摘要:

AbstractIn recent years a number of programs have been developed for the calculation of plastic processes, but up to now the use of these programs in industrial practice has been limited to particular cases.On the one hand, reasons for this can be found with the users who often, not knowing the theoretical principles and the restrictions of the calculations, obtain wrong results and thus generally doubt the applicability of the program.On the other hand, in many cases calculations are only possible with low accuracy since information and data on the boundary conditions and the material behaviour are not available.This paper describes the possibilities and limits of the numerical simulations as well as the compromises which have to be accepted.

ISSN:0029-5981    

DOI:10.1002/nme.1620250103

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA finite streamline element method for use with integral type constitutive equations in viscoelastic flow simulation, including thermal effects, is presented and some new results using this method in modelling the IUPAC extrusion experiments for low‐density polyethylene (LDPE), involving both long and short circular dies, are reported and discussed. It will be shown that the special streamline‐based elements provide a convenient way of particle tracking and strain tensor calculation. The extrusion calculation when using a relatively realistic KBKZ type integral model with multiple relaxation times is stable, and practically important Weissenberg numbers and swelling ratios have been reached without difficulty. The agreement with experimental swelling ratios is on the whole satisfactory. In order to make the model a good fit to the Trouton viscosity experimental data of the LDPE sample, a spectrum of elongational parameters has been introduced. The second normal stress term has also been added to the integral model to examine its effect on extrusion swelling. The non‐isothermal effects and the possibility of a wall slip near the die exit at high apparent shear rates are also disc

ISSN:0029-5981    

DOI:10.1002/nme.1620250104

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA very simple and reliable error estimator has recently been developed for problems of linear elasticity.1This leads naturally toa predication of anh‐mesh refinement required for a given accuracy and with a suitable mesh generator2for an efficient adaptive process. In this paper we extend the methodology developed previously to incompresible plastic flow of metals or polymers using the ‘flow formulation’ approach.3The examples of application include steady state extrusion problems for which exact solutions are available and hence allow the efficiency of the error estimates to be tested as well as more complex problems of upsetting in which the mesh is updated. It is found that the estimator performs well under various circumstances and provides an economical adaptive pr

ISSN:0029-5981    

DOI:10.1002/nme.1620250105

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe application of the penalty‐function formulation of the finite element method is made possible for analysing visco‐elastic fluid flows by the method which decouples the momentum and continuity equations from the constitutive equation. An upwind finite element scheme is combined with the method in order to solve the constitutive equation. As visco‐elastic fluid models, Jaumann derivative, upper and lower convected derivatives are considered. The Poiseuille flow and the flow through a plane converging channel are ana

ISSN:0029-5981    

DOI:10.1002/nme.1620250106

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe cold rolling of rectangular section slabs is analysed for a range of width‐to‐height ratios (one to three) for which spread of the workpiece is appreciable. This necessitates the use of a three‐dimensional model. An elastic‐plastic finite‐element method is used to provide a complete description of the slab rolling process.The pressure distribution at the workpiece/roll interface is found to show the typical ‘friction‐hill’ observed in near‐plane‐strain experiments, but the pressure varies across the width of the interface. The shear‐stress distribution at the roll interface provides detailed information about the ‘neutral line’ which is usually assumed to occur where the shear stress changes direction. The 3‐D analysis shows clearly that there is a flow divide in both longitudina

ISSN:0029-5981    

DOI:10.1002/nme.1620250107

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThree‐dimensional finite element analysis is applied to operation sequences in open‐die forging. Flat tools with rounded edges for open‐die forging are geometrically modelled using Bézier curves. With this technique, the problems at the die‐workpiece interface, such as the integration of frictional stress, node touching on dies and node separating from dies, can be handled effectively. It is shown that in solving general symmetric problems computation time can be saved by reducing variables and rearranging them in the stiffness matrix. One‐bite operations and operation sequences for producing two‐size bars and two‐size pipes in several bites are investigated in regard to geometry, load, energy and deformatio

ISSN:0029-5981    

DOI:10.1002/nme.1620250108

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractA fully three‐dimensional elastic–plastic finite‐element program for the study of metalforming operations is described. Several applications are discussed, and the finite‐element (FE) predictions of metal flow, strain rate and temperature distributions, and the sites of initiation of ductile fracture are pr

ISSN:0029-5981    

DOI:10.1002/nme.1620250109

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractApproximate methods for analysing steady‐state cold drawing processes in polymer forming are discussed. These methods are applied to both axisymmetric and plane‐strain drawing. The cold drawing process is associated with steady‐state neck propagation along the specimen. Modifications are introduced in the approximate steady‐state analysis which reflect the neck initiation and localization phases prior to steady‐state drawing. This is accomplished without resorting to an analysis of the entire load–deformation history of the process. Finite element results are also presented and compared with those of the proposed approximate analyses. These comparisons show the approximate analysis to be an extremely efficient and quite accurate computational scheme for the analysis of steady‐state cold draw

ISSN:0029-5981    

DOI:10.1002/nme.1620250110

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620250111

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractConstitutive relations based on finite‐deformation‐valid analysis require the formulation of coupling effects that were not needed in earlier developments which included small deformation restrictions. However, the feasibility to introduce such coupling effects mathematically requires that the new terms introduced must be in accord with physically based concepts of the phenomena involved. An example came to light in which objectivity of a constitutive relation, considered to be generalized for finite deformation applications involving strain‐induced plastic anisotropy, had been achieved by use of the Jaumann derivative in place of the material derivative for the growth of a tensor variable which expressed the anisotropic characteristics. The spin terms thus added to the infinitesimal displacement analogue were not in accord with a physically based assessment of the underlying micro‐mechanical phenomena and in fact led to the prediction of anomalous stress response. This paper comprises comments on the subsequent development of the theory, including a tensor equation for the evolution of the anisotropy. By solving a sample test problem with different initial conditions both the numerical implementation of the constitutive relation and the response according to the proposed growth law of the anisotropy are described and di

ISSN:0029-5981    

DOI:10.1002/nme.1620250112

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY