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Gas transport and water vapourization in out-of-autoclave prepreg laminates

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Title: Gas transport and water vapourization in out-of-autoclave prepreg laminates
Author: Hsiao, Kevin
Degree Master of Applied Science - MASc
Program Materials Engineering
Copyright Date: 2012
Publicly Available in cIRcle 2013-01-31
Abstract: Primary load-bearing aerospace structures have traditionally been manufactured using autoclave processing. However, recent advances in material technology have led to the development of pre-impregnated (prepreg) composites that are designed to be cured out-of-autoclave (OOA) and can potentially reduce the costs of processing. In OOA processing, voids are removed by vacuum evacuation through gas pathways in the prepreg. The availability and interconnectivity of these pathways determine the prepreg’s gas transport ability. Voids enter into the prepreg via moisture absorption during storage and physical air entrapment during manufacturing and material handling. Environmental effects, such as relative humidity, can alter the moisture content of prepregs and lead to significant vapour generation during cure. This study examines the gas transport and water vapourization characteristics of OOA prepreg CYCOM 5320/T650 (epoxy/carbon). Gas permeabilities in the in-plane and through-thickness directions are measured, and the effects of processing history (debulk time, temperature etc.) on gas transport are examined. The relationships between relative humidity, moisture content, and vapour generation are analyzed, and the use of mass flow sensors for water vapour quantification is validated. Gas transport is shown to be highly anisotropic in CYCOM 5320/T650, with inplane gas permeability being three orders of magnitude greater than through thickness. Processing history has a significant effect on permeability, with extended debulking sessions reducing in-plane permeability by 50%. Increasing temperature causes in-plane and through-thickness permeabilities to fall. Microscopy analyses reveal that permeability change is a result of collapsing voids and resin flow during heating. Moisture content is relatively unaffected by relative humidity until reaching 30% RH, after which increases in moisture content become more apparent. Vapourization of absorbed moisture between 0 %RH and ambient conditioned vacuum bagged laminates are similar, suggesting that under typical process conditions moisture vapourization mainly comes from the vacuum bag consumables. During vacuum bag processing, vapourization of absorbed moisture occurs immediately upon heating, peaks around 40 to 60oC, and then dissipates as heating reaches the hold temperature. The mass flow sensors are demonstrated to be capable of detecting the onset and termination of moisture vapourization and quantifying the total mass of water vapourized to within 10% error.
URI: http://hdl.handle.net/2429/42610
Scholarly Level: Graduate

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