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Designation UD PW 8HS Fibre architecture (filaments per tow) Unidirectional tape (NA) Plain weave (3k) 8-harness sating (3k) Areal weight Resin content Laminate stacking (g/m2) (%) sequence 145 33 [0]30 196 36 [0]21 370 36 [0]11 Nicolas Krumenacker and Pascal Hubert four-point bending, as opposed to tensile or compressive fibre failure in the corner due to bending or interlaminar shear failure in the flanges [23]. Table 1 – Selected fibre architecture specifications. Three processing conditions detailed in Table 2 are additionally investigated for each of the three fibre architectures, resulting in a total of nine samples (i.e. UD-B H and R, PW-B, H and R, and 8HS- B, H, and R). First the baseline condition (B) is representative of near-optimal processing conditions and sets a benchmark, against which the two selected processing deficiencies can be compared. Second the half vacuum-bag pressure loss condition (H) is representative of a very deficient consolidation pressure. Third and last, the restricted air-evacuation condition (R) is representative of the curing of large-scale laminates on the order of several meters or more such as primary aerospace structures. OOA prepregs are designed to be much more air permeable in-plane than through-the- thickness, most notably in the case of UD tape. Large-scale laminates therefore have a propensity to trap air at their center as air-evacuation distance increases, which is of great research interest. Table 2 – Selected processing conditions. Designation B H R Process condition Baseline Half-vacuum loss Restricted air-evacuation Vacuum bag pressure (atm) ~1 atm ~0.5 atm ~ 1 atm Air- evacuation Edge-only Edge-only Restricted De-bulk steps 5 min/ply 5 min/ply None Room-temp. Hold 12 hr 12 hr None 2.2 Layup, processing and specimen machining Preparation: The laminates are manually laid-up and vacuum-bagged following the vacuum- bagging consumables sequence illustrated in Figure 1. The aluminum tool surface is first treated with a solvent-based tool sealer followed by a solvent-free semi-permanent release agent (Zyvax® Sealer GP and EnviroShield, respectively). Release agent is used instead non-perforated release film in order to better fix the first ply to the tool surface and to prohibit the possible transfer of wrinkles onto the laminate’s inner corner surface. That being the case, narrow strips of non-perforated release film (Airtech A4000) are placed under the laminate edges in order to prevent local roughing of the released tool surface during de-bulking, which increases the likelihood of post-cure tool-part adherence. Layup: Plies measuring 55 by 25 cm are laid up according to the respective laminate stacking sequences (Table 1). A de-bulk step of 5 min is applied between each ply layup to improve consolidation, except for the restricted air-evacuation sample. Edge breathing is achieved via dry fiberglass tape wrapped around sealant tape (Airtech GS-213-3) and placed around the laminate edges, while restricted air-evacuation is achieved by using sealant tape only to seal the edges. A layer of non- perforated release film is then placed over the laminate to prohibit resin bleeding into the breather layers and to better seal the laminate in the case of restricted air-evacuation. The breather layer consists principally of a fiberglass, plain-weave peel ply instead of a standard polyester breather in order to reduce the bulk of bagging consumables and mitigate the possible formation of wrinkles on the outer laminate surface during de-bulking. Breather strips (Airtech Airweave® N4) are also used around the laminate edges to create a supplemental air-evacuation channel leading to the vacuum ports. Lastly, the top surface of the mould is sealed with a standard nylon vacuum-bagging film (Airtech Wrightlon® 6400) and sealant tape around the edges of the tool surface.PDF Image | VACUUM-BAG-ONLY COMPLEX-SHAPE PREPREG LAMINATE
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