The current study is focused on understanding the role of different void removal mechanisms in VBO processing of advanced thermoplastic composites. For this purpose, two commercially available Carbon/Poly-Ether-Ketone-Ketone (C/PEKK) tape materials were evaluated, distinct in morphologies, such as surface roughness and fiber-matrix distribution, and physical characteristics, mainly the presence of volatiles. The VBO consolidation results proved that the void reduction and removal mechanisms varied depending on the tape material. However, restricting the void reduction mechanism to dissolution and diffusion alone. Depending on the tape material, a significant difference in the consolidation dwell time was observed to achieve <1% void content parts. Thus, indicating that despite the tapes having the same polymer matrix, they differ in their diffusion behavior. The difference in the times required for consolidation may be due to the following. Firstly, the diffusion coefficients may be different for the two tapes. Although the matrix material in both tapes is PEKK, the exact formulation is unknown. Secondly, the volume of gases, which comprises entrapped air and the volatiles that evaporate during the process, that need to be removed maybe be different.
Vacuum-bag-only (VBO) consolidation of automated fiber placed (AFP) thermoplastic composites can be a cost-effective processing route for large and complex thermoplastic composite structures. This paper explores the possibility of two-step AFP and VBO consolidation of advanced thermoplastic composites. Two commercially available carbon fiber reinforced Poly-Ether-Ketone-Ketone (C/PEKK) thermoplastic tapes were evaluated. Different process parameters were needed for the two material systems. Further, for the first time, an attempt was made to create in-plane air evacuation channels by deliberately introducing gaps between the tapes in the preforms during the placement. In the case of one material system, the VBO consolidation of preforms with and without gaps yielded good consolidation quality with less than 1% voids. In the other case, VBO consolidation of preforms with gaps showed a improved consolidation quality with less than 1% voids than the preform without gaps, indicating that the gaps possibly help accelerate the gas evacuation process.
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