Advanced fiber composites: towards recyclable bio-inspired composites

  • Libonati, Flavia (University of Genoa)
  • Stagni, Alessandro (University of Genoa)

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Fiber-reinforced composites are replacing metals for various applications thanks to their superior mechanical properties: high stiffness-to-weight and strength-to-weight ratio. As an example, the automotive industry is redesigning its cars in order to be compliant with the new EU regulations in terms of vehicle emissions and safety. The main drawback of composites is poor dam-age tolerance, which is critical in structural applications. To cope with this issue, we can draw inspiration from Nature. Amplification in toughness and balance with stiffness and strength are fundamental characteristics of biological structural materials, such as bone and nacre, derived from a billion-year-long evolution. Bone shows astonishing mechanical properties in terms of stiffness-to-weight and damage tolerance. Such properties derive from the bone hierarchical structure and organization at different levels, spanning from the nano- to the macro-scale. At the micro-scale, we find characteristic features, called osteons, which play a fundamental role in triggering specific toughening mechanisms, such as deflecting and stopping cracks, increasing the fracture energy. Osteons are hollow cylindrical structures, made of several fiber-reinforced concentric layers with different fiber orientations. Building on previous works, where we mimicked the osteons through carbon-fiber sleeves filled up with UD fiberglass or through pultruded hollow tubes, here we aim to implement multilayer tubes, similar to the osteon features of bone tissue, into novel multiscale bio-inspired composites. Besides, we also design, manufacture, and test classic layered laminates to allow direct comparison and provide proof-of-concept of the new bioinspired designs. We use a comprehensive approach, including numerical design via FE simulations, material manufacturing, and experimental characterization. Despite the presence of some defects, due to the more complex lamination process, the bio-inspired laminates show improved energy absorption capacity. Our next goal is to implement this bio-inspired de-sign into natural fiber composites with a thermoplastic resin, to improve recyclability. On one side the thermoplastic resin will allow the separation of fibers from the matrix (not possible in the case of thermosets), on the other side the implementation of natural fibers will provide a negative CO2 emission as the plants absorb CO2 during their life cycle.