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Overview Topology optimization is a digital method for designing objects in order to achieve the best structural performance, sometimes in combination with other physical requirements. Topology optimization tools use mathematical algorithms, such as the finite element method and gradient computation, to generate designs based on desired characteristics and predetermined constraints. Initially a purely academic tool, topology optimization has advanced rapidly and is increasingly being applied to the design of a wide range of products and components, from furniture to spacecraft. While this work has resulted in sophisticated and com- mercially useful designs, there remain challenges related to the manufacturability of topology-optimized objects, the ability to design for multiple physical processes, and the ability to apply topology optimization to the design of soft and compliant structures. Sometimes the manufacturability issue can be solved by adding specific predetermined constraints to the design or avoiding certain types of solutions alto- gether, such as closed-cell structures in favor of strut designs. Given the sometimes rather organic-looking solutions of a design, it is a process that lends itself well to additive manufacturing. The challenges for topology optimization going forward lie partially in how well the algorithms used can handle multiple geometrical and physical constraints and the ease of use. To explore these issues, the Workshop on Exploiting Advanced Manufacturing Capabilities: Topology Optimization in Design was organized as part of a work- shop series on Defense Materials Manufacturing and Its Infrastructure (DMMI), as requested by Reliance 21. Reliance 21 is a group of professionals that was estab- lished in the Department of Defense (DoD) sciences and technology community 1
2 E x p l o i t i n g A d va n c e d M a n u fa c t u r i n g C a pa b i l i t i e s to increase awareness of DoD science and technology activities and improve coordinaÂtion among DoD services, components, and agencies. Specifically, within Reliance 21, there is a materials and manufacturing processes community of interest (COI) dedicated to providing leadership in the development of technology-based options for advanced materials and processes for DoD and for delivering technol- ogy products and scientific and engineering expertise to maintain and enhance U.S. defense capabilities. Technical teams within this COI focus on a wide range of issues related to structures and protection; propulsion and extreme environments; sensors, electronics, and photonics; power and energy; readiness; warfighters; civil engineer- ing; and corrosion. Hosted by the National Academies of Sciences, Engineering, and Medicine, the event brought together approximately 60 speakers and attendees rep- resenting physics, materials science, engineering, and manufacturing from industry, academia, and government agencies. The two-day workshop was organized around three main topics: (1) how topology optimization can incorporate manufactur- ability along with functional design; (2) challenges and opportunities in combining multiple physical processes; and (3) approaches and opportunities for design of soft and compliant structures and other emerging applications. Speakers identified the unique strengths of topology optimization and explored a wide range of techniques and achievements in the field to date. For example, they described how topology optimization has been used to create incredibly detailed designs for large structures, such as airplane wings, and enabled new applications using carbon nanotube yarns, architected materials, elastomeric materials, and 3D woven materials. In the case of the airplane wing, the unique combination of high resolution and large size enables the optimization to be closer to a theoretical maximum in comparison with just optimizing individual wing subcomponents. In the case of woven Âmaterials, metallic wires can be combined into lattices, with a weaving pattern that can be optimized for such properties as stiffness, flow, or thermal transport. The production of elastomeric materials has reached new possibilities for com- plex optimization with a very fast process that uses the balance between light to drive polymerization and oxygen to inhibit polymerization. In addition to tÂ opology optimizations applications, several speakers pointed out that topology optimization can be used to advance fundamental scientific discoveries. For example, research to enhance understanding of how characteristics like surface roughness and porosity can be predicted and managed in a multi-physics, multi-materials environment will be dependent on careful analysis of the optimized structures and the manu- facturing methods. Speakers also discussed how topology optimization can enable processes that greatly accelerate the design-to-manufacture pipeline compared with traditional approaches; how performance of a design can be maximized while minimizing the volume of material utilized, and thus, how it can be used to create structures and products that enhance sustainability; and how designers can plan for recyclability in their designs.
Overview 3 Attendees identified a number of challenges and limitations in the field. One key issue is manufacturing constraints. Without consideration for manufactur- ability, topology optimization can result in designs that are theoretically optimal but that could never be realized. In particular, participants explored how the capabilities and limitations of topology optimization methods interact with the capabilities and limitations of additive manufacturing technologies, including consideration of the importance of build direction, feature sizes, layer height, and the materials used. They also noted limitations in the ability of current topology optimization approaches to accurately reflect physical constraints, the ability to apply these tools to the design of large-scale structures. Topology optimization and additive manufacturing also have implications for qualification and certification processes, representing another potential barrier to adoption. Since the properties of materials influence the properties of structures and how they can be manufac- tured, speakers also underscored the importance of characterizing new materials to enable and enhance topology optimization methods in combination with additive manufacturing. To fully realize the fieldâs potential, several speakers suggested a need for greater interdisciplinary collaboration, along with greater exchange among materials sci- entists, design engineers, commercial application designers, and process engineers.