This simple equation is derived fro

This simple equation is derived from a more complex expres-sion of the stress state of a sphere subjected to compression. Thenumerator is defined as the critical force for failure times a factorgiven by the loading condition, geometrical features and poisonsratio. The denominator is defined as a disc-area where D is the dis-tance between the loading points. An average value of 13.3 MPa forthe tensile particle strength was calculated from the data using Eq.(4). The calculated critical strength data fits well to a log normaldistribution as can be seen in Fig. 12a