Application of critical state to uniaxial compaction

Abstract

From the radial stress σ R and the normal stress σ A , measured continuously during uniaxial loading and unloading on three compactable (sodium chloride, polyethylene and tartaric acid) and two non-compactable (polypropylene and polystyrene plastics) materials, characteristic compaction profiles of (σ A − σ R ) versus (σ A + σ R ) can be observed. The uniaxial loading stress pathways for both compactable and non-compactable materials validated the assumption that the Coulomb yield criterion, which is usually applicable for the shear testing of soils, can be applied to the uniaxial compression of particulate materials. In addition, the unloading stress profiles for the compactable materials produced two characteristic parameters: a normal stress value at zero shear (σ A + σ R ) o and a minimum shear stress value (σ A − σ R ) min . Correlation of (σ A + σ R ) o and (σ A − σ R ) min values with either the tensile strength f c or the Vickers hardness number H V from the resultant compacts showed a linear logarithmic relationship. No such relationship was found, however, with non-compactable materials.