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.

Study on yield function and plastic potential under non-associated flow for accurate earing prediction in cup drawing

Prediction of more than four ears in a cup drawing process can be successfully achieved by considering r-value and stress directionalities. Yld2004-18p based on associated flow rule and Yld2000-2D based on non-associated flow rule are the examples. The former, however, is more costly in terms of computational efficiency than the latter. In this work, an anisotropic constitutive model based on non-associated flow rule which combines two different functions, Hill (1948) and Yld2000-2d, is implemented to a user defined material model. The accuracy of the anisotropic directionalities (yield stresses and plastic strain ratios) is evaluated. Simulation of a mini-die cup drawing with a body stock alloy predicted eight ears, in good agreement with the experimental results. The use of Hill (1948) model for the yield function and Yld2000-2d for plastic potential under the framework of non-associated flow rule led to accurate prediction of up to eight ears at the lower computational cost.

Wrinkling during cup drawing with NUMISHEET2014 benchmark test

Wrinkling occurs when a blank is subjected to compressive stresses during the forming process as in the flange of a cup during drawing. Although the failure limit due to plastic flow localization can be simply defined by the FLC at each point of a continuum, the wrinkling limit cannot be defined with simple variables such as strain, stress, and thickness. Wrinkling is strongly affected by the mechanical properties of the sheet material, the geometry of the tools and blank, and contact conditions. The analysis of wrinkling initiation and growth is, therefore, difficult to perform due to the complex synergistic effects of the controlling parameters. Because of these difficulties, the study of wrinkling has generally been conducted case by case. A unique wrinkling criterion, which could be used effectively for various sheet forming processes, has not yet been proposed. There were many investigations on the effect of process parameters (BHF and friction) and geometry on wrinkling. However, there are few reported results on the influence of the material model on wrinkling. This paper shows how strain hardening and r-values affect wrinkle formation in its magnitude, initiation, and direction through the NUMISHEET2014 benchmark test for wrinkling during cup drawing.

Size effects in micro cup drawing

Experimental studies into the effect of blank thickness on the deep drawing response of the coarse-grained and ultrafine-grained copper demonstrated the occurrence of a size effect: the dependence of the maximum load and the limit drawing ratio on the blank thickness in sub-millimetre range. A dislocation based constitutive model taking into account the thickness effects was used for numerical simulations of the process. It was demonstrated that the occurrence of the blank thickness effect is governed by the ratio of the blank thickness t to the grain size D of the material. Critical values of the t/. D ratio below which the size effect comes to bearing were determined. The obtained results can be seen as a demonstration of more general suitability of the model developed for predicting microforming operations with full account of the specimen or work-piece dimensions.

The influence of temperature on the forming behavior of metal/polymer laminates in sheet metal forming

The influence of temperature on the forming behavior of an aluminum/polypropylene/aluminum (APA) sandwich sheet was studied. Shear and tensile tests were performed to determine the mechanical properties of the laminate and the component materials as a function of process temperature. The forming limit diagram (FLD) of the laminate was established for two different temperatures, and its springback behavior was examined in four-point bend and channel bend tests. Cup forming tests were performed at various test temperatures to determine the limiting drawing ratio (LDR) and the tendency for wrinkling at these temperatures. Although there was only a minor influence of temperature on the mechanical properties and the FLD values of the laminate, the bend test results reveal that springback can be reduced by forming at higher temperature. The decreasing strength of the core material with rising process temperature led to an increased tendency of the laminate to wrinkle in the heated cup drawing tests.

Experimental and numerical evaluation of forming and fracture behaviour of high strength steel

Car manufacturers are under pressure to reduce vehicle mass while maintaining comfort and passenger safety for current and future vehicles. To meet this demand the steel industry has developed Advanced High Strength Steels (AHSS) that promise higher strength and improved formability compared to conventional steel grades. Even though significant research has already been performed to evaluate the material properties and forming behaviour of most AHSS types, only a limited literature is available on their necking and fracture behaviour and the effect on formability. This paper examines and compares the thinning, necking and fracture behaviour of two AHSS and one conventional steel type, namely TRIP, DP and HSLA. Uniaxial, plane and biaxial strain conditions are investigated by tensile, cup drawing and stretch forming tests and by using numerical methods. The test results indicate that significant differences exist in necking and fracture behaviour between all three steel types.

Analytical solutions and finite element modelling of deep drawing process for cylindrical metal cups

Analytical modelling of deep drawing process is of value in preliminary process design to illustrate the influence of major variables including friction and strain hardening on punch loads, cup dimensions and process limits. In this study, analytical models including theoretical solution and a series of finite element models are developed to account for the influences of process parameters including friction coefficient, tooling geometry and material properties on deep drawing of metal cups. The accuracy of both the theoretical and finite element solutions is satisfactory compared with those from experimental work.

Representation in the first African World Cup:'world-class', Pan-Africanism, and exclusion

This paper explores the representation of the first African World Cup in the British and South African press. Drawing on the output of a variety of media outlets between 2004, when South Africa was awarded the right to host the 2010 event, and the culmination of the tournament in July 2010, this paper contends that a range of representations of Africa have been put forward by the British and South African media. These can be interpreted as alarmist, sensationalist and even racist in certain extreme instances, and hypernationalist and overly defensive in other cases. © 2012 Copyright Taylor and Francis Group, LLC.