PSI - Issue 68

J.M. Parente et al. / Procedia Structural Integrity 68 (2025) 160–165

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J.M. Parente et al. / Structural Integrity Procedia 00 (2025) 000–000

May, 2018). Among the most widely used nano-reinforcements, those based on carbon, such as carbon nanotubes (CNTs) and graphene (GNP), stand out the most due to their mechanical and electrical properties (Gantayat et al., 2017). Combining more than one type of nano-reinforcement, also known as hybridization, has emerged as a promising strategy for further improve the mechanical and electrical properties of a nanocomposite (Białkowska et al., 2023; Parente et al., 2024; Safdari and Al-Haik, 2018; Tajdari et al., 2021). In this context, hybridization is a very promising strategy for obtaining materials with various applications in structural engineering, electronics or in the sensors field. For example, due to their high aspect ratio, superior mechanical strength, and high electrical conductivity, CNTs are responsible for a significant increase in tensile modulus, toughness, and piezoresistive response (Cha et al., 2017; Gojny et al., 2004; Khashaba, 2018; Nag and Mukhopadhyay, 2022), while GNPs provide extensive surface areas, which can facilitate improved interfacial bonding between the nanofillers and the polymer matrix (Galpayage Dona et al., 2012; Huang et al., 2012; Kuilla et al., 2010). Literature, for example, reports several studies on the benefits of hybridizing nanoparticles. Wang et al. (2020) combined graphene nanoplatelets and carbon nanotubes and investigated the mechanical and piezoelectric effects. They concluded that combining both types of nanoparticles resulted in a synergistic mechanical effect, leading to an improved elastic modulus compared to using a single type of nanoparticle. Wang et al. (2022) investigated the use of CNT and carbon black nanoparticles and concluded that the hybrid mixture led to an increase in strength and modulus compared to reinforcement with a single type of nano-reinforcement. Additionally, the use of the mixture led to lower resistivity. Therefore, the aim of this study is to analyse the benefits of using hybrid nano-reinforcements, such as CNTs and GNP, on the mechanical performance and piezoresistive sensitivity of epoxy-based nanocomposites. By focusing on the mechanisms governing the hybridization effect, it is possible to identify the optimal combinations to achieve the desired performance in applications such as sensors, actuators, and structural components. 2. Materials and methods This work used a two-component epoxy resin (SR8100 resin and SD8824 hardener supplied by Sicomin) duly reinforced with 195 g/m² plain woven fiberglass fabric supplied by Rebelco. The matrix was reinforced with graphene nanoplatelets (GNP), supplied by Graphenest, and multiwall carbon nanotubes (CNT), supplied by Nanocyl. The nanoparticles content is shown in Table 1.

Table 1. Different nanocomposites configurations analysed in this study.

Weight Content (wt. %)

Nanoparticles

Hybrids

Single nano-reinforcement

Control

Graphene

0.25 0.375

0.5

0.25

0.5 0.75

1

-

-

0 0

Carbon nanotubes

0.5

0.375 0.25

-

-

-

- 0.5 0.75

To produce the nanocomposites, GNPs and CNTs were mixed into the resin for three hours using a mechanical mixer at 1000 rpm and in an ultrasound bath. The hardener was then added and mixed at 300 rpm for 5 minutes, followed by degassing in a vacuum chamber. The mixture was moulded (120 ´ 80 ´ 3 mm 3 ) and cured at room temperature for 24 hours, with a 24-hour post-cure at 40ºC. The samples were cut into sizes of 100×10×3 mm³ and 100×10×1.6 mm³. Mechanical performance was assessed using 3-point bending (3-PB) tests, in accordance with EN ISO 178:2003 standard on a Shimadzu AGS-X testing machine with load cell of 10 kN. Fracture surfaces were analysed by digital microscope and SEM. For the cyclic piezoresistive tests, silver electrodes were applied in top and bottom surfaces, and a cyclic load, with constant amplitude, was applied by a Shimadzu AGS-X machine, while the electrical resistance was monitored by a Keysight multimeter for 100 cycles. The gauge factor and surface resistivity were then calculated.