Co-authors​ :

 Monica CAPRETTI (ITALY), Giulia DEL BIANCO , Valentina GIAMMARIA (ITALY), Simonetta BORIA (ITALY), Vincenzo CASTORANI  

In response to the growing emphasis on sustainability and environmental preservation, recent years have witnessed a surge in research and development efforts dedicated to crafting eco-friendly composite solutions. Natural fibers play a pivotal role in advancing green composites, offering significant advantages such as low density, cost-effectiveness, high strength-to-weight ratio, and efficient energy absorption capabilities. Despite these reinforcements showing promise in addressing pollution concerns and meeting lightweight requirements to reduce fuel consumption and emissions, their mechanical performance falls short compared to synthetic counterparts, such as carbon fibers. Consequently, the exclusive use of natural fiber composites in structural components remains challenging. In this context, the incorporation of both natural and synthetic fibers in hybrid structures is advocated as a widely recognized and promising strategy. This integration allows synthetic fibers to compensate for the shortcomings of natural fibers, resulting in the fulfillment of different and competitive design specifications. Such an approach outperforms conventional engineering materials while contributing to the reduction of the carbon footprint. Recently, the automotive industry has demonstrated an increasing concern for delivering lightweight and crashworthy composite structures to address both vehicle performance and safety issues. Focusing on the crashworthiness of circular tubes made from flax/epoxy and hybrid carbon-flax/epoxy, this study highlights the potential of natural fibers compared to carbon in energy-absorber composite structures during axial crushing. To achieve progressive crushing, a chamfer is implemented as a trigger mechanism to ensure the localization of stress and the initiation of failure. The energy-absorbing capabilities of these composite tubes are investigated through both experimental and numerical methods, comparing quasi-static and dynamic loading conditions. After mechanical characterization of composite materials, a finite element (FE) model of such structures is developed to reproduce their crushing phenomenon through LS-DYNA software. The numerical and experimental results are compared to validate the effectiveness of the designed model. The high consistency of results indicates good model predictability. Furthermore, an optimization procedure for crashworthiness is conducted with the LS-OPT optimizer, aiming to identify optimal material parameters for accurately predicting experimental responses and numerically simulating observed damage mechanisms. In conclusion, the outcomes underscore the potential of hybrid materials as efficient crashworthy components, offering an alternative to carbon-based structures. The FE model precisely captures the energy absorption capabilities and failure modes of tested tubular composite samples under crushing.