Topology optimization has become an integrated part of the design cycle where light-weighting and robustness are important for vehicle structures. With advances in novel manufacturing methods, it has become easier to manufacture parts and assemblies with multiple materials, like over-molds of plastic and metal, hybrid steel-aluminum frames, etc. Multi-material optimization in OptiStruct can provide the benefits of achieving optimal designs in limited areas, light-weighting structures by selecting materials more efficiently, and saving cost at manufacturing volumes for automotive applications. In this paper, a practical methodology for multi-material topology optimization with OptiStruct is presented with examples to determine the optimal load-paths for structural components, including an automotive cradle and chassis. An available “design space” is considered as in a standard topology optimization, where material can be kept or removed. Models are constrained at mounting locations and loading is applied at attachment points, as in a typical optimization setup. Next, topology optimization is performed with different objectives and constraints, e.g. to minimize mass and minimize the effective cost with constraints on displacements, and various concepts are generated based on multiple material models that are considered in the design space. By formulating the problem in this manner with multi-material optimization, trade-offs between the materials can be evaluated, i.e. the stiffness of steel vs. the mass savings of aluminum, and the potential difference in material costs. Including a cost function within the structural optimization with relative expenses of different materials takes consideration of production costs into the optimization problem. The results of the multi-material optimization workflow are presented and summarized with recommendations for common design scenarios. Inclusion of all relevant constraints is important to formulate and drive the optimization approach correctly. The multi-material topology optimization method can be utilized to determine optimal material placement with a structure from a list of available options, and balance the trade-offs between materials with different weight, stiffness, and raw material cost in a concept-level topology optimization.
Keywords: OptiStruct, HyperMesh, Multi-material Topology Optimization
