Editing Pre-preg (section)

== Resin properties ==
The properties of the resin and fiber constituents influence the evolution of VBO (vacuum-bag-only) prepreg microstructures during cure. Generally, however, fiber properties and fiber bed architectures are standardized, whereas matrix properties drive both prepreg and process development.<ref>{{Cite journal|last=BOEING CO SEATTLE WA|title=Dyna Soar Testing for the Boeing Company|date=1963-02-01|location=Fort Belvoir, VA|doi=10.21236/ad0336996|doi-access=}}</ref> The dependence of microstructural evolution on resin properties, therefore, is critical to understand, and has been investigated by numerous authors. The presence of dry prepreg areas may suggest a need for low viscosity resins. However, Ridgard explains that VBO prepreg systems are designed to remain relatively viscous in the early stages of cure to impede infiltration and allow sufficient dry areas to persist for air evacuation to occur. Because the room temperature vacuum holds used to evacuate air from VBO systems are sometimes measured in hours or days, it is critical for the resin viscosity to inhibit ''cold flow'', which could prematurely seal the air evacuation pathways.<ref>{{Cite journal|last1=Helmus|first1=Rhena|last2=Centea|first2=Timotei|last3=Hubert|first3=Pascal|last4=Hinterhölzl|first4=Roland|date=2015-06-24|title=Out-of-autoclave prepreg consolidation: Coupled air evacuation and prepreg impregnation modeling|journal=Journal of Composite Materials|volume=50|issue=10|pages=1403–1413|doi=10.1177/0021998315592005|s2cid=136977442|issn=0021-9983}}</ref> However, the overall viscosity profile must also permit sufficient flow at cure temperature to fully impregnate the prepreg, lest pervasive dry areas remain in the final part.<ref>Citation error. See inline comment how to fix. {{verify source |date=September 2019 |reason=This ref was deleted Special:Diff/872132953 by a bug in VisualEditor and later identified by a bot. The original cite can be found at Special:Permalink/871789755 (or in a rev close to it) in either cite #4 or cite #3 - find and verify the cite and replace this template with it (1). [[User:GreenC_bot/Job_18]]}}</ref> Furthermore, Boyd and Maskell<ref>{{Cite book|title=Composites manufacturing : materials, product, and process engineering|last=K.|first=Mazumdar, Sanjay|date=2002|publisher=CRC Press|isbn=978-0849305856|location=Boca Raton, Fla.|oclc=47825959}}</ref> argue that to inhibit bubble formation and growth at low consolidation pressures, both the viscous and elastic characteristics of the prepreg must be tuned to the specific processing parameters encountered during cure, and ultimately ensure that a majority of the applied pressure is transferred to the resin. Altogether, the rheological evolution of VBO resins must balance the reduction of both voids caused by entrapped gases and voids caused by insufficient flow.