Thermomechanical behavior of carbon nanotube/graphene nanoplatelet-reinforced shape memory polymer nanocomposites: A micromechanics-based finite element approach

Abstract

Stimuli-responsive shape memory polymer (SMP) nanocomposites, characterized by their shape memory capability and customizable properties, have significantly expanded their range of applications when compared to pristine SMPs. This pioneering paper is centered on describing an efficient numerical approach for evaluating the thermomechanical behavior of ternary acrylate-based SMP nanocomposites containing carbon nanotube (CNT) and graphene nanoplatelet (GNP) hybrids. To this aim, a micromechanical procedure based on thermo-visco-hyperelastic constitutive model, which aids in avoiding employing intricate user-defined material subroutines, is developed through the finite element method (FEM). The parameters required for satisfying the governing equations of the rheological model, including thermal expansion and Prony series coefficients, plus Williams-Landel-Ferry equation and Neo-Hookean strain energy function parameters, are derived from accessible experiments to assign SMP properties. A Python-based script is implemented in a stochastic-iterative process to generate appropriate periodic representative volume elements (RVEs) with various microstructures. Thereupon, thermomechanical shape memory cycles in uniaxial tension are simulated by creating loading, cooling, unloading, and heating steps in the Abaqus solver. Following achieving satisfactory agreement between the presented scheme and experimental measurements, case studies are performed to reflect the influences of dispersion type, volume fraction, and geometry of carbonaceous nanofillers, as well as the contribution of nanofiller/matrix interphase region, upon stress-free/shape-recovery and fixed-strain/stress-recovery thermomechanical cycles.