Failure Processes in Embedded Monolayer Graphene under Axial Compression

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of -0.60 % corresponding to a yield stress of -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1-2 nm. These results were compared with DFT computations performed on analogue coronene/ PMMA oligomers and a reasonable agreement was obtained.Comment: 28 pages. Manuscript 20 pages, 8 figures. Supporting information 10 pages, 6 figure

Suspended monolayer graphene under true uniaxial deformation

2D crystals, such as graphene, exhibit the higher strength and stiffness of any other known man-made or natural material. So far, this assertion has been primarily based on modelling predictions and on bending experiments in combination with pertinent modelling. True uniaxial loading of suspended graphene is not easy to accomplish; however such an experiment is of paramount importance in order to assess the intrinsic properties of graphene without the influence of an underlying substrate. In this work we report on uniaxial tension of graphene up to moderate strains of 0.8% ca.. This has been made possible by sandwiching the graphene flake between two polymethylmethacrylate (PMMA) layers and by suspending its central part by the removal of a section of PMMA with e-beam lithography. True uniaxial deformation is confirmed by the measured large phonon shifts with strain by Raman spectroscopy and the indication of lateral buckling (similar to what is observed for thin macroscopic membranes under tension). Finally, we also report on how the stress is transferred to the suspended specimen through the adhesive grips and determine the value of interfacial shear stress that is required for efficient axial loading in such a system

PHILANTHROPIC FOUNTAIN OF KORNAROU SQUARE: USING SFM TO CALCULATE THE FOUNTAIN’S GEOMETRIC CHARACTERISTICS IN ORDER TO DETERMINE ITS INELASTIC DYNAMIC RESPONSE

[EN] This paper proposes the use of Structure from Motion (SfM) techniques to survey inaccessible monument structures and presents its application on capturing Kornarou Square's philanthropic fountain in Heraklion, Crete. A series of aerial and terrestrial photos of the fountain were combined in order to build the 3D geometry of the monument using Agistoft's Photoscan. This 3D model was used to study the dynamic behavior of the fountain. Its response was determined through multiple inelastic dynamic analyses. The analysis results were summarized in the average dynamic curveLiratzakis, A.; Parthenios, P.; Stavroulaki, M. (2016). PHILANTHROPIC FOUNTAIN OF KORNAROU SQUARE: USING SFM TO CALCULATE THE FOUNTAIN’S GEOMETRIC CHARACTERISTICS IN ORDER TO DETERMINE ITS INELASTIC DYNAMIC RESPONSE. En 8th International congress on archaeology, computer graphics, cultural heritage and innovation. Editorial Universitat Politècnica de València. 472-476. https://doi.org/10.4995/arqueologica8.2015.4167OCS47247

COMBINING STRUCTURE FROM MOTION TECHNIQUES WITH LOW COST EQUIPMENT FOR A COMPLETE 3D RECONSTRUCTION OF A 13TH CENTURY CHURCH: The case of transformation of the saviour church in Meskla, in Crete Island

[EN] The use of 3D digitization and modelling in documenting heritage sites has increased significantly over the past few years. This paper presents the process of a monument’s virtual 3D reconstruction using Structure from Motion techniques with common, user friendly, low cost equipment. The byzantine church of the Transformation of the Saviour in Meskla, Crete, aged back to the 13th c., has been photographed by two student groups and the two models were merged into one unified 3D scene.The detailed and high quality products of the 3D modelling can be used for educational and research purposes but also for the touristic promotion of the area through light, easy to use, 3D visualizations on the web.Parthenios, P.; Androulaki, T.; Gereoudaki, E.; Vidalis, G. (2016). COMBINING STRUCTURE FROM MOTION TECHNIQUES WITH LOW COST EQUIPMENT FOR A COMPLETE 3D RECONSTRUCTION OF A 13TH CENTURY CHURCH: The case of transformation of the saviour church in Meskla, in Crete Island. En 8th International congress on archaeology, computer graphics, cultural heritage and innovation. Editorial Universitat Politècnica de València. 476-479. https://doi.org/10.4995/arqueologica8.2015.4169OCS47647

Failure Processes in Embedded Monolayer Graphene under Axial Compression

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/PMMA oligomers and a reasonable agreement was obtained

Mechanical, Electrical, and Thermal Properties of Carbon Nanotube Buckypapers/Epoxy Nanocomposites Produced by Oxidized and Epoxidized Nanotubes

High volume fraction carbon nanotube (CNT) composites (7.5–16% vol.) were fabricated by the impregnation of CNT buckypapers into epoxy resin. To enhance the interfacial reaction with the epoxy resin, the CNTs were modified by two different treatments, namely, an epoxidation treatment and a chemical oxidation. The chemical treatment was found to result in CNT length severance and to affect the porosity of the buckypapers, having an important impact on the physico-mechanical properties of the nanocomposites. Overall, the mechanical, electrical, and thermal properties of the impregnated buckypapers were found to be superior of the neat epoxy resin, offering an attractive combination of mechanical, electrical, and thermal properties for multifunctional composites