Upon loading, atomic networks can feature delayed irreversible relaxation. However, the effect of composition and structure on relaxation remains poorly understood. Herein, relying on accelerated molecular dynamics simulations and topological constraint theory, we investigate the relationship between atomic topology and stress-induced structural relaxation, by taking the example of creep deformations in calcium silicate hydrates (C─S─H), the binding phase of concrete. Under constant shear stress, C─S─H is found to feature delayed logarithmic shear deformations. We demonstrate that the propensity for relaxation is minimum for isostatic atomic networks, which are characterized by the simultaneous absence of floppy internal modes of relaxation and eigenstress. This suggests that topological nanoengineering could lead to the discovery of nonaging materials.

VL - 119 IS - 3 JO - Phys. Rev. Lett. ER - TY - JOUR T1 - Fracture toughness anomalies: Viewpoint of topological constraint theory JF - Acta Materialia Y1 - 2016 A1 - Mathieu Bauchy A1 - Wang, Bu A1 - Wang, Mengyi A1 - Yu, Yingtian A1 - Mohammad Javad Abdolhosseini Qomi A1 - Smedskjaer, Morten M. A1 - Christophe Bichara A1 - Franz-Josef Ulm A1 - Roland Jean-Marc Pellenq AB -

The relationship between composition, structure, and resistance to fracture remains poorly understood. Here, based on molecular dynamics simulations, we report that sodium silicate glasses and calcium–silicate–hydrates feature an anomalous maximum in fracture toughness. In the framework of topological constraint theory, this anomaly is correlated to a flexible-to-rigid transition, driven by pressure or composition for sodium silicate and calcium–silicate–hydrates, respectively. This topological transition, observed for an isostatic network, is also shown to correspond to a ductile-to-brittle transition. At this state, the network is rigid but free of eigen-stress and features stress relaxation through crack blunting, resulting in optimal resistance to fracture. Our topological approach could therefore enable the computational design of tough inorganic solids, which has long been a “holy grail” within the non-metallic materials chemistry community.

VL - 121 ER -