Evaluation of the Role of Pores during Strength Testing in Compacts Made from Different Particle Size Fractions of Sucrose

Abstract

The purpose of this study was to investigate the role of pores in the fracture of circular compacts and to predict compact properties and critical crack lengths. Four different particle size fractions of sucrose, ranging from 20 to 500 microm, were compressed into circular discs (i.e. flat tablets) and rectangular beam specimens of porosity between 30 and 14%. Modelling of the relationship between the tensile strength of the circular discs and the compact porosity indicated extensive fragmentation during compaction for particles in the size range of 250-500 microm, accompanied by a change in densification mechanism for very coarse particles (355-500 microm). When determining the critical stress intensity factor from rectangular single edge notched beam specimens by 3-point bending, an apparent influence of particle size on the values could be seen, whereby here the results indicated that the critical particle size for fragmentation to occur is about 20-40 microm. It was possible to predict the critical stress intensity factor of the compacts from the median pore size and the tensile strength of the circular disc specimens by interpolation of the critical crack length for propagation to occur. The results indicated that for sucrose compacts regardless of their porosity, the pores themselves acted as stress concentrators, not as sharp cracks. For sucrose compacts, crack propagation hence proceeds most likely along grain boundaries.