This structure is composed of the aggregation of polygonal prisms arranged densely. Each prism is made of small calcite crystallites arranged perpendicular to a growth shell surface. Organic materials, named organic sheaths, accumulate around prisms and stain well with heamatoxylin-eosin.The Bivalvia, which make prismatic structures, are divided into two groups. One group has the inner shell layer made up of a nacreous structure, and the other has the inner shell layer made up of a foliated structure. The aragonite prismatic layer and the prismatic layer are closely related to each other, as is the aragonite prismatic layer to the composite prismatic one.     

Characteristics of acoustic scattering from a double-layered micro shell for encapsulated drug delivery

This work examines the characteristic differences in acoustic scattering between air-filled double-layered encapsulating (DLE) shells and air-filled single-layered encapsulating (SLE) shells. The analysis shows that the presence of an outer layer softer than the inner layer results in a shift of the first monopole of the reflectivity-frequency response to a higher frequency and a reduction in the monopole peak; and it leads to a frequency-separation of the two dipoles that trace the monopole. The frequency shift and the peak reduction of the monopole and the frequency separation of the two dipoles all increase with the increasing thickness of the softer outer layer. The numerical results reveal that variations in the Lame constant of the model material for the protein albumin have little effect on the low-frequency scattering characteristics, while they affect the high-frequency scattering characteristics significantly. The authors have shown that this phenomenon is due to the fact that the model material for the protein albumin has a Lame constant substantially larger than its shear modulus. Their further numerical studies conclude that, for each DLE shell, one can construct an equivalent SLE shell, using a simple scheme originated from the mechanics of composite materials in the sense that the so-constructed SLE shell has essentially the same acoustic scattering characteristics as the DLE shell within a low frequency range.     

Three-layer core/shell structure in Au-Pd bimetallic nanoparticles

This paper describes the internal structure of Au-Pd nanoparticles exhibiting newly discovered three-layer core/shell morphology, which is composed of an evenly alloyed inner core, an Au-rich intermediate layer, and a Pd-rich outer shell. By exploitation of spatially resolved imaging and spectroscopic and diffraction modes of transmission electron microscopy (TEM), insights were gained on the composition of each one of the observed three layers, indicating a significant extent of intimate alloy among the monometallic elements.     

Magnetic spherical Couette flow in linear combinations of axial and dipolar fields

We present axisymmetric numerical calculations of the fluid flow induced in a spherical shell with inner sphere rotating and outer sphere stationary. A magnetic field is also imposed, consisting of particular linear combinations of axial and dipolar fields, chosen to make B _r  = 0 at either the outer sphere, or the inner, or in between. This leads to the formation of Shercliff shear layers at these particular locations. We then consider the effect of increasingly large inertial effects and show that an outer Shercliff layer is eventually destabilized, an inner Shercliff layer appears to remain stable, and an in-between Shercliff layer is almost completely disrupted even before the onset of time-dependence, which does eventually occur though.