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(~400°F), produces water as a by-product. Furthermore, the LARCTM PETI-8 prepreg contains volatile NMP solvent (~14% by weight) that is left during the prepregging process for handlability. For the composite process to be successful in producing a quality, void free part, it must adequately manage the water from imidization and the residual solvent left over from the prepregging process. An identical temperature profile was used for composites molded by either the SVB or DVB process: an initial 250°C/1 hr B-stage ramp-and-hold from RT at ~3°C/min, followed by a second ramp-and-hold at the same rate to 371°C/1 hr final curing. The laminate lay-up scheme is 3” x 3” - [0]8 . Vacuum pressure (i.e., 14.7 Psi created by the 30” Hg vacuum) was applied throughout the cure cycle for the SVB process. In the DVB process, full vacuum (30” Hg) is applied to the Outer Bag, while a slightly lower vacuum level (i.e., 28” Hg) is set in the Inner Bag during the B-stage period. At the end of the 250°C/1 hr B-stage, the Outer Bag was purged to atmosphere and the Inner Bag vacuum was increased to 30” Hg. The atmospheric pressure created by the Inner Bag vacuum helped to consolidate the volatile-free composite during the 371°C/1 hr ramp-and-hold period. (a) SVB molded laminate (100X) (b) DVB molded laminate (100X) Figure 5. Optical photomicrographs of SVB and DVB molded IM7/LaRC‘ PETI-8 Composite. The cross section photomicrographs of the resultant laminates are shown in Figure 5. Excessive resin squeeze-out and high void content were observed for the SVB molded laminate. The domains between plies that are typically resin-rich, are particularly high in void content when compared to those domains within the fiber bundles (Figure 5(a)). Apparently, the oven SVB processing is ineffective and creates problems not only in maintaining the targeted resin content, but also in avoiding volatile entrapments in the final consolidated laminate parts. Much less resin flash was observed in laminatesPDF Image | Evaluation of Double-Vacuum-Bag Process For Composite Fabrication
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