title: Structural hierarchies define toughness and defect-tolerance despite simple and mechanically inferior brittle building blocks.
abstract: Mineralized biological materials such as bone, sea sponges or diatoms provide load-bearing and armor functions and universally feature structural hierarchies from nano to macro. Here we report a systematic investigation of the effect of hierarchical structures on toughness and defect-tolerance based on a single and mechanically inferior brittle base material, silica, using a bottom-up approach rooted in atomistic modeling. Our analysis reveals drastic changes in the material crack-propagation resistance (R-curve) solely due to the introduction of hierarchical structures that also result in a vastly increased toughness and defect-tolerance, enabling stable crack propagation over an extensive range of crack sizes. Over a range of up to four hierarchy levels, we find an exponential increase in the defect-tolerance approaching hundred micrometers without introducing additional mechanisms or materials. This presents a significant departure from the defect-tolerance of the base material, silica, which is brittle and highly sensitive even to extremely small nanometer-scale defects.
authors.affiliation: Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, 77 Massachusetts Ave. Room 1-235A&B, Cambridge, MA 02139, USA.
authors.forename: Dipanjan
authors.initials: D
authors.lastname: Sen
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Buehler
mesh_terms: D019245:Compressive Strength; D003198:Computer Simulation; D006244:Hardness; D008903:Minerals / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D012822:Silicon Dioxide / Q000737:chemistry*; D013718:Tensile Strength
chemical_list: D008903:Minerals; D012822:Silicon Dioxide