Thermal Residual Stress Analysis of CNTs Reinforced Polymer Using a Cyclic Symmetry Semi-Continuum Model

In this research, the thermo-mechanical behavior of SWCNTs reinforced polymer has been characterized using an analytical method based on semi-continuum modeling. For this reason, a representative volume element of CNT reinforced polymer with cyclic symmetry boundary condition is used while the nanotube reinforcement is modeled in nanoscale and its surrounding polymer is considered as a continuum environment. Applying the cyclic symmetry boundary conditions in the problem-solving procedure causes satisfactory agreement between the results of the analytical method and the actual conditions. The interphase between the nanotube and polymer is also modeled using the cohesive stresses and the mechanical properties extracted from the Vander-Waals forces between the atoms of nanotube and polymer. In general, the thermal residual stresses in polymer/CNT nanocomposites can occur due to the significant differences between the thermal expansion coefficient of polymer and CNT. In the present paper, the semi-continuum modeling has been firstly explained and then the role of some effective parameters such as volume fraction, aspect ratio, and temperature change on the residual thermal stresses has been studied. Although, based on some available researches in macro scale, it seems that adding the CNTs to polymer leads to decreasing the thermal expansion of nanocomposite and consequently decreasing its thermal residual stresses. However, the results of this paper show that by inappropriate selection of some parameters such as the volume fraction and aspect ratio of nanotubes and also the temperature change, the residual thermal stresses increase between the polymer and nanotube which it can weaken the material strength.