C.E.N. Sturgess

Benchmark tests for 3-D, elasto-plastic, finite-element codes for the modelling of metal forming processes

Abstract Today the finite-element method is the most widely used tool in the prediction of both linear and nonlinear structural behaviour. An inherent danger of such widespread use, however, is an overconfidence in the accuracy and correctness of the results obtained. It is necessary to produce simple benchmark tests which may be performed to justify the users faith in such finite-element packages. The results of these benchmarks should compare favourably with experimental results, exact theoretical models or with recognised finite-element standards. In linear elastic problems it is relatively straightforward to find exact solutions to which the finite-element results may be compared. In nonlinear elasto-plastic analyses in general, and particularly for 3-dimensional forming, analyis it is extremely difficult to determine suitable benchmarks. However, in these cases it is even more important to establish a set of benchmarks to which quantitative or qualitative comparisons may be made. A series of such tests are presented for both single and multi-element analyses, which may be applied to 3-dimensional, elasto-plastic, large strain, finite-element codes. Further benchmarks are introduced which provide standards for friction, isotropic and anisotropic materials, and multi-material problems. It is hoped that the application of these benchmarks will help finite-element users to develop their analyses with legitimized assurance in the validity of their results.

Anisotropic Finite-Element Analysis of Plastic Metalforming Processes

This paper describes some aspects of the incorporation of plastic anisotropy of textured materials into an elastic-plastic finite-element program in order to simulate the deformation of such materials.

Fractal modelling of materials

Abstract The modelling of inhomogeneities within materials is a complex task that takes a large amount of computational time. With ever increasing commercial pressures within manufacturing industry for enhanced design, the heterogeneous deformation characteristics of materials is an area that is in need of a greater understanding. Fractals can be used to describe chaotic phenomena within natural systems in an efficient manner. A key property of fractals is their ability to store data relating to all scales of observation. This paper demonstrates ways in which fractals may be used as an aid to incorporate the inhomogeneous properties and chaotic behaviour that real materials exhibit.

The Introduction of Anisotropic Yield Loci Derived from Texture Measurements in Elasto-Plastic Finite Element Calculations

ABSTRACT A new description of the anisotropic yield locus of a plastically incompressible material with a given crystallographic texture is presented. It is a rather general analytical formulation that can be used in applications such as finite element method (F.E.M.) calculations of plastic forming operations.

Application of an Elastic-Plastic Finite Element Model for the Simulation of Forming Processes

A model for the anisotropic material behaviour of textured materials is currently being incorporated into an elastic-plastic finite-element (FE) program for the simulation of forming processes of such materials. In this paper the developed anisotropic software is tested by simple FE simulations of tensile tests on steel sheet specimens for the prediction of r-values.

THE INCORPORATION OF AN ANISOTROPIC YIELD LOCUS DERIVED FROM THE CRYSTALLOGRAPHIC TEXTURE IN FE MODELLING OF FORMING

In the last decades, classical elastic finite elements (FE) methods have served as a basis for the development of more general methods that can also treat plastic deformation and are able to simulate complex metal forming processes. Most of these models still use the isotropic von Mises yield criterion and its associated flow law. It will be shown how the latter can be replaced by an anisotropic yield criterion and its associated flow law which are directly derived from the crystallographic texture of the metal that is the cause of the anisotropy. The first stage of the procedure is the determination of the orientation distribution function (ODF) that describes the texture. The next stage is the calculation of the anisotropic yield locus that corresponds to it by means of the Taylor-Bishop Hill theory. The final stage is the implementation of this yield locus in the FEM code.