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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Table 2 Articles on fatigue behaviour in reinforced elastomers published since 2013 with matrix and nanoparticle used.

Author/ year

Matrix

Nanoparticle

Type of fatigue test Crack propagation Crack propagation Crack propagation

Natural rubber Natural rubber Natural rubber

Graphene nanoplatelets

Yan et al. (2013) Dong et al. (2015)

Graphene oxide

Li et al. (2015)

Graphene/carbon nanotubes

Graphene oxide

Tensile

Zhang et al. (2017) Styrene-butadiene rubber

Natural rubber

Graphene oxide/carbon nanotube

Crack propagation

Wei et al. (2018) Xu et al. (2020)

Silica/styrene-butadiene rubber Graphene oxide/carbon nanotubes Crack propagation

Fatigue crack propagation of natural rubber composites containing graphene oxide was investigated by Yan et al. (2013). For this purpose, fatigue tests were performed at displacement-control mode, under the uniaxial tensile cyclic loading condition, at room temperature and frequency of 3 Hz. They observed two different behaviours, whereas at lower strains the crack growth accelerates when the graphene oxide was added to the rubber, for higher strains the crack growth is retarded by the addition of nanoparticles. The strain induced crystallization at crack tip was the authors' explanation for this behaviour. For strains higher than 30%, nanocomposite starts to crystallize near the crack tip, while for the neat rubber this phenomenon does not occur. This crystallinity increases with increasing strain and, consequently, larger crystalline zones were observed. In this context, higher crack growth resistance was found compared to the neat rubber. Fatigue behaviour of graphene oxide reinforced natural rubber composites was investigated by Dong et al. (2015). Different concentrations of graphene oxide were considerate, and the experimental tests were performed on SENT specimens with pre-cut length of 1mm, at room temperature, frequency of 5 Hz and under constant strain conditions (30%, 40%, 50%, 60%, 70% and 80%). A digital camera was used to monitor the crack length. These authors found an optimal concentration of graphene oxide responsible for longer lives and slower crack growth rates (for all strains investigated). In this context, and under a constant strain of 50%, nanocomposites filled with 1 phr graphene oxide achieved fatigue lives 38% longer than those observed for neat rubber and the crack growth rate was reduced by 40%. These values decreased significantly for nanocomposites with the highest concentrations (3 phr and 5 phr graphene oxide) due to their high hysteresis loss and tearing energy input. In a similar work, the same authors evaluated the fatigue resistance of natural rubber filled with different dimensional carbon-based fillers: zero-dimensional spherical carbon black, one-dimensional fibrous carbon nanotubes and two-dimensional planar graphene oxide (Dong et al. 2017). They observed that the crack growth rates increased with increasing tearing energy, and natural rubber filled with carbon black exhibited the best crack growth resistance. On the other hand, higher hysteresis loss of the natural rubber filled with carbon nanotubes weakened its fatigue resistance, while planar graphene oxide played a limited role in preventing crack growth. Li et al. (2015) dispersed hybrid nanofillers into natural rubber in order to achieve better mechanical properties than those obtained only with neat natural rubber. For this purpose, the hybridization was composed by different contents of graphene and carbon nanotubes, and fatigue tests under different tear energy values were carried out at 10 Hz, at room temperature and with R=0. These authors observed that incorporation of 0.5 phr graphene or 1 phr carbon nanotubes leads to an increase in energy dissipated per unit depth of cracking. However, hybridizing 0.5 phr graphene with 1 phr carbon nanotubes leads to an increase of about twice the value obtained with single fillers. In this context, nanocomposites are more resistant to crack growth than unfilled natural rubber. For example, natural rubber enhanced with 0.5 wt.% of graphene has a lower crack growth rate than natural rubber enhanced with 1 wt.% of carbon nanotubes, due to the better dispersion of graphene; while natural rubber enhanced with 0.5 wt.% of graphene and 1 wt.% of carbon nanotubes shows the lowest crack growth rate, due to its highest energy dissipation capability. Zhang et al. (2017) studied the fatigue behaviour of graphene oxide and silica reinforced styrene-butadiene rubber composites. Three concentrations of graphene oxide were used: 1, 2 and 3 phr. Fatigue tests were carried out at 5 Hz and the strain ranged from 150 to 350%. Considering the same constant strain, the fatigue life increased with increasing graphene oxide content. This is explained by the large sheet structure of the graphene oxide, which stop the crack growth or cause crack deflection or branching and, consequently, longer fatigue lives are observed. More recently, Zhou et al. (2019) demonstrated an improved crack resistance of natural rubber – solution polymerized butadiene