Atomic-scale modelling of elastic and failure properties of clays

Abstract

The elastic and failure properties of a typical clay, illite, are investigated by means of molecular simulation. 2 We employ a reactive (ReaxFF) as well as a non-reactive (ClayFF) force field to assess the elastic properties 3 of the clay. As far as the failure properties are concerned, ReaxFF was used throughout the study, however 4 some calculations were also performed with ClayFF. A crack parallel to the clay layers is found to have low 5 fracture resistance (equivalent fracture toughness K Ic = 0.09 MPa.m 1/2) when submitted to a tensile loading 6 perpendicular to the crack (mode I). The nanoscale mechanism of both yield and fracture failures is 7 decohesion in the interlayer space, and the critical energy release rate characterizes both failures. In contrast, 8 under shear loading (mode II), the nanoscale failure mechanism is a stick-slip between clay layers. No fracture 9 propagation is observed as the clay layers slide on top of each other. The low fracture resistance in mode I and 10 the stick-slip failure in mode II are both the consequence of the lack of chemical bonds between clay layers 11 where the cohesion is provided by electrostatic interactions only. We also consider the mode I loading of a 12 crack perpendicular to the clay layers and find that, in this case, the material exhibit strain softening as the 13 result of the clay layers breaking one after the other. In this orientation illite displays a much higher fracture 14 resistance (0.61 MPa.m 1/2) due to the breaking of chemical bonds involved when fracturing in this direction. 15 This work, which provides a description of the failure properties of clays at the microscopic scale, is a first 16 step needed to describe the failure of clays at a larger scale where the polycrystalline distribution of clay 17 grains is a key parameter that must be taken into account.

Physical Origins of Thermal Properties of Cement Paste

“…Some of the above-mentioned adsorbed water molecules are chemically unstable and dissociate into hydroxyl groups and protons upon first-principle or reactive force-field modeling. REAXFF potential is subsequently utilized to enforce reaction between the interlayer water molecules and defective calcium-silicate layers [18,35]. These molecular structures are extensively validated against nuclear magnetic resonance, elastic and inelastic neutron scattering, x-ray diffraction, and drying experiments (for further details on model constructions and validations, see Abdolhosseini et al [18,24] ×½0.8ðx − 1Þ þ 0.3H 2 O, where x is the Ca∶Si ratio and ðOHÞ Ca and ðOHÞ Si represent hydroxyl groups coordinated to interlayer calcium atoms and silica groups, respectively.…”

The impact of different clay minerals on the anisotropy of clay matrix in shale

“…; Hantal et al . ; Zhang et al . ; Zheng and Zaoui ), using molecular dynamics (MD) simulations with the Clay force field (CLAYFF).…”

The Role of Water on C-S-H Gel Shear Strength Studied by Molecular Dynamics Simulations

“…The water in the interlayer spaces controls the mechanical response in terms of yield strength, buildup of pressure during shear deformations, and magnitude of stress drops at large strain. Indeed, molecular simulation have identified this type of mechanism in layered materials like clays (Hantal et al 2014;Duque-Redondo et al 2014), tobermorite (Hegoi Manzano et al 2013), and the C-S-H (Pellenq et al 2009;Hegoi Manzano et al 2013), and also indicate the presence of interfacial friction at the nanoscale (Bhushan et al 1995;Yue et al 2013). The objective here is to use these existing methodologies to assess how the shear response of the interparticle interface changes with the thickness of the water layer between them, going from an ideal to a non-ideal configuration.…”