Funding

FCT - Portuguese Foundation for Science and Technology

EPSRC - Engineering and Physical Sciences Research Council

Modelling and developing ductile composites

The HiPerDuCT project – High Performance Ductile Composite Technology (with Imperial College and University of Bristol) – aims to develop a new generation of composites with improved ductility. Soraia is proposing new material concepts and developing models for their mechanical response, so as to guide and support the experimental developments.

Modelling the tensile failure of composites

The fibre-dominated failure of composites is a very complex process, dominated by the statistics of fibre failure, presence of the matrix, and size effects. Soraia developed models for predicting the tensile strength and fracture toughness of fibre-reinforced composites, based on fibre-bundle theory, micromechanics and self-similar fracture surfaces. Strength distributions for varying specimen sizes are predicted in less than a second, so the model can be coupled with FE simulations or Monte-Carlo analysis.

Mechanical analysis of recycled composites

Technologies for recycling CFRP waste are now maturing, so the great challenge is now to reintroduce the recyclates in non-critical structural applications. Soraia’s PhD focused on analysing the mechanical response of different state-of-the-art recycled composites, and developing models to predict the response of these novel materials.

In-depth experimental investigations showed that recycled CFRPs with a woven architecture can recover nearly 100% of the stiffness and 80% of the strength of their virgin precursors, depending on the recycling process. Moreover, the presence of fibre-bundles – held together by residual matrix not removed during recycling – improved the fracture toughness of discontinuous-fibre recycled composites by more than one order of magnitude.

This work demonstrates that residual fibre bundles – until then perceived as defects – actually enhance the damage tolerance of recycled composites.  This was a paradigm-shifting finding for composites recycling, and triggered a collaboration between Imperial and The Boeing Company (a key player in the recycling community) to further explore the potential of bundled architectures. The significance of this finding led to this work being covered by media (http://www.iom3.org/news/lifeline-waste-carbon-fibres), to the Tsai Award (from the International Committee for Composite Materials) in 2011 for the Best Student Paper in ICCM 18 (Jeju, Korea), and to invited presentations in the Global Outlook for Carbon Fibre 2009 and 2010 (http://www.gocarbonfibre.com).

Compressive failure of composites

Fibre kinking is the most common failure mode of fibre-reinforced composites under longitudinal compression. This work investigates the mechanics of kink-band formation through experiments and FE simulations at the micro-scale. The understanding obtained supported the derivation of a physically-based analytical model, which predicts the sequence of events and failure of composites under longitudinal compression. This work received the SAMPE Schliekelmann Award in 2009 for the Best Paper in the European Students' Seminar.

Modelling hybrid laminate joints

Bolted joints are critical points in most structures. The BOJO project (lead by ESA/ESTEC and DLR) explored the potential for improving the strength of joints in CFRP laminates by replacing selected composite plies with Titanium layers. Soraia‘s contribution (within INEGI/Faculty of Engineering, University of Porto) focused on modelling the mechanical response of the hybrid laminates – particularly the ply-substitution zone and the hybrid bolted region. The optimised Ti-CFRP hybrid joints exhibited a specific bearing strength 29% higher than that of the baseline CFRP laminate.