Transport phenomena in vacuum bag only prepreg processing of honeycomb sandwich panels
Notice bibliographique
Résumé
Honeycomb sandwich panels offer an extremely lightweight solution for aerospace structures. As efficiency demands increase, low-cost non-autoclave manufacturing solutions are sought for honeycomb and other composite structures. Vacuum-bag-only (VBO) manufacturing is one possible solution that relies on vacuum to remove all entrapped volatiles prior to cure, and then the differential pressure between the inside and outside of the vacuum bag consolidates the layers during cure. This technique can be very effective for monolithic laminates made with out-of-autoclave (OOA) prepregs, but honeycomb structures introduce two additional manufacturing nuisances. First, the core entraps up to 98 % of its volume during lay-up, and second, non-metallic cores readily absorb ambient moisture. Entrapped air and moisture can increase the honeycomb core pressure during processing, reducing part quality. Given that the honeycomb core pressure is crucial to achieving success in VBO manufacturing of honeycomb panels, a threefold approach was used in this thesis to study the transport phenomena that influence this behaviour. First, the transport phenomena of the constituent materials were characterized. Applying an impermeable boundary condition to the tool-side skin allowed for simple air permeability characterization of honeycomb skins by considering only the bag-side skin. An instrumented test fixture was used to measure the honeycomb core pressure during the pre-processing vacuum hold. The results revealed that a transverse interconnected pore space was required in OOA prepreg skins for gas evacuation to proceed in honeycomb panels. The same test fixture was used to characterize the honeycomb skin air permeability and honeycomb core moisture diffusivity during elevated temperature processing. The evolving skin air permeability and core diffusivity were observed to cause the honeycomb core pressure to increase during the temperature ramp and decrease during the temperature hold. Second, a process model was developed to predict honeycomb core pressure throughout the manufacturing process. The process model identified that the honeycomb core pressure can exceed the vacuum bag consolidation pressure due to the high core moisture adsorption and elevated temperature diffusivity. Choosing, or creating, a honeycomb skin with high air permeability was identified as a key process parameter to avoid exceeding the consolidation pressure. Finally, the material characterization and process modelling were successfully scaled to reproduce the honeycomb core pressure behaviour in holistic honeycomb panels. The in-situ honeycomb core pressure was measured throughout the manufacturing process in dual-skin honeycomb panels using embedded pressure sensors. The embedded pressure sensor response validated the material characterization assumptions and model simplifications used to predict the honeycomb core pressure during the VBO manufacturing process. Manufacturing honeycomb panels is a complex activity with many material and processing variables. A suitable skin material and bagging configuration was selected for VBO manufacturing of honeycomb panels by coupling transport phenomena modelling and tailored material characterization. This approach could be used to reduce manufacturing trial and error before scaling these materials to larger applications.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».