Microstructural Characterization and Hardness Behavior of a Biological Saxidomus purpuratus Shell

The microstructures of the Saxidomus purpuratus shell were observed.It was found that the inner and middle layers of the shell are composed of crossed lamellae,while the outer layer exhibits porous structures.With the characteristic structure of each layer,the hardness of inner layer with narrow domains in crossed lamellar structure is the highest,and that of middle layer with wide domains is lower,while the outer layer has the lowest hardness.The damage morphologies of the indentations change a lot,depending not only upon the magnitude of the indentation load,but also upon the orientation between the indentation direction and the crossed lamellae in the microstructure of the shell,which illustrates the anisotropy in mechanical properties of such shells.     

Structural and dynamic modeling of mechanical behavior of solids

An examination of the mechanisms of brittle fracture in solids is conducted via molecular dynamics simulations of the behavior of a model silica glass and crystal under applied uniaxial strain. The results show an effect of applied strain rate on the mechanism of fracture and differences between the crystal and glass. The crystal exhibits failure by bond extension until local rearrangements, made possible by the thermal motions of the atoms, can construct a fracture surface. The glass shows a pronounced variation in fracture mechanism as a function of strain rate. If the strain is applied so fast that no thermal motions are allowed, the glass fractures similarly to the crystal by bond extension. If the strain rate is sufficiently slow to allow thermal motions to take place before fracture, then the deformation mechanism is dominated by rotation of the silica tetrahedra. The fracture strength at slow strain rates is 60% less than the strength at high strain rates. All values of the glass strength are lower than the crystal strength (by at least 30%) despite using the same interatomic potential for both phases. Fracture in the glass appears to result from a coalescence of void spaces under strain, around regions of the glass that exhibited a lower density of atoms than average. In effect, the regions of low density observed in the glass phase appear to act as internal flaws, able to initiate failure by acting to collect strain.     

Structural, mechanical and tribological behavior of fullerene-like carbon film

Hydrogenated carbon films containing fullerene-like structures (FL-C:H) were synthesized using magnetron sputtering of a graphite target in methane and argon atmospheres. The results indicate clearly that a substantial part of the film is made up of fragments of such fullerene-like structures mixed in a hydrogenated amorphous carbon matrix. The film exhibits excellent mechanical properties with a hardness of 27.4 GPa and almost complete elastic recovery (as high as 95%). The tribological properties of the FL-C:H film were tested and compared with a-C:H and a-C films. The results show that the lowest friction coefficient of the FL-C:H film, about 0.02, is recorded in oxygen environment. The ranges of dispersion of the friction coefficient for the FL-C:H film are merely 0.02 in different testing environments, much lower than that of a-C:H and a-C films, which indicates the friction-coefficient-insensitivity of the FL-C:H film to different atmospheres.     

A study on the structure and mechanical behavior of the Dasypus novemcinctus shell

Multiscale hierarchical structures, materials properties, and mechanical behaviors of the nine-banded armadillo (Dasypus novemcinctus) shell were studied to provide fundamental knowledge for understanding biological composite systems. The nine-banded armadillo's dermal shell is characterized into three regions: the forward, band, and rear shells. The forward and rear shells comprise a sandwich composite structure of functionally graded material having relatively denser exterior bony layers and an interior bony network of foam. The forward and rear shell's strength (~ 1500 MPa) was greater than the intermediate band shell (~ 500 MPa). The band shell revealed a more complicated structure where adjacent bands are partially overlapped and connected with each other to provide flexibility, in addition to protection. Hardness tests showed that the top surfaces of each shell had hardness (~ Hv50) greater than the front and side surfaces (~ Hv40). Compression test results on the forward and rear shells showed a typical nonlinear deformation behavior similar to synthetic foams, where microbuckling is a key inelastic deformation mechanism. A comparison and contrasting study of the structure-property relations between the armadillo shell and other biological structural materials could provide fundamental understandings for deformation mechanisms that can lead to the development of novel bio-inspired safety system design methodologies.     

Physical and mechanical characterization of Fiber-Reinforced Aerated Concrete (FRAC)

Fiber-Reinforced Aerated Concrete (FRAC) is a novel lightweight aerated concrete that includes internal reinforcement with short polymeric fibers. The autoclaving process is eliminated from the production of FRAC and curing is performed at room temperature. Several instrumented experiments were performed to characterize FRAC blocks for their physical and mechanical properties. This work includes the study of pore-structure at micro-scale and macro-scale; the variations of density and compressive strength within a block; compressive, flexural and tensile properties; impact resistance; and thermal conductivity. Furthermore, the effect of fiber content on the mechanical characteristics of FRAC was studied at three volume fractions and compared to plain Autoclaved Aerated Concrete (AAC). The instrumented experimental results for the highest fiber content FRAC indicated compressive strength of approximately 3 MPa, flexural strength of 0.56 MPa, flexural toughness of more than 25 N m, and thermal conductivity of 0.15 W/K m.     

Structural and mechanical characterization of lithium-ion battery electrodes via DEM simulations

Electrode structural stability and mechanical integrity is of major importance regarding not only lithium-ion battery performance but also safety aspects. The goal of this study is to design a simulation procedure to reproduce the microstructural and mechanical properties of such lithium-ion battery electrodes. Taking into consideration the particulate state of these electrodes, a discrete element method (DEM) approach is proposed, which comprises a procedure to reproduce real electrode structures and the application of a proper contact model to capture the bulk mechanics. This is accomplished by considering particle interactions as well as the performance of the binder. Three different electrodes are manufactured with the aim of calibrating and validating the Hertzian-bond contact model. Experimental nanoindentation measurements prove to be in good agreement with the simulation outcome, concluding that the method constitutes a valuable physical and mechanical basis for further applications.     

Modelling a modified atmosphere packaging system for fresh scallops (Argopecten purpuratus)

Seafood is a highly perishable food, which has a relative short shelf‐life. Modified atmosphere packaging (MAP) is a system that offers a way of extending the shelf‐life of seafood products, maintaining quality and inhibiting bacterial growth. The objective of this research was to study and determine the optimal conditions for packaging scallops in a modified atmosphere system, which includes CO₂/O₂/N₂ mixture, headspace:food ratio and storage temperature, utilizing an integrated mathematical model for MAP systems with its respective experimental validation. For validation purposes, two experiments were conducted, using gas mixtures of: (a) 45% CO₂/10% O₂/45% N₂; and (b) 60% CO₂/10% O₂/30% N₂. In addition, two experiments, at 6°C and 20°C, were conducted to obtain the shelf‐life model, utilizing the following gas mixtures: 30% CO₂/10% O₂/60% N₂; 45% CO₂/10% O₂/45% N₂; 60% CO₂/10% O₂/30% N₂; and 75% CO₂/10% O₂/15% N₂. Gas mixtures with CO₂ concentrations between 30% and 70% and different headspace:food ratios were tested during simulations. The optimal conditions for scallop storage were a 60% CO₂/10% O₂/30% N₂ gas mixture and a headspace:food ratio of 2:1. With these conditions, a simulated shelf‐life of 21 days was obtained. Optimal conditions consider maximum shelf‐life, an adequate film collapse criterion, and time to reach the pseudo‐equilibrium condition. The predictive mathematical model, coupled with experimental studies for specific products, can be efficiently utilized to evaluate packaging alternatives (size, material and selected thickness) for different temperatures and initial gas concentration scenarios of MAP products. Copyright © 2006 John Wiley & Sons, Ltd.     

复合材料负泊松比格栅结构设计及力学性能评价

对复合材料负泊松比格栅新结构的设计、制备与评价进行了研究,采用有限元方法模拟了负泊松比结构单元在轴压载荷作用下的力学行为,通过热压罐成型制备复合材料负泊松比格栅结构,并评估其成型质量、蒙皮及筋条的力学性能、结构抗轴压性能。数值模拟结果表明,负泊松比格栅结构与正交格栅结构相比,变形形式从马鞍形变为波纹形,横向膨胀量降低,应力分布均匀性提升,筋条-轴线夹角θ=30°时,负泊松比格栅结构达到最优。采用热压罐成型的MT300/603碳纤维/环氧树脂负泊松比格栅试件成型质量良好,蒙皮及筋条的力学性能优异。力学测试结果表明,筋条-轴线夹角θ=30°时,MT300/603负泊松比格栅结构轴压模量为65.92 GPa,轴压失效载荷为64.65 kN。轴压失效模式为筋条节点处的蒙皮-筋条开裂。筋条-轴线夹角θ=30°的MT300/603负泊松比格栅结构抗压强度高于正交格栅结构,且力学行为呈现明显的负泊松比特征,是一种具备优异综合力学性能的新格栅结构,在航天飞行器蒙皮结构等领域具有潜在的应用价值。      

Electrical,mechanical and piezo-resistive behavior of a polyaniline/poly(n-butyl methacrylate) composite

Dodecilbenzene sulfonate doped-polyaniline/poly(n-butyl methacrylate) composites were prepared by cast molding. The electrical, mechanical and morphological behaviors of composite films were studied. The tensile strength of the composite increased by approximately a 66% for 15 wt.% of polyaniline and this increase is attributed to the homogeneous distribution and improved interface properties between the conducting particles and the matrix. Qualitative analysis of tensile fracture surfaces reveals the presence of conductive agglomerates with matrix polymer still coating them after failure, giving an indication of a good interfacial interaction of the conducting particles and the thermoplastic matrix. The piezo-resistive behavior of the films at different compositions was measured under tensile loading and the composite shows higher electromechanical sensitivity for films compositions slightly above the percolation threshold i.e. contents of 4 wt.% and 5 wt.%. The piezo-resistive response had a good reproducibility over five cycles of loading/unloading in the elastic region of deformation. In general, the reversibility of the piezo-resistive behavior revealed that there is a very small hysteresis of the composites, with particle contents close to the threshold and it becomes smaller for higher polyaniline contents, suggesting a potential application of this material in electromechanical devices.     

Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior

Mechanics of Time-Dependent Materials - A significant number of materials show different mechanical behavior under dynamic loads compared to quasi-static (Salvado et al. in Prog. Mater....     

Facile electrochemical characterization of core/shell nanoparticles. Ag core/Ag(2)O shell structures

We report in this paper a facile approach for the formation and electrochemical characterization of silver-silver oxide core-shell nanoparticles (NPs). Thus, thermal treatment at temperatures between 200 and 360 degrees C of Ag NP, in the gas phase or in an organic solvent, has been used to achieve the formation Ag@Ag2O NP. The evidence of formation of such a core-shell structure was obtained by cyclic voltammetry using a Nafion modified electrode (where Nafion containing carbon particles is used as the matrix to encapsulate the core-shell NP). Initial positive scans measure free Ag. Initial negative scans measure Ag2O, with the following positive scan, compared to the initial one, providing a measure of "trapped" or core Ag. The results presented demonstrate the utility of this approach in characterizing core-shell structures, like Ag@Ag2O, which could be extended to other core-shell forms, such as bimetallic core-shell NP.     

Structural,thermal and vibrational characterization of mechanical alloyed In50Te50

Structural, chemical, thermal and vibrational studies of InTe produced by mechanical alloying were carried out using X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry and Raman spectroscopy. The main crystalline phases formed after 2 h of milling were the tetragonal (TlSe-type) and high-pressure cubic (NaCl-type) InTe phases. Minority cubic In₂O₃ phase was also nucleated. Mean crystallite size and phase fraction variations with the increase of the milling time were obtained from Rietveld analyses. The distribution of the particle size (centered at about 39 nm) was obtained by images of transmission electron microscopy. Differential scanning calorimetry measurements showed no evidence of nonreacted materials and Raman measurements showed peaks that can be associated with the InTe (TlSe-type) phase and/or the existence of molecular structures of Te (chains/rings). The structural stability of the nanocrystaline phases of the In₅₀Te₅₀ sample milled for 15 h was attested by systematical X-ray diffraction measurements performed up to one year after its production.     

Structural characterization and thermal and mechanical properties of poly(propylene carbonate)/MgAl-LDH exfoliation nanocomposite via solution intercalation

Poly(propylene carbonate)/MgAl layered double hydroxide (PPC/MgAl-LDH) exfoliated nanocomposites were synthesized by solution intercalation of PPC into the galleries of organic modified MgAl-LDH (OMgAl-LDH) in cyclohexanone. The crystal morphological structures, thermal degradation behavior, and mechanical properties have been studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction, and thermogravimetric analysis (TGA). The nanoscale dispersion of OMgAl-LDH layers in the PPC matrix has been verified by the disappearance of d_0 0 1 XRD diffraction peak of OMgAl-LDH and the observation of TEM image. The TGA data give evince that the thermal degradation temperature of the exfoliated PPC/MgAl-LDH nanocomposites with 1% OMgAl-LDH is 10 °C higher than that of pure PPC resin when 20% weight loss was selected as a point of comparison. The data from the mechanical test show that the tensile strength of the PPC/MgAl-LDH nanocomposites with 5% LDH is 36.9 MPa, which is 72% and 30% higher than those of pure PPC resin and simple mixed sample with the same content of LDH, and its Young’s modulus is 1303 MPa, which is 57% and 21% higher than those of the same two samples, respectively.     

Tensile mechanical behavior of TiAl(FL) at high strain rate

The tensile mechanical behavior of Ti-47at%Al-1.5at%Cr-0.5ar%Mn-2.8at%Nb in full lamellar microstructure has been studied in the strain rate range from 100 s^–1 to 800 s^–1 and the complete stress-strain curves were obtained. Results show that the alloy is extremely brittle at different strain rate, exhibiting near-zero ductility. Both UTS and fracture strain of material are strain rate sensitive, increasing with the strain rate at room temperature. Fractography analysis indicates that the alloy fractures in a mixed mode of predominant transgranular cleavage and minor intergranular cracking. On basis of the experiment results and Weibull distribution theory, a statistic model has been developed to describe mechanical behavior of TiAl(FL) at different strain rate. The statistical parameters for material and their relationships with strain rate are obtained from tensile impact experimental results. The simulated stress strain curves from the model are in good agreement with the test data. The theoretical model and test results show that both the scale parameter ₀ and the shape parameter are rate dependent, and a linear dependence of ₀ and on lg has been found.     

Ni(3)Si(Al)/a-SiO(x) core-shell nanoparticles: characterization, shell formation, and stability

We have used an electrochemical selective phase dissolution method to extract nanoprecipitates of the Ni(3)Si-type intermetallic phase from two-phase Ni-Si and Ni-Si-Al alloys by dissolving the matrix phase. The extracted nanoparticles are characterized by transmission electron microscopy, energy-dispersive x-ray spectrometry, x-ray powder diffraction, and electron powder diffraction. It is found that the Ni(3)Si-type nanoparticles have a core-shell structure. The core maintains the size, the shape, and the crystal structure of the precipitates that existed in the bulk alloys, while the shell is an amorphous phase, containing only Si and O (SiO(x)). The shell forms around the precipitates during the extraction process. After annealing the nanoparticles in nitrogen at 700?°C, the tridymite phase recrystallizes within the shell, which remains partially amorphous. In contrast, on annealing in air at 1000?°C, no changes in the composition or the structure of the nanoparticles occur. It is suggested that the shell forms after dealloying of the matrix phase, where Si atoms, the main constituents of the shell, migrate to the surface of the precipitates.     

Structural characteristics and mechanical properties of Ti(Cr) films produced on Si substrate

A series of nanogranular Ti₉₀Cr₁₀ thin films have been fabricated by pulsed-laser deposition on Si substrates at different temperatures. The crystal structure and mechanical properties of these films were investigated. The X-ray diffraction and transmission electron microscope images with selected area diffraction showed that the structure of as-prepared films is dependent on film thickness and deposition temperature. It was found that the Ti₉₀Cr₁₀ films consisted of fine hexagonal close packed microstructure with columnar grains, while body close-packed cubic structure of Cr films are composed of irregular grains, meanwhile, a chromium disilicide (CrSi₂) layer formed in the interface between the substrate and Cr films which deposited at temperature of greater than 600 °C. The crystalline and columnar grains improved with an increase of the thickness of the films and an optimum microstructure is obtained under the present experimental condition of about 50 nm thickness and deposited temperature of 500 °C for Ti₉₀Cr₁₀ films. Deposited at 300 °C, the Ti₉₀Cr₁₀ films have hardness of 12.7 GPa and elastic modulus of 174.6 GPa. Improved to 600 °C the sample shows higher hardness of 13.1 GPa and higher elastic modulus of 183.2 GPa. Using Benjamin-Weaver model, adhesion shearing force can be calculated as 34.9 MPa for 300 °C Ti₉₀Cr₁₀ film while higher value of 44.4 MPa for higher temperature of 600 °C.     

Physico-chemical and mechanical characterization of hydrogels of poly (vinyl alcohol) and hyaluronic acid

Hydrogels are three-dimensional polymeric networks very similar to biological tissues and potentially useful as soft tissue substitutes and drug delivery systems. Many synthetic polymers can be used to make hydrogels: poly (vinyl alcohol) is widely employed to make hydrogels for biomedical applications. Improvements in the biocompatibility characteristics of synthetic materials could be achieved by the addition of biological macromolecules. The resulting materials named bioartificial polymeric materials could possess the good mechanical properties of the synthetic component and adequate biocompatibility due to the biological component. We have used poly (vinyl alcohol) to make hydrogels containing various amounts of hyaluronic acid. These bioartificial materials were studied to investigate the effect of the presence of the hyaluronic acid on the structural properties of the hydrogels. Thermal, mechanical, morphological and X-ray analyses were performed. A close correspondence between the network consistency and the degree of crystallinity developed in the matrix suggested that the hyaluronic acid, when its content is about 20%, could provide heterogeneous crystallization nuclei for poly (vinyl alcohol) thus increasing the crystallization degree, and consequently, the storage modulus.     

Optical and mechanical characterization of evaporated SiO(2) layers. Long-term evolution

Numerous characterizations were performed on 120-nm thick evaporated SiO(2) layers in order to understand how their features change as a function of deposition conditions and time. Density decreases with increasing deposition pressure. It governs all the layer properties (refractive index, hardness, and stress). In situ stress measurements show that stress can be divided into intrinsic and water-induced components, respectively linked to local density (outside the pores) and porosity. Intrinsic stress increase with decreasing pressure is explained by a diminution of the Si-O-Si bond angle (IR measurements). Long-term evolution is characterized by stress relaxation related to Si-O-Si strained bond hydrolysis.     

Structural and mechanical study of a self-assembling protein nanotube

We report a structural characterization of self-assembling nanostructures. Using atomic force microscopy (AFM), we discovered that partially hydrolyzed alpha-lactalbumin organizes in a 10-start helix forming tubes with diameters of only 21 nm. We probed the mechanical strength of these nanotubes by locally indenting them with an AFM tip. To extract the material properties of the nanotubes, we modeled the experiment using finite element methods. Our study shows that artificial helical protein self-assembly can yield very stable, strong structures that can function either as a model system for artificial self-assembly or as a nanostructure with potential for practical applications.