Mechanism‐Resolved Reinforcement of Natural Rubber by Discrete <scp>CNT</scp> Fragments: A Coarse‐Grained Molecular Dynamics Study

ABSTRACT Carbon nanotubes (CNTs) are highly efficient reinforcements for elastomers, yet their practical performance is often compromised by severe agglomeration and unstable network evolution under large deformation. In this work, we employ coarse‐grained molecular dynamics simulations to systematically investigate the reinforcement mechanisms of natural rubber filled with carbon nanotube fragments (CNTF), where each CNTF consists of 10 coarse‐grained beads representing short (5,5) CNT segments. By varying the CNTF loading from 0 to 20 phr, both macroscopic mechanical responses and microscopic deformation mechanisms are quantitatively analyzed. The results show that CNTF incorporation leads to a pronounced and nonlinear enhancement in Young's modulus, yield strength, and tensile strength, with increases of over one order of magnitude at high loadings. Stress analysis reveals that reinforcement is accompanied by progressive interfacial stress localization and strain‐induced cavitation at high CNTF contents, which governs post‐peak softening behavior. Importantly, distance‐based contact statistics and radial distribution functions demonstrate that tensile deformation does not induce CNTF re‐agglomeration. Instead, the observed reduction in indirect contacts and filler‐filler correlations indicates the disruption of polymer‐mediated CNTF networks due to interfacial debonding and cavitation. Further analyses of interfacial energetics and chain‐level dynamics reveal that load transfer is primarily mediated by increasingly strong CNTF‐rubber interactions, which constrain polymer mobility and drive a transition from polymer‐network‐dominated deformation to filler‐network‐mediated load bearing. These findings establish a clear mechanistic link between filler length reduction, dispersion stability, interfacial load transfer, and macroscopic reinforcement, providing particle‐resolved insights that are difficult to access in conventional long‐CNT‐filled rubber systems.