正交各向异性压磁电弹性矩形板的稳定问题

从压磁电弹性力学的三维平衡方程和本构关系出发,推导得到了正交各向异性压磁电弹性矩形板稳定问题的状态方程。求解状态方程并结合边界条件得到了稳定问题的屈曲方程。给出了临界应力的算例。     

Analysis of blank thickening in deep drawing processes using the theory of a Cosserat generalized membrane

This paper analyzes a transient, nonlinear deep drawing process where a circular blank of a rigid-plastic material is forced by a rigid circular punch to deform into a cylindrical cup. Attention is focused on the plastic flow beneath the blank-holder. Using the Cosserat theory of a generalized membrane it is possible to obtain analytical solutions which examine the following two major effects: (a) the importance of added “rim pressure” acting on the outer edge of the blank; and (b) the importance of a controlled moveable blank-holder to allow blank thickening during the drawing process. Guided by these analytical results, a new deep drawing machine was built to exploit these effects and increase the limit drawing ratio (LDR) of the drawing process. Specifically, the LDR (in one stroke) reached the value of 3.16 compared with the value of about 2.0 in the conventional process. Moreover, the analytical prediction of the punch force versus the punch stroke is in good agreement with the experimental data and with simulations using the computer code DYTRAN.     

Solution of Müller's paradox of frame dependence in mixtures of polymeric liquid crystals

Recently, there appeared in this journal a short review article by Müller ((2002), 14: 227–229), in which it was argued that the internal energy of a reacting mixture of liquid crystals should not be an objective quantity (i.e., a quantity independent of the referential frame). Such a paradoxical conclusion has revealed the urging necessity for a better comprehension of the interactions taking place in structured mixtures, specially when referred to non-inertial observers. This work shows that Müller's paradox is avoided when all inertial effects are carefully accounted for. Further, it predicts interesting phenomena without analogue in reacting mixtures of structureless fluids: internal inertial effects, produced by a combination of mass exchanges (e.g. by chemical reactions or phase changes) with the extra degrees of freedom posed by the microstructure. Such effects clarify the reasons why inertial forces and couples acting on a mixture do not always coincide with the sum of the inertial forces and couples exerted upon its individual constituents. The present conclusions establish a reinterpretation of some fundamental concepts of continuum mechanics and thermodynamics, including a deeper understanding of the manner in which total energy and momenta are conserved in complex media. Received: July 25, 2002 / Published online: February 17, 2003 Communicated by Kolumban Hutter, Darmstadt e-mail: faria@mechanik.tu-darmstadt.de     

压电介质二维边界积分方程中的基本解

由于压电介质的变形－电场耦合效应及压电响应的各向异性，使解析求解压电介质问题的工作变量十分复杂，若采用边界元数值方法求解，必须具备积分方程中的基本解，本文根据电磁场方程及连续介质力学的耦合性质论层出了二维无限域中分别在单位力及单位电荷载作用下的位移场，电势场、应力场和电位移场的解，从而确立了边界积分方程中所必需的八个基本解。     

粗糙表面滑动轴承非牛顿介质润滑的计算

分析了轴承润滑中非牛顿介质的流变特性以及轴承表面形貌对润滑效果的影响,推导出了修正的雷诺方程,在方程中用差分粘度和第一正应力差函数表征非牛顿介质的流变特性,采用流量因子表征表面形貌的作用.结果表明:差分粘度的变化是影响润滑结果的主要因素,它取决于不同介质的动态参数和剪切频率范围,非牛顿介质润滑的承载力并非总高于或低于牛顿介质;在动载荷条件下,第一正应力差效应使油膜压力明显增大;影响流量因子的2个因素为表面形貌的粗糙度和纹理,但其作用远小于非牛顿介质流变特性的影响.     

Finite Inhomogeneous Shearing Deformations of a Transversely Isotropic Incompressible Material

The present paper deals with finite inhomogeneous shearing deformations of a slab of a special anisotropic solid. Two cases according to the directions of the anisotropic director of the medium are examined. In one case the solution reduces to a quadrature and gives an exact deformation field for particular values of the material constants. In the other case an exact solution is obtained. All such solutions reduce to the same existing solution for the corresponding isotropic elastic material. This revised version was published online in August 2006 with corrections to the Cover Date.     

Numerical simulation of a fluid-saturated soil under a dynamically loaded pile

The behaviour of the soil under a dynamically loaded pile toe is studied. The soil is modelled as a fluid saturated porous continuum. The constitutive behaviour of the solid skeleton is described by the elasto-plastic model of Drücker-Prager. The wave propagation is simulated with a dynamical finite-element program.A two-phase model of soil gives useful information about effective stress and pore pressure in the soil. In saturated soil the main wave under the pile toe propagates more downards than in dry soil, due to the higher compressional stiffness in saturated soil. The plastic zone under the pile toe propagates with the velocity of the fast compressional wave. The pore fluid influences the plasticity strongly and can be expected to affect pile driving too.The distribution of effective stress and pore pressure under the pile toe depends on the permeability of the soil and cannot be calculated uniquely from a single-phase calculation. Therefore, a nonlinear soil cannot be modelled correctly as a conventional single-phase material.     

Flow through isotropic granular porous media

A generalization of the Navier-Stokes equation is developed to include laminar flow through a rigid isotropic granular porous medium of spatially varying permeability. The model is based on a theory of interspersed continua and the mean geometrical properties of an idealized granular porous microstructure. The derived momentum transport equations are applicable to granular porous media over the entire porosity range from zero through unity. No restriction with respect to flow velocity is imposed, except for the assumption of laminar flow within the pores. The results provide useful and versatile equations and substantiate many of the empirical equations currently in use. One of the major advantages of the generalized momentum equation is its adaptability to numerical simulation.     

One‐Pot Cannizzaro Cascade Synthesis of ortho‐Fused Cycloocta‐2,5‐dien‐1‐ones from 2‐Bromo(hetero)aryl Aldehydes

An intramolecular Cannizzaro‐type hydride transfer to an in situ prepared allene enables the synthesis of ortho‐fused 4‐substituted cycloocta‐2,5‐dien‐1‐ones with unprecedented technical ease for an eight‐ring carboannulation. Various derivatives could be obtained from commercially available (hetero)aryl aldehydes, trimethylsilylacetylene, and simple propargyl chlorides in good yields.     

基于区间直觉模糊不确定语言的中小企业电子商务网站建设决策方法研究

阐述中小企业在整个国民经济中的重要地位,指出电子商务对于中小企业具有天然的适应性和可行的推广性.揭示研究对象中蕴含着广泛的模糊性,应用区间直觉模糊不确定语言的必要性.介绍区间直觉模糊不确定语言的基本概念、基本运算、算术平均和加权平均、距离、期望函数、精度函数、期望函数值、精度函数值以及对象比较方法等内容.提出区间直觉模糊不确定语言决策步骤:设定方案集、指标集、专家集,确定评判矩阵,确定指标权重,计算加权平均,计算期望函数、精度函数,期望函数值、精度函数值,进行排序.以盛东商贸有限公司电子商务网站设计方案测评为例,碍出方案3优于方案2优于方案5优于方案1优于方案4的结论.