Effect of Distribution Media Length and Multiwalled Carbon Nanotubes on the Formation of Voids in VARTM Composites

Abstract

The first part of this paper characterizes the effect of tooling and process parameters such as the length of distribution media used in vacuum assisted resin transfer molding (VARTM) of composite laminates. To achieve this goal, a number ofó-ply, woven carbon fiber/epoxy laminates are fabricated by using various lengths of distribution media. The spatial variations of mechanical properties of these laminates are characterized using a three-point bending fixture. It is shown that for relatively thinner laminates, extending the distribution media degrades the flexura! properties by as much as 14%, possibly due to air pockets entrapped during through-the-thickness impregnation of the fibrous fabric. In the second part, a minimum distribution media length is used to investigate the mechanical property and microstructure changes due to multiwalled carbon nanotubes (MWNTs) dispersed in the composite laminates. In addition, effects of different nanotube functionalization and morphology are characterized via scanning electron microscopy and optical microscopy. To achieve adequate nanotube dispersion in the epoxy resin, both tip sonication and mechanical mixing have been used. The effect of sonication time on the dispersion of nanotubes is reported bv monitoring the temporal changes in the nanotube cluster size. Even at volume fractions ¡ess than 1%, almost 10% improvements in flexural properties is obsened. Extensive void formations are reported for laminates containing MWNTs, possibly preventing greater improvements in mechanical properties.

Three-Dimensional Nano-Morphology of Carbon Nanotube/Epoxy Filled Poly(methyl methacrylate) Microcapsules

“…Rather, CNTs were observed to form a cage-like structure inside the microcapsules [48]. CNTs seem to disperse relatively well in both PMMA and epoxy resin [45,49,50]. On the other hand, CNTs have been reported to require some form of functionalization in order to disperse into poly(urea-formaldehyde) [18,19].…”

“…These materials were used as received in order to avoid further costly processing that may limit the industrial use of the microcapsules. For instance, instead of CNT purification, sonication of CNT/epoxy mixtures was reported to be equally effective in alleviating the agglomeration or bonding challenges of CNT clusters [44,45].…”

“…DCM was selected since it acts as a solvent for both epoxy and PMMA. Once completely dissolved into DCM, the PMMA/epoxy/CNT mixture was sonicated to improve the CNT dispersion as suggested by Aktas et al [45]. In fact, most of the favorable effects of the sonication, such as smaller cluster size and more uniform spatial distribution, were reported to occur early during a 5 s on/5 s off sonication scheme [45].…”

“…Once completely dissolved into DCM, the PMMA/epoxy/CNT mixture was sonicated to improve the CNT dispersion as suggested by Aktas et al [45]. In fact, most of the favorable effects of the sonication, such as smaller cluster size and more uniform spatial distribution, were reported to occur early during a 5 s on/5 s off sonication scheme [45]. Therefore, the mixture was sonicated accordingly for 10 min on a Vibra-Cell, high intensity ultrasonic processor (Sonics & Materials, Newtown, CT, USA) at 55 W and 20 kHz.…”

Identification of the effect of nanofiller morphology on interlaminar fracture toughness of hybrid composites

“…Attempts to infuse the nanofiller suspension via vacuum assisted resin transfer molding (VARTM) was limited to very low nanofillers content, often less than 1 wt.%. 27 The sharp rise in matrix viscosity by adding nanofillers is a major processing barrier. At sufficiently high nanofiller contents ($1 wt.…”