Abstract
Large compacts (3.93 cm x 4 cm) formed from commercial direct compression bases have been prepared by hydraulic compression and then loaded in axial compression when removed from the die. Avicel and Sta-Rx formed compacts resistant to shear, and failure in free axial compression was due to induced tensile stresses both radial and circumferential. Paracetamol DC, a direct compression form of paracetamol, behaved as a brittle solid and split axially along its length. Emdex and Encompress formed compacts weak in shear and failed along double shear cones at low axial loading. Emdex gave force v displacement plots for both axial and radial displacement which suggests that it flows plastically at low loads insufficient to cause failure. The other compacts behaved as elastic solids at low axial loadings. A method was devised to compare radial pressure at various points along the axial length of the compacts when they were formed or recompressed in the die. Although easily ejeeted, compacts of Avicel and Sta-Rx were the best transmitters of radial pressure. Emdex and Encompress compacts were both difficult to eject. It is suggested that this is due to shear failure and and rebonding along the shear cones demonstrated infreeaxial compression.

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