Design of a tubular frame made of natural fiber reinforced composite with epoxy matrix for the cycling industry

This thesis focuses on the design and structural analysis of a bicycle frame made of composite material. Given the increasing necessity of reducing waste and recycling, the aim is to analyse its behavior when made with natural fiber reinforced composite compared to carbon fiber, looking for a trade off between sustainability and performance. It has been decided to apply these kind of materials on a bicycle typically used by amateurs, that can ride both on road both off road: a gravel bike. The first section of the paper deals with design itself of the frame and explains the geometrical choices and constraints given by calculations, experience and standards developed through the years in the cycling world. In order to properly design a frame it has been necessary to choose the components to be mounted on the gravel and to study their interfaces with the frame itself. The CAD design of the frame has been performed on Solidworks by Dassault Systems and the final result is shown and described. Sequently, the paper deals with the main principles of FEM analysis and it aims to explain the proper meshing process of such a structural component through Hypermesh. Emphasis is then given on composite materials in general, describing their properties and potential and discussing one of their failure criterion: the Tsai - Wu failure criterion. This last one will give an idea of the structural reliability of the laminated component and it will be used by Hypermesh itself to run its calculations. Carbon fiber and hemp fiber are discussed into detail, as well as their mechanical characteristics and the data sheet of the exact materials used into the simulations. Once the frame is designed and meshed, it is described how the material stratification is set on Hypermesh, as well as the model creation and settings. The analysis will be performed simulating the different loading conditions experienced by carbon frames during their everyday use, such as the pedaling fatigue, the static weight and the different torsions of the bicycle. The loads and their values are set from the standards that rule the bicycle frame testing made by manufacturers nowdays. The last and most importat step consists into performing an optimization of the laminate in order to minimize the material and maximize stiffness. A correct stratification will allow to obtain a light and functional component, while reducing waste and garanteeing the required reliability. The results are shown both for the carbon fiber frame both for the natural fiber frame.