STUDIES ON THE DEFORMATION OF COMPACTS

A 39.4 mm diameter punch and die set has been instrumented to record punch force, punch displacement, and compact temperature. Using pressures of up to 200 MPa, the recompression behaviour of a range of materials has been investigated, by the determination of force v displacement curves for preformed compacts. For each of the materials tested, cyclic recompression resulted in energy dissipation. which was largely of viscoelastic origin. During recompressive cycles in which heat flow could occur, energy was dissipated by mechanical hysteresis. thermoelastic aftereffect, and friction at the die wall; rapid recompressive cycles, in a lubricated die, showed only the dissipative effect of mechanical hysteresis. The dependence of energy dissipation characteristics on deformation rate and compaction pressure has been investigated, and energy dissipation during recompressive cycles has been correlated with the temperature changes which accompanied deformation. To investigate a further possible aspect of viscoelastic behaviour, compacts of Asagran, paraceteimol granulation and ibuprofen granulation have been stored for 100 days. under varying conditions of temperature and humidity. The axial and radial expansion during extended storage was assessed by periodic measurements at points across the faces and around the sides of the compacts. At low humidities. ibuprofen and paracetamol granulation compacts showed appreciable dimensional increases , despite small decreases in moisture content; at high humidities, the additive effect of moisture sorption considerably increased the observed rates of expansion. The expansion process was also found to be strongly temperature sensitive, possibly indicating that the phenomenon was due to grain boundary sliding, under the influence of residual elastic stresses. Compacts were found to develop characteristic shapes during the storage period, and to exhibit a well defined pattern of cracking. An attempt was made to correlate the expansion observed in these materials with possible changes in their indentation hardness profiles, during extended storage Although no time dependent changes in hardness were demonstrated, the data obtained provided useful comparisons with the results of previous workers.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

De Montfort University

Year dc:date.issued

1977

Author dc:creator

• WHITE, PETER J. P.

Licence

• https://dora.dmu.ac.uk/bitstreams/f254c41b-fec2-49cb-85e1-5c0799a057fe/download