  Thermoset resin-based composite materials are widely used in the aerospace
industry, mainly due to their high stiffness-to-weight and strength-to-weight
ratios. A major issue with the use of thermoset resins in fiber composites is
the process-induced residual stresses that are formed from resin chemical
shrinkage during the curing process. These residual stresses within the
composite material ultimately result in reduced durability and residual
deformations of the final product. Polybenzoxazine (PBZ) polymer resins have
demonstrated near-zero volumetric shrinkage during the curing process. Although
the low shrinkage of PBZ is promising in terms of reduced process-induced
residual stresses, little is known about the physical causes. In this work,
Molecular Dynamics (MD) simulations are performed with a reactive force field
to predict physical properties (gelation point, evolution of network, mass
density, volumetric shrinkage) and mechanical properties (Bulk modulus, Shear
modulus, Young's modulus, Poisson's ratio, Yield strength) as a function of
crosslinking density. The MD modeling procedure is validated herein using
experimental measurements of the modeled PBZ resin. The results of this study
are used to provide a physical understanding of the zero-shrinkage phenomenon
of PBZ. This information is also a critical input to future process modeling
efforts for PBZ composites.
