Breakage of Granules with Layered Structure

As already discussed in Section 7.2, fluidized bed spray granulation leads to particles with a layered structure. By spraying on cores, particles with a firm nucleus and a soft onion-like shell can be formed. Such a particle made of sodium benzoate is depicted in Fig. 7.21. 

During compression testing of the layered structure, the high tensile stress, which is perpendicular to the direction of loading, leads - as before - to the formation of meridian cracks. According to Fig. 7.22, the shell first deforms around the contact point. Then, a crack (1) is released and reaches the surface that separates the stiff nucleus (2) from the shell (3). The force-displacement curve of Fig. 7.23 shows that, after the formation of a meridian crack in the shell (Point Bi), deformation and then 

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