TABLET BOND .1. A THEORETICAL-MODEL

A model is developed that describes the processes involved in tablet bonding. The processes occurring at the contact region between two particles are developed first; an average value is assumed. This is multiplied by the number of contacts in a cross-section to obtain the tensile strength. It is assumed that: (a) plastic deformation occurs during the compression; (b) the separation of contact areas follows the principles of fracture mechanics; (c) viscoelastic properties increase the strength because of the effect on the work done during the separation of surfaces and on the radius of curvature of the surfaces in contact; and (d) in tension all points of contact are deformed sufficiently near to their maximum strength for the observed tensile strength to be close to the sum of their individual strengths. For some materials, two mechanisms are needed to describe the strength over a complete range of solid fractions. At low solid fractions, ductile extension of the contact region may occur when certain criteria, as derived herein, are met. Otherwise, the strength is determined by a brittle mechanism. The transition from the ductile to the brittle mechanism occurs when the unloaded radii of curvature of the contacting surfaces increase beyond an upper limit as a result of the plastic deformation during compression.