A detailed theoretical/numerical framework is established to study the mechanical erosion of graphite-nozzle materials in solid rocket motors with aluminized ammonium perchlorate/hydroxyl-terminated polybutadiene composite propellants. The analysis is based on a combined Eulerian–Lagrangian approach for treating multiphase motor flowfields. The multicomponent reacting gas-phase dynamics is formulated using the conservation equations of mass, momentum, and energy in the Eulerian framework. Turbulence closure is achieved using the standard two-equation model. The dispersed phase, consisting of aluminum and alumina droplets, is treated in the Lagrangian framework. Combustion of aluminum droplets to aluminum-oxide smoke is considered. Two empirical correlations are first calibrated and then employed to predict the mechanical-erosion rate of the nozzle surface. The estimated erosion rates fall within the range of the available experimental data. Mechanical erosion is prevalent in the convergent section of the rocket nozzle due to the particle impingement on the nozzle surface. No such erosion, however, is observed at the nozzle throat or downstream because the droplet trajectories move away from the nozzle surface in those regions.