Dual-peak long-period fiber gratings with enhanced refractive index sensitivity by finely tailored mode dispersion that uses the light cladding etching technique

We have experimentally investigated the mode dispersion property and refractive index sensitivity of dual-peak long-period fiber gratings (LPGs) that were sensitized by hydrofluoric acid (HF) etching. The nature of the coupled cladding modes close to the dispersion turning point makes the dual-peak LPGs ultrasensitive to cladding property, permitting a fine tailoring of the mode dispersion and index sensitivity by the light cladding etching method using HF acid of only 1% concentration. As an implementation of an optical biosensor, the etched device was used to detect the concentration of hemoglobin protein in a sugar solution, showing a sensitivity as high as 20 nm/1%.     

Simulation of the coupling behaviors of particle and matrix irradiation swelling and cladding irradiation growth of plate-type dispersion nuclear fuel elements

Within plate-type dispersion nuclear fuel elements, besides irradiation swelling of fuel particles induced by nuclear fissions, the metal matrix and the cladding are attacked continuously by the fast neutrons released from the fuel particles. As a consequence, the matrix undergoes a bit irradiation swelling and the cladding takes on irradiation growth, which both might have remarkable effects upon the mechanical behaviors within fuel elements. In this paper, the three-dimensional large-strain constitutive relations for the fuel particles, the metal matrix and cladding are developed; based on them, the method of virtual temperature increase proposed by Ding et al. (2008) is further developed to model the irradiation swelling; the method of anisotropic thermal expansion is introduced to model irradiation growth of the cladding; and a method of multi-temperature-loadstep is proposed to simulate the coupling features of the irradiation swellings of both the metal matrix and the fuel particles together with the irradiation growth of the cladding. In order to clarify the critical factors that affect their mechanical performances and carry out optimal design, with the aid of the research thoughts of particle-reinforced composites, numerical simulations of the irradiation-induced mechanical behaviors are implemented with the finite element method in consideration of the micro-structure of the fuel meat. The obtained results indicate the effects of irradiation swelling of the matrix and irradiation growth of the cladding as that: (1) they might weaken the in-pile mechanical performances at the matrix to some extent; and (2) the former increases interfacial stresses between the fuel meat and the cladding, while the latter relatively relieve those interfacial stresses; and the interfacial mechanical strength might be improved by getting suitable irradiation growth mode of the cladding.     

Interaction of screw dislocation and anisotropic (or isotropic) circular inclusion in isotropic (or anisotropic) matrix

Interaction of a screw dislocation (or an out-of-plane force) and anisotropic circular inclusion in isotropic matrix is studied. Similar problems for an anisotropic circular inclusion in an anisotropic matrix or the isotropic circular inclusion in the isotropic matrix have been solved, however, the anisotropic/isotropic problem (we will here after use this notation, meaning anisotropic circular inclusion in isotropic matrix) has not been solved yet. Recently, Choi et al.(2003) proposed a method based on ‘equivalence theorem’ to deal with a bimaterial interface (straight interface such as x₂ = 0) of anisotropic material bonded onto isotropic material. We apply this method to the stated problem.     

Contact angle measurement on xerogel sensitive layer for optical fibre sensor

This paper deals with approach for the detection of chemical vapours based on refractive-index changes of a silica xerogel layer deposited as an optical cladding on the fibre core. The fibre is multimode fibre excited with an inclined collimated beam. The refractive-index changes are evaluated by means of changes of the output power at the end put of the fibre. The optical properties of the sensitive cladding (refractive index and absorption coefficient) can be obtained with modelisation program. The sensitivities of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS)-based xerogel layers to toluene and water are presented in the paper. The hydrophobicity of the two-xerogel layers and their surface-free energy has been determined with contact angle measurements. A correlation between optical detection results and contact angle measurements can be done.     

Quasicontinuum simulation of crack propagation in bcc-Fe

We have investigated fracture in bcc-Fe through multiscale simulations. The quasicontinuum (QC) method with an embedded atom method (EAM) interatomic potential is applied. The analyses have been carried out assuming different crystallographic orientations and different T-stress under Mode I loading. Both anisotropic and isotropic formulations of the modified boundary layer (MBL) approach has here been investigated and compared. The results show that the mechanisms at the crack tip and the critical stress intensity factor K_Ic are sensitive to both the crystallographic orientation and whether or not the formulation of the boundary conditions are isotropic or anisotropic. Mechanisms such as cleavage crack propagation, twinning, and dislocation emission are observed in the analyses. A short literature review on atomistic and multiscale simulations of fracture in bcc-Fe has been performed and evaluated, and also compared with the current results.     

各向异性的粘结钕铁硼／铁氧体永磁复合材料的磁性能

采用高性能的各向异性ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ磁粉和铁氧分与塑料复合,制成了各向异性粘结ＮｄＦｅＢ／铁氧体复合永磁材料研究了它们的磁性能。结果表明,随ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ含量增加,各向异性的塑料粘结ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ／铁氧体复合永磁材料磁性能ｂＨｃ和密度几乎是线性增大,而ｊＨｃ,（ＢＨ）ｍａｘ和Ｂｃ开始都增大,当达到一定值后基本保持不变,出现一平台,随后又继续增大,但ｊＨｃ与Ｂｒ和（ＢＨ）     

Shape design sensitivity analysis for non-linear anisotropic heat conducting solids and shape optimization by the BEM

Shape design sensitivity analysis (SDSA) expressions have been derived for non-linear anisotropic heat conducting solid bodies by following the material derivative concept and adjoint variable method of optimal shape design given in the literature. The variation of a general integral functional has been described in terms of primary and adjoint quantities evaluated at the varying boundaries. As an example problem in shape optimization, optimal outer boundary profiles of an orthotropic solid body are obtained by the boundary element method (BEM), after reformulating the SDSA equations in a form which is most suitable for the BEM.     

Characteristics of multi-element alloy cladding produced by TIG process

A multi-element alloy cladding was fabricated on low carbon steel by the TIG (tungsten inert gas) process using a multi-element alloy filler. The microstructure, crystal structure, and microhardness were evaluated using an SEM (scanning electron microscope), XRD (X-ray diffraction), EDS (energy dispersive X-ray analysis), and a microhardness tester. The wear resistance was also tested. A molybdenum-rich phase with a tetragonal structure and an Fe-rich phase with a body-centered cubic structure were obtained for the single layer cladding and double layer cladding of the alloy filler, respectively. The microhardness of the double layer (Hv 800) was greater than that of the single layer (Hv 500) due to the considerable increase in the molybdenum-rich phase. The cladding layer exhibited an excellent solution strength mechanism, and the wear resistance of the cladding was distinctly enhanced.     

Transient infinite elements for contaminant transport problems

A time-dependent infinite element which can be used to simulate contaminant transport problems in infinite media is presented in this paper. Since this transient infinite element is constructed in a global co-ordinate system instead of a local one, a closed-form solution for the property matrices of the element has been derived from an advection–diffusion/dispersion problem in a homogeneous, anisotropic infinite medium. The numerical results from the present transient infinite element have excellent agreements with the corresponding analytical solutions. Compared with the previous infinite elements, the present infinite element has the following special characteristics: (1) both space and time variables were explicitly considered in the formulation; (2) its property matrices were expressed in a closed form; (3) it can be used to represent the far field of a mass/contaminant transport problem in a homogeneous, anisotropic infinite medium; (4) it was constructed in a global co-ordinate system. Therefore, it is highly recommended that the transient infinite element be used for the numerical simulation of contaminant transport problems in infinite media.     

Control of the characteristics of a long-period grating by cladding etching

We have analyzed the effects of the fiber cladding radius on the characteristics of long-period fiber gratings. By etching the cladding of a common single-mode fiber, we verified the characteristics experimentally. When by etching we reduce the cladding radius of a common single-mode fiber on which a long-period refractive-index modulation has been imposed, the coupling strength of the core and the cladding modes increases. In addition, the difference in the propagation constants (for a fixed wavelength) between the core mode and the cladding modes increases; hence the resonant transmission dip wavelengths shift to longer wavelengths. The proposed method can be useful in making and detuning long-period fiber grating filters.     

Analysis and design of terahertz photonic crystal fibers by an effective-index method

An effective-index method (EIM) is used to analyze and design photonic crystal fibers (PCFs) for the terahertz radiation. By building an analogy between a conventional optical fiber and a PCF, the EIM solves the effective index of the fiber cladding and the effective modal index of a PCF analytically. The EIM is first validated by comparison with available data in the reference, showing that the role of material dispersion is negligible at higher frequencies. Terahertz PCFs with flattened dispersion are designed based on this method and the scaling property of the Maxwell equations.     

HDDR各向异性钕铁硼磁粉研究及应用进展

吸氢-歧化-脱氢-再复合工艺(HDDR)是生产各向异性钕铁硼磁粉的有效方法,其制备的各向异性粘结磁体性能高,重量轻,在提高微特电机功效、减轻重量等方面发挥着重要作用,目前在汽车、无人机等领域已产业化应用。为了提高磁粉性能,科研人员仍不断探究HDDR工艺与各向异性机理,采用晶界扩散法优化磁粉晶界结构,提高磁粉矫顽力与温度稳定性,同时将上述成果应用到废旧烧结钕铁硼回收中,节约稀土资源。HDDR各向异性磁粉性能显著高于各向同性磁粉的,但形变塑性次之,研究者试图将其作为热变形磁体前驱原材料,进一步提升热变形磁体性能。HDDR工艺细化晶粒的效果为提高烧结钕铁硼矫顽力提供了一条新的研究途径,但目前还未获得理想的成果。本研究主要介绍近年来HDDR工艺与机理的发展以及其在稀土磁体回收、热变形磁体、烧结磁体等方面的应用情况。     

Development of ternary-boride-based hard cladding material

A type of ternary-boride-based (TBB) hard cladding material (YF-2) has been developed successfully by a reaction sintering technique at 1563 K. The hardness of the cladding layer of YF-2 is about 84.5 HRA. Microstructure of YF-2 has been studied using scanning electron microanalyzer (SEM), X-ray diffraction (XRD) and electron probe microanalyzer (EPMA). Results show that the main composition of the cladding layer of YF-2 is TBB hard phase and ferrous-base binder phase, both of them distributed uniformly in the cladding layer. The bonding at the interface of the cladding layer and steel substrate is excellent, which has been confirmed by the three-point bend tests.     

The loss of the polarization dependence of diffraction reflection in chiral photonic crystals in the presence of anisotropic defects

The properties of defect modes in chiral photonic crystals with anisotropic defects are considered. The problem has been solved using the modified method of Ambartsumyan layer addition. The influence of the defect layer thickness and the optical axis orientation on the properties of defect modes is analyzed. At a certain thickness of the defect layer, the medium loses its main property, namely, the polarization dependence of diffraction reflection.     

Guided-mode analysis by the Lanczos-Fourier expansion

The Lanczos-Fourier series expansion is employed to analyze the guided-mode field in an asymmetrical slab waveguide, the core of which has an anisotropic and inhomogeneous dielectric permittivity. A system of linear homogeneous equations is derived by the collocation technique with consideration of the wave equation and the appropriate boundary conditions at the interfaces between the core and cladding media. The propagation constants are found from a determinant equation that ensures the existence of a nontrivial solution of the system. Numerical results are presented for several cases of dielectric permittivity, including the constant, parabolic, linear, and anisotropic cases. This approach is found to converge reasonably fast, and Richardson's extrapolation technique is applied to accelerate the convergence further. The approach can be easily generalized from the scalar to the vector equation, and, as an example, we consider the guided modes of a circular fiber.     

Refractive index and temperature sensitivity characteristics of a micro-slot fiber Bragg grating

Fabrication and characterization of a UV inscribed fiber Bragg grating (FBG) with a micro-slot liquid core is presented. Femtosecond (fs) laser patterning/chemical etching technique was employed to engrave a micro-slot with dimensions of 5.74 μm(h)×125 μm(w)×1388.72 μm(l) across the whole grating. The device has been evaluated for refractive index (RI) and temperature sensitivities and exhibited distinctive thermal response and RI sensitivity beyond the detection limit of reported fiber gratings. This structure has not just been RI sensitive, but also maintained the robustness comparing with the bare core FBGs and long-period gratings with the partial cladding etched off.     

45钢表面Ni基激光熔覆层的耐蚀性能

为改善45钢表面的力学性能和耐蚀性,在相同功率下采用不同扫描速率在其表面激光熔覆制备了Ni基(Ni35A)复合涂层。利用金相显微镜、X射线衍射仪、显微硬度计和电化学腐蚀测试系统对熔覆试样进行组织形貌、相组成、显微硬度和耐蚀性能分析。结果表明:熔覆试样由熔覆层、结合区和基体3部分组成;熔覆层组织细密并与基体冶金结合,扫描速率过大时易形成裂纹;熔覆层主要由FeNi3和Ni3B相组成,不同速率所得熔覆层显微硬度均超过400 HV;扫描速率为500 mm/min时熔覆试样自腐蚀电位提高了40 mV。     

Singular stress analysis of an anisotropic elastic medium containing polygonal holes using a novel hybrid finite element method

A novel hybrid finite element method based on a numerical procedure is proposed to compute singular field near V-shaped notch corners in an anisotropic material containing polygonal holes. The finite element method is established by the following three steps: (1) an ad hoc one-dimensional finite element formulation is employed to determined numerical eigensolutions of the singular field near an V-shaped notch corner; (2) a super corner tip element is constructed to determine the strength of the singular field, in which the independent assumed stress fields are extracted from the eigensolutions; (3) a novel hybrid finite element equation is obtained by coupling the super corner tip element with the conventional hybrid stress elements. In numerical examples, generalized stress intensity factors for interactions between two polygonal holes with various geometry, space position and material property are mainly discussed. All the numerical results show that present method yields satisfactory singular stress field solutions with fewer elements. Compared with the conventional finite element methods and integral equation methods, the present method is more suitable for dealing with micromechanics of anisotropic materials.     

A novel approach via combination of electrospinning and FDM for tri-leaflet heart valve scaffold fabrication

In this paper, a novel combination method of electrospinning and rapid prototyping (RP) fused deposition modeling (FDM) is proposed for the fabrication of a tissue engineering heart valve (TEHV) scaffold. The scaffold preparation consisted of two steps: tri-leaflet scaffold fabrication and heart valve ring fabrication. With the purpose of mimicking the anisotropic mechanical properties of the natural heart valve leaflet, electrospun thermoplastic polyurethane (ES-TPU) was introduced as the tri-leaflet scaffold material. ES-TPU scaffolds can be fabricated to have a well-aligned fiber network, which is important for applications involving mechanically anisotropic soft tissues. We developed ES-TPU scaffolds as heart valve leaflet materials under variable speed conditions and measured fiber alignment by fast Fourier transform (FFT). By using FFT to assign relative alignment values to an electrospun matrix, it is possible to systematically evaluate how different processing variables affect the structure and material properties of a scaffold. TPU was suspended at certain concentrations and electrospun from 1,1,1,3,3,3-hexafluoro-2-propanol onto rotating mandrels (200–3000 rpm). The scaffold morphological property and mechanical anisotropic property are discussed in the paper as a function of fiber diameter and mandrel RPM. The induction of varying degrees of anisotropy imparted distinctive material properties to the electrospun scaffolds. A dynamic optimum design of the heart valve ring graft was constructed by FDM. Fabrication of a 3D heart valve ring was constructed using pro-engineer based on optimum hemodynamic analysis and was converted to an STL file format. The model was then created from PCL which was sewed and glued with electrospun nanofibrous leaflets. This proposed method was proven as a promising fabrication process in fabricating a specially designed graft with the correct physical and mechanical properties.     

金属包覆材料固-液铸轧复合技术研究进展

金属包覆材料属于典型层状金属复合材料,是航空航天、石油化工、电力电子等领域的关键材料,其高效成形与性能控制技术一直是行业难点和国际研究热点.首先系统梳理了目前国内外金属包覆材料的典型制备工艺,并且根据初始时基体与覆层物理状态的不同将其分为3类,分别是固-固相复合法、固-液相复合法和液-液相复合法,对比分析了各种制备工艺的成形原理和主要特点.随后,从工艺原理、成形机理、复合机理、工艺优化等方面重点介绍了金属包覆材料固-液铸轧复合技术的最新研究进展.分析结果表明,以固-液铸轧复合技术为代表的融合塑性变形的固-液相复合工艺将成为行业未来一个重要发展方向,并且以固-液相复合法和液-液相复合法进行初态复合组坯,以固-固相复合法进行终态性能调控的一体化组合成形工艺具有良好发展前景.