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

Authors: André Vieira; Viviana Correia Pinto; Artur Pinto; Fernão D. Magalhães

Addresses: Aeronautical Engineering Department, São Carlos School of Engineering, University of São Paulo, Av. João Dagnone n.1100, 13573-000, São Carlos, São Paulo, Brazil ' Institute of Mechanical Engineering and Industrial Management, University of Porto, Rua Roberto Frias, 4200-465 Porto, Portugal; Faculty of Engineering, University of Porto, Rua Roberto Frias, 4200-465 Porto, Portugal; Porto Biomechanics Laboratory, University of Porto, Rua Dr. Plácido Costa, 91, 4200-450, Porto, Portugal ' Laboratory for Process Engineering, Environment, Biotechnology and Energy, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Roberto Frias, 4200-465 Porto, Portugal; Institute of Biomedical Engineering, Biomaterials Division, University of Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal ' Laboratory for Process Engineering, Environment, Biotechnology and Energy, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Roberto Frias, 4200-465 Porto, Portugal

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.

Keywords: creep; fatigue; mechanical properties; prediction; time-dependent mechanical behaviour; polylactic acid; PLA; graphene nanoplatelets; GNP; graphene reinforcement; biodegradable polymers; nanocomposites; automotive applications; viscoplastic constitutive modelling; reinforced nanoplatelets; nanotechnology; cumulative damage; tensile tests; strain rates; loading-unloading cycles; hyperelastic springs; viscoplastic dashpots; thixotropic influence.

DOI: 10.1504/IJAUTOC.2015.070568

International Journal of Automotive Composites, 2015 Vol.1 No.2/3, pp.244 - 257

Received: 16 Aug 2014
Accepted: 31 Dec 2014

Published online: 10 Jul 2015 *

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