Robert E. Dick

Characterizations of Aluminum Alloy Sheet Materials Numisheet 2005

This report reproduces the contents of a document provided in the Numisheet 2005 Benchmark Study for the characterization of aluminum alloys.

Prediction of Critical Blank-Holding Force Criterion to Prevent Wrinkles in Axi-Symmetric Cup Drawing

The repression of wrinkling during sheet metal forming has been a significant issue in recent years. In order to provide a reliable and efficient tool to predict the critical blank holding force to prevent wrinkles, an axi-symmetric analytical model for flange wrinkling is introduced here. Using a conventional theory of the critical condition, the critical blank-holding force and wave numbers are numerically predicted. Comparison between the numerical and experimental results shows excellent agreement for various blank dimensions and materials.

Benchmark 4 - Wrinkling during cup drawing

Benchmark-4 is designed to predict wrinkling during cup drawing. Two different punch geometries have been selected in order to investigate the changes of wrinkling amplitude and wave. To study the effect of material on wrinkling, two distinct materials including AA 5042 and AKDQ steel are also considered in the benchmark. Problem description, material properties, and simulation reports with experimental data are summarized.At the request of the author, and Proceedings Editor, a corrected and updated version of this paper was published on January 2, 2014. The Corrigendum attached to the updated article PDF contains a list of the changes made to the original published version.

Benchmark 1 - Failure Prediction after Cup Drawing, Reverse Redrawing and Expansion Part A: Benchmark Description

This Benchmark is designed to predict the fracture of a food can after drawing, reverse redrawing and expansion. The aim is to assess different sheet metal forming difficulties such as plastic anisotropic earing and failure models (strain and stress based Forming Limit Diagrams) under complex nonlinear strain paths. To study these effects, two distinct materials, TH330 steel (unstoved) and AA5352 aluminum alloy are considered in this Benchmark. Problem description, material properties, and simulation reports with experimental data are summarized.

Fracture prediction using modified mohr coulomb theory for non-linear strain paths using AA3104-H19

Experiment results from uniaxial tensile tests, bi-axial bulge tests, and disk compression tests for a beverage can AA3104-H19 material are presented. The results from the experimental tests are used to determine material coefficients for both Yld2000 and Yld2004 models. Finite element simulations are developed to study the influence of materials model on the predicted earing profile. It is shown that only the YLD2004 model is capable of accurately predicting the earing profile as the YLD2000 model only predicts 4 ears. Excellent agreement with the experimental data for earing is achieved using the AA3104-H19 material data and the Yld2004 constitutive model. Mechanical tests are also conducted on the AA3104-H19 to generate fracture data under different stress triaxiality conditions. Tensile tests are performed on specimens with a central hole and notched specimens. Torsion of a double bridge specimen is conducted to generate points near pure shear conditions. The Nakajima test is utilized to produce points in bi-axial tension. The data from the experiments is used to develop the fracture locus in the principal strain space. Mapping from principal strain space to stress triaxiality space, principal stress space, and polar effective plastic strain space is accomplished using a generalized mapping technique. Finite element modeling is used to validate the Modified Mohr-Coulomb (MMC) fracture model in the polar space. Models of a hole expansion during cup drawing and a cup draw/reverse redraw/expand forming sequence demonstrate the robustness of the modified PEPS fracture theory for the condition with nonlinear forming paths and accurately predicts the onset of failure. The proposed methods can be widely used for predicting failure for the examples which undergo nonlinear strain path including rigid-packaging and automotive forming.

A New Axi‐Symmetric Element for Thin Walled Structures

A new axi‐symmetric finite element for sheet metal forming applications is presented in this work. It uses the solid‐shell element’s concept with only a single element layer and multiple integration points along the thickness direction. The cross section of the element is composed of four nodes with two degrees of freedom each. The proposed formulation overcomes major locking pathologies including transverse shear locking, Poisson’s locking and volumetric locking. Some examples are shown to demonstrate the performance and accuracy of the proposed element with special focus on the numerical simulations for the beverage can industry.

Convolute Cut-Edge Design with a New Anisotropic Yield Function for Earless Target Cup in a Circular Cup Drawing

A convolute cut-edge design is performed using FEM (Finite Element Method) for a single step cup drawing operation in order to produce an earless cup profile. Mini-die drawing based on a circular blank shape is initially carried out in order to verify the earing prediction of the Yld2004 anisotropic model (Barlat et al. [1]) for a body stock material. Realistic cup geometry is then employed to design a non-circular convolute edge shape. An iterative procedure based on finite element method is initially used to design a convolute shape for an earless target cup height. A constant strain method is suggested to obtain a new convolute prediction for the next iteration from the current solution. It is proven that Yld2004 model is accurate to predict the anisotropy of the material.

Microstructure-based constitutive modeling for the analysis and design of aluminium sheet forming processes

Finite Element (FE) modeling technology is one of the most powerful tools to design new products (i.e. autobody parts, rigid packaging, aerospace components, appliances, etc.) and processes. Among other features, the material description is an important input to the FE models. This work describes a methodology that provides phenomenological constitutive equations based on the main microstructure components of aluminum alloys including crystallographic texture, dislocation density and precipitate particle distribution. An example constitutive equation with its application to numerical sheet forming process analysis is provided in this work. Introduction During the past 15 years, nonlinear Finite Element (FE) models have become a significant component in the design process of rigid packaging, automotive, aerospace and other aluminum alloy products. Nonlinear modeling has become feasible due to significant advances in software, hardware (CPU, memory, disk), and experienced analysts. Models have become increasingly complex as complete, realistic systems, are simulated. By relying more on numerical simulations the time required to go from conceptual design to production has been drastically reduced. However, as the need for faster turnaround, improved accuracy and increased reliability continues, improvements in every aspect of nonlinear FE modeling are required. The geometry, finite element mesh, material behavior, element properties, and boundary conditions are the main features of typical FE models. In this paper, only material aspects are discussed. Material Behavior FE users need data and models to characterize the mechanical behavior of materials used to fabricate new products. In fact, they need more information than the traditional and standard yield strength, ultimate strength and elongation. Constitutive models and their associated coefficients represent a new way to describe material properties, a way that can be used by FE users. In order to help manufacturers use more aluminum alloy sheets in their products, appropriate material models are needed to specifically analyze and design for these materials. In this context, constitutive modeling is a local description of the strain response that occurs when a local region of the material is subjected to multiaxial loading. In forming processes that involve plastic deformation, models based on the microstructure must be developed to accurately describe the behavior of aluminum alloys. Failure strains depend on the material behavior and can be calculated using an appropriate failure model along with material constitutive equations. These strains are used as limiting strains but cannot be, in general, computed with FE models. In addition, testing procedures need to be developed and improved to obtain coefficients for these models. The plasticity of materials can be described using two types of models, microstructural (based on features such as crystallographic texture, dislocations, precipitates, solutes, etc.) and phenomenological. Anisotropy has been identified as a factor contributing to failure in materials. One of the main sources of anisotropy is crystallographic texture, the distribution of the grain orientations in polycrystalline materials. This motivates the need for polycrystalline models. Key Engineering Materials Online: 2002-10-25 ISSN: 1662-9795, Vols. 230-232, pp 497-500 doi:10.4028/www.scientific.net/KEM.230-232.497

Image Processing to Automate Mesh Generation

Abstract. Finite element modeling is now a standard approach used in the industry to minimize costly trials and help reduce the overall lead time in product and process design. However, building surface/solid models defining the product shape and generating finite element meshes for analyses still require a significant amount of the engineers’ time. In this paper, we present a new method for automatically generating a finite element mesh directly from bitmap images obtained from an artist’s concept of a label for an embossed aluminum beverage can, and demonstrate its application towards the building of tooling mesh models used in the modeling of the embossing process. This approach completely eliminates the need for creating a surface/solid model, thus resulting in a dramatic reduction in the time required for process design.

Finite element analysis of plates on elastic foundations: an automated approach

Abstract An automated approach for the analysis of plates on an elastic foundation is presented. The approach combines automatic mesh generation with nonlinear analysis to analyse plates of arbitrary shape on an elastic foundation subject to uplift. Two separate complete systems are presented, the first employing an ACM element to analyse rectangularly-shaped plates and the second employing a heterosis element to analyse plates of arbitrary shape. Solutions of the systems are presented and compared to theoretical results. A convergence study is also presented.