The Effect of Overlap Distance on the Strength and Toughness of “Brick-Mortar” Graphene–Polyethylene Nanocomposites: Competition Between Tension and Shear in the Polymer Phase

This study employs coarse-grained molecular dynamics simulations to investigate how the overlap distance between graphene nanosheets influences the mechanical properties of “brick-mortar”-structured graphene–polyethylene nanocomposites. Simulations are conducted in a fixed box size while varying the overlap distance from 2.4 to 24 nm. The stress–strain response exhibits three distinct stages: elastic increase, plastic plateau, and slow decrease. The yield strength increases nearly linearly from 115.3 ± 3.8 to 347.9 ± 33.0 MPa with increasing overlap distance, a trend well captured by an extended shear-lag model incorporating polymer stretch. The critical failure strain, marking the onset of strain localization, first increases and then decreases, peaking at an overlap distance of 4.8 nm. This non-monotonic behavior is attributed to a competition between polymer stretch and polymer shear in interfacial stress transfer. Similarly, the plateau stress and toughness show two-stage evolution: the plateau stress remains constant (~100 MPa) up to 4.8 nm before increasing significantly, while toughness rises from 16.9 ± 0.2 to 51.0 ± 4.0 MJ/m3 across the range. These findings reveal the nanoscale mechanisms behind strength and toughness in bioinspired nanocomposites and provide guidelines for optimizing performance through overlap distance tuning.