Haririan, Ismael; (1994) The influence of punch face-curvature on the mechanical strength of compacted powders. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

The mechanical strength of a compact is dependent on the material, its dimensions, the method of testing and the method of formation. In order to study the influence of shape upon the mechanical strengths of tablets, circular Avicel PH 102 specimens of differing face-curvature and cylinder length were prepared at different compaction pressures and their fracture loads were assessed by diametral loading. As a standard procedure, the tensile strength of the tablets, which was determined from their fracture load values, was used to compare all the tablets. Optimum face-curvatures and cylinder lengths to produce the strongest tablets were found. The ability of the bending theory to analysis of mechanical strengths of beam-shaped tablets was investigated. The 180-125 pm size fractions of Avicel PH102, Aspirin, Emcompress and Starch 1500 were compacted at different pressures to form flat and two curved-face beam-shaped tablets of various dimensions. The three-point bending test method was carried out to fracture beam-shaped tablets through their central surface. Mixed tablets of the same materials were prepared and the relationships between the tensile strength values of single and mixed beams under a given compaction pressure, thickness and face-curvature were determined. By applying the modulus of elasticity of each material, the ability of bending theory to interpret the composite beam data was also proved. Several factors such as material properties, compaction conditions and specimen shape have been shown to have a quantifiable effect upon the tensile strength of tablets.

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