PSI - Issue 25

J.M. Parente et al. / Procedia Structural Integrity 25 (2020) 282–293 J.M. Parente/ Structural Integrity Procedia 00 (2019) 000 – 000

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compile the benefits obtained with this nano-reinforcement.

2. Fatigue behaviour of graphene reinforced polymeric resins

Most fatigue studies on graphene-reinforced polymeric materials involve nano-enhanced resins, because it is easy to add low concentrations of graphene into polymers without compromising their density, toughness or manufacturing process. These studies focus mainly on graphene-resin interaction, because a poor interface between these two materials causes lower mechanical performance, and the other ones on graphene dispersion and orientation. Poor dispersions create agglomerates that decrease the mechanical properties of nanocomposites and non-ideal orientations may provide less strength. Table 1 summarizes the existing studies on this subject.

Table 1. Articles on fatigue behaviour in polymeric resins published since 2009 with nanoparticle and matrix used.

Author/year

Matrix Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin Epoxy resin

Nanoparticle

Type of fatigue test

Rafiee et al. (2009)

Graphene nanoplatelets

Crack propagation

Rafiee et al. (2010)

Graphene

Crack propagation

Bortz et al.(2012)

Graphene oxide

Flexural

Li et al. (2013)

Graphene oxide/carbon nanotubes

Flexural

Shokrieh et al. (2014)

Graphene nanoplatelets

Tip bending

Shokrieh et al. (2014)

Graphene nanoplatelets

Tip bending

Shokrieh et al. (2014)

Graphene nanoplatelets/carbon nanofiber

Tip bending

Mészáros and Szakács (2016)

Graphene

Tensile

Wan et al. (2017)

Graphene

Tensile

Ladani et al. (2018)

Graphene nanoplatelets/carbon nanofibers Crack propagation

Bhasin et al. (2018)

Graphene nanoplatelets

Interlaminar

Probably the first studies on fatigue behaviour of graphene-reinforced polymeric resins were carried out by Rafiee et al. (2009). Considering an epoxy resin, they compared the benefits obtained with 0.1% by weight of different fillers, including graphene platelets. The mechanical properties measured were the stiffness, ultimate tensile strength, fracture toughness, fracture energy, and resistance to fatigue crack growth. The stiffness of graphene nanocomposite was 31% higher than the value obtained for neat epoxy resin and about 40% higher in terms of tensile strength. The mode I fracture toughness increased around 53%, while in terms of fatigue the da/dN curve obtained for different  K values was below that obtained with neat epoxy resin. Fatigue tests were performed at a constant ratio R of 0.1 and 5 Hz with compact tension specimens. The better results obtained, compared to other nanoparticles, were consequence of the enhanced specific area of graphene platelets that improved the mechanical interlocking/adhesion at the nanofiller matrix interface, and the two-dimensional geometry of graphene platelets. In 2010, the same authors published a paper where the fracture and fatigue mechanisms of an epoxy nanocomposite with 0.125 wt.% of graphene were investigated (Rafiee et al. 2010). Similar results were found, where a significant reduction in crack growth rate was observed for all range of stress intensity factor amplitudes analysed. A fractography analysis of the fracture surface was carried out, and the data indicated a doubling in the average surface roughness with an increase in graphene content from 0 to 0.125 wt.%. In this case, higher roughness promotes crack deflection, which generates an increase in the total fracture surface area. Therefore, higher energy absorption is expected compared to unfilled polymeric material. On