Nature of heterophase inclusions in high-purity optical fiber materials as studied with 3D laser ultramicroscopy

3D laser ultramicroscopy (3D LUM) is intended specially for determining the concentration and size distribution of submicron inclusions in the bulk samples of high-purity materials for visible and IR fiber optics. In this work the 3D LUM technique is shown to be able to identify the nature of individual inclusions detected. The measurement of the light scattered by an inclusion at a varied probe beam wavelength and polarization and at a varied scattered light collection angle makes it possible to determine the inclusion refractive index. The 3D LUM possibilities are illustrated by the example of studying the inclusion nature in the As₂S₃ glass samples prepared by the direct synthesis from elements in a quartz container at elevated temperatures.     

一种基于传像束的新型微三维形貌测量系统

文章根据结构光的测量原理提出了一种基于传像束的微三维形貌检测系统。充分利用传像束自由度大、能弯曲、易实现长度超过1m的光路等优点，在投射结构光条纹及摄取变形条纹图像时用它来代替传统的光学系统，从而使该系统比一般的微三维形貌测量系统多了内腔测量和远距离测量的功能。文中给出了实验结果，该系统的可行性得到了验证。     

Precise measurement of refractive index spectral dependence of optical materials for laser,fiber, and integrated optics

An interferometric technique for measuring the spectral dependence of the refractive index of solid-state materials to an accuracy of 10^?5 over the entire transparency region is described. The possibilities of the technique are demonstrated by the example of new phosphate glasses formulated for laser and fiber optics. It is shown that, in the presence of absorption bands in the transmission spectrum, the technique allows their associated jumps in the refractive index values to be recorded on the order of 10^?4?10^?5 and below. The shift in the spectral dependence of the refractive index in the region of the absorption band with intensity at 1.7 cm^?1 is measured for the first time.     

Preparation and characterization of gypsum-based materials used for 3D robocasting

In this study, gypsum-based materials (GM) comprising mainly α-hemihydrate gypsum, polycarboxylate, hydroxypropyl methyl cellulose and starch ether were prepared and used for 3D robocasting (3DR). The setting time and rheological properties of the GM slurry and the physical properties of the GM sample, including bulk density, porosity and mechanical strength, were investigated. The results indicate that the GM slurry exhibits an obvious shear thinning behavior and a good shape fidelity. The measured dynamic yield stress, final viscosity and initial storage modulus of the GM slurry are as high as 420.73 Pa, 7.29 Pa s and 273.86 kPa, respectively. Meanwhile, the GM slurry presents an adequate initial setting time of 68 min compared with a printing time of 14 min. In addition, the GM sample prepared by 3DR has a high compressive strength of 64.96?±?5.98 MPa and a bending strength of 15.24?±?1.58 MPa. These mechanical strengths are comparable with those of the GM and pure gypsum plaster sample prepared by traditional molding. Generally, the 3DR of GM is a promising method to improve the mechanical strength of printed gypsum products and presents great application prospects in the building of complex large-scale structures.     

A review of patented works on the mechanical characterization of materials at micro- and nano-scale

In recent years, the development of cost-effective processing techniques, novel design concepts and new materials paved the way to a widespread diffusion of micro- and nano-electro-mechanical systems (NEMS/MEMS). Obviously, the reliability as well as the performance of NEMS/MEMS depend on the corresponding materials properties, which in turn should be determined using ad-hoc small samples fabricated at the relevant size-scale. For this reason, in the last decade research efforts have been devoted to the development of experimental techniques suitable for the mechanical characterization of materials at micro- and nano-scale. There are many contributions stemming from this research area, the purpose of the present work is to give an overview of the most recent patented works. The focus will be directed to selected patents on the mechanical characterization of both micro- and nanosamples, like nanotubes and nanowires. Special emphasis will be given to the methods suited for the determination of elastic properties, fracture resistance and residual stresses of materials.     

A method for the generation of 3D representative models of granular based materials

The morphology of many naturally occurring and man‐made materials at different length scales can be modelled using the packing of correspondingly shaped and sized particles. The mechanical behaviour of this vast category of materials – which includes granular media, particle reinforced materials and foams ‐ depends strongly upon the shape and size distribution of the particles. This paper presents a method for the generation and packing of arbitrarily shaped polyhedral particles. The algorithm for the generation of the particles is based on the Voronoi tessellation technique, whilst the packing is performed using a geometrical approach, which guarantees the non‐overlapping of the bodies without relying upon any, otherwise typically computationally expensive, contact detection and interaction algorithm. The introduction of three geometrical parameters allows to control the shape, size and spacial density of the polyhedral particles, which are used to build numerical models representative of densely packed granular assemblies, granular reinforced materials and closed‐cell foams. Copyright © 2017 John Wiley & Sons, Ltd.     

Fast in situ 3D nanoimaging: a new tool for dynamic characterization in materials science

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Fabrication and mechanical characterization of 3D woven Cu lattice materials

3D metallic lattices designed to have two distinctly different material architectures have been woven with metallic Cu wires. A vacuum soldering technique was employed to metallurgically bond the wire nodes and form stiff 3D lattice materials. The structures and mechanical properties of the as-woven and soldered lattices were characterized by optical microscopy and micro-scale mechanical property experiments. The measured in-plane shear stiffness shows good agreement with predictions from finite element (FE) models that account for variations in the manufacturing and solder bonding. The study indicates that stiffness is influenced by the percentage of bonded nodes and the location of bonding. The 3D woven lattice materials manufactured in this study exhibited a very high percentage (80%) of bonded nodes and a unique combination of stiffness and density as compared to that typically reported for ultra lightweight lattice materials.     

An advanced 3D boundary element method for characterizations of composite materials

Some recent developments in the modeling of composite materials using the boundary element method (BEM) are presented in this paper. The boundary integral equation for 3D multi-domain elasticity problems is reviewed. Difficulties in dealing with nearly-singular integrals, which arise in the BEM modeling of composite materials with closely packed fillers or of thin films, are discussed. New and improved techniques to deal with the nearly-singular integrals in the 3D elasticity BEM are presented. Numerical examples of layered thin films and composites with randomly distributed particles and fibers are studied. The advantages and limitations of the BEM approach in modeling advanced composites are also discussed. The developed BEM with multi-domain and thin-body capabilities is demonstrated to be a promising tool for simulations and characterization of various composite materials.     

Preparation and characterization of poly(3-octylthiophene)/carbon fiber thermoelectric composite materials

Poly(3-alkylthiophene) (P3AT) with a high Seebeck coefficient has recently been reported. However, P3AT/inorganic conductive composites exhibit relatively poor thermoelectric performance because of their low electrical conductivity. In this work, carbon fiber sheets with a high electrical conductivity were chosen as the inorganic phase, and poly(3-octylthiophene)(P3OT)/carbon fiber composites were prepared by casting P3OT solution onto the carbon fiber sheets. The carbon fiber sheets incorporated into the composites can provide good electrical conductivity, and P3OT can provide a high Seebeck coefficient. The highest power factor of 7.05 μW m⁻¹ K⁻² was obtained for the composite with 50 wt% P3OT. This work suggests a promising method for preparing large-scale thermoelectric composites with excellent properties.     

二维非均质材料应力场的数值化计算方法

等效夹杂方法是求解含杂质材料弹性应力场的一种有效方法,但是其解析求解只适用于椭球/椭圆类杂质问题。本文提出一种基于等效夹杂方法的数值化计算方法,介绍了其基本理论,并引入共轭梯度法求解该方法的一致性条件线性方程组。该方法通过计算区域的数值离散,能够实现对二维任意形状杂质弹性场的求解。将该方法得到的结果与解析解进行比较,验证了该方法的有效性。讨论了数值化等效夹杂方法在效率以及收敛性上的表现。通过对比证明,利用共轭梯度法实现该方法,能在保持精度的同时,相较于高斯消元法具有较大的效率优势。最后通过半椭圆杂质和氧化锆/氧化铝共挤复合材料算例验证了该方法处理任意形状杂质的能力。     

A method to quantify the 3D microstructure of fibrous materials containing mineral fillers using X-ray microtomography: application to paper materials

This article proposed and validated an original and automatic method based on synchrotron X-ray microtomography to characterise non-destructively, in 3D, the mineral fillers that may be present in fibrous composite materials. The approach consists of (i) obtaining the 3D internal structure of the sample in a non invasive way, (ii) identifying the fillers in the 3D microstructure using appropriate image processing tools, (iii) calculating the filler content on the numerical data, and (iv) validating the representativity of the data sets by evaluating the representative elementary volume. This method was successfully applied in the case of paper samples. The numerical filler content were in good agreement with standards. This method opens new perspectives in terms of characterisation of filler spatial repartition.     

3D printing of smart materials: A review on recent progresses in 4D printing

ABSTRACT

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing or rapid prototyping, has been introduced since the late 1980s. Although a considerable amount of progress has been made in this field, there is still a lot of research work to be done in order to overcome the various challenges remained. Recently, one of the actively researched areas lies in the additive manufacturing of smart materials and structures. Smart materials are those materials that have the ability to change their shape or properties under the influence of external stimuli. With the introduction of smart materials, the AM-fabricated components are able to alter their shape or properties over time (the 4th dimension) as a response to the applied external stimuli. Hence, this gives rise to a new term called ‘4D printing’ to include the structural reconfiguration over time. In this paper, recent major progresses in 4D printing are reviewed, including 3D printing of enhanced smart nanocomposites, shape memory alloys, shape memory polymers, actuators for soft robotics, self-evolving structures, anti-counterfeiting system, active origami and controlled sequential folding, and some results from our ongoing research. In addition, some research activities on 4D bio-printing are included, followed by discussions on the challenges, applications, research directions and future trends of 4D printing.     

A uniform multiscale method for 2D static and dynamic analyses of heterogeneous materials

A uniform extended multiscale finite element method is developed for solving the static and dynamic problems of heterogeneous materials in elasticity. To describe the complex deformation, a multinode two‐dimensional coarse element is proposed, and a new approach is elaborated to construct the displacement base functions of the coarse element. In addition, to improve the computational accuracy, the mode base functions are introduced to consider the effect of the inertial forces of the structure for dynamic problems. Furthermore, the orthogonality between the displacement and mode base functions is proved theoretically, which indicates that the proposed multiscale method can be used for the static and dynamic analyses uniformly. Numerical experiments show that the mode base functions almost do not work for the static problems, while they can improve the computational accuracy of the dynamic problems significantly. On the other hand, it is also found that the number of the macro nodes of the multinode coarse element has a great influence on the accuracy of the numerical results for both the static and dynamic analyses. Numerical examples also indicate that the uniform extended multiscale finite element method can obtain sufficiently accurate results with less computational cost compared with the standard FEM. Copyright © 2012 John Wiley & Sons, Ltd.     

A new method for meshless integration in 2D and 3D Galerkin meshfree methods

A method for the evaluation of regular domain integrals without domain discretization is presented. In this method, a domain integral is transformed into a boundary integral and a 1D integral. The method is then utilized for the evaluation of domain integrals in meshless methods based on the weak form, such as the element-free Galerkin method and the meshless radial point interpolation method. The proposed technique results in truly meshless methods with better accuracy and efficiency in comparison with their original forms. Some examples, including linear and large-deformation problems, are also provided to demonstrate the usefulness of the proposed method.     

Contactless nondestructive inspection method and measuring system for the thermophysical characteristics of materials, with adaptive compensation for heat loss

A new method with loss compensation is proposed for contactless measurements of thermal conductivity and heat capacity. A microprocessor unit for implementing the method is described in detail. Translated from Izmeritel'naya Tekhnika, No. 8, pp. 49–52, August, 1997.     

Scanning near-field optical nanotomography: a new method of multiparametric 3D investigation of nanostructural materials

A new experimental approach to multiparametric three-dimensional (3D) investigation of a broad class of composite nanostructural materials is developed on the basis of scanning near-field optical nanotomography (SNONT). Using this method, it is possible to simultaneously study the optical properties, 3D morphology, and distribution of the mechanical and electrical properties of the same region of a sample. The proposed method combines features of the confocal and near-field optical microspectroscopy (fluorescence and Raman spectroscopy) with a lateral resolution of up to 50 nm and scanning-probe microscopy. The possibility of studying the volume distribution of optical, morphological, electrical, and mechanical characteristics of a material with nanoscale resolution is related to the probing of sequential layers at a step of up to 20 nm and a total Z-scan depth of up to 3 mm. In particular, the SNONT method has been used to study a liquid-crystalline polymer doped with fluorescent nanocrystals.     

Gas anti-solvent precipitation assisted salt leaching for generation of micro- and nano-porous wall in bio-polymeric 3D scaffolds

The mass transport through biocompatible and biodegradable polymeric 3D porous scaffolds may be depleted by non-porous impermeable internal walls. As consequence the concentration of metabolites and growth factors within the scaffold may be heterogeneous leading to different cell fate depending on spatial cell location, and in some cases it may compromise cell survival.In this work, we fabricated polymeric scaffolds with micro- and nano-scale porosity by developing a new technique that couples two conventional scaffold production methods: solvent casting-salt leaching and gas antisolvent precipitation. 10–15 w/w solutions of a hyaluronic benzyl esters (HYAFF11) and poly-(lactic acid) (PLA) were used to fill packed beds of 0.177–0.425 mm NaCl crystals. The polymer precipitation in micro and nano-porous structures between the salt crystals was induced by high-pressure gas, then its flushing extracted the residual solvent. The salt was removed by water-wash. Morphological analysis by scanning electron microscopy showed a uniform porosity (~ 70%) and a high interconnectivity between porous. The polymeric walls were porous themselves counting for 30% of the total porosity. This wall porosity did not lead to a remarkable change in compressive modulus, deformation, and rupture pressure. Scaffold biocompatibility was tested with murine muscle cell line C2C12 for 4 and 7 days. Viability analysis and histology showed that micro- and nano-porous scaffolds are biocompatible and suitable for 3D cell culture promoting cell adhesion on the polymeric wall and allowing their proliferation in layers. Micro- and nano-scale porosities enhance cell migration and growth in the inner part of the scaffold.