Abstract

We present a three-dimensional continuum model for layered crystalline materials made out of weakly interacting two-dimensional crystalline sheets. We specialize the model to multilayer graphene materials, including multi-walled carbon nanotubes (MWCNTs). We view the material as a foliation, partitioning of space into a continuous stack of leaves, thus loosing track of the location of the individual graphene layers. The constitutive model for the bulk is derived from the atomistic interactions by appropriate kinematic assumptions, adapted to the foliation structure and mechanics. In particular, the elastic energy along the leaves of the foliation results from the bonded interactions, while the interaction energy between the walls, resulting from van der Waals forces, is parametrized with a stretch transversal to the foliation. The resulting theory is distinct from conventional anisotropic models, and can be readily discretized with finite elements. The discretization is not tied to the individual walls and allows us to coarse-grain the system in all directions. Furthermore, the evaluation of the non-bonded interactions becomes local. We test the accuracy of the foliation model against a previously proposed atomistic-based continuum model that explicitly describes each and every wall. We find that the new model is very efficient and accurate. Furthermore, it allows us to rationalize the rippling deformation modes characteristic of thick MWCNTs, highlighting the role of the van der Waals forces and the sliding between the walls. By exercising the model with very large systems of hollow MWCNTs and suspended multilayer graphene, containing up to 109 atoms, we find new complex post-buckling deformation patterns.

Abstract

The microscopic stress field provides a unique connection between atomistic simulations and mechanics at the nanoscale. However, its definition remains ambiguous. Rather than a mere theoretical preoccupation, we show that this fact acutely manifests itself in local stress calculations of defective graphene, lipid bilayers, and fibrous proteins. We find that popular definitions of the microscopic stress violate the continuum statements of mechanical equilibrium, and we propose an unambiguous and physically sound definition.

Abstract

Blisters induced by gas trapped in the interstitial space between supported graphene and the substrate are commonly observed. These blisters are often quasi-spherical with a circular rim, but polygonal blisters are also common and coexist with wrinkles emanating from their vertices. Here, we show that these different blister morphologies can be understood mechanically in terms of free energy minimization of the supported graphene sheet for a given mass of trapped gas and for a given lateral strain. Using a nonlinear continuum model for supported graphene closely reproducing experimental images of blisters, we build a morphological diagram as a function of strain and trapped mass. We show that the transition from quasi-spherical to polygonal of blisters as compressive strain is increased is a process of stretching energy relaxation and focusing, as many other crumpling events in thin sheets. Furthermore, to characterize this transition, we theoretically examine the onset of nucleation of short wrinkles in the periphery of a quasi-spherical blister. Our results are experimentally testable and provide a framework to control complex out-of-plane motifs in supported graphene combining blisters and wrinkles for strain engineering of graphene.

Abstract

In the present work, a graphene nanocomposite material using as matrix a high performance thermoplastic polymer (PEEK) is presented. Composite was made by a simple extrusion-compounding process, followed by an injection-moulding process. The main advantage of this process is that it could produce large quantities at the scales needed for use in industrial applications as structural applications. Nanocomposites with different percentages of graphene 0.5, 1, 3, 5 and 10 wt.% were characterized and compared with neat PEEK as baseline. The mechanical tests showed that the Young´s modulus increased when adding graphene while the strenght remained constant. In addition, a change in the failure mode was observed when the graphene was added. Nanocomposites with high contents of graphene had lower strain at break than neat PEEK.

Abstract

Aeronautical sector, like many others, is trying to benefit from exceptional properties of graphene as soon as possible (low density, unique electrical, thermal, optical, mechanical properties…). In fact composite airframe enhancement by graphene related materials is part of the biggest European research project, the Graphene Flagship, which is trying to bring graphene from lab to society. Then, within this context, a first high potential application of graphene in aeronautical composite structure has been selected by Airbus: de- / anti-icing system.

The graphene concept studied for anti-icing application is an electro-thermal system, where heat is generated by applying electrical voltage by Joule effect. Key work performed in this study was focused on following aspects: identification of use cases and requirements, selection of graphene based related material, integration concepts within carbon fiber reinforced polymers (CFRP), demonstration or proof of concept through manufacturing and functionality tests, and, finally, preliminary value and risk assessment of solution.

As per work performed, it can be concluded that the potential of proposed innovative graphene based electro-thermal system for composite aeronautical part anti-icing function has been preliminary proven and demonstrated. However, there is still a long way to increase the maturity, scale-up the concept, demonstrate cost saving and benefits versus other solutions, as well as to overcome the identified risks.

Abstract

The present work shows the development of temperature sensors based on flexible polymers reinforced with carbon nanoparticles. More specifically, they have been manufactured with polydymethysiloxane (PDMS) reinforced with graphene nanoplatelets (GNPs). The analysis of electrical properties reveal that an increase of the GNP contents promotes an enhancement of the electrical conductivity due to the higher number of conductive pathways inside the material. On the other hand, the electrical conductivity decreases with temperature because of the polymer expansion, as well as due to some scattering effects in the contacts between adjacent nanoparticles. This decrease is more significant at lower GNP contents as, in this case, the scattering effects inside the matrix are also very prevalent. The analysis of the proof-of-concept as temperature sensors shows an outstanding sensitivity, especially at low GNP contents, with a linear-exponential correlation of the electrical resistance with temperature. Their use as alarm sensors is proved due this excellent thermal sensitivity.

Abstract

One of the most critical challenges in the aerospace industry is the mismatch in the coefficient of thermal expansion (CTE) between optical components in satellites and their metallic supports, which limits system reliability and performance. Ceramic materials, due to their superior thermal properties, offer a potential solution; however, their adoption has been limited by the complexity of their geometries and conventional manufacturing constraints. Additive manufacturing has opened new opportunities for the development of advanced ceramics, including ceramic matrix composites (CMCs). Within the framework of the AERORECORD-3D project, funded by the Spanish Ministry of Science and Innovation, ceramic cordierite-based supports reinforced with reduced graphene oxide (rGO) have been developed for aerospace applications. In this study, cordierite nanocomposites with varying rGO contents were successfully fabricated via 3D printing. Their thermal, electrical, and mechanical properties were evaluated to assess their performance, exploring their potential as advanced materials for demanding space applications. This work represents a significant step toward the implementation of 3D-printed ceramic nanocomposites by combining innovative materials with advanced additive manufacturing technologies.

Abstract

Graphene deposited on planar surfaces often exhibits sharp and localized folds delimiting seemingly planar regions, as a result of compressive stresses transmitted by the substrate. Such folds alter the electronic and chemical properties of graphene, and therefore, it is important to understand their emergence, to either suppress them or control their morphology. Here, we study the emergence of out-of-plane deformations in supported and laterally strained graphene with high-fidelity simulations and a simpler theoretical model. We characterize the onset of buckling and the nonlinear behavior after the instability in terms of the adhesion and frictional material parameters of the graphene-substrate interface. We find that localized folds evolve from a distributed wrinkling linear instability due to the nonlinearity in the van der Waals graphene-substrate interactions. We identify friction as a selection mechanism for the separation between folds, as the formation of far apart folds is penalized by the work of friction. Our systematic analysis is a first step towards strain engineering of supported graphene, and is applicable to other compressed thin elastic films weakly coupled to a substrate.

Abstract

In modeling and numerically implementing a follower pressure in a geometrically nonlinear setting, one needs to compute the volume enclosed by a surface and its variation. For closed surfaces, the volume can be expressed as a surface integral invoking the divergence theorem. For periodic systems, widely used in computational physics and materials science, the enclosed volume calculation and its variation is more delicate and has not been examined before. Here, we develop simple expressions involving integrals on the surface, on its boundary lines, and point contributions. We consider two specific situations, a periodic tubular surface and a doubly periodic surface enclosing a volume with a nearby planar substrate, which are useful to model systems such as pressurized carbon nanotubes, supported lipid bilayers or graphene. We provide a set of numerical examples, which show that the familiar surface integral term alone leads to an incorrect volume evaluation and spurious forces at the periodic boundaries.

Abstract

''':This study investigates the anti-erosion mechanisms of a novel graphene-modified tungsten carbide coating under high-speed solid-liquid two-phase flow conditions. A liquid-solid two-phase flow erosion simulation device was employed, and fluid dynamics simulations were conducted using FLUENT software to determine the maximum experimental flow velocity. The influence of flow velocity, sand particle diameter, sand concentration, and fluid temperature on the erosion rate of the coating was systematically analyzed using the control variable method. Experimental results reveal that the erosion rate follows a power-law exponential relationship with flow velocity. When the sand particle diameter is below 0.5 mm, the erosion rate remains relatively stable; however, when the diameter exceeds 0.5 mm, the erosion rate increases significantly with particle size. Furthermore, the erosion rate exhibits a slight increase with higher sand concentrations, while a notable rise in fluid temperature leads to a substantial increase in the erosion rate, with the difference in erosion rates between the 150°C and 200°C coatings becoming more pronounced at elevated temperatures. Scanning electron microscopy (SEM) and numerical simulations were utilized to further elucidate the anti-erosion mechanisms of the coating. The incorporation of tungsten carbide significantly enhances the coating's hardness, while the addition of graphene results in a denser microstructure, effectively reducing porosity and improving the coating's resistance to impact and erosion. The findings demonstrate that the novel graphene-modified tungsten carbide coating exhibits superior erosion resistance, making it highly suitable for enhancing the durability and performance of rigid PDC drill bits in complex downhole environments.