Viktoptimering av ett kompositchassi till en multimodal lättviktsfarkost
This report describes the master thesis project ?Weight Optimization of a Composite Chassis for a Multimodal Lightweight Vehicle? which is a part of the Master program in Naval Architecture and a part of a research project at the Centre for Naval Architecture, KTH. Demands on smart and energy efficient transport solutions are continuously increasing. In the Stockholm region the citizens are expected to increase with 25% and the road vehicles with 80% until 2030, putting high demands on the traffic system. Using a small multimodal vehicle deals with this problem and uses both the land and waterways for transportation. When it comes to energy savings the structural mass is considered to account for 30% of the energy consumption of a car, why a weight optimized structure is desired when designing an energy efficient vehicle.The first part of the work consists of a load analysis. It includes a general arrangement of the vehicle which illustrates the different modes of transportation, including speeds, main dimensions and mass distributions. Based on this information, different critical load conditions that can occur during operation are calculated.The second part of the work consists of a FEM-based weight optimization of the chassis, with respect to its global strength. A structural arrangement has been defined, which is a single skin concept made of a quasi-isotropic carbon fiber/vinylester composite material. The design constraint for the optimization is the ultimate strength of the material and the design variable is the laminate thickness. The chassis is optimized against the different load conditions defined.When the optimizations are performed a final design is defined which withstands all the load conditions used. The results give a chassis that has a structural weight of 44.7 kg, where the most critical loads occur in the bottom/mid part of the chassis. According to this analysis, a quasi-isotropic laminate seems to be the most appropriate layup alternative, because of the variation in the stress propagation for different areas in the chassis.