Abstract
The consideration of anisotropic and asymmetric tension-compression behaviour in some materials has proved to be of great importance for the modelling of plastic behaviours that allow for accurate results in sheet metal forming analysis. However, obtaining this compression behaviour of a sheet metal in the principal plane directions is one of the most complex aspects from an experimental point of view. This complexity is notably increased when this behaviour needs to be analysed under high temperature conditions. This paper presents a compression test system with load application in the in-plane sheet directions which is characterised by a relative technical simplicity allowing its application under temperature conditions of up to 750 °C and different strain-rates. Due to the specific test conditions, namely the high temperature, it is not possible to use the common systems for measuring the strains involved and to obtain the stress-strain curve. Therefore, this paper proposes two methods for this purpose. The first is the performance of interrupted tests and measurement of the central cross sections. The second consists of inverse calibration using finite element simulations. The sensitivity of the proposed test methodology is validated through the characterisation, at room temperature, of the compression and tensile behaviour of six materials with different plastic deformation phenomena. In this way, the asymmetric tension-compression phenomena are accurately identified and high compression strains of around 0.3, higher than those existing in the literature, are investigated. A novel test methodology is thus established that is easily applicable for the mechanical characterisation of sheet metal at high temperature.
Highlights
The development of products with more complex geometries, applications and materials has led to FEM simulation systems becoming the fundamental industry tool in the study of complex sheet metal forming processes, significantly reducing development cycle costs and times by avoiding much of the prototype stage
The accuracy of predicting stress distributions in the bending produced in any sheet metal forming process is one of the key factors in the overall accuracy of the designed parts
And in spite of some complexity in the numerical results analysis exists, the approach is relatively simple as the hard equipment needed is only a conventional tensile test machine, which avoids the use of complex devices such as those proposed by other authors
Summary
The development of products with more complex geometries, applications and materials has led to FEM simulation systems becoming the fundamental industry tool in the study of complex sheet metal forming processes, significantly reducing development cycle costs and times by avoiding much of the prototype stage. The development of these theoretical models is not sufficient to predict the response of the material under different temperatures or strain rate conditions. For this purpose, experimental test systems must be developed to identify. The agreement between the experimental and simulated results of bending tests was excellent, highlighting the displacement of the neutral axis that took place. This heterogeneous strain distribution through the thickness direction, caused by tension-compression asymmetry, has a significant influence on the subsequent springback. Noma et al, demonstrated the importance of considering asymmetric phenomena in the springback simulation of a curvature-hat press-formed part [2]
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