On Deformation Mechanism And Modeling Of Graphene-reinforced Nanocomposites

As an emerging class of carbon nanomaterials,graphene has gained a considerable attention owing to its exceptional mechanical properties,thus graphene nanoplatelets(GNPs)have become an ideal nano-reinforcement alternative for lightweight strong composites especially in aeronautic and astronautic industries.However,the research efforts so far have mainly focused on experimental study of graphene-reinforced nanocomposites,which is insufficient to facilitate theirwidespread applications.To accurately describe the flow stress and strengths of the graphene-reinforced nanocomposites during the elastoplastic deformation process,a macro-micromechanical model has been developed in this paper.For the graphene-reinforced metal matrix nanocomposites(GNP-MMNCs),prior to the micromechanical modeling,the microstructure of graphene nanoplatelets(such as multilayered thickness and surface area)was characterized by microscopic techniques.And then the key influence of the orientation(?)and effective load-carrying length(le)of randomly-distributed graphene nanoplatelets were especially considered.The step-response problem of flow stress at the zero point of true strain in most present strength models of nanoparticle-reinforced MMNCs had been solved.At the same time,the effects of temperature softening and strain rate hardening were also introduced into the present model through a dislocation-mechanics-based metal matrix model.With applications to the nanocomposites of GNP/A12024,GNP/AI and GNP/Cu,the new model was in agreement with the experimental data,showing a good engineering applicability.The yield and ultimate strengths of the nanocomposites can be dramatically enhanced by adding a small volume percent of graphene;In addition,the proposed model suggests that the strengthening stress of graphene shows an approximately linear increase with the volume fraction within a small concentration range;The stiffness of GNP-MMNCs can be effectively enhanced by increasing the graphene size while keeping an unvarying thickness of GNPs,and there exists a final saturation tendency for the size-strengthening.The model predictions show that the dependence of the flow stress of GNP-MMNCs on strain rate as well as temperature is approximately linear within a broad strain rate or temperature range.The temperature softening effect would decline under dynamic loading conditions,while the rate hardening effect would become stronger at elevated temperatures.Finally,for the graphene-reinforced polymer nanocomposites(GNP-PMNCs),on the quasi-static condition,the strengthening effect not only takes into account the orientation(?)and effective load-carrying length(le)of the graphene sheets,but also considers the effect of the interface.On the dynamic loading conditions,the Maxwell unit was introduced to present the influence of strain rate on the matrix.Subsequently,the effect of temputure on mechanical properties of GNP-PMNCs was discussed.Finally,with applications to the nanocomposites of GNP/EP,the new model was in agreement with the experimental data,showing a good engineering applicability.