Comparison of two Drucker-Prager-type constitutive models for granular material behaviour in uniaxial compression

Theoretical research on powder compaction requires models to describe the development of mechanical properties. Elastoplasticity theory is particularly appropriate. Two relatively simple constitutive models have been considered, which differ in their formulation of the yield criterion. The predictions of the two models disagree, when the model parameters are related by assuming the same global dimensions of the instantaneous yield surfaces. A comparison is presented for uniaxial compression which shows that model parameters can be selected to force the two models to predict quantitatively similar stress development. To discriminate between potential models, it is necessary to increase the number of measurements against which they are compared. In general, the yield criterion in a model to describe a specific granular material should be formulated using sufficient adjustable parameters to obtain satisfactory reliability. A model which is too constrained and is evaluated against limited data may give completely erroneous predictions for other circumstances.