Multi-Scale, Multi-Criteria Design of Meta-Materials with Offset Periodicity

Meta-materials are a class of artificial materials with a wide range of bulk properties, completely different from the base material they are made of. Some notable examples include negative Poisson\u27s ratio materials, materials designed for specific electromagnetic, acoustic, or thermal properties. The term meta-material in the context of this research refers to a continuous, heterogeneous structure with prescribed elastic properties. Such meta-materials are designed using Topology Optimization (TO). Tools like SIMP interpolation, mesh filtering and continuation methods are used to address the numerical issues with Topology Optimization. The most popular tool to design such materials is Asymptotic Homogenization. However, it has its limitations. Homogenization requires the meta-material to obey periodicity and scaling requirements. Dr. Chris Czech in his Ph.D. dissertation proposes a way to design meta-materials that may, due to manufacturing limitations, break the scaling requirements. Using Volume Averaging, he designs thin-layered meta-materials for use in the shear beam of a non-pneumatic wheel. By offsetting the said meta-material layers by a half-width of the Unit Cell, auxetic honeycomb-like geometry was obtained. This was the first time such a shape was observed as the result of Topology Optimization targeting the effective shear modulus. This research will further study the offset periodicity by considering offsets other than just zero or half-widths. The same shear beam of a non-pneumatic wheel is designed using such offsets. The optimization formulations in literature and the ones proposed by Dr. Czech have been extensively studied and used for single-criteria design problems. This research demonstrates the use of these formulations for the design of meta-materials with multiple prescribed elastic properties, such as prescribed behaviors in shear and in tension or compression. This research also identifies a possible physical limitation in the combinations of elastic properties that can be achieved for meta-materials when designed using Topology Optimizatio

Design and Development of a Multi-material, Cost-competitive, Lightweight Mid-size Sports Utility Vehicle’s Body-in-White

Vehicle light-weighting has allowed automotive original equipment manufacturers (OEMs) to improve fuel efficiency, incorporate value-adding features without a weight penalty, and extract better performance. The typical body-in-white (BiW) accounts for up to 40% of the total vehicle mass, making it the focus of light-weighting efforts through a) conceptual redesign b) design optimization using state-of-the-art computer-aided engineering (CAE) tools, and c) use of advanced high strength steels (AHSS), aluminum, magnesium, and/or fiber-reinforced plastic (FRP) composites. However, most of these light-weighting efforts have been focused on luxury/sports vehicles, with a relatively high price range and an average production of 100,000 units/year or less. With increasing sports utility vehicle (SUV) sales in North America, focus has shifted to developing lightweight designs for this segment. Thus, the U.S. Department of Energy’s (DOE) Vehicle Technologies Office has initiated a multi-year research and development program to enable cost-effective light-weighting of a mid-size SUV. The proposed designs shall enable weight reduction of a minimum of 160 lb. (~72.7 kg), with a maximum allowable cost increase of $5 for every pound of weight reduced. The proposed designs shall enable vehicle production rates of 200,000 units/year and will be aimed at retaining the joining/assembly line employed by the OEM. A systems approach has been utilized to develop a multi-material, light-weight redesign of the SUV BiW that meets or exceeds the baseline structural performance. This study delves into the development of design targets for the proposed redesign at the system, sub-assembly, and component levels. Furthermore, results from topology optimization studies on a design volume were assessed to understand the load paths under various loading conditions. Several multi-material concept designs were proposed based on the insights provided by the topology optimization study. Novel multi-material joining methodologies have been incorporated to enable maximum retention of the OEM’s joining and assembly process without significantly increasing cost. This paper presents the systems approach, and results from design studies undertaken to meet the program challenges