ELASTOPLASTIC FINITE-ELEMENT MODEL DEVELOPMENT AND VALIDATION FOR LOW-PRESSURE UNIAXIAL COMPACTION OF DRY COHESIVE POWDERS

A basic elastoplastic model (modified Cam-clay) was applied to wheat f lour, a dry cohesive powder. Five constitutive parameters for the modi fied Cam-clay model have been previously determined for wheat flour us ing triaxial tests. To apply the elastoplastic constitutive model, a t est cylinder was built that uniaxially compacted the wheat flour under constant axial displacement. Hoop and vertical strains in the cylinde r wall were measured at three levels while the flour inside was compac ted. Predicted vertical strains, using a finite element model (FEM), w ere within 25% (worst case error) of average measured values for all t hree levels up to 59.4 kPa axial pressure. Predicted hoop strains, at the cylinder bottom, were within 45% (worst case error) of average mea sured values up to 59.4 kPa. Along with predicting strains in the cyli nder wall, the FEM also predicted stress distribution in the powder ma ss. Stress distribution proved useful in identifying potential regions of stress concentration and large shear stresses in the powder mass.