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Journal publications

Towards separator-free structural composite supercapacitors

Olivier Hubert, Nikola Todorovic, Alexander Bismarck

Structural supercapacitors can both carry load and store electrical energy. An approach to build such devices is to modify carbon fibre surfaces to increase their specific surface area and to embed them into a structural electrolyte. We present a way to coat carbon fibres with graphene nanoplatelets by electrophoretic deposition in water. The effect of time and voltage on the mechanical properties of the carbon fibres, the structure of the coating and the specific surface area of the coated carbon fibres are discussed. A specific capacity of 1.44 F/g was reached, which is 130% higher than state-of-the-art structural electrodes. We demonstrate the scalability of the deposition process to continuous production of coated carbon fibres. These carbon fibre electrodes were used to realise large (21 cm long) structural supercapacitor demonstrators without the need for a separator, having a specific capacity of 623 mF/g.

Experimental Method for Tensile Testing of Unidirectional Carbon Fibre Composites Using Improved Specimen Type and Data Analysis

Rajnish Kumar, Lars P Mikkelsen, Hans Lilholt and Bo Madsen

This paper presents an experimental method for tensile testing of unidirectional carbon fibre composites. It uses a novel combination of a new specimen geometry, protective layer, and a robust data analysis method. The experiments were designed to test and analyze unprotected (with conventional end-tabs) and protected (with continuous end-tabs) carbon fibre composite specimens with three different specimen geometries (straight-sided, butterfly, and X-butterfly). Initial stiffness and strain to failure were determined from second-order polynomial fitted stress–strain curves. A good agreement between back-calculated and measured stress–strain curves is found, on both composite and fibre level. For unprotected carbon composites, the effect of changing specimen geometry from straight-sided to X-butterfly was an increase in strain to failure from 1.31 to 1.44%. The effect of protection on X-butterfly specimens was an increase in strain to failure from 1.44 to 1.53%. For protected X-butterfly specimens, the combined effect of geometry and protection led to a significant improvement in strain to failure of 17% compared to unprotected straight-sided specimens. The observed increasing trend in the measured strain to failure, by changing specimen geometry and protection, suggests that the actual strain to failure of unidirectional carbon composites is getting closer to be realized.

Improving the performance of pseudo-ductile hybrid composites by film-interleaving [OPEN ACCESS]

Salvatore GiacomoMarino, GergelyCzél

Improvement of the interfacial fracture toughness of the layer interfaces is one way to increase the performance of interlayer hybrid laminates containing standard thickness carbon/epoxy plies and make them fail in a stable, progressive way. The layer interfaces were interleaved with thermoset 913 type epoxy or thermoplastic acrylonitrile–butadienestyrene (ABS) films to introduce beneficial energy absorption mechanisms and promote the fragmentation of the relatively thick carbon layer under tensile loads. Carbon layer fragmentation and dispersed delamination around the carbon layer fractures characterised the damage modes of the epoxy film interleaved hybrid laminates, which showed pseudo-ductility in some cases. In the ABS film interleaved laminates, a unique phase-separated ABS/epoxy inter-locking structure was discovered at the boundary of the two resin systems, which resulted in a strong adhesion between the fibre-reinforced and the thermoplastic layers. As a result, the delamination cracks were contained within the ABS interleaf films.

Conference publications

Improving flexural modulus of interleaved composites using reinforced thermoplastic interleaves

Gokul Ganesh Murali, Paul Robinson, Alexander Bismarck, Christoph Burgstaller

Interleaving the plies of carbon fibre reinforced epoxy composites with thermoplastic interleaves have previously been shown to enable these composites to display controllable stiffness and shape memory properties. However, the incorporation of unreinforced thermoplastic interleaves leads to a decrease in flexural modulus of the interleaved composites. In this study, the flexural modulus of composites with reinforced polystyrene interleaves was investigated. The reinforcements used in this study were: (1) stainless steel mesh (SS), (2) unidirectional carbon fabric (UD), (3) woven carbon fabric, (4) woven carbon fabric with epoxy coating and (5) non-woven short carbon fibre mesh. The flexural moduli of the interleaved composites with reinforced interleaves were predicted theoretically and determined experimentally. Among these composites, significant increases in the flexural modulus were achieved in the interleaves with UD, woven and woven+epoxy reinforcements. Additionally, these interleaved composites were shown to retain their controllable stiffness and shape memory properties.

Design of a deployable composite mesh to form a segment of a circular cylindrical surface

Gokul Ganesh Murali, Paul Robinson, Alexander Bismarck, Christoph Burgstaller

In this work, we have used finite element (FE) modelling to develop an interleaved composite mesh structure capable of deploying along a curved path to form a segment of a circular cylindrical surface. Such mesh structures could allow the creation of semi-permanent deployable shelters for people and vehicles, especially during disaster relief and humanitarian assistance. Abstract can be found in the link below.

Development of intrinsically heated, interleaved composites with controllable flexural stiffness and shape memory capability

Gokul Ganesh Murali, Paul Robinson, Alexander Bismarck, Christoph Burgstaller

Abstract can be found in the link below