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42 W. HU AND S. NUTT Figure 4. Void evolution during pre-cure dwell of PW prepregs: (a) initial state, (b) after 4-h RT vacuum hold, (c) after 4-h 60C vacuum hold; and for pre-cure dwell of UD prepregs: (d) initial state, (e) after 4-h RT vacuum hold, (f) after 4-h 60C. Figure 5. Void content as a function of time during debulk for (a) PW and (b) UD laminates. exhibited a lower initial void content of $13%. However, the evacuation of inter-ply air was much slower in UD prepregs. The void content decreased to $6% and $3% after a 4-hour debulk at 20 C and 60 C, respectively. As mentioned before, inter-ply air bubbles must migrate a short distance to the dry fiber tows to reach evacuation pathways. PW prepregs exhibit large open pores at the intersections of the tow bun- dles (Figure 4(b) circled in red), affording a grid of pathways for efficient evacuation of inter-ply air. In contrast, UD prepregs feature resin film that is more uniformly distributed on the surface, and air can be evacuated only via some resin-starved regions [6]. As debulk temperature increases, resin viscosity decreases, facilitating resin flow, which promotes air evacuation through those resin-starved regions. However, the larger, artificial air bubbles require further resin flow to allow air bubbles to migrate towards evacuation pathways [6]. 3.2. Through-thickness permeability during heated debulk The effects of debulk temperature and number of plies on the through-thickness permeability of PW and unidirectional laminates are shown in Figures 6a–e. These plots show transverse permeability of PW laminates as a function of time at different debulk temperatures. Initially, permeability decreasesPDF Image | VACUUM BAGGING SUPPLIES Peel Ply Fabric
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