Process parameter selection for the consolidation of continuous fiber reinforced composites using finite element simulations

The foil/fiber/foil process is one of the most common techniques used to fabricate continuous fiber reinforced composites. In composites consisting of several alternate layers of foils and fibers, some of the fibers form a triangular array, while others are arranged in a rectangular pattern directly one above another. A finite element analysis using the commercial code ABAQUS has been employed in order to determine which of these fiber arrays densifies at a slower rate, and hence controls the densification process. The simulation results, based on composites comprised of Ti-6A1-4V foils and SCS-6 silicon carbide fibers, showed that the triangular array densifies much faster than the rectangular. Foils comprising the rectangular array must undergo much higher strain than those comprising the triangular array in order to produce a fully densified composite. A slowing of the densification in both types of fiber arrays was observed in the latter stages of pore closure after two neighboring foils had estabished contact with each other. This slowing may be attributed to the required increase in strain as well as the low stress levels existing in the vicinity of the pore. The simulation results were used to describe the process by a closed form relationship, and to generalize our results so they may be applied to any composite system, since it includes the processing parameters, as well as fiber spacing (or fiber volume fraction), foil thickness and fiber diameter. Densification maps showing the change of density with time for a range of processing temperatures and applied stresses were also constructed. These maps may be used to select the consolidation parameters that will minimize the reaction zone formation at the matrix-reinforcement interface, the residual stresses and other adverse effects.