An improved ‘assumed enhanced displacement gradient’ ring‐element for finite deformation axisymmetric and torsional problems

Analyzing axisymmetric solids under torsional loading the 3d(imensional) problem can always be reduced by one dimension, since the displacement field and the rotation field are independent of the cylindrical (angle) co‐ordinate Θ, respectively. For this purpose a four‐node ring‐element for finite deformation axisymmetric and torsional problems was recently developed and is now going to be up‐dated. The original assumption of the enhanced displacement gradient H̃ = α _i⊗ G ⁱ is expanded in two steps according to Simo, Armero and Taylor and to Glaser and Armero, respectively: firstly in defining the additional unknowns (parameters) α _i as objects in the material configuration and pushing forward H̃ by ( 1 + U ⊗ Grad ) ∣ξ=0—this provides ‘objectivity’—and secondly in replacing α _i⊗ G ⁱ by G _i⊗ α ⁱ. Numerical results of three classical benchmarks, the in‐plane torsion test, the copper rod impact and the thermomechanical localization of a rectangular strip are presented. Copyright © 2001 John Wiley & Sons, Ltd.     

Effects of mechanical deformations on the structurization and electric conductivity of electric conducting polymer composites

Structural changes proceeding in composites under the effect of various mechanical deformations (stretching, compression, shear, etc.) affect the structure of an electrical conducting system. Mechanical stresses, induced by deformation of composite materials during deformation, affect both the molecular and supermolecular structure of polymers. As a consequence, they also affect a substructure bound to it and composed of filler particles. It is evident that in the case of conducting polymer composites, mechanical deformations should reflect electric conductivity of materials. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 601–621, 1999     

热压罐成型工艺所用框架式模具的变形分析

模具在使用过程中的变形会影响到复合材料制件的固化变形,为了控制复合材料制件的成型质量,就要了解框架式模具在热压罐固化成型工艺过程中的变形情况。建立了模具变形的数值模拟预报方法,将计算结果与实际模具测量结果进行对比,本文中所提供的有限元分析计算模型可对实际情况进行较为精确的模拟。考察了平板型框架式模具在整个固化工艺过程中的变形情况,数值计算结果表明：型面翘曲变形量与模具温度的分布有关,而与模具温度的大小无关;模具翘曲变形量的峰值出现在降温阶段的中间时刻,且该变形量能够保持一段时间;最大变形时刻整个模具型面与进入热压罐前相比中心位置的变形最大,周边位置的变形最小。     

Smooth C1‐interpolations for two‐dimensional frictional contact problems

Finite deformation contact problems are associated with large sliding in the contact area. Thus, in the discrete problem a slave node can slide over several master segments. Standard contact formulations of surfaces discretized by low order finite elements leads to sudden changes in the surface normal field. This can cause loss of convergence properties in the solution procedure and furthermore may initiate jumps in the velocity field in dynamic solutions. Furthermore non‐smooth contact discretizations can lead to incorrect results in special cases where a good approximation of the contacting surfaces is needed. In this paper a smooth contact discretization is developed which circumvents most of the aformentioned problems. A smooth deformed surface with no slope discontinuities between segments is obtained by a C¹‐continuous interpolation of the master surface. Different forms of discretizations are possible. Among these are Bézier, Hermitian or other types of spline interpolations. In this paper we compare two formulations which can be used to obtain smooth normal and tangent fields for frictional contact of deformable bodies. The formulation is developed for two‐dimensional applications and includes finite deformation behaviour. Examples show the performance of the new discretization technique for contact. Copyright © 2001 John Wiley & Sons, Ltd.     

An extension of Key's principle to nonlinear elasticity

A variational principle for finite isothermal deformations of anisotropic compressible and nearly incompressible hyperelastic materials is presented. It is equivalent to the nonlinear elastic field (Lagrangian) equations expressed in terms of the displacement field and a scalar function associated with the hydrostatic mean stress. The formulation for incompressible materials is recovered from the compressible one simply as a limit. The principle is particularly useful in the development of finite element analysis of nearly incompressible and of incompressible materials and is general in the sense that it uses a general form of constitutive equation. It can be considered as an extension of Key's principle to nonlinear elasticity. Various numerical implementations are used to illustrate the efficiency of the proposed formulation and to show the convergence behaviour for different types of elements. These numerical tests suggest that the formulation gives results which change smoothly as the material varies from compressible to incompressible.     

Running Accuracy Analysis of a 3-RRR Parallel Kinematic Machine Considering the Deformations of the Links

Parallel kinematic machines have drawn considerable attention and have been widely used in some special fields.However,high precision is still one of the challenges when they are used for advanced machine tools.One of the main reasons is that the kinematic chains of parallel kinematic machines are composed of elongated links that can easily suffer deformations,especially at high speeds and under heavy loads.A 3-RRR parallel kinematic machine is taken as a study object for investigating its accuracy with the consideration of the deformations of its links during the motion process.Based on the dynamic model constructed by the Newton-Euler method,all the inertia loads and constraint forces of the links are computed and their deformations are derived.Then the kinematic errors of the machine are derived with the consideration of the deformations of the links.Through further derivation,the accuracy of the machine is given in a simple explicit expression,which will be helpful to increase the calculating speed.The accuracy of this machine when following a selected circle path is simulated.The influences of magnitude of the maximum acceleration and external loads on the running accuracy of the machine are investigated.The results show that the external loads will deteriorate the accuracy of the machine tremendously when their direction coincides with the direction of the worst stiffness of the machine.The proposed method provides a solution for predicting the running accuracy of the parallel kinematic machines and can also be used in their design optimization as well as selection of suitable running parameters.     

官庄铁矿深埋破碎矿体开采岩体变形测试分析

 以大量实测资料为基础,分析官庄铁矿北区深埋破碎厚矿体开采引起的围岩变形和地表移动规律。实测结果表明,官庄铁矿北区地表下沉属于连续下沉,岩层破坏主要是缓慢型破坏。分析过程中,把几种实测分析方法和数值分析法有机结合在一起,形成岩体移动变形综合研究方法,对地下开采引起的岩体移动机制进行具体分析。分析中所采用的实测分析类方法包括蠕变试验分析、地表移动观测分析、围岩变形监测分析、原岩应力量测分析;数值分析类方法包括ANSYS和FLAC。结合官庄铁矿工程实例,通过具体测试分析,探讨深部开采岩体移动变形规律及特点,即深部开采覆岩移动变形具有均匀、整体压缩变形等特点,地表移动连续且周期较长。实践证明,所采用的综合研究方法是分析岩体移动和地表下沉机制的有效途径。     

Factors determining the performance of thermoplastic polymer/wood composites; the limiting role of fiber fracture

Thermoplastic polymer/lignocellulosic fiber composites were prepared with a considerable range of matrices and fibers in an internal mixer. Tensile properties were determined on bars cut from compression molded plates. Local deformation processes initiated around the fibers were followed by acoustic emission testing supported by electron and polarization optical microscopy. The analysis of results proved that micromechanical deformation processes initiated by the fibers determine the performance of the composites. Debonding usually leads to the decrease of composite strength, but decreasing strength is not always associated with poor adhesion and debonding. The direction of property change with increasing wood content depends on component properties and interfacial adhesion. Good interfacial adhesion often results in the fracture of the fibers. Depending on their size and aspect ratio, fibers may fracture parallel or perpendicular to their axis. At good adhesion, the maximum strength achieved for a particular polymer/wood pair depends on the inherent strength of the fibers, which is larger for perpendicular than parallel fracture. Inherent fiber strength effective in a composite depends also on particle size, larger particles fail at smaller stress, because of the larger number of possible flaws in them. A very close correlation exists between the initiation stress of the dominating local deformation process and composite strength proving that these processes lead to the failure of the composite and determine its performance.