Single-fiber electromechanical pull-out testing and its application to studying the interface between steel fiber and cement

The experimental technique of single-fiber electromechanical pull-out testing was introduced and used to study the interface between steel fiber and cement. The technique involves measuring both the contact electrical resistivity between fiber and matrix and the shear bond strength in a fiber-matrix interface sample. Samples that are identically prepared differ in contact resistivity and bond strength, which correlate. The correlation allows determination of even small differences in bond strength due to differences in sample preparation conditions, such as fiber surface treatment, cement curing age and admixtures to the cement paste. It also gives information on the structure of the interface and allows the bond strength to be non-destructively determined by measuring the contact resistivity.     

A possible interpretation of CDF dijet mass anomaly and its realization in supersymmetry

Recently, the CDF Collaboration reports an anomaly in dijet mass distribution in association with a lepton and missing energy. We discuss a possibility that the origin of the lepton and missing energy comes not from a W boson but a new boson particle, which is also responsible for the dijet mass peak. We show that such a situation can be realized in the framework of the minimal supersymmetric standard model and the dijet anomaly can be explained.     

干涉条纹大数计数软件新方法及其实现

提出了一种根据干涉条纹信号过上升沿与下降沿阈值计数的异同及其起始和结束位置幅值判断的软件大数计数新方法,解决了在干涉条纹信号开始和结束位置可能出现±1计数误差的问题,进行了实现新计数方法的干涉测量实验。实验结果表明了该软件大数计数新方法的正确性。     

一种二维自适应网格构造方法及其实现

讨论了一种二维自适应网格的构造方法,在二维插值法的基础上做出了自适应网格。最后利用自适应网格技术对一个二维流体力学问题的实例进行了计算。     

Adhesive bonding of composite aircraft structures: Challenges and recent developments

In this review paper,the challenges and some recent developments of adhesive bonding technology in composite aircraft structures are discussed.The durability of bonded joints is defined and presented for parameters that may influence bonding quality.Presented is also,a numerical design approach for composite joining profiles used to realize adhesive bonding.It is shown that environmental ageing and pre-bond contamination of bonding surfaces may degrade significantly fracture toughness of bonded joints.Moreover,it is obvious that additional research is needed in order to design joining profiles that will enable load transfer through shearing of the bondline.These findings,together with the limited capabilities of existing non-destructive testing techniques,can partially explain the confined use of adhesive bonding in primary composite aircraft structural parts.     

用双线列阵区分左右舷目标的延时估计方法及其实现

双线列阵声呐可以利用自身的指向特性区分左右舷目标,但是其性能受线阵间距的约束,且存在分辨盲区。本文提出利用两个单线阵接收信号的时延差区分左右舷目标的方法。该方法对线阵间距具有宽容性,并且盲区明显减小。给出了理论分析结果和实施技术方法,提出了基于内插法的延时精确估计方法,从而可以解决左右舷目标的分辨问题。     

The time-delay estimation method of resolving left-right target ambiguity for twin-line array and its realization

The directivity function of twin-line array sonar can be used to identify left/right target. But the performance is limited by the distance between two lines and also exists the blind area for target identification. A method, which is based on the time-delay estimation between two line arrays, is proposed to identify left/right target. The method is robust with the variation of distance between two line array, the blind area is considerable decreased. The theoretical analysis results and realization method is described. An algorithm base on interpolation method for precisely estimating tune-delay of two line array are derived, therefore the left-right ambiguity problem is solved.     

Interface and its effect on the interlaminate shear strength of novel glass fiber/hyperbranched polysiloxane modified maleimide-triazine resin composites

Interface is the key topic of developing advanced fiber reinforced polymeric composites. Novel advanced glass woven fabric (GF) reinforced composites, coded as GF/mBT, were prepared, of which the matrix resin was hyperbranched polysiloxane (HBPSi) modified maleimide-triazine (mBT) resin. The influence of the composition of the matrix on the interfacial nature of the GF/mBT composites were studied and compared with that of the composite based on GF and BT resin using contact angle, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and dielectric properties over wide frequency and temperature ranges. Results show that the interfacial nature of the composites is dependent on the chemistries of the matrices, mBT matrices have better interfacial adhesion with GF than BT resin owing to the formation of chemical and hydrogen bonds between mBT resin and GF; while in the case of mBT resins, the content of HBPSi also plays an important role on the interfacial feature and thus the macro-performance. Specifically, with increasing the content of HBPSi in the matrix, the interlaminate shear strength of corresponding composites significantly improves, demonstrating that better interfacial adhesion guarantees outstanding integrated properties of the resultant composites.     

Effect of electric field,stress and environment on delayed fracture of a PZT-5 ferroelectric ceramic

The combined effect of electric and mechanical loading on fracture of a PZT-5 ferroelectric ceramic in silicone oil has been investigated using a single edge notched specimen. The results show that the fracture toughness and the threshold stress intensity factor of delayed fracture in silicone oil, i.e. stress corrosion cracking, decrease linearly with the increasing applied electric field, either positive or negative. For the PZT-5 ferroelectric ceramics, delayed fracture in silicone oil under sustained positive or negative field can occur, and the threshold field for delayed fracture under sustained positive or negative field decreases linearly with applied stress intensity factor. The combined effect of electric and mechanical loading on delayed fracture in silicone oil includes field-enhancing delayed fracture under sustained load and stress-enhancing delayed fracture in silicone oil under sustained field.     

Physical model of acoustic forward scattering by cylindrical shell and its experimental validation

Research on the underwater target scattering can provide important theoretical support for target detection. The scattering model of cylindrical shell is established in this paper. It is found that the forward target strength is much stronger and varies with angles of incident wave less significantly than backward target strength. The received forward signal strength fluctuates with the target moving due to the interference between direct signal and scattering signal, which is most significant when target approaches the baseline. An experiment is carried out in an anechoic tank to validate the scattering model. The method of acquisiting forward scattering in the tank is proposed. The forward and the backward target strengths are achieved by using the pulse compression technology, and they are about 3dB less than the modeling results. The forward scattering phenomena of quiescent and moving target are measured, which are similar to modeling results with different target types.     

叶栅风洞控制方法分析与实现

为解决叶栅风洞气罐容量小气源压力下降快给流场控制带来的难题,采用动态变参数和积分分离PID控制算法实现了叶栅风洞流场快速稳定和目标压力高精度控制目的;以调压阀后压力为控制点,采用叶栅入口压力误差值对控制点压力进行修正的方法,解决了常压和增压试验中控制滞后问题;变参数PID控制和选用具有确定对应关系控制点并对实际误差进行修正的方法,对小型暂冲风洞高精度压力控制和滞后问题的解决具有一定借鉴意义。     

Quantifying the grain boundary resistance against slip transfer by experimental combination of geometric and stress approach using stage-I-fatigue cracks

In recent studies, many groups have investigated the interaction of dislocations and grain boundaries by bi-crystals and micro-specimen experiments. Partially, these experiments were combined with supplementary simulations by discrete dislocation dynamics, but quantitative data for the grain boundary resistance against slip transfer is still missing. In this feasibility study with first results, we use stage-I-fatigue cracks as highly localised sources for dislocations with well-known Burgers vectors to study the interaction between dislocations in the plastic zone in front of the crack tip and selected grain boundaries. The stress concentration at the grain boundary is calculated with the dislocation-free zone model of fracture using the dislocation density distribution in the plastic zone from slip trace height profile measurements by atomic force microscopy. The grain boundary resistance values calculated from common geometric models are compared to the local stress distribution at the grain boundaries. Hence, it is possible to quantify the grain boundary resistance and to combine geometric and stress approach for grain boundary resistance against slip transfer to a self-contained concept. As a result, the prediction of the grain boundary resistance effect based on a critical stress concept is possible with knowledge of the geometric parameters of the grain boundary only, namely the orientations of both participating grains and the orientation of the grain boundary plane.     

超混沌振荡器的单变量单向耦合同步及其电路实验仿真

研究了一个超混沌振荡器的耦合同步问题,只用单变量单向耦合就可实现两个超混沌振荡器的同步.本方法的最大特点是易于工程实现.数值研究和电路实验仿真证明了本方法的有效性.电路实验仿真中出现一种新的同步现象,即系统的某个变量达到广义同步时,其他变量还可以实现精确同步     

Diffractive optics: Design, realization, and applications

This paper presents methods for designing and recording optimal computer-generated diffractive optical elements. The design method is based on an analytic ray-tracing procedure for minimizing aberrations. The recording involves computer-generated masks and multiple lithographic processes in order to form reflective and transmissive multilevel, surface relief-phase, diffractive elements. As a result, the elements can have high diffraction efficiencies over a broad range of incidence angles. Even generalized diffractive elements that operate with highly uniform diffraction efficiency and polychromatic radiation can be designed and recorded by optimizing the shape and height of the relief gratings. To illustrate the effectiveness of the diffractive optical elements, they have been incorporated into a number of applications, involving visible as well as infra-red radiation. Some that deal with coordinate transformation, beam shaping, and polarization control are briefly reviewed.     

A method for measuring bending stresses based on electromagnetic actuation and Raman spectroscopy

Bending stress and fracture strength of micromachined structures are the parameters determining the function and life span of microelectromechanical systems (MEMS) and are also indispensable data for MEMS design. This paper reports the results of a study in which a bending stress measurement method based on electromagnetic actuation and Raman spectroscopy has been examined. In this study, an eight‐cantilever mass structure is chosen as the experimental object. The results have indicated that it can accurately measure the bending stresses and fracture strength. Copyright © 2006 John Wiley & Sons, Ltd.     

Microstructure and Mechanical Properties of Novel High-Strength,Low-Activation Wx(TaVZr)100−x (x = 5, 10, 15, 20, 25) Refractory High Entropy Alloys

In this work, novel high-strength, low-activation W_x(TaVZr)_100−x (x = 5, 10, 15, 20, 25) refractory high entropy alloys (RHEAs) were prepared by vacuum arc melting. Their microstructure, compressive mechanical properties, hardness, and fracture morphology were investigated and analyzed. The results show that the RHEAs possess a disordered BCC phase, ordered Laves phase, and Zr-rich HCP phase. Their dendrite structures were observed, and the distribution of dendrites became gradually more dense with an increase in W content. The RHEAs demonstrate high strength and hardness, with these properties being higher than in most reported tungsten-containing RHEAs. For example, the typical W₂₀(TaVZr)₈₀ RHEA has a yield strength of 1985 MPa and a hardness of 636 HV, respectively. The improvement in terms of strength and hardness are mainly due to solid solution strengthening and the increase in dendritic regions. During compression, with the increase in the applied load, the fracture behavior of RHEAs changed from initial intergranular fractures to a mixed mode combining both intergranular and transgranular fractures.     

Compositional effect on thermo-mechanical,thermal and tensile properties of cis-polyisoprene and chloroprene rubber blends

Blends of cis-polyisoprene (CPI) and chloroprene rubber (CR) have been prepared in different blend compositions by solution casting. Structural characterization of these blends has been done using X-ray diffraction and scanning electron microscopy. The experimental values of thermo-mechanical properties, mechanical properties and thermal conductivity of so-prepared blends determined using dynamic mechanical analyzer and thermal constant analyzer have been presented. Crosslink density has been determined using different models. Experimental results from thermo-mechanical properties show that all the blends are immiscible. Tensile strength, toughness, Young's modulus and thermal conductivity of these blends were found to be higher than that of pure CPI and pure CR. However, mechanical properties of 25/75(V/V) of CPI/CR blend and thermal conductivity of 75/25(V/V) of CPI/CR blend have been found to be highest.     

Effect of Point and Line Defects on Mechanical and Thermal Properties of Graphene: A Review

New materials with distinctive properties are arising and attracting the scientific community at regular intervals. Stiffness and strength are the important factors in determining stability and lifetime of any technological devices, but defects which are inevitable at the time of production can alter the structural properties of any engineering materials. Developing graphene with specific structural properties depends upon controlling these defects, either by removing or deliberately engineering atomic structure to gain or tailoring specific properties. In this article, a comprehensive review of defective graphene sheets with respect to its mechanical and thermal properties are presented and examined.     

Binary polarization pupil filter: Theoretical analysis and experimental realization with a liquid crystal display

The Jones matrix formalism has been applied to evaluate the response of an optical system when a non-uniform polarizing pupil is introduced. With this formalism we analyze and experimentally demonstrate the properties of a binary polarization pupil filter having two regions with two orthogonal linear polarization orientations. We first study the case when no analyzer is placed behind the pupil filter, and both, the transversal and the axial behavior are described in terms of the intensity and the local state of polarization. Then it is shown how the response of the optical system can be easily changed through the orientation of an analyzer placed behind the pupil. We experimentally verified the theory using a twisted nematic liquid crystal display, which produces two orthogonal linear polarization states for two different addressed voltages.