ABSTRACT
One commonly assumes that a cohesive powder with a given porosity sustains stationary combinations of shear and normal stresses within a convex region, the “stability region”, in (σ, τ)-space, Fig. 3 (Roscoe 1970; Schwedes 1975). σ is the normal and τ the tangential force per unit area transmitted through a plane with normal vector n inside the material. (Tensile forces are defined as being negative here.) Usually one assumes that the material is isotropic. Then only vectors n that are linear combinations of the eigenvectors for the largest and smallest eigenvalue of the stress tensor are taken into account, because the corresponding Mohr circle is largest and therefore reaches the boundary of the stability region first. Quasi-static compaction takes place at the boundary of the stability region. We shall also discuss shock compaction in this paper, where a load in the unstable region is applied.
