Fiber optimization of a carbon windsurfing boom

Abstract

The goal of this research is to optimize the fiber layup of a carbon windsurfing boom for weight and stiffness. A windsurfing boom should be stiff to provide an efficient basis for the energy transfer from the sail through the surfer to the board. The weight of the boom is important as the total weight of the rig influences the performance, especially during movements where the swing weight of the rig is important. To optimize the fiber layup the FEM simulation software of SolidWorks is used. This software allows the user to divide the part in sections and specify the layup per section in terms of orientation, thickness, and material. The output of the FEM simulation is the mass and the displacement under different load cases. The load cases are based on an experiment where the loads during sailing are determined with load cells and strain gauges.
The FEM simulation is validated and scaled based on two experimentally determined force-displacement relations. The FEM is scaled with the force-displacement relation of the first loading point by scaling the given material parameters by 0.78. The FEM is then validated with the force-displacement relation of the second loading point. New fiber layups are generated based on stress direction, previous iterations, and engineering intuition. The 50 new generated layups and their respective mass and displacement results are evaluated with a performance equation to determine which layup has the highest performance for the combination of mass and displacement. The coefficients in the performance equation are chosen so that both parameters have equal weight. The chosen layup is further evaluated with a required fiber overlap section. Two booms with the new layup are evaluated with the same experiment that is used to validate and scale the original FEM. At the first loading point, where the main loading during sailing is applied, the new layup is 16 percent stiffer than the original layup, as predicted by the FEM. The experiment results for the second loading point showed that the new layup was 5.5-7.5 percent stiffer than the original layup instead of the predicted 13 percent. This difference is due to the straight tubes that are glued to the end of the optimized boom body which are made by a different manufacturer. Changing the stiffness of these pipes makes the FEM results converge to the experimentally determined values. The experiment results of both layups are evaluated with the performance equation as the stiffness has increased but the mass has increased from 2.19 to 2.25 kg as well. The performance equation showed that the new layup outperforms the original layup for both loading points. The project goal to optimize the layup for mass and stiffness is therefore achieved. For the layup of the boom, a sandwiched layup of unidirectional fibers with biaxial fibers at the in- and outside of the circular cross-section was determined as the best performing layup for the sections loaded under bending. For sections that are loaded under both torsion and bending additional layers of biaxial fibers are added at the inside of the circular cross-section. These biaxial fibers are added at the inside as the unidirectional fibers are used at the outside to create the largest moment of inertia for these fibers as the displacement due to bending is leading in this case. Even the small translation of fibers from the inside to the outside of the layup can make a significant difference.