Dual thermodynamics approach to the temperature dependence of viscoplastic creep durability in graphene-based nanocomposites

The ambient temperature at which creep deformation takes place is known to exert significant influence on the creep durability of graphene-based nanocomposites, but at present no theory could illustrate the underlying microstructural evolution to predict such a phenomenon. In this paper, a novel dual thermodynamics approach in conjunction with a time-temperature superposition principle (TTSP) is established to address this issue. First, temperature-dependent secant moduli are exclusively adopted as the unique homogenization variables shifted through TTSP, and then the time- and temperature-dependent effective stresses inside the matrix are calculated via the principle of equivalent work rate combined with the field-fluctuation method. Next, the dual irreversible thermodynamic processes, including the stress-induced creep damage inside the matrix and the temperature-dependent degradation at the interphase, are introduced through two independent sets of evolution equations. The predicted creep rupture strain and rupture time are calibrated with experiments over a wide range of temperature. It is demonstrated that the creep rupture strain increases with the rise of ambient temperature, while the creep rupture time decreases with it. The onset of creep-damage process also commences earlier at higher temperature. This research can provide a design guidance to assess the damage process and failure of low-dimensional nanocomposites at elevated temperature environment.