Deformation of aluminium sheet at elevated temperatures : experiments and modelling

Haaren, L. van (2002) Deformation of aluminium sheet at elevated temperatures : experiments and modelling.

Abstract:There is a growing demand to reduce the weight of vehicles in order to minimise energy consumption and air pollution. To accomplish this weight reduction, car body panels could be made of aluminium sheet, which has a better strength to weight ratio than traditionally used mild steel. The formability of aluminium is less than that of mild steel, but it can be improved by deforming aluminium at elevated temperatures. Since there is not much experience in industry in deforming aluminium sheet at elev- ated temperatures and trial and error in the workshop is very expensive, numerical simulations are used to predict and optimise the deformation process. To accurately simulate a deformation process it is necessary to know and model the material beha- viour. The purpose of this graduation project is to develop a material model for aluminium that takes variations in temperature and strain rate into account. Two di®erent ma- terial models have been examined: a phenomenological model (extended Nadai model) and a physically based model (BergstrÄom model). The parameters of these models have been determined using the results of experiments performed at TNO Eindhoven. These experiments have been conducted for various constant strain rates and tem- peratures. It was seen that both material models describe the constant strain rate experiments reasonably well and that the BergstrÄom model performs slightly bet- ter than the extended Nadai model. A number of numerical simulations have been performed to demonstrate the applicability of the BergstrÄom model. When a strain rate jump is applied, large di®erences between the models appear. The extended Nadai model describes an instantaneous response and the BergstrÄom model describes a more gradual response. To determine which of the models predicts the behaviour best, tensile tests with a strain rate jump have been performed at the University of Twente. It was concluded that the actual material behaviour in case of a strain rate jump is somewhere in the middle of the two material models.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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