Atomic-scale modelling of elastic and failure properties of clays

• Published in: Molecular physics 2014-05, Vol.112 (9-10), p.1294-1305
• Main Authors: Hantal, György, Brochard, Laurent, Laubie, Hadrien, Ebrahimi, Davoud, Pellenq, Roland J.-M., Ulm, Franz-Josef, Coasne, Benoit
• Format: Article
• Language: English
• Subjects: Clay; Clays; Condensed Matter; Elastic constants; elastic properties; Failure; fracture; Fracture mechanics; Fracture toughness; Materials Science; Molecular physics; Nanostructure; Physics; reactive molecular simulation; Shear
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2014.897393

The elastic and failure properties of a typical clay, illite, are investigated using molecular simulation. We employ a reactive (ReaxFF) and a non-reactive (ClayFF) force field to assess the elastic properties of the clay. As far as failure is concerned, ReaxFF was used throughout the study; however, some calculations were also performed with ClayFF. A crack parallel to the clay layers is found to have low fracture resistance when submitted to a tensile loading perpendicular to the crack. The mechanism of both yield and fracture failures is decohesion in the interlayer space. In contrast, under shear loading, the nanoscale failure mechanism is a stick-slip between clay layers. No fracture propagation is observed as the clay layers slide on top of each other. The low fracture resistance in mode I and the stick-slip failure in mode II are both the consequence of the lack of chemical bonds between clay layers where the cohesion is provided by non-covalent interactions. This work, which provides a description of the failure of clays at the microscopic scale, is the first step towards describing the failure of clays at a larger scale where the polycrystalline distribution of clay grains must be taken into account.