Are biomineralized composites tougher due to their nano-scale size? Atomistic studies of the resistance to crack propagation in nano-sized ceramic platelets that exist in teeth, bone, or the shells of mollusks, reveal that they are far more ductile than their bulk counterparts. The principal reasons are concerned with the increased ease of crack tip blunting and the inability for cracks to sustain the stress concentration required for brittle fracture.
Examples of crack tip response are shown for cracked plates of thickness 4 nm and 16 nm, subjected to uniaxial tension; the former displays ductile rupture whereas the latter demonstrates more brittle-like crack growth. At left, cross-sections of cracked plates with thickness 16 nm (far left) and 4 nm (left) show crack propagation in the 16 nm thick plate and crack tip blunting in the 4 nm thick plate due to profuse dislocation nucleation.