Effect of water content and structural anisotropy on tensile mechanical properties of montmorillonite using molecular dynamics

The mechanical behavior of montmorillonite is sensitive to water content and structural anisotropy. In this study, the evolution of atomic structure and mechanical behavior of different hydrated montmorillonite under tension has been investigated using Molecular Dynamics simulations. External deformation has been applied to montmorillonite with a strain rate of 5 × 10−7 fs−1 for uniaxial tensile test, stretched along directions parallel (x- and y-direction) and perpendicular (z-direction) to the clay sheets. The bond-breakage criterion based on the radial distribution function of atom pairs and the evolution of broken bonds with tensile strain, were applied to explore the deformation and failure mechanism of the montmorillonite-water system. Simulation results indicated that the water content increased, causing a decrease in the ultimate tensile strength and Young's modulus, as well as more and more plasticity for montmorillonite, especially in z-direction. Moreover, the sequence of tensile mechanical strength was y > x > z. Stretching along the x- and y-direction, fractures occurred in the silicon‑oxygen tetrahedral and aluminum‑oxygen octahedral sheets, where the aluminum‑oxygen bond was easier to be broken, and the normalized number of total broken bonds in the y-direction was superior to the x-direction. Stretching along the z-direction, only the hydrogen bonds in the interlaminar space were broken. In terms of three directions, the anisotropy behavior was found in ultimate tensile strength, Young's modulus, residual tensile strength, and the evolution of broken bonds.