Prof. Costas Galiotis Costas Galiotis is a Professor at the Department of Chemical Engineering (Univ. of Patras) and former Director of the Institute of Chemical Engineering Sciences (ICE-HT) which is one of the 7 academic research institutions of the Foundation of Research and Technology-Hellas (FORTH). He also holds a visiting (adjunct) professorship at the Department of Engineering & Material Sciences, Queen Mary University of London (since 1997). He is the National Representative in the NMBP Committee of Horizon 2020 (current) and has also served as National Representative in the NMP Committee of FP7 (2011-2013) and as the President (2004-2006), Vice President (2002-2004) and Member of the Executive Council (1999-current) of the European Association of Composite Materials which comprises 500 members across Europe. He also serves since 2006 in the Executive Council of the European Centre of Nanostructured Polymers (ECNP) which was founded by the Nanofun-Poly Network of Excellence of the European Communities. He is also a founding member of the GRAPHENE FLAGSHIP (2013-2022).
His research interests are in the field of mechanical properties of nanomaterials such as graphene and nanotubes, the production of nanocomposites, the investigation of interfacial interactions between dissimilar materials, the design and characterisation of smart materials and structures etc. He has published overall ~300 journal papers, monographs, chapters in books etc. He is the Editor-in-chief of the journals of Advanced Composites Letters (since 1993) and Journal of Nanostructured Polymers and Nanocomposites (since 2005). Since 2015 he is serving as an Editorial Board Member of Scientific Reports (Nature). He has been the Chairman and Organiser of the International Conferences ECCM-11 (2004), NANOCONF (2007), GrapHEL (2012) and INDUSTRIAL TECHNOLOGIES (2014). His current research funding includes ERC-ADVANCED GRANT (“Tailor Graphene), GRAPHENE FLAGSHIP, FP7-NMP etc. and a number of National Projects (ARISTEIA-ERC, THALIS etc.).
The mechanical response of monolayer (1LG), bilayer (2LG) and trilayer (3LG) graphenes to uniaxial tensile and compressive stresses will be fully reviewed in this presentation. Important effects such as orthogonal buckling during tension and Euler buckling in compression will be discussed. Recent results on true biaxial strain on 1LG, 2LG and 3LG in combination with laser Raman monitoring at the sub-micron scale will also be presented. The mechanical behaviour under a biaxial strain will be compared with that of thin membrane at the macroscale. Finally, the stress transfer mechanism from a polymer substrate or matrix will be monitored with laser Raman microscopy. It will be shown that in the case of simply supported and also fully embedded monolayer graphene (1LG) into a PMMA matrix the distribution of axial stress (strain) along the flake deviates from the classical shear-lag type of loading at least for a region of about 1-2 μm from the edge. In certain cases for which the flake exhibits significantly doping near the edges the stress transfer is minimal if any at all. By considering a simple balance-of-shear-to-normal stresses at the interface we are able to convert the stress (strain) gradient into values of interfacial shear stress for the various systems examined. The upper ceiling of interfacial shear stress was found to be less than 1 MPa. In all cases for efficient stress transfer, the required length for 1LG flake in the loading direction should be twice the elastic transfer length (> 4 μm) plus the length affected by any charged impurities. This size effect explains clearly that in composites for which the reinforcing graphene flakes are less than 10 μm in length no significant benefits are expected in terms of strength or stiffness improvement.