Numerical Study of Scale Effects of Ultra-Thin Nickel Beams

Recent experiments have shown that metallic materials display significant size effects when the characteristic length scale of non-uniform plastic deformation is close to a micron. Couple stress plasticity has been developed to explain such phenomena by Fleck and Hutchinson. The mechanical behaviors of ultra-thin nickel beams in different boundary conditions were studied with the hybrid element developed for couple stress plasticity before. Strong scale effects are found when the beam's thickness is close to the material characteristic length scale. Such phenomena will disappear if the beam' s thickness is greatly larger than the material characteristic length scale. The scale effect is the beams inherent property and it does not change with the change of support conditions.     

Finite element simulation of the mechanics of flat contact pad fretting fatigue tests

An understanding into the macro kinetic and kinematic behaviour of fretted surfaces is provided. Making use of a modified version of a previously developed in‐house two‐dimensional elastic–plastic finite element analysis numerically simulates flat contact pad fretting fatigue tests. Basic macro mechanics concepts are adopted to idealise two bodies with rough contact surfaces and loaded at two different sites with arbitrary axial loading profiles. A time scale factor is devised to recognise the earliest candidate out of the events possibly accommodated at each loading increment. The present analysis utilises a relevant experimental set up developed in the Structural Integrity Research Institute of the University of Sheffield as an application. Computational results accurate to within 1.2% and corresponding to one contact pad span and six constant normal loads acting individually with four amplitudes of two sinusoidal axial load cycles are presented. The present computations include (1) the development of the global and local normal and tangential reactions and relative sliding displacement acting along the fretting surfaces and (2) contact pad deformation, generated stress fields and plasticity development within the neighbouring region of the fretted area.     

Influence of Membrane Stresses on Postbuckling of Rectangular Plates Using a Nonlinear Elastic 3-D Cosserat Brick Element

This paper has two main objectives. The first is to examine the influence of membrane stresses on postbuckled deformations of nonlinear elastic isotropic rectangular plates. The second is to further examine the accuracy of a new 3-D Cosserat eight noded brick element (Nadler and Rubin in Int J Solids Struct 40: 4585–4614, 2003) which was developed within the context of the theory of a Cosserat point. The equations of the Cosserat element include both material and geometric nonlinearities. A number of example problems are considered which examine predictions of the Cosserat element for beams and plates and comparison has been made with results from the commercial codes ANSYS and ADINA. Also, the approximate nonlinear postbuckling solution described in Timoshenko and Gere (Theory of elastic stability, Mc Graw-Hill, New York) is shown to be more limited than originally expected. These results suggest that the Cosserat element is robust, can perform well under extreme conditions and is capable of modeling combinations of three-dimensional bodies with attached thin structures.     

碳铬镍含量对高铬铸铁测温保护管性能的影响

通过高温氧化和高温磨损实验,研究了C、Cr、Ni 3个主要元素对高铬铸铁在高温条件下抗氧化和抗磨损性能的影响。结果表明:Cr含量越高,抗氧化性能和抗磨损性能越好;提高碳含量,明显提高高铬铸铁的高温抗磨性能;当w(Cr)=16％时,加入Ni能提高高铬铸铁的高温抗氧化性能;w(Cr)=30％时,Ni对高铬铸铁的抗氧化性能和抗磨损性能影响不明显.在1100℃以下,选用w(C)=2.8％,w(Cr)=30％、不加Ni的高铬铸铁铸造高温抗磨热电偶保护管,既有较好的使用寿命,又可降低成本.     

How disorder can diminish avalanche risks: effect of size distribution

We study the behavior of disk assemblies with a variable disorder distribution. The packing is first consolidated and then continuously tilted very slowly. The amount of displaced disks for each tilted angle is recorded. Large displacements of the disks can occur due to some local or global mechanical instabilities. The definition of neighboring disks is based on radical (extension of Voronoï) tessellation rules to decompose, in a unique and perfectly defined manner, the two-dimensional space for polydisperse disks. In this way, by comparing the characteristics of stability for one disk to the neighboring ones for local ordered cluster, we can predict the global amount of displaced disks. Some tilting cycles have been performed to check the correlation between the instability of the packing structure (collective displacements) with micro and macro order parameters.     

Numerical experiments of preconditioned Krylov subspace methods solving the dense non-symmetric systems arising from BEM

Discretization of boundary integral equations leads, in general, to fully populated non-symmetric linear systems of equations. An inherent drawback of boundary element method (BEM) is that, the non-symmetric dense linear systems must be solved. For large-scale problems, the direct methods require expensive computational cost and therefore the iterative methods are perhaps more preferable. This paper studies the comparative performances of preconditioned Krylov subspace solvers as bi-conjugate gradient (Bi-CG), generalized minimal residual (GMRES), conjugate gradient squared (CGS), quasi-minimal residual (QMR) and bi-conjugate gradient stabilized (Bi-CGStab) for the solution of dense non-symmetric systems. Several general preconditioners are also considered and assessed. The results of numerical experiments suggest that the preconditioned Krylov subspace methods are effective approaches solving the large-scale dense non-symmetric linear systems arising from BEM.     

Nodally exact Ritz discretizations of 1D diffusion–absorption and Helmholtz equations by variational FIC and modified equation methods

This article presents the first application of the Finite Calculus (FIC) in a Ritz-FEM variational framework. FIC provides a steplength parametrization of mesh dimensions, which is used to modify the shape functions. This approach is applied to the FEM discretization of the steady-state, one-dimensional, diffusion–absorption and Helmholtz equations. Parametrized linear shape functions are directly inserted into a FIC functional. The resulting Ritz-FIC equations are symmetric and carry a element-level free parameter coming from the function modification process. Both constant- and variable-coefficient cases are studied. It is shown that the parameter can be used to produce nodally exact solutions for the constant coefficient case. The optimal value is found by matching the finite-order modified differential equation (FOMoDE) of the Ritz-FIC equations with the original field equation. The inclusion of the Ritz-FIC models in the context of templates is examined. This inclusion shows that there is an infinite number of nodally exact models for the constant coefficient case. The ingredients of these methods (FIC, Ritz, MoDE and templates) can be extended to multiple dimensions     

Modeling the effect of pigment morphology on the dynamic compression of coating layers using DEM

In the present paper, discrete element method (DEM) was employed to investigate the effect of pigment morphology on packing dynamics and compressive behavior of paper coating layers in calendering process. Spherical, platy, and needle-like particles, representing GCC, delaminated clay, and aragonite PCC pigments, were considered in this study. For each particle shape, the compression of coating structures formed by mono-sized and poly-dispersed pigments were modeled. Stress–strain behavior of the coating layers and in-plane and out-of-plane movements of the pigment particles during the compression were computed under the same maximum compressive stress. Simulation results revealed that the in-plane movements of the pigment particles during compression in the calender nip were small in magnitude (<0.35 μm). These findings help to better understand the smoothening phenomena of coating structures during the calendering process.     

基于ANSYS的铸嘴流体耦合场三维有限元仿真分析

作者用大型有限元分析软件ANSYS对铸嘴内稳态层流铝熔体进行仿真分析。实现了三维建模。解决了三维热一流耦合求解的问题，得到铝流体的速度、压力及温度的分布图。分析了铸嘴出口速度和温度的分布规律及其对连续铸轧的影响。     

Hybrid numerical scheme for time-evolving wave fields

Many problems in geophysics, acoustics, elasticity theory, cancer treatment, food process control and electrodynamics involve study of wave field synthesis (WFS) in some form or another. In the present work, modelling of wave propagation phenomena is studied as a static problem, using finite element method and treating time as an additional spatial dimension. In particular, WFS problems are analysed using discrete methods. It is shown that a fully finite element-based scheme is very natural and effective method for the solution of such problems. Distributed WFS in the context of two-dimensional problems is outlined and incorporation of any geometric or material non-linearities is shown to be straightforward. This has significant implications for problems in geophysics or biological media, where material inhomogeneities are quite prevalent. Numerical results are presented for several problems referring to media with material inhomogeneities and predefined absorption profiles. The method can be extended to three-dimensional problems involving anisotropic media properties in a relatively straightforward manner. Copyright © 2006 John Wiley & Sons, Ltd.