Potential and prospective implementation of carbon nanotubes on next generation aircraft and space vehicles: A review of current and expected applications in aerospace sciences

Single-walled carbon nanotubes (SWCNTs) were incorporated at low loading (up to ∼1 wt%) into an unfilled aerospace-grade epoxy system, to impart electrical conductivity while maintaining structural bonding capability, as a route for development of a structural and conductive adhesive At these low SWCNT loadings the tensile properties were maintained or improved, while strength decreased in a higher loading case The structural bonding performance of composite-to-composite joints, evaluated in lap-shear and peel tests, was reasonably maintained for adhesives containing 05 wt% or 1 wt% SWCNTs In the case of the 05 wt% SWCNT–adhesive, peel and lap-shear strength were unchanged while the addition of 1 wt% resulted in 30% increase of peel strength but the lap-shear strength was reduced by 10–15% For 1 wt% SWCNT–adhesives, conductivities as high as 10−1 S m−1 and typically ∼10−3 S m−1 were achieved Joint electrical resistance measured between aluminum adherends was larger than predicted by the bulk conductivity, but was reduced by a post-treatment step resulting in apparent joint conductivities within one order of magnitude of the bulk samples

Single-walled carbon nanotube–epoxy composites for structural and conductive aerospace adhesives

Colloidal processing of fine ceramic powders enables the production of complex shaped ceramics with unique micro and macro structures which are not possible to produce via conventional dry processing routes. Because of this enhanced structural control and shaping capabilities, colloidal processing has been exploited to produce ceramic components with ever increasing complexity and functionalities. In this review, we revisit some of the research efforts on this topic to highlight its relevance and growing importance for the advanced manufacturing of functional ceramics. Selected examples of colloidal systems with increasing level of complexity are discussed to showcase the wide range of structures that can be generated through wet processing approaches. The historical development and background knowledge pertaining to colloids and surface interactions is first briefly reviewed. The major colloidal shape forming and additive manufacturing processes that utilize colloidal pastes and inks are then reviewed, highlighting the control of suspension rheology needed in these techniques. Next, methodologies that combine suspended particles with a pore-forming phase are discussed as a means to produce porous ceramic materials. Further control over the interactions between anisotropic particles and their alignment in suspensions can be gained via externally applied fields (such as magnetic) to produce texturally aligned green bodies. This leads to bioinspired ceramics that can programmably morph into complex shaped objects upon sintering. Hierarchical porous structures with high mechanical efficiency are also shown as an example of the multiscale designs that can be generated through advanced colloidal processing. As drying of ceramic bodies is an inevitable consequence of wet colloidal processing, the current understanding of this critical processing step is reviewed. Finally, the gaps in knowledge in these fields are discussed to provide our perspective on where the field may support advances in ceramics in the future.

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Colloidal Processing: Enabling Complex Shaped Ceramics with Unique Multiscale Structures

Adhesive bonding is a viable technique for joining a wide range of materials. However, increasing the lifetime, reducing the costs, and improving the safety of structures are highly demanded nowadays. Hence, the development of new technologies and processes for easy recycle, heal, or self-heal of bonded structures are becoming of great interest for the industry. This paper provides an overview of the current developments in the use of “smart” adhesive technology and introduces the reader to early findings on the use of self-healing materials, thermally expandable particles, and nanoparticles, among others, in adhesives and their potential to increase the reliability of adhesive joints.

Smart Adhesive Joints: An Overview of Recent Developments

The aim of this work was to develop new adhesive formulations based on epoxy/nanostructured carbon forms. Different types of nanofillers were dispersed into an epoxy matrix for developing toughened epoxy paste aeronautic adhesives. The reinforced adhesives were used for bonding carbon nanofilled/epoxy composite adherents. Data were also compared to the results obtained both for the unfilled adhesive and/or adherents. Tensile butt joint, and single lap joint samples were prepared to measure mechanical strength and adhesion properties of the different joint configurations. The inclusion of carbon nanofillers inside the epoxy adhesive caused a significant improvement in the bond strength of the joints, changing the failure mode of joints in single lap joint shear tests. Significant change of the bonding performance was observed as the weight fraction of carbon nano-fillers increased from 1.37 to 5 wt/wt%. Adhesion between nano-reinforcements and adherents substrate was studied by means of Scanning Electron Microscopy.

Nanofilled Epoxy Adhesive for Structural Aeronautic Materials

http://mss-nde.uoi.gr/publications-pdf/journal-papers/Periodika%20Nektaria/Enhanced%20Bonded%20Aircraft%20Repair%20Using%20Nano-Modified%20Adhesives.pdf

Enhanced bonded aircraft repair using nano-modified adhesives

Conventional and nanostructured WC-12 wt.% Co powders were HVOF sprayed on Al7075-T6. The nanocoatings presented slightly less microporosity, higher microhardness, higher fracture toughness but higher decarburization, than the conventional ones. The nanocoatings exhibited greater resistance to general corrosion and localized corrosion in 3.5% NaCl than their conventional counterparts. Other than an occasional removal of WC nanoparticles, corrosion modes appeared similar for both types of coatings, characterized by selective dissolution of Co, formation of protective surface films and crevice corrosion along interlayer boundaries. Both types of coatings exhibited high dry sliding wear resistance. Nevertheless, the wear performance of the nanocoatings was even superior than that of their conventional counterparts. Main wear modes included plastic deformation of binder, oxidative wear leading to the formation of lubricating oxides and adhesive wear leading to the formation of alumina-rich surface depositions (from the Al 2 O 3 counter balls). Coating of Al7075 with nano WC–12Co was proved effective in terms of microstructural features, corrosion and wear behaviour.

A comparative study on the microstructure and surface property evaluation of coatings produced from nanostructured and conventional WC–Co powders HVOF-sprayed on Al7075

The aim of this work is to study the lap shear strength as well as the response to galvanic corrosion and environmental degradation of Multi Wall Carbon Nanotube (MWCNT) enhanced adhesive bonding on metallic substrates so as to establish whether the response of MWCNT enhanced adhesive patches to environmental degradation is percolation or material system dependent. The incorporation of MWCNTs into an epoxy patch may mediate the galvanic effect between substrate/patch, but also enhances localised degradation phenomena into the polymer matrix. The introduction of 0·1 wt-%MWCNTs positively affects both the galvanic and environmental durability of the adhesive, whereas higher contents adversely affect its behaviour suggesting a percolation threshold between 0·1 and 0·5 wt-%CNT, which, however, is system dependent.

Effect of carbon nanotube enhanced adhesives on degradation of bonded joints in corrosive environments

Purpose – Bonded composite patches are ideal for aircraft structural repair as they offer enhanced specific properties, case‐tailored performance and excellent corrosion resistance. Bonding minimizes induced stress concentrations unlike mechanical fastening, whilst it seals the interface between the substrate and the patch and reduces the risk of fretting fatigue that could occur in the contact zone. The purpose of this paper is to assess the electrochemical corrosion performance and the environmentally induced mechanical degradation of aerospace epoxy adhesives when carbon nanotubes (CNTs) are used as an additive to the neat epoxy adhesive.Design/methodology/approach – The galvanic effect between aluminium substrates and either plain or CNT enhanced carbon fibre composites, was measured using a standard galvanic cell. Also, rest potential measurements and cyclic polarizations were carried out for each of the studied systems. The effect of the CNT introduction to a carbon fiber reinforced plastic (CFRP) o...

Corrosion and environmental degradation of bonded composite repair

MoTaNbVxTi refractory high entropy alloys were tested with dynamic indentation technique in order to assess their creep behavior. The loading rate was kept constant and three indentation depths were applied. It was found that, by increasing the indentation depth and the V content of the alloys, the stress exponent was reduced. This reduction was associated with the maximum applied stress at the peak load before the holding period and the increase of lattice distortion parameter with increasing the V content.

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D. Sioulas

Papers

Enhanced bonded aircraft repair using nano-modified adhesives

A comparative study on the microstructure and surface property evaluation of coatings produced from nanostructured and conventional WC–Co powders HVOF-sprayed on Al7075

Effect of carbon nanotube enhanced adhesives on degradation of bonded joints in corrosive environments

Corrosion and environmental degradation of bonded composite repair

A first approach on the assessment of the creep behavior of MoTaNbVxTi high entropy alloys by indentation testing