Fragmentation of inhomogeneous materials always starts near the point of inhomogeneities
due to the fact that local stresses and strains are always highest near such
imperfections. Larger defects cause fracture to occur at lower overall stresses and
strains. In homogeneous materials such imperfections can be errors in crystalline
structure, or small holes in or just below the surface (Luyten et al., 1992; de Jong,
1993). When dealing with pellets, by nature of the material, particles of different sizes,
hardnesses and various shapes are aggregated. It is at these cracktips that stresses will
accumulate. When the local stress at the tip of a crack becomes higher than the cohesive
or adhesive stresses, the crack (defect) in the material starts to grow, fracture starts and
ultimately the material will fall apart. Fracture will propagate spontaneously as the
deformation energy released is, at least, equal to the energy needed to create new
surfaces.