Simulation of process-induced residual stresses in thick filament wound tubes

The development of residual stresses throughout the cure process in thick composite components is strongly influenced by the cure history. Residual stresses in thick filament wound tubes can lead to delamination and intralaminar cracking during the cure. A major challenge in the manufacturing of filament wound structures is to have a fundamental understanding of the development of residual stresses.

A quasi three-dimensional finite element model has been developed to predict the process-induced residual stresses in thick composite cylinders. The focus of the process modelling of the residual stresses in the composite tubes is on the early stage of the cure, namely the cure cycle prior to cool-down, during which the residual stresses could cause delamination since the composite has low strength. The main identified factors affecting residual stresses such as heat transfer, resin cure kinetics, gelation, resin thermal expansion, chemical shrinkage and mandrel interaction have been integrated into the main model. The simulation identifies the important influence of the thickness of the tubes, the chemical shrinkage of the resin, and the mandrel interaction on the development of residual stresses. A good match between the model prediction and experimental results obtained at QinetiQ was obtained in most cases. A heated mandrel was proposed for reducing the residual stresses during the cure of the composite tube, which has been proven effective in the experimental work at QinetiQ.