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Effect of MWCNTs on Creep of Epoxy for CFRP Deployable Composites



Deployable aerospace joints are proposed to be made of thin laminated carbon fiber reinforced polymer (CFRP) composites. To enable efficient deployment, a method to dissipate the elastic strain energy that develops in the CFRP deployable composites is necessary. A three layer tape spring, incorporating two outer plain weave carbon fiber laminas loaded off-axis and one middle unidirectional carbon fiber lamina loaded onaxis, has been suggested. The proposed tape spring will enable damping of the deployment process by enabling creep/stress-relaxation in the plain weave carbon fiber laminas. Studies show that creep behavior of the tape spring is governed by creep of epoxy used in fabrication of the CFRP deployable composites. In this work, we suggest that creep of epoxy used for CFRP deployable composites can be controlled using Multi-walled Carbon Nanotubes (MWCNTs). Three contents of MWCNTs including 0.0 wt.%, 0.5 wt.% and 1.0 wt.% of the total weight of epoxy are examined. DMA testing of neat epoxy and epoxy-MWCNTs nanocomposites incorporating surface functionalized MWCNTs is reported to extract the creep master curves for epoxy incorporating three different weight content of MWCNTs. Laplace transform is used to identify Prony series coefficients for stressrelaxation curves of epoxy with three different weight content of MWCNTs. A finite element model incorporating the viscoelastic behavior of plain weave lamina was developed and used to simulate the stress-relaxation behavior of the tape spring. It is apparent that incorporating functionalized MWCNTs resulted in altering the mechanical performance of epoxy. In particular, the use of MWCNTs results in increasing stress-relaxation of the plain weave lamina during stowage time period. The observed change in creep of epoxy incorporating MWCNTs would improve strain energy dissipation during the stowage period and thus better control of CFRP tape spring deployment compared with that produced with neat epoxy without MWCNTs.

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