Viscoplastic model analysis about the influence of graphene reinforcement in poly (lactic acid) time-dependent mechanical behaviour

Abstract

Biodegradable polymers can be applied to produce automobile parts, following ecological recommendations and eco-design philosophies. In some applications, a constant or dynamic load applied to the part can further reduce its life cycle due to creep or fatigue cumulative damage. Hence, the reinforcement of these polymers with graphene may enhance the mechanical properties and change the time-dependent mechanical behaviour. In this work, experimental results are presented and discussed, that enable the comparison between pure polylactic acid (PLA) and PLA reinforced with 2 wt.% of graphene nanoplatelets (GNP). Monotonic tensile tests under different strain rates and loading-unloading cycles are used to access and compare the time-dependent mechanical behaviour of both materials. Furthermore, the material parameters of a time-dependent constitutive model, that combines hyperelastic springs and viscoplastic dashpots, were calibrated based on these experimental test results. The differences between material model parameters enable to verify the thixotropic influence of graphene.