Process Modeling for Strain Evolution during Autoclave Composite Cure

Carbon fiber composites with epoxy matrix are widely used in many aerospace applications due to their high strength-to-weight ratio compared with commonly used metals. In addition to high mechanical performance, low dimensional tolerance and low defect count are requirements for primary aerospace structures in fuselage and wings. The continuous evolution of thermal and chemical strains and the resulting residual stresses during autoclave processing critically affect the dimensional stability and processing-induced defects in the composite structures. This research focuses on modeling the cure phenomenon inside an autoclave and presents a cure design technique to reduce the processing induced strains and stresses. The cure kinetics of the thermoset matrix of a carbon fiber prepreg is calculated through reaction kinetic equations parameterized using differential scanning calorimetry (DSC). A thermomechanical finite element model of autoclave composite processing incorporating cure kinetics is then developed. Processing induced deformations in a few four-ply layups are analyzed using this model and compared with prior experimental results. The effect of abrupt cooling operation in lowering the processing induced strains is investigated. The computational model accurately predicted the evolution of strains during cure and deformations post-cure. This approach can be applied to other thermoset matrix materials to predict and reduce processing-induced strains and residual stresses.