A nanoscale simulation study of the elastic behaviour in kaolinite clay under pressure

Abstract

In this paper, Molecular dynamics simulation based on energy minimization technique has been used to study the structural and mechanical properties of kaolinite under pressure from 0GPa to 25GPa. Using the shell model, we have optimized the potential parameters according to Newton–Raphson procedure. Various mechanical properties have been calculated, such as the elastic constants, bulk modulus, shear modulus, Young modulus along a, b and c directions. Moreover the S- and P-wave velocities as well as Poisson ratio were also evaluated. Results reveal that kaolinite is quite compressible compared to the other clays. This reflects the possible uses in several applications including external constraints.In addition, we study the pressure effect on the elasticity of kaolinite. Results show that the elastic constants such as C33, C13, C23 and C34 have a positive slope under pressure with 15%, 6%, 6% and 1.3%, respectively. The remaining elastic constants are almost stable with a small change. A decrease of the Young modulus is noticed in a and b directions, whereas an increase in c direction appears with a slope equal to 10%. The ratio of the S- and P-wave velocities, which are key in the interpretation of seismic behaviours, gives Vp/Vs=1.787, a value in favourable agreement with experimental data.