Mechanical Characterization of Multiscale SMA Fiber-Graphene Nanoplatelets/Epoxy Composites

Fiber reinforced polymer (FRP) composites have been extensively used in various engineering applications due to their lightweights, high strength, and high corrosion resistance. More recently, multiscale composites reinforced with nanoscale materials along with macroscale fibers have received attention of researcher at different disciplines. Graphene nanoplatelets (GNPs) consist of small stacks of individual graphene sheets and possess large surface area with high aspect ratio. They have excellent material properties at a relatively low cost and considered as an ideal filler for composite materials. Shape memory alloys (SMA) are a class of metallic alloys that possess remarkable characteristics such as superelasticity and shape memory effect. Superelastic SMA have been considered as fiber in polymer composites due to their ability to recover their deformation upon removal of load, good energy dissipation capacity and impact resistance.

This study first investigated the tensile behavior of nanocomposites fabricated by GNPs as nanofillers and epoxy (thermoset polymer) as host matrix. Two different epoxy matrices, one ductile and another brittle, were considered. First, an efficient dispersion technique to fabricate GNP/epoxy nanocomposites was explored. The use of ultrasonication alone or in combination with high shear mixing was considered to disperse GNPs into the epoxy matrix. Then, the effect of GNP concentration on the tensile properties of GNP/epoxy composites fabricated by selected three dispersion techniques were studied. A large number of specimens were tested under uniaxial tensile loading and the results were analyzed in terms of tensile strength, fracture elongation, and tensile modulus. Scanning electron microcopy imaging was used to assess the fractured surface of the selected specimens. Next, SMA/epoxy and SMA-GNPs/epoxy composites were produced using a vacuum assisted hand lay-up technique with the selected epoxy resin and GNP content. The developed multiscale reinforced epoxy composites were tested under tensile loading and their full-field strain and temperature behavior were monitored and evaluated using a digital image correlation system and an infrared thermal camera.

It was found that the addition of GNPs into studied brittle epoxy does not provide significant improvements in tensile properties of the developed nanocomposites. On the other hand, considerable enhancements in both tensile strength (up to 40%) and in tensile modulus (up to 55%) was observed when 1 wt. % GNPs are added. In addition, both SMA/epoxy and SMA-GNP/epoxy composites exhibited very good superelastic response with minimal residual deformations and large fracture strains. The addition of GNPs as nanofiller did not alter the tensile characteristics of the multiscale reinforced SMA fiber-based polymer composites, but their potential effects on other mechanical properties such as impact resistance and functional properties such as thermal or electrical conductivity need to be further investigated.