Understanding the Mechanisms Behind Increased Load Transfer in BMI-flCNT Composites Using Molecular Dynamics

Crewed deep-space exploration is a future milestone for the aerospace industry. Such aerospace missions demand ultrastrong, lightweight structural materials to minimize the payload mass. Polymer matrix composites (PMCs) with carbon-based reinforcements, such as carbon fiber, graphene, and carbon nanotubes (CNTs), are of primary interest as structural materials for these applications. Although PMCs are lightweight and strong, their mechanical performance is limited to the weak interface region. The interface region can be strengthened by chemical functionalization of the reinforcement materials and covalent cross-linking of the matrix and the reinforcement. Molecular dynamics (MD) offers a platform for computationally investigating the effects of interface conditions on mechanical performance. In this research, the interfacial region of a bismaleimide (BMI)/flattened carbon nanotube (flCNT) composite is investigated by virtually introducing functionalization of the flCNTs and interfacial cross-links between BMI and flCNTs via MD simulation. As a result, the flCNT pullout forces are predicted as a function of the degree of functionalization and the number of interfacial cross-links. Results reveal that functionalization and covalent cross-links are crucial to improve the interfacial strength of the composite, with higher degrees of functionalization degrading the material integrity. This research provides important physical insights into potential strengthening mechanisms of aerospace composites.