Abstract

In today’s engineering processes, optimisation plays a key role in finding good solutions upfront in the concept definition. Especially topology optimisation can drive the design to find new layouts. This is important in the automotive industry these days as new trends as electrification and autonomous driving offer the opportunity to heavily influence the vehicles. For the design of structures, topology optimisation methods are well established for linear elastic loadcases. However, for vehicle structures, a good performance in case of crash events is extremely important and amongst the driving criteria for the concept selection. The extension of the topology optimisation to these highly non-linear loadcases is a fairly recent development. In recent work, the work use of heuristics – i.e. design rules – for the optimisation procedure of 3-D structures has been explored. In order to allow a topological modification, the structure is being represented by a graph description, giving the information about the location of structural members and their connectivity. This graph is turned into a finite element model of the structure. After the simulation run, a number of criteria are evaluated, such as the distribution of the internal energy density or the relative velocity of the deforming members. Based on these, the design rules are activated, e.g. to support a buckling structure with a new member. This new structure is added in the graph description, which then again gives a new finite element model. In order to keep the mass of the structure constant, the thickness of the parts can be varied. In addition to this outer loop, for each structure a shape optimisation is added in an inner loop. Several alternative and competing topological modifications are being evaluated in each iteration, and the best is used for the subsequent iteration. This method has proven to be successful for different loadcases, e.g. to reduce the maximum intrusion of an impactor, or to reduce the maximum acceleration of the structure – which is relevant for the protection of the occupants of a vehicle. One criterion for a reliable optimisation result is the adequate finite element representation of the structure. In addition to the existing tool set, a method is being developed to create a model that contains typical features of vehicle body-in-white sheet metal structures such as flanges and spot weld connections, in addition to more detailed structural joints. A library of members and joints has been created, out of which a new external tool will convert the graph description into an SFE-Concept model. These models can be included in the optimisation loop of the topology optimisation, resulting in more realistic final structures.