Thermosetting polymer materials are widely used for composite materials in aerospace structural applications. Many high-performance resins require curing cycles that involve high temperatures and pressures. Because reinforcing fibers typically have thermal expansion properties that differ from the polymer, residual stresses typically form when the cured laminate is brought to ambient conditions. Polymer shrinkage during curing contributes to the residual stress build-up during manufacturing. These residual stresses can compromise the mechanical durability of composite laminates subjected to significant thermal and mechanical in-service loading. Unfortunately, developing models to predict the magnitude of process-induced residual stresses in laminates is greatly complicated by the multiscale nature of the composite architecture. 
In this work, molecular simulations at the nanoscale and finite element simulations at the micro-scale are combined to predict the residual stress build-up in a carbon fiber/epoxy composite system using a DEGBF epoxy. Molecular dynamics (MD) simulations using the Interface force field - Reactive (IFF-R) are performed to evaluate thermomechanical properties of the epoxy as a function of temperature and crosslinking density. The properties thus obtained are utilized as input in the Finite Element (FEM) model to predict the residual stress build-up during the curing of epoxy and its effect on the strength of the composite. The results obtained from MD are validated experimentally. The study showed that the molecular and microscale analyses can be successfully integrated under Integrated Computational Materials Engineering (ICME) to investigate the evolution of residual stresses during laminate curing.



Multi-scale approach to predict cure-induced residual stresses in Bis-F/DETDA epoxy system

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