Institute of Fundamental Technological Research

Consideration is given to a model of a granular medium which is time-independent, elastic­plastic, with the yield condition depending on the stress state and the variable material density. Due to density variation, the initial yield surface may expand, contract or undergo more complex changes. Constitutive rate equations are derived and applied to the problem of a thick-walled tube subjected to internal! pressure. Both stable and unstable behaviour is discussed assuming the axi-symmetric deformation mode for large and small plastic deformations.

A static solution is presented for the case of compression of short circular cylinders between rough, rigid plates. It is assumed that the material is perfectly plastic, satisfying the Coulomb yield condition and the associated flow law. The stress state is calculated for the edge régime of the Coulomb hexagon for which the Haar-Kármán hypothesis is satisfied. The solution is obtained for several height-diameter ratios, various friction conditions at the cylinder-plate interface and for various angles of internal friction. Results of theoretical solutions are compared with available experimental data. The analysis may be useful in experimental determination of the angle of internal friction and cohesion by compressing short cylinders between rigid plates.