Microscale air permeability characterization of lafp composites using micro-ct imaging: comparison with pulse-decay measurements

Vacuum bag only (VBO) processing has gained increasing interest as an out-of autoclave (OoA) route for composite consolidation, offering an alternative to conventional autoclave-based manufacturing. For this process to be effective, the laminate must provide adequate air-flow pathways to allow trapped air to be removed during consolidation. In laser-assisted fiber placement (LAFP), the development of these pathways is governed by both the selected processing conditions and the stacking sequence of the laminate. Although the pulse-decay method is widely applied for measuring the permeability of low-permeability porous materials, its use for composite laminates can be time-consuming and requires relatively large, well-sealed specimens. Moreover, it does not directly reveal the internal pore-network structure. X-ray micro-computed tomography (Micro-CT) provides a non-destructive alternative that enables three-dimensional analysis of void morphology, pore connectivity, and fiber arrangement. In this work, the air permeability of LAFP-fabricated thermoplastic composite laminates produced with different lay-up speeds and stacking sequences was investigated using both pulse-decay and Micro-CT-based approaches. The two techniques showed comparable permeability trends across the examined configurations. In addition, Micro-CT provided detailed information on connected porosity and void morphology, with lower variability in the calculated permeability values. The results suggest that Micro-CT can be used as an effective tool for permeability evaluation and for supporting the optimization of LAFP processing toward OoA composite manufacturing.