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Development of intrinsically heated, interleaved composites with controllable flexural stiffness and
shape memory capability
Authors: G.G. Murali1, P. Robinson1, A. Bismarck2, and C. Burgstaller3
1 The Composites Centre, Department of Aeronautics, Imperial College London, South Kensington
Campus, London SW7 2AZ, United Kingdom
Email: g.murali@imperial.ac.uk, p.robinson@imperial.ac.uk
2 Polymer and Composite Engineering (PaCE) group, Department of Material Chemistry, University of
Vienna, Waehringer Strasse 42, A-1090 Wien, Austria
Email: alexander.bismarck@univie.ac.at
3 Transfercenter für Kunststofftechnik (TCKT), Franz-Fritsch-Straße 11, A-4600 Wels, Austria
Email: christoph.burgstaller@tckt.at
Abstract:
Carbon fibre reinforced epoxy polymer (CFRP) composites interleaved with Polystyrene (PS)
have been shown to exhibit controllable flexural stiffness properties [1]–[3]. A significant reversible
reduction in flexural stiffness is produced when the composite is heated above the glass transition
temperature of PS. At this temperature, the composite can be readily deformed and if cooled in this
deformed state, it will retain the new shape. These composites also display shape memory behaviour;
if the composite is reheated in its new shape, it will return to its original cured shape [4].
In the previous studies investigating the controllable flexural stiffness and shape memory
characteristics, the interleaved composite specimens were heated in an oven. In the current work, we
have explored the use of an embedded SS304 stainless-steel (SS) mesh (plain weave, wire diameter:
0.028 mm, aperture: 0.082 mm) procured from The Mesh Company (UK) as a heating element within
the interleaved composite (Hexcel Fibredux 914/TS/6K/5/34% 0⁰ CFRP plies interleaved with 0.07 mm
Empera 124N PS sheets). The composites were laid up in [0⁰/PS]7/ 0⁰ sequence with (1) Layup A having
no embedded SS mesh, (2) Layup B having 1 SS mesh and (3) Layup C having 3 SS meshes. For Layup
B the SS mesh was embedded in the central PS interleaf (i.e. interleaf layer 4 when counting from the
top). For Layup C the SS meshes were incorporated in interleaf layers 2, 4 and 6.
For layups with embedded SS meshes, the meshes were attached to a DC power supply to
allow Joule heating of the composites. A DC power input of 30 W was chosen as the power input for
Joule heating necessary to reach a surface temperature of around 120°C for controllable stiffness and
shape memory studies (120°C is the temperature used in previous works [1]–[4]). In layup A (which
was heated in an oven) and in layups B and C (subjected to Joule heating), the temporary loss in
flexural stiffness (measured by ASTM D7264-07 standard) due to heating was over 98.5%.
Furthermore, the shape memory capability of these composites was also investigated. Flat
coupons of these composite layups were heated (as described previously), bent to a ~90° angle in a 3-
point bend test setup and then cooled down in the deformed state. The ~90° shape was retained by
the composite and when these coupons were again subjected to heating (using an oven for layup A
and Joule heating for layups B and C) the original flat shape was fully recovered. For layups B and C,
the shape recovery was completed in approximately 1 minute after switching on the Joule heating.
The recovery time for Layup A was around five minutes. Optical microscopy was performed to
investigate any change in the internal structure of the composites after the shape memory trials.
References:
[1] H. A. Maples, S. Wakefield, P. Robinson, and A. Bismarck, “High performance carbon fibre
reinforced epoxy composites with controllable stiffness,” Compos. Sci. Technol., vol. 105, pp.
134–143, 2014.
[2] H. Maples, “Composites with Controllable Stiffness,” Imperial College London, 2014.
[3] H. A. Maples, O. Smith, C. Burgstaller, P. Robinson, and A. Bismarck, “Improving the
ply/interleaf interface in carbon fibre reinforced composites with variable stiffness,” Compos.
Sci. Technol., vol. 128, pp. 185–192, May 2016.
[4] P. Robinson, A. Bismarck, B. Zhang, and H. A. Maples, “Deployable, shape memory carbon
fibre composites without shape memory constituents,” Compos. Sci. Technol., vol. 145, pp.
96–104, Jun. 2017.
Acknowledgement:
The research leading to these results has been performed within the framework of the
HyFiSyn project and has received funding from the European Union’s Horizon 2020 research and
innovation programme under the Marie Skłodowska-Curie grant agreement No 765881.
