In the present work an investigation of constitutive equations is made to obtain good fit to experimental data and ensure proper extrapolation out of experimental range of plane strain compression tests to low and high values of Zener-Hollomon parameter, which are required in finite element modelling. A computer program for optimisation of rheological parameters of material was developed. Optimisation using experimental data for two ultra low carbon steels was made and the results are compared with measured stress-strain curves. The obtained constitutive equations were used in the finite element model and comparison between experimental and computed displacement-force curves is made. The influence of inhomogeneity of strain rate, strain and temperatures distribution during compression tests on flow curves is illustrated.
Plane strain compression tests to investigate the effects of heterogeneity of deformation on various initial specimen geometries have been carried out. Equations for correction of nominal strain and strain rate to slip line eld strain and strain rate have been developed and applied to experimental ow stress -strain data. Investigation of the deformed specimens showed evidence of changing friction conditions during deformation, therefore a simple function allowing friction to change was applied. The corrections eliminate the geometry effect observed in the initial data and lead to modi ed constitutive equations for ow stress.MST/5792
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