Nanoscale mechanical behavior of kaolinite under uniaxial strain conditions

Abstract

Nanoscale mechanical behavior of kaolinite as a fundamental failure mechanism has been investigated under uniaxial tension and compression using Molecular Dynamics (MD) simulation methods. External deformation has been applied on kaolinite with a strain rate of 5 × 10−7fs−1 for tensile and compressive tests in the directions parallel (x-, y-direction)/perpendicular (z-direction) to clay mineral layers. Results showed that better mechanical performance was presented in the directions parallel to clay mineral layers than the other direction due to its continuous lattice in this plane. However, the elastic modulus of kaolinite in the z-direction was almost half of that in the other directions, which nearly equals the overall elastic modulus of kaolinite with a value of about 72.6 GPa. Compression in the x- and y-directions resulted in the separation of clay mineral layers then bending toward the octahedral sheet till crack. Compression in the z-direction resulted in slippage of clay mineral layers at the first fracture then resistance till the second fracture at the strain of about 0.2. Tension would cause cracks in the direction perpendicular to the strain direction, which may be a cleavage fracture or cracks in clay mineral sheets. Different failure modes under tension and compression were originated from the layered structure of kaolinite.