A Coarse-Grained Molecular Dynamics Study on the Role of Cross-Links and Applied Strain in the Recovery Behavior of Carbon Nanotube–Graphene Foam Composites: Implications for Flexible Applications

The recovery performance of carbon nanotube (CNT)–graphene foam composites (CGFCs) plays a crucial role in flexible device applications, but the microscopic mechanisms governing the performance are not fully understood. To uncover the underlying mechanisms, coarse-grained molecular dynamics simulations were carried out on CGFCs with pure graphene foam (GrF) as a reference. By analyzing the distribution and evolution of deformation energy in graphene and CNTs at an applied strain of 0.5 under both tension and compression, the deformation mechanisms of recovery are revealed, and the corresponding effects of cross-linking density and maximum applied strain are also investigated. Compared to pure GrF, CGFCs demonstrate lower residual plastic strain after both tensile loading–unloading and compressive loading–unloading processes due to the role of CNTs in restricting irreversible microstructural deformations in graphene; during tension, CNTs bridge adjacent graphene sheets and inhibit their separation, while during compression, CNTs constrain the sliding and rotation of graphene. Consequently, the external work is primarily stored as deformation energy─mainly CNT stretching and graphene bending─which is released upon unloading, resulting in reduced residual plastic strain. In contrast, pure GrF dissipates energy through irreversible microstructural rearrangements, such as separation, sliding, and rotation of graphene, leading to greater residual plastic strain. The suppressive effect of CNTs relies on the presence of CNT–graphene (CG) bonds; consequently, the recovery performance of CGFCs improves with increasing CG bond density. Furthermore, residual strain increases with greater maximum applied strain, indicating that irreversible microstructural rearrangements become more pronounced as the maximum applied strain increases. The study clarifies the recovery mechanisms of CGFCs and informs the design of nanocomposites with enhanced elasticity for flexible applications.