多连体平面问题的差分解法及实例

本文仿结构力学的方法，用ｎ—１条截线，在某一特殊位置将多连体截成单连体，本文导出了截线处的以应力函数　为变量的应力衔接条件和位移连续条件，还导出了以　为变量的且满足上述条件的多连体在孔洞内承受不自相平衡荷载情况下相容差分方程，它与位移单值条件的差分表达式联立求解，就可求得各节点的　值，并用该方法解了一个具体问题，结果与光弹实验比较吻合．     

Effects of Filler Content on Mechanical Properties of Macroporous Composites

The mechanical properties of hydroxyapatite related macroporous biocomposites (MPBs) are influenced by a number of factors, such as the pore size, the filler content and the properties of the matrix and the inclusion. Failure often occurs when the strength of the implant cannot bear the applied mechanical load. In this study, the effects of filler content on the mechanical properties of MPBs have been investigated. A finite element (FE) unit cell model of a macroporous hydroxyapatite–polyetheretherketone (HA–PEEK) biocomposite structure with uniform and interconnected pores has been constructed. In the FE model, the HA particles were assumed to have random distribution, and particle volume fraction would be varied in the PEEK matrix. The material behaviours of both HA and PEEK have been implemented in the ABAQUS finite element code. HA was modelled to exhibit elastic behaviour and undergo plastic softening to a residual strength when a critical stress was reached, while the PEEK matrix would follow elastic–plastic behaviour. The macroscopic compressive stress–strain relations of the macroporous biocomposite structures have been predicted. Increasing particle volume fraction could lead to an increase in the compressive elastic modulus of the structures but a reduction in the compressive strength. The von Mises stress distribution and the effect of stress concentration in the structures with different filler content are also discussed. The proposed model could provide macro-structural and microscopic information of the macroporous biocomposite structure to the designers in order to facilitate the fabrication of this kind of structure with optimum mechanical properties.     

A numerical modeling for eigenvibration analysis of honeycomb sandwich panels

The eigenvibration properties of honeycomb sandwich panels are investigated in this paper. A new numerical modeling for eigenvibration analysis of the honeycomb sandwich panels is proposed under the assumption that the orthotropic shell and two kinds of beam elements represent face materials, adhesive layers and honeycomb core, respectively. The shell element is also connected to the beam element through the thickness. The effects of geometry of honeycomb core and thickness of face material on the eigenfrequency are examined through the comparisons between finite element simulation and experimental results. It is shown as a result that the eigenvibration properties depend strongly on the face material rigidity and honeycomb core geometry. The implications of the findings for the design of eigenvibration of honeycomb sandwich panels are discussed from the point of view of overall flexural rigidity.     

Effect of Geometry,Loading and Elastic Moduli on Critical Parameters in a Nanoindentation Test in Polymeric Matrix Composites with a Nonhomogeneous Interphase

Fiber nanoindentation models are developed for polymeric matrix composites with nonhomogeneous interphases. Using design of experiments, the effects of geometry, loading and material parameters on the critical parameters of the indentation test such as the load–displacement curve, the maximum interfacial shear and normal stresses are studied. The sensitivity analysis shows that the initial load–displacement curve is dependent only on the indenter type, and not on parameters such as fiber volume fraction, interphase type, thickness of interphase, and boundary conditions. The interfacial tensile radial stresses are not sensitive to indenter type, or to type and thickness of interphase, while the interfacial compressive radial stresses are sensitive mainly to boundary conditions and thickness of interphase; however, the influence of these factors on the interfacial radial stresses can be large. In contrast, the interfacial shear stress is sensitive to all factors, but the influence of the factors is relatively small.     

A Fiber-Bundle Pull-out Test for Surface-Modified Glass Fibers in GF/Polyester Composite

The development of high-performance polymer composites is tightly bound with the functional surface modification of reinforcements. A new method, based on the principle of the fiber-bundle pull-out test, is proposed to analyze the interfacial properties between the long fibers in the form of a bundle and the polymer matrix. Specimen geometry and a test fixture were designed using finite element analysis. The method was verified for unsized and sized glass fibers embedded in polyester resin to demonstrate its applicability for a wide range of adhesion between fibers and the polymer matrix. The pull-out test can be used for a relative comparison of different surface modifications if the bundle geometry is unknown. The results of high reproducibility and sensitivity for interfacial properties make the method attractive.     

Analysis and computation of thermal residual stresses at the fiber/matrix interface

Because of the importance of thermal residual stresses in composite materials, our study aims to compute them by the finite element method. Numerical analysis shows that these stresses need to be taken into account. The interface is affected by these stresses, particularly in the free edge. The discontinuity of the normal stresses along the interface and the shear value at the free edge influence the composite material behaviour during its use (e.g. the composite used as a patch for repairing a crack).     

Fracture and debonding behavior of coated brittle alumina layer on ductile aluminum substrate wire

The fracture and debonding behavior of the Al₂O₃ layer coated on a ductile aluminum substrate wire was studied experimentally and analytically. When tensile strain was applied, the brittle Al₂O₃ coating layer showed multiple cracking perpendicular to the tensile axis. After the multiple cracking, compressive fracture of the Al₂O₃ layer arose in the circumferential direction when the layer was thinner than around 30 μm, while interfacial debonding between the Al₂O₃ layer and aluminum substrate arose when it was thicker. Such a difference in behavior between thin and thick layers could be accounted for by the difference in the layer thickness-dependence of the tensile radial stress at the interface and the compressive hoop stress of the Al₂O₃ layer calculated by the finite element method; the former stress increases while the latter one decreases with increasing layer thickness.     

微盘电极上计时电流的数值模拟及其验证

本文引入了一种适用于二维电化学扩散问题研究的新的数值模拟方法[有限分析(FA)法], 并对微盘电极上的二维扩散问题进行了研究。模拟了微盘电极上的可逆及准可逆过程的计时电流, 并进行了实验验证, 实验与模拟结果很好地相符。     

Stress intensity factors for a finite plate with an inclined crack by boundary collocation

In this paper, we combine the Muskhelishvili＇s complex variable method and boundary collocation method, and choose a set of new stress function based on the stress boundary condition of crack surface, the higher precision and less computation are reached. This method is applied to calculating the stress intensity factor for a finite plate with an inclined crack. The influence of θ （the obliquity of crack） on the stress intensity factors, as well as the number of summation terms on the stress intensity factor are studied and graphically represented.     

Gelfand-Hille theorems for cesàro means

The growth conditions on the powers in the Gelfand-Hille theorems can be replaced by the same conditions on the Cesàro means, retaining the conclusions. Moreover, the assumptions can be further weakened on one of the two sides.