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The first phase of this study aimed to validate multi-scale approaches based on Representative Volume Elements (RVEs) for graphene–polyethylene nanocomposites. stress–strain curves of experimental results were compared with numerical homogenization results. The stress amplification obtained from these simulations was used to predict GNP aspect ratios, demonstrating good agreement with permeability results. After validation of the multiscale approach, this study investigates the adhesion between nanoparticles and matrix in anisotropic GNP-HDPE metamaterial nanocomposites, emphasizing the role of the carboxyl (COOH) functional group in improving adhesion. The RVE model is used to investigate the debonding initiation and progression in these anisotropic nanocomposites under tensile and shear loading. Results indicate a variance in debonding onset and growth depending on orientation relative to the GNP axis. In tensile loading, debonding initiates at higher strains along the GNP axis than perpendicularly. Under shear loading within an anisotropic distribution, debonding behaviour varies significantly between planes perpendicular and parallel to the GNP axis. GNP surfaces with fully debonded surfaces slightly exceed 0.6% perpendicular to the GNP axis but increase to over 10.5% parallel to it. [ABSTRACT FROM AUTHOR]

In the in situ tensile tests of polymer-GNP nanocomposites, the damage initiation in the interfacial zone is directly related to the surface adhesion in the interface. Adding functional groups to GNP increases the adhesion between polymer and inclusion and significantly reduces damage in the interfacial zone. This research was developed based on hierarchical multiscale modeling to investigate damage initiation in polymer-GNP nanocomposites. In the first step, the effect of functional groups on the surface adhesion between GNP and HDPE at the nanoscale was investigated by MD simulations, and the Pull-out test and force–displacement curve were obtained. A cohesive finite element approach was exploited in the second step to model debonding. The results show that the functional groups (H, OH, and COOH) will cause delayed damage in the interfacial zone, and debonding will begin at higher strains. Also, the damage initiation is directly linked to the type of functional groups. The effect of functional groups in different volume fractions of nanoparticles shows that the damage initiates earlier with an increase in the volume fraction of GNPs in constant percentage coverage of each type of the functional group. However, the effect of the functional groups in reducing effective strain in the damage initiation is more significant than the volume fraction of GNPs. After applying a 20% strain at various volume fractions, the COOH functional groups significantly reduced fully debonded surfaces. Furthermore, we investigated the impact of volume fraction on fully debonded surfaces in both pure and COOH functional groups. A nonlinear trend is apparent as the volume fraction increases from 0.3 to 1.5%. The effects of multiple bonding types are taken into account by creating several RVEs with a constant volume fraction of 1.5 and a different proportion of functional groups. [ABSTRACT FROM AUTHOR]