Understanding structural anisotropy and mechanical properties of Na-montmorillonite with crystalline swelling and uniaxial deformation under different hydration degrees

Montmorillonite (MMT) is the main component of bentonite and its mechanical behaviour is sensitive to hydration degrees and structural anisotropy. In this study, molecular dynamics (MD) simulations were used to investigate the atomic structures and fracture behaviour of Na-MMT. The different deformation scenarios are applied to the Na-MMT with different hydration levels within the crystalline swelling phase of hydration. It is found that the mechanical behaviour of Na-MMT is significantly influenced by interlayer hydration degree and structural anisotropy. For example, the ultimate tensile strength and Young's modulus of Na-MMT exhibit decreasing trends with increasing hydration degrees. When tensile strain is applied along the two in -plane directions of the MMT layer, the fracture is observed in the silica -oxygen octahedra. The increase in hydration degree also raises the interlayer potential energy of the clay plate and reduces its stability. Meanwhile, buckling behaviour is observed under compression. These findings provide important insights into the origin of Na-MMT anisotropy, elucidating the complex interplay between the degree of hydration, structural anisotropy, and uniaxial deformation of Na-MMT. This work also provides key scientific insights for future studies of temperature effects, interlayer cation, and other mechanical responses.