Abstract
Epoxy resin with excellent mechanical properties, chemical stability, and corrosion resistance has been widely used in automotive and aerospace industries. A thin film of epoxy deposited on a substrate has great application in adhesive bonding and protective coating. However, the intrinsic brittleness of epoxy with a relatively low fracture toughness limits its applications. In this work, graphene nanoplatelets (GNP) were added to the epoxy resin to enhance its toughness, hardness, and elastic modulus. A series of nanocomposites with different loadings of GNP were fabricated. Ultrasonic sonication in combination with surfactant Triton X-100 were employed to disperse GNP in the epoxy matrix. A nanocomposite film with a thickness of 0.3 mm was deposited on an Al substrate using a spinning coating technology. The hardness and elastic modulus of the nanocomposite film on the Al substrate were experimentally measured by a nanoindentation test. Analytical expression of the mode II interfacial fracture toughness for the nanocomposite film on an Al substrate with an interfacial edge crack was derived utilizing the linear elastic fracture mechanics and Euler’s beam theory. End-notched flexure (ENF) tests were conducted to evaluate the mode II fracture toughness. It was found that the hardness, elastic modulus, and mode II fracture toughness of the nanocomposite film reinforced with 1 wt % of GNP were improved by 71.8%, 63.2%, and 44.4%, respectively, compared with the pure epoxy. The presence of much stiff GNP in the soft epoxy matrix prompts toughening mechanisms such as crack deflection and crack pinning, resulting in the improvements of the fracture toughness, hardness, and elastic modulus. Microscopic observation for the nanocomposite was examined by scanning electron microscopy (SEM) to investigate the dispersion of GNPs in the epoxy matrix. The performance of a nanocomposite film deposited on a substrate was rarely studied, in particular, for the interfacial fracture toughness of the film/substrate composite structure. Utilizing the theoretical model in conjunction with the ENF experimental test presented in this study, an accurate determination of the mode II interfacial fracture toughness of film/substrate composite structure is made possible.
Highlights
Graphene was first discovered by Novoselov et al [1] in 2004
scanning electron microscopy (SEM) images of the surface morphologies for the neat epoxy and nanocomposites incorporated with 0.3 wt % and 0.8 wt % of graphene nanoplatelets (GNP) are presented in Figure 8a–c, respectively
The debonding did not occur at the interface between the GNP and epoxy matrix
Summary
Graphene has attracted attention due to its large surface to volume ratio and unique structure (a 2D single layer of carbon atoms bonded by sp to form a hexagonal honeycomb structure). It has become one of the most promising nanofillers owing to exceptional material properties such as an ultimate strength of 130 GPa [2], an elastic modulus of 1 TPa [3], thermal [4] and electrical [5] conductivities. Zhang et al [12] studied the correlation between the mechanical and dielectric properties of functionalized graphene/polyurethane nanocomposites. Shadmand et al [15] fabricated a graphene-based microcantilever as a flow sensor to measure the velocity of water flow with a piezoresistive sensitivity of 1.22 Ω/(m·s−1) in the range of 0 to 0.7 m/s
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
