Characterisation of bio-based structures: models and experiments

Over the last decades the use of natural fibre-reinforced polymer composites (NFCs) has received increased attention and found application in many engineering fields: automotive, trains, marine and aeronautics. In fact, natural fibres, such as flax, cotton, sisal, hemp, etc., have many advantages compared to glass fibres, such as low density, recyclability and cost. Additionally they are renewable raw materials and have high specific strength and stiffness. Their low-density values allow producing composites that combine good mechanical properties with a low specific mass. The present thesis is focussed on characterisation of bio-based structures made of flax fibres reinforced polyethylene resin. The main aim of this dissertation is to evaluate the performance, in terms of vibroacoustic properties, of these structures in order to replace the conventional ones in engineering applications where high load levels are not expected. Several panels were manufactured and tested. Firstly the mechanical properties were carried out by means of the static tests. Than these properties were validated, both numerically and experimentally, by using ultrasonic wave propagation techniques and frequency response functions. Finally, some functional properties, such as acoustic damping, vibration damping and energy absorption, of several bio-based sandwich panels were evaluated investigating the influence of different geometrical and material parameters on functional properties.