Fabrication and Mechanical Performance of Graphene Nanoplatelet/Glass Fiber Reinforced Polymer Hybrid Composites

From Frontiers via Jisc Publications RouterHistory: collection 2021, received 2021-09-09, accepted 2021-10-20, epub 2021-11-16Publication status: PublishedGlass fiber reinforced polymer (GFRP) composites are promising alternatives for the traditional carbon steel pipes used in the oil and gas industry due to their corrosion and chemical resistance. However, the out-of-plane mechanical properties of GFRPs still need further improvement to achieve this goal. Hence, in this work, two methods combining either vacuum mixing or spray coating with vacuum-assisted resin infusion were studied to fabricate graphene nanoplatelet (GNP)/GFRP hybrid composites. The former method resulted in a severe filtering effect, where the GNPs were not evenly distributed throughout the final composite, whereas the latter process resulted in a uniform GNP distribution on the glass fabrics. The addition of GNPs showed no modest contribution to the tensile performance of the GFRP composites due to the relatively high volume and in-plane alignment of the glass fibers. However, the GNPs did improve the flexural properties of GFRP with an optimal loading of 0.15 wt% GNPs, resulting in flexural strength and modulus increases of 6.8 and 1.6%, respectively. This work indicates how GNPs can be advantageous for out-of-plane mechanical reinforcement in fiber-reinforced composites

Effect of graphene nanoplatelets on the mechanical and gas barrier properties of woven carbon fibre/epoxy composites

From Springer Nature via Jisc Publications RouterHistory: received 2021-05-14, accepted 2021-08-14, registration 2021-08-23, pub-electronic 2021-09-05, online 2021-09-05, pub-print 2021-12Publication status: PublishedFunder: Engineering and Physical Sciences Research Council; doi: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/K016946/1Abstract: Carbon-fibre-reinforced polymer (CFRP) composites are promising materials for non-metallic pipe applications in the oil and gas industry owing to their high corrosion resistance, specific strength and stiffness. However, CFRP has poor gas barrier performance meaning that a liner has to be inserted. Graphene-based nanomaterials have been demonstrated to improve gas barrier properties in thermoplastic polymers, and thus, a CFRP–graphene hybrid composite could provide an alternative to lined pipes. In this work, a method combining spray coating with vacuum-assisted resin infusion was developed to fabricate CFRP hybrid composites with preferred in-plane aligned graphene nanoplatelets. Tensile and flexural properties, as well as CO2 gas permeability, were evaluated. It was illustrated that both tensile and flexural properties performed better under relatively low GNP loadings (< 0.2 vol%), while gas barrier property was significantly improved with the increasing GNP loadings which fits the Nielsen model with an effective GNP aspect ratio of 350. Graphical abstract

Smart and repeatable easy-repairing and self-sensing composites with enhanced mechanical performance for extended components life

Structural composites with smart functionalities of self-healing and self-sensing are of particular interest in the fields of aerospace, automotive, and renewable energy. However, most of the current self-healing methodologies either require a relatively complex design of the healing network, or sacrifice the initial mechanical or thermal performance of the carbon fibre composite system after introducing the healing agents. Herein, an extremely simple methodology based on commonly used thermoplastic interleaves has been demonstrated to achieve repeatable easy-repairing and self-sensing functionalities, alongside enhanced mechanical performance in comparison with unmodified carbon fibre/epoxy system. Moreover, due to the high glass transition temperature of the thermoplastic, the repairable composites are shown to have an unchanged storage modulus up to 80 °C, solving the previous limitation of repairable epoxy matrix systems with thermoplastics. High retention of peak load (99%) and a decent recovery of interlaminar fracture toughness (34%) was achieved. Most importantly, the mechanical properties remained greater than the unmodified system after four consecutive cycles of damage and healing. Repeatable in-situ damage sensing was achieved based on the piezoresistive method. This “new” discovery based on an “old” approach, which is fully compatible with current composite manufacturing, may overcome existing conflicts between mechanical performance and healing functions, providing a new solution to extend components’ service life towards a more sustainable development of the composite sector

A repairable carbon nanotube web-based electro-thermal heater and damage sensor for aerospace applications

We previously described an efficient, lightweight and flexible electro-thermal system, based on directly drawn carbon nanotube web (CNT web), as part of an icing protection system for carbon fibre reinforced polymer (CFRP) composite aircraft structures. The location of the heating elements on critical lifting surface leading edges or nacelle intake lips makes them particularly susceptible to impact damage, which may leave no visible mark. This makes it desirable to have both a mechanism for identifying the location of damage to the CNT structure (and by inference, potential damage to the underlying CFRP) and a process for restoring the CNT heater to full operation. With the CNT web acting as a sensor, impact damage is identified by an increase in electrical resistance and, particularly, by infrared imaging, which reveals a cold spot or zone depending upon the CNT web layup. Whereas a unidirectional CNT web layup exhibits a large increase in resistance and loss of a full width band of operation, a cross ply quasi-isotropic CNT web arrangement suffers only a small increase in resistance and a loss of function that is highly localised to the damaged area. A novel methodology, based on dispersed CNT in resin, is described for repairing and reconnecting the CNT structure and restoring functionality. A CNT web-based electro-thermal element was applied to the leading edge of a representative carbon-fibre composite wing section to demonstrate the flexibility of this system

Improved Mechanical Properties of Graphene/Carbon Fibre Composites via Silanization

Despite their excellent mechanical performance, carbon fibre reinforced polymer (CFRP) composites are limited by the interfacial properties due to the inherent nature of laminated structures. One way to modify the interface is by the inclusion of nanomaterials on the surface of carbon fibres. Here, we use electrochemical exfoliation to produce graphene (EEG) flakes which have hydroxyl and epoxy functional groups on their surface. To further improve the interfacial bonding between the flakes and the epoxy matrix, silanization was carried out on the graphene, with 3-aminopropyl triethoxysilane (APTES) which could react with both oxygen and amino groups, and then EEA flakes achieved. Combing SEM and AFM, lateral size and thickness of both flakes were characterized, which showed comparable values, and thus removed the effect of aspect ratio during the comparison. Both EEG and EEA flakes were dispersed in ethanol and sprayed coated onto carbon fibres, followed by vacuum assisted resin infusion to make hybrid composites. Testing of their mechanical properties showed that EEG flakes tend to act as points of stress concentration which accelerated the delamination; while the EEA flakes improved interfacial properties owing to the covalent bonding. As a result, with only 0.5 wt.% EEA flakes spray coated onto the carbon fibres, the tensile and flexural strength of graphene/carbon fibre composites improved by 17.6% and 5.4% respectively

An advanced anti-icing/de-icing system utilizing highly aligned carbon nanotube webs

A carbon nanotube (CNT) web is a horizontally oriented continuous film, obtained by drawing CNT forests produced by chemical vapour deposition (CVD). As the CNTs are highly conductive and predominantly aligned along the draw direction, by controlling the aspect ratio of these CNTs and the number of stacked web layers, a tailored resistance can be achieved. Layers of CNT web are compared to plies of carbon fiber (CF), as the heating elements within a glass fiber laminate assembly. Compared with the CF-heater as well as existing state-of-the-art heating systems, the highly aligned CNT-web-heater possesses negligible weight (e.g. compared with eight CF plies (3633.8 g m−2), an equivalent 20-CNT-web heater (0.38 g m−2) is ∼104 times lighter), rapid and uniform heating, efficient energy consumption and its electro-thermal behaviour can be tuned to suit any surface and power requirement to achieve rapid anti-icing/de-icing. Both anti-icing and de-icing performance have been verified and in particular, for de-icing, with a constant 4.9 kW m−2 power supply, the GF laminate with 40 layers of CNT web could remove accreted ice within 15 s

Aligned carbon nanotube webs embedded in a composite laminate: A route towards a highly tunable electro-thermal system

Highly aligned CNT webs, with an areal density of 0.019 g/m2, were produced by direct drawing of CNT ‘forests’ grown by chemical vapor deposition, to form a conductive heating element. These were subsequently inserted between pre-cured layers of unidirectional carbon fibre reinforced polymer (CFRP) and the electrical and thermal conductivity of the combined system were assessed under different curing conditions. Control composites specimens, cured under high-pressure, demonstrated a higher fibre volume fraction, as well as higher electrical and thermal conductivities. With a single CNT 20-layer web interlayer added, the electrical conductivity increased by 25% when the CNT web alignment was perpendicular to that of the fibres, and by 15% when the CNT web alignment was parallel to the fibres. In addition, three types of CNT interlayer distribution were investigated. Through tailoring the pressure, carbon fibre layup and CNT interlayer, an efficient electro-thermal system was obtained which could be deployed as part of an ice-protection system on aircraft