Nano-scale modulus mapping of biological composite materials: Theory and practice

The mechanical behavior of materials depends to a large extent on their properties at the nanoscale and, therefore, novel characterization techniques with sub-micron spatial resolution were developed in the last decades. Among them are the variety of tools for probing local elastic and viscoelastic properties of materials, the methods such as nanoindentation and AFM- and nanoindenter-based measurements using force modulation. In this review, we describe the nanoindenter-based nanoscale modulus mapping technique, which emerged as an extremely powerful tool for providing quantitative information on the storage and loss moduli distributions in complex nanocomposites. Since the tip penetrates only a few nanometers into the materials, this technique provides a superior lateral resolution in the order of 20 nm. All aspects of the method are covered, including a historical perspective, theoretical analysis, instrumentation, and examples of its application for studying multiphase structures and interfaces. The main focus of this review is the challenging field of natural bio-composites, which consist of stiff and compliant components, often with nanometric dimensions. Gradients of mechanical properties across the nm-sized features in biological materials are of upmost importance for their mechanical performance. Quantitative information on the nano-scale moduli distributions in these structures can hardly be achieved by other means.     

类金刚石梯度膜的微观力学性能研究

采用非平衡磁控溅射及等离子体源离子混合注入方法在奥氏体不锈钢1Cr18Ni9Ti基体上制备N／TiNi/Ti(N,C)/DLC梯度涂层,采用原子力显微镜等手段观察分析梯度膜的显微组织与相组成,同时采用纳米压入技术评定膜层的力学性能。实验结果表明,采用此方法制备的金刚石膜组织致密,性能良好。     

Elastic modulus determination of a thin layer

The titanium alloy TA6V was nitrogen implanted to improve its wear resistance. In order to extract the value of the elastic modulus of the thin layer that is formed by ion implantation of this titanium alloy, a modelling taking into account different features occurring during implantation is considered, namely erosion, concentration profile and nature of the layer. Then, the elastic modulus of the thin layer is deduced. The estimated value is shown to be consistent with the formation of a TiN rich layer about 0.2 μm thick. In this paper, a procedure based on the resonance frequency of a cantilever is presented leading to the optimisation of the measurement. Then the actual modelling proposed above is described and reliability of calculated values is discussed.     

Determination of Vickers microhardness on porous silicon surfaces

The Vickers microhardness values of two different sets of porous silicon layers were determined at applied load of 98 mN. The sets consisted of Boron-doped substrates anodized at diverse current densities for two different amounts of hydrofluoric acid (HF) in the etching solution. We found that the microhardness of the samples with lower content of HF at the anodization process showed higher values, whereas the Vickers parameter diminishes consistently for higher current densities. A possible explanation of this behavior is proposed.     

Calculation of bulk modulus of titanium alloys by first principles electronic structure theory

A theoretical study of the electronic structure and binding energy of some hypothetical Ti-X alloys was carried out using a first-principles discrete variational cluster method. The formation energy of an alloying atom in solution of titanium was estimated based on such calculations, and the case of multi-constituent practical Ti alloys was considered in the dilute limit by a linear superimposition approach. The influences of alloying additions on the bulk modulus of the alloys were evaluated from the variation of the formation energy. The calculated moduli of the Ti alloys were found to vary linearly with the experimental values. This indicates that the present approach is appropriate for the simulation of modulus of titanium alloys. This revised version was published online in July 2006 with corrections to the Cover Date.     

材料硬度与弹性模量比(H/E)的简便测定方法

介绍一种简便测定材料硬度与弹性模量比(H/E)的新方法,根据维氏硬度压痕的加载和卸载曲线的差别就可直接计算 H/E 值。     

Elastic modulus of close-packed randomly oriented Maxwell elements

The paper describes a model composite material in which behavior on the macroscopic scale is related to random orientation of closely packed microscopic Maxwell elements. Equations are developed which yield satisfactory agreement with experimental data from four sources. Although the experimental data came from concrete, the theory is adaptable to other composites.

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Résumé Les réponses des matériaux composites aux stimuli physiques sont souvent reliées aux différentes réponses des matériaux composants par interpolation entre les limites supérieures et inférieures des lois, des mélanges, et que représentent des éléments de Maxwell orientés parallèlement ou perpendiculairement aux lignes de force des stimuli. Les auteurs ont établi des relations qui expriment la réponse élastique d'un élément de Maxwell prismatique à deux phases, incliné selon un angle arbitraire par rapport à l'axe de chargement; puis, par l'emploi d'une fonction de densité probabilistique, ils introduisent une équation simple qui décrirait la réponse élastique d'une couche de ces éléments irrégulièrement orientés et fortement compactés. Cette équation permet des évaluations qui concordent bien avec les valeurs expérimentales du module d'élasticité du béton relevées chez un grand nombre d'auteurs. On s'est servi de l'équation pour estimer la variation du module d'élasticité de la pate de ciment due au vieillissement. Il s'est révélé ainsi que la bonne concordance avec l'expérience se restreignait aux cas où un accroissement du module d'élasticité était associé aux augmentations en quantité d'eau non évaporable. Un accroissement anomal du module d'élasticité se produisait après la fin de l'hydratation des pates de ciment à faible rapport eau/ciment.

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新鲜构树叶柄的弹性模量测量

通过悬臂梁自由端集中载荷实验测量5、6月份新鲜构树叶柄的弹性模量.为了减小误差,实验中搭建光学放大装置对悬臂梁最大挠度进行示值放大.实验分析发现,假设叶柄粗细均匀,构树叶柄的弹性模量值在50~600 MPa之间.它是一种非线性弹性材料,单一叶柄的弹性模量随载荷和挠度增大而减小.同一树枝上靠近根部的叶柄弹性模量更大,且与叶柄直径、密度相关.     

Nanoindentation in polymer nanocomposites

This article reviews recent literature on polymer nanocomposites using advanced indentation techniques to evaluate the surface mechanical properties down to the nanoscale level. Special emphasis is placed on nanocomposites incorporating carbon-based (nanotubes, graphene, nanodiamond) or inorganic (nanoclays, spherical nanoparticles) nanofillers. The current literature on instrumented indentation provides apparently conflicting information on the synergistic effect of polymer nanocomposites on mechanical properties. An effort has been done to gather information from different sources to offer a clear picture of the state-of-the-art in the field. Nanoindentation is a most valuable tool for the evaluation of the modulus, hardness and creep enhancements upon incorporation of the filler. It is shown that thermoset, glassy and semicrystalline matrices can exhibit distinct reinforcing mechanisms. The improvement of mechanical properties is found to mainly depend on the nature of the filler and the dispersion and interaction with the matrix. Other factors such as shape, dimensions and degree of orientation of the nanofiller, as well as matrix morphology are discussed. A comparison between nanoindentation results and macroscopic properties is offered. Finally, indentation size effects are also critically examined. Challenges and future perspectives in the application of depth-sensing instrumentation to characterize mechanical properties of polymer nanocomposite materials are suggested.     

Biofunctionalization of surfaces of nanostructured porous silicon

For the biomedical applications of porous silicon (PS), biomolecules have to be first immobilized on its surface through functional groups deposited on it. In this work, PS was biofunctionalized through the deposition on its surface of functional groups by thermally activated chemical vapour deposition of 3-aminopropyltriethoxysilane (APTS) used as precursor. The presence of amine radicals was checked by XPS and their functionality was assessed by confocal microscopy. Polyclonal mouse immunoglobulines were used to confirm the immobilization of biomolecules and also in order to check if they keep their native character, once attached to the surface. Finally, the reflectance of PS substrates in the different stages of this development was measured to assess their possible use in biosensing applications.     

较浅压入下针尖曲率半径对纳米压入硬度影响的比较研究

基于3种不同曲率半径压头针尖对熔融石英进行纳米压入,用原子力显微镜（AFM）直接法测得压头针尖的面积函数及针尖曲率半径。研究表明,在极浅压入条件下,压头曲率半径的变化会导致硬度值的测量误差,曲率半径越小的压头针尖随接触深度的变化会更快得到真实值;相同的压入深度,曲率半径小的压头针尖测得的压入硬度值比曲率半径大的测得的压入硬度值更接近其真实值。     

On estimating stress intensity factors and modulus of cohesion for fractal cracks

Existing solutions for the singular stress field in the vicinity of a fractal crack tip have been adapted for a somewhat modified problem. Since the integration along the fractal curve is prohibitive and does not lend itself to the presently available mathematical treatments, a simplified one has replaced the original problem. The latter involves a smooth crack embedded in a singular stress field, for which the order of singularity is adjusted to match exactly the one obtained from the analyses pertaining to the fractal crack. Of course, this is only an approximation, and we may only hope that it leads toward correct results, at least in a cursory sense. The advantage of such an approach becomes obvious when one inspects the final closed-form solutions for (a) the stress intensity factor in mode I fractal fracture, and (b) cohesion modulus, which results from the cohesive zone model and serves as a measure of the material resistance to crack propagation. As expected for the fractal geometry employed here, our results are strongly dependent on the fractal dimension D (or roughness exponent H).     

纳米级类金刚石梯度膜机械特性研究

本文采用非平衡磁控溅射及等离子体源离子混合注入方法在奥氏体不锈钢 1Cr18N9Ti基体上制备N TiN Ti(N ,C) DLC梯度涂层。采用原子力显微镜 (AFM)及喇曼光谱等手段观察分析梯度膜的显微组织与相组成 ,同时采用了纳米压入技术评定膜层的力学性能。实验结果表明 ,采用此方法制备的金刚石膜组织致密 ,性能良好     

Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm⁻². A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

The investigation of internal friction and elastic modulus in surface nanostructured materials

In this paper, 304 stainless steel and pure Fe specimens, which were processed by high-energy shot peening (HESP) and ultrasonic shot peening (USP) respectively, were studied by the internal friction method. Measurements were carried out on a vibrating reed apparatus. The change of internal friction and elastic modulus shows that the treatment duration of specimen is not accompanied by the corresponding persistent increase of internal friction and elastic modulus. There is a transition layer from the top surface to the inside of the materials. Young’s modulus of surface shows obviously a fluctuation along the depth profile. The phenomena have never been shown by other measurement methods. The microstructure change should be related to some basic mechanism of surface layer formation. It may also explain why the improvement of mechanical properties in surface nanocrystallized materials does not simply correspond to the duration time of severe deformation.