Multistage Structural Optimization in the Design of a Lightweight Electrical Vehicle in the Project VisioM

The Technical University of Munich has developed an electrical vehicle in the framework of VisioM. The Institute of Lightweight Structures has contributed to the layout process of the vehicle’s structure by performing optimization in consecutive stages of development.

Topology optimization was applied at an early design phase to identify an advantageous geometry for the structure. For creating a safe and efficient vehicle, the performance of its structure is vital, as it has to withstand the loads while being lightweight. Hence, several load cases had to be considered in the optimization. Nonlinear Simulation of the crash behavior raises the computational costs in an unacceptable way. Therefore, quasi static loads via inertia relief analyses were used. In addition chassis loads as well as torsional and bending stiffness were considered.

The results showed regions of plane geometry and regions of bar structures. This contributed to the decision of creating a hybrid construction, of a carbon fiber laminate moncoque combined with an aluminum space frame for the front, rear and roof of the vehicle. In this second phase the idea was to improve the monocoque by insertion of stiffeners. Again topology optimization was used to identify promising locations for fortifications. Based on the results the stiffeners were modeled as shell structure and a size optimization was performed, to define a manufacturable geometry.

To obtain a reliable result for the design of the monocoque, it was important to include the orthotropic material properties of the laminate. Based on the monocoque a shell structure was modeled and sequentially several unidirectional patches were defined. Due to manufacturing constraints the monocoque was modeled as a symmetric fabric that was enforced by the patches. In this way a weight optimal design was found, that fulfilled the failure criterion under the given loads.

Using optimization in the development of the structure has the advantage, to be able to better judge and understand the performance of the design, as one is always seeking the frontiers of the design instead of developing a structure that only satisfies the specifications. In this way challenges can be revealed earlier in the design process. Finding an optimal design is much more meaningful than just finding a better or satisfying design.


The Author

Dipl.-Ing. Bernhard Sauerer
Lehrstuhl für Leichtbau / Fakultät Maschinenwesen / TUM