Stress Transmission

Compaction Rate Processes The performance of compac tion techniques is controlled by the ability of the particulate phase to uniformly transmit stress and the relationship between apphed stress and the compaction and strength characteristics of the final compacted particulate phase. The general area of study relating compac tion and stress transmission is referred to as powder mechanics (Brown Richards, Principles of Powder Mechanics, Pergamon Press Ltd., Oxford, 1970). 

The compaction properties of pharmaceutical formulations can be studied experimentally using a variety of techniques, ranging from instrumented production presses to compaction simulators, and methods of analysis. The results are usually plotted as porosity-axial stress functions, which is of interest to compare different materials. However, there are some drawbacks on this type of evaluation. As mentioned by Cunningham et al. [20], this approach is deficient once it considers only the average stress along the direction of compaction, ignoring radial stress transmission and friction. 

Barakat, A.l. and Davies, P.F., Mechanisms of shear stress transmission and transduction in endothelial cells. Chest, 114, 58S, 1998. 

These results show that even with possible differences in stress transmission due to the excipient, the basic response must (as expected) be dictated by the underlying crystal structure of the API. Also, all of the crystal structure related analysis gives the formulator the tools needed to estimate or at least anticipate which crystal structures should deform most easily and for a given structure, which shape is the most likely to behave well... 

DIE-WALL FRICTION AND AXIAL TO RADIAL STRESS TRANSMISSION... 

Stress transmission in powders controls flow out of hoppers, feeders, filling of tubes, and compaction problems such as tableting and roll pressing. (See Powder Compaction. )... 

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