Prediction of fibre waviness in a thermosetting composite panel with ply drop-off's.

Botete, Makoena Raymond (2019-04)

Thesis (MA)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: is because of a large number of defects that may occur during the curing process. Thermal deformations such as fibre waviness are the most critical, since they can lead to a total scrap of the component if not accounted for in the design. The aim of this project was to predict the formation of fibre waviness defects in a thermosetting composite panel that comprises ply drop-offs. This composite panel was constructed from 24 unidirectional plies (IM7/977-2 carbon epoxy tape) and cured in the autoclave with a tool made from Invar material. The predictions were accomplished by performing cure simulations using a newly developed Ansys Composite Cure Simulation (ACCS) analytical tool-kit. The simulation results showed that the composite panel goes through material evolutions throughout the curing process that leads to the development of stresses and strains. The alternation of transverse strains (between high and low values) and shear strains (between negative and positive values) when plies are in compression in their fibre direction was shown to result in the formation of fibre waviness defects when the resin viscosity is at its minimum. The fibre waviness defects were predicted to occur at the drop-off stations on the bag side of the composite panel and validated by practical observations after manufacturing. Using this fibre waviness mechanism, the effect of various parameters were investigated to understand the main drivers of fibre waviness defects. Stagger length and the cure-pressure had an effect on the formation of fibre waviness, while parameters such as drop-off sequence, pressure ramp-up rate and the heat-up rate did not show any effect.

AFRIKAANSE OPSOMMING: Die produksie van saamgestelde strukture van hoë-kwaliteit is ‘n uitdagende proses. Dit is as gevolg van moontlike defekte wat kan ontstaan gedurende die verhardingsproses. Termiese deformasies soos vesel-golwing is die mees kritiese tipe defek, omdat hierdie soort defek kan lei tot ’n totale afskryf van die vervaardigde komponent indien dit nie in ag geneem is tydens die ontwerpsfase nie. Die doel van hierdie projek was om die formasie van veselgolwing in ’n termiese-set saamgestelde paneel waarvan die lagies binne die paneel ophou (“ply drop-offs”) te voorspel. Hierdie saamgestelde paneel bestaan uit 24 eenrigting lagies (IM7/977-2 koolstof epoksie in band vorm), en word gekuur in ’n outoklaaf met ’n werkstuk wat van Invar vervaardig is. Die voorspellings is bereik deur kuursimulasies uit te voer met die nuut ontwikkelde “Ansys Composite Cure Simulation (ACCS)” sagteware. Die resultate van die simulasies toon dat die saamgestelde paneel se materiaal ’n evolusie proses gaan tydens die kuurproses, wat lei tot die ontwikkeling van spanning en vervorming in die paneel. Die afwisseling van dwars-vervormings (tussen hoë en lae waardes) en skuif-vervormings (tussen negatiewe en positiewe waardes) wanneer ’n lagie in kompressie is in die veselrigting, het aangedui dat veselgolwing defekte plaasvind wanneer die epoksie viskositeit by ’n minimum is. Die vesel-golwing defekte is voorspel om plaas te vind in die areas waar die interne lagies ophou aan die sak-kant van die saamgestelde paneel, en is verder bevestig met praktiese waarnemings na vervaardiging. Met die gebruik van hierdie golwingvormingsmeganisme is die effek van verskeie parameters ondersoek om die hoof-drywers van vesel-golwing defekte te verstaan. Ophou volgorde lengte (stagger length) en die verhardingsdruk het die formasie van vesel-golwing beïnvloed, terwyl parameters soos die volgorde waarin die lagies opgelê word, die druktoeneemtempo en die opwarmingstempo nie enige invloed getoon het nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106183
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