Tensile and compressive behavior of Na-, K-, Ca-Montmorillonite and temperature effects

Molecular dynamics (MD) method was applied to simulate the nano mechanical behavior of Na-, K-, Ca-montmorillonite (MMT) under uniaxial tension and compression, and to explore the effects of the loading di-rection and temperature. The relation between nano mechanical properties of Na-, K-, Ca-MMT and the hydration was investigated, a comparison was made considering the bulk modulus, shear modulus, elastic modulus and Poisson's ratio. There are significant differences for the nano mechanical behavior of montmorillonite in different directions, the in-plane tensile and compressive elastic modulus and strength are greater than those in perpendicular to the crystal plane. The nano mechanical properties of Na-MMT have a negative relation with temperature. The nano mechanical properties were found to decrease with the increasing hydration for the montmorillonite. The stiffness coefficients are also influenced by the hydration and interlayer cations. The tensile strength of Ca-MMT is smallest among three types of montmorillonite. The bulk modulus, shear modulus, and Young's modulus of polycrystal Na-, K-, Ca-MMT are also decreasing with the hydration water layers, while Poisson's ratio remains unchanged with the increasing hydration. By observing the nano structure change, the tension failure is caused by a slip plane due to bond breaks and the compression failure caused by the local buckling of the crystal sheet in x-and y-direction, while in z-direction, the failure is due to the separation of the interlayer water molecules in tension and bond breaks to form a shear band in compression.