Simulation of the elastic-plastic behavior of polyolefin-based nanocomposites with a different structure of layered filler

A phenomenological model is proposed for the correct description of the mechanical behavior of nanocomposites based on a polymer matrix and a layered silicate under finite elastic—plastic deformations. The constitutive equations are constructed according to the approach based on an interpretation of the mechanical behavior of the material in terms of symbolic circuits. This model makes it possible to describe not only strain hardening of the material but also its loss of strength or weakening. This model takes into account the specific features of yielding and allows one to model the accumulation of structural changes upon loading. At high strains, stress in intercalated systems appears to be lower than that in exfoliated nanocomposites with the same filler content. This is probably related to the fact that intercalated tactoids (crystallites of layered silicates), whose interplanar spaces are occupied by polymer molecules, move in the material as individual large-sized particles, which are strongly anchored to the matrix, and this process requires higher stresses. Changes in the shape of isolated silicate platelets (in the exfoliated nanocomposites) and tactoids in the course of deformation are studied. Calculations show that various silicate platelets lose their stability, and this loss in stability is shown to depend on their orientation in the composite with respect to the direction of tensile drawing, on the number of platelets in each stack, and on the external force applied. Upon loading, the edges of silicate platelets in the tactoids are able either to come closer or move apart, depending on the orientation of platelets with respect to the direction of the external force.