Atomistic study on thermo-mechanical behavior and structural anisotropy of montmorillonite under triaxial tension and compression

The macroscopic thermo-mechanical behavior and structural anisotropy of swelling clay are mainly driven by the local deformation and failure of clay particles in nanoscale. Microscopic thermo-mechanical behavior of clay particles is rarely explored under triaxial compression and tension with constant mean stress. In this work, the effect of temperature on the mechanical behavior and structural anisotropy of montmorillonite under the above loading paths in the parallel ( x- and y-) and perpendicular ( z -) directions to crystal layers, has been investigated using Molecular Dynamic (MD) simulations. The obtained stress-strain response showed that the higher the temperature, the lower the absolute value of peak differential stress and peak strain. In terms of overall peak stress (axial or radial stress), the resistance of montmorillonite to compression deformation was greater than that to tension. Furthermore, the sequence of peak differential stress in three directions was y > x > z at 200–500 K and y > z > x at 700–900 K for tension, while z > y > x at all temperatures for compression. The deformation mechanism of montmorillonite was mainly driven by the collapse of the clay mineral layers or bending deformation, determined by different loading paths and directions. The bond-breakage of montmorillonite structure was determined, showing the structural anisotropy of clay particles. The higher the temperature, the earlier the bond-breakage, and the greater the deformation of montmorillonite. The evolution of various types of energy with strain was obtained during the failure process, where the energy of montmorillonite was dissipated via changes in position between atom pairs, mainly showing changes in non-bond energy.