金属基耐磨铸造表面复合材料的现状及其今后研究工作的主攻方向

为了推动国内在金属基耐磨铸造表面复合材料领域的基础理论研究和应用的发展，对这类复合材料的制造工艺、耐磨性能和影响其质量的有关因素进行了综合介绍与评述。目前，金属基耐磨铸造表面复合材料的发展方兴未艾，尽管其制造工艺的研究，特别是对于它的摩擦学性能和影响其质量的因素之研究报道都还不多，然而毕竟已经取得了不少成果，这为它的进一步发展奠定了基础。通过对几个方面已经成功应用和可望投入应用之实例的简明阐述，展现了金属基耐磨铸造表面复合材料良好的实用前景，并就其今后的研究工作提出了几个值得重视的主攻方向。应当特别还强调指出的是，在对这类复合材料深入进行基础理论研究的同时，还必须大力开展其在工程上的应用研究，以不断拓展它的适用范围。     

Elastic fields of 2D and 3D misfit particles in an infinite medium

In micromechanics, accurate quantification of the elastic field (stress, strain, and displacement) caused by the presence of an inclusion in an infinite body is desired for both the particle and matrix materials. Ideally, the solution should be applicable to any particle geometry or shape and for any distribution of misfit along the interface (i.e. misfit profile). This work presents a dislocation-based numerical method, that is an extension to earlier work in this journal [Lerma, J.D., Khraishi, T., Shen, Y.L., Wirth, B.D., 2003. The elastic fields of misfit cylindrical particles: a dislocation-based numerical approach. Mech. Res. Commun. 30, 325–334], for determining the elastic fields of volume misfit particles with arbitrary misfit distribution or particle shape.     

瞬态波在层合板中传播的粘弹比拟法

本文发展了粘弹比拟理论,并将之用于求解半无限空间三层复合材料在垂直层合方向传播的瞬态波问题。对于层合板中应力波的传播问题,寻找到了一等效粘弹体,并用一种较好的Laplace变换的数值反演法求得了等效松弛函数和其它一些必要的辅助函数。用特征线法求得了等效粘弹体的应力和速度,进而得到了三层复合材料中心的应力、速度,进一步就得到了层中任意点的应力和速度。对于一个可由精确理论(射线理论)给出计算结果的问题,将粘弹比拟理论的结果和射线理论的结果进行了比较,结果表明,粘弹比拟理论对三层复合材料的瞬态波传播问题是相当成功的。     

A numerical approximation to the elastic properties of sphere-reinforced composites

Three-dimensional cubic unit cells containing 30 non-overlapping identical spheres randomly distributed were generated using a new, modified random sequential adsortion algorithm suitable for particle volume fractions of up to 50%. The elastic constants of the ensemble of spheres embedded in a continuous and isotropic elastic matrix were computed through the finite element analysis of the three-dimensional periodic unit cells, whose size was chosen as a compromise between the minimum size required to obtain accurate results in the statistical sense and the maximum one imposed by the computational cost. Three types of materials were studied: rigid spheres and spherical voids in an elastic matrix and a typical composite made up of glass spheres in an epoxy resin. The moduli obtained for different unit cells showed very little scatter, and the average values obtained from the analysis of four unit cells could be considered very close to the “exact” solution to the problem, in agreement with the results of Drugan and Willis (J. Mech. Phys. Solids 44 (1996) 497) referring to the size of the representative volume element for elastic composites. They were used to assess the accuracy of three classical analytical models: the Mori-Tanaka mean-field analysis, the generalized self-consistent method, and Torquato's third-order approximation.     

Effect of CNT length and CNT-matrix interphase in carbon nanotube (CNT) reinforced composites

The load transfer mechanisms and effective moduli of single-walled nanotube (SWNT) reinforced composites are studied using a continuum model. A “critical” fiber length is defined for full load transfer by numerically evaluating the strain-energy-changes for different fiber lengths. The effective longitudinal Young’s modulus and bulk modulus of the composite are derived. The effect of the interphase is also discussed. The results indicate the fiber length is critical both to the load transfer efficiency and effective moduli of the composite. The SWNT-matrix interphase plays an important role in load transfer efficiency but affects the effective moduli only slightly.     

Strain energy release rate for interfacial cracks in hybrid beams

The finite element modeling and fracture mechanics concept were used to study the interfacial fracture of a FRP-concrete hybrid structure. The strain energy release rate of the interfacial crack was calculated by the virtual crack extension method. It is shown that the crack growth has three phases, namely, cracking initiation, stable crack growth and unstable crack propagation. The effects of geometric and physical parameters of the hybrid beam on the energy release rate were considered. These parameters include Young’s moduli of the FRP, the concrete and the adhesive, thickness of the FRP plate and adhesive, and the distance of FRP plate end from the beam end. The numerical results show that the energy release rate of the interfacial crack is influenced considerably by these parameters. The present investigation can contribute to the mechanism understanding and engineering design of the hybrid structures.     

用内埋电阻丝检测复合材料层压板损伤的可行性研究

本文利用低速冲击装置冲击四周简支复合材料板试样，用以模拟低速低能量冲击而造成的分层损伤；用中心钻孔复合材料板试样用以模拟因高速冲击而造成穿透性损伤。探讨利用内埋康铜电阻丝阵列构成检测网络实现对复合材料中损伤位置和损伤程度检测。这种方法可利用较成熟的电测技术，装置简单，具有良好的工程应用前景     

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向钨中添加稀土氧化物能显著细化晶粒和提高钨合金的高温稳定性,且具有弥散强化效应,在抑制晶粒长大、控制再结晶晶粒的形状以及提高材料的力学性能方面效果显著。从制备稀土氧化物弥散强化钨基复合材料(ODS-W)粒子方法出发,阐述了几种ODS-W制备工艺的研究现状并对其发展趋势进行展望。     

Three Dimensional Branched Gold Nanostructures on Reduced Graphene Oxide Films Formed at a Liquid/Liquid Interface

Interfacing anisotropic gold nanostructures with graphene can open up new avenues for modifying the light–matter interaction of graphene. A chemical route is explored to synthesize branched gold nanostructures on reduced graphene oxide (rGO) layers by in situ reduction, assisted by binary surfactant mixtures containing tetraoctylammonium bromide with cetyltrimethy­lammonium bromide, sodium dodecylsulfate, or sodium citrate. The hybrid material self‐assembles at a liquid/liquid interface forming a free‐standing film. Electron microscopy studies reveal the morphology, microstructure, and crystallinity of the hybrids. The gold nanostructures are branched in three dimensions and possess various shapes, such as irregular stars, multipods, and spiky features, interspersed with rGO layers. The hybrids exhibit plasmon modes in the visible and near‐infrared region due to the shape anisotropy. The enhancement effect of the spiky features is also observed in the Raman spectra. The growth mechanism of the branched nanostructures is followed by kinetic studies and indicates that the formation of multiple twinned crystals is the key factor for branching.     

Influence of Position on the Microstructure of Carbon Black/Polyvinyl Alcohol Composite Obtained by the Directional Freeze-drying Process

Carbon black (CB)/polyvinyl alcohol (PVA) composites with porous structure were obtained by a directional freeze-drying process of their solution in water. The microstructures of this composite at different positions through the thickness were investigated. The study shows that the composite formed a lamellar structure at the lower surface of the specimen because of the basic crystallographic and crystal growth characteristics of ice. The composite near the top surface of the specimen showed an alignment direction of the ice vertical to the container's wall and the direction of solution lowering into the liquid nitrogen. The alignment direction deflects gradually and finally converges with the aligned direction grown from the bottom position near the middle part of the CB/PVA composite. The ice crystals grow very fast along the direction of temperature gradients, which results in that a small fraction of PVA solute was entrapped within the ice crystals, leading to the formation of trans-bridge lamellar structure near the top surface of the specimen. This result shows that the position in the sample has a great influence on the structure of the porous CB/PVA composite obtained by the directional freeze-drying process.