Browsing by Subject "cellular materials"
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Item The Anisotropic Yield Surface of Cellular Materials(University of Texas at Austin, 2021) Conway, Kaitlynn M.; Romanick, Zachary; Cook, Lea M.; Morales, Luis A.; Despeaux, Jonathan D.; Ridlehuber, Marcus L.; Fingar, Christian; Doctor, Daquan; Pataky, Garrett J.Mechanical metamaterials are often limited in engineering applications because of uncertainty in their deformation behavior. This uncertainty necessitates large factors of safety and behavior assumptions to be included in mechanical metamaterial designs, detracting from the largest benefit of metamaterials: their ultralight weight. In this study, a yield envelope was created for both a bending dominated and a stretching dominated cellular material topology to improve the understanding of the response of cellular materials under various load types and orientations. Experimental studies revealed that the shear strength of a cellular material is significantly less than that predicted by the Mohr’s criterion, necessitating a modification of the Mohr’s yield criterion for cellular materials. Both topologies experienced tension-compression anisotropy and anisotropy dependent on the topology orientation during loading with the stretching dominated topology experiencing the largest anisotropies.Item Beam Deletion in Square Honeycombs for Improved Energy Absorption Under Quasi-Static In-Plane Compression(2022) Ramirez-Chavez, Irving E.; Lee, Christine; Bhate, DhruvWhen selecting cellular materials for energy absorption applications, there have traditionally been two choices: a periodic structure such as a honeycomb, or a stochastic one, as seen in foams. Both choices involve a global definition governing the allocation of the members of the structure, be they beams or surfaces. With Additive Manufacturing, the exploration of more complex structures enables the creation of aperiodicity through the local modification of periodic structures. This paper explores one application of this approach by deleting beams in square honeycombs, with the aim of avoiding localization of failure that generates significant undulations in the stress plateau under in-plane quasi-static compression. These perturbed structures show improved energy absorption behavior by generating higher Specific Energy Absorption for a given transmitted stress and relative density than their periodic counterparts. This work thus argues for further exploration of localized aperiodicity as an approach to finely tune energy absorption performance.Item Cellular Structures for Optimal Performance(University of Texas at Austin, 2009-09) Engelbrecht, Sarah; Folgar, Luis; Rosen, David W.; Schulberger, Gary; Williams, JimCellular material structures, such as honeycombs and lattice structures, enable unprecedented stiffness and strength characteristics, for a given weight. New design and CAD technologies to construct cellular materials are presented in this paper. Such materials have very complex geometries, hence the need for additive manufacturing processes to produce them. A series of experiments was performed to build and test parts fabricated using Selective Laser Sintering. Variations in mechanical properties were quantified and related to processing conditions. Examples help illustrate the variety of applications of cellular materials in the aerospace, automotive, motorsports, energy, electronics, and related industries. A software tool is being developed to enable users to design and construct parts with cellular structures.Item A Comparison of Synthesis Methods for Cellular Structures with Application to Additive Manufacturing(2008-09-10) Chu, Jane; Engelbrecht, Sarah; Graf, Greg; Rosen, David W.Cellular material structures, such as honeycombs and lattice structures, have been engineered at the mesoscale for high performance and multifunctional capabilities. We desire efficient algorithms for searching the large, complex design spaces associated with cellular structures. In this paper, we present a comparison of two synthesis methods, Particle Swarm Optimization (PSO) and least-squares minimization (LSM), for the design of components comprised of cellular structures. Computational characteristics of the algorithms are reported for design problems with hundreds of variables. Constraints from SLS and direct-metal manufacturing processes are incorporated to ensure that resulting designs are realizable. Two 2- dimensional examples are used to study the characteristics of the proposed synthesis methods.Item Freeform Fabrication of Stochastic and Ordered Cellular Structures(University of Texas at Austin, 2010) Lipton, Jeffrey; Boban, Mathew; Hiller, Jonathan; Lipson, HodCellular materials provide a unique challenge to SFF technology. Such materials have unique properties of low mass, high strength, and good insulation properties. To produce such cellular structures, SFF systems require a designed microstructure with a feature size significantly lower than the resolution of the process. In this paper, we examine means of producing stochastic foams using the instability of a viscous thread and various methods for production of closed celled foams. These techniques allow for the production of foams without the need for pre-described cell structures. Such foams, when made from elastic materials can act as novel actuating materials.Item In-Plane Pure Shear Deformation of Cellular Materials with Novel Grip Design(University of Texas at Austin, 2019) Conway, K.M.; Kulkarni, S.S.; Smith, B.A.; Pataky, G.J.; Mocko, G.M.; Summers, J.D.Cellular materials are popular due to their high specific strength, but their in-plane shear behavior is not well understood. Current experimental methods are limited due to the lack of pure shear loading as common arcan-style grips have not been adjusted for cellular materials. A significant concern is a mixture of shear loading with grip induced tension. While in bulk materials the tensile force can be assumed negligible, it has a significant impact on the deformation behavior of cellular materials. In this study, finite element modeling simulations were used to demonstrate that using a new sliding grip design reduced grip induced tension on cellular materials. Experimental studies were performed on honeycomb cellular materials with traditional and newlydeveloped grips to calculate and compare the shear strength and ductility of honeycomb cellular materials. The study concluded that traditional grips overestimate the shear strength of honeycomb cellular materials and honeycomb cellular materials in pure shear with limited grip induced tension has significantly lower strength and ductility due to the early formation of plastic hinges.Item An Investigation of the Material Properties of Laser Sintered Parts Incorporating Conformal Lattice Structures (CLS™) Technology(University of Texas at Austin, 2013) Cooke, A.L.; Folgar, C.E.; Folgar, L.N.; Williams, J.; Park, S.; Rosen, D.W.Cellular materials, including foams, honeycombs, lattices, and similar constructions, offer the key advantages of high strength-to-weight ratios and favorable energy absorption characteristics. The concept of designed cellular materials enables customized material placement to best suit the demands of specific applications or achieve particular performance targets. The design, generation, and fabrication of conformal lattice structures via laser sintering are at the center of the disruptive manufacturing technologies proposed by 3D Systems Corporation. The primary work reported here is the maturation and mechanical testing of the conformal lattice structure technology developed between 3D Systems Corporation and the Georgia Institute of Technology.Item ME Design and Freeform Fabrication of Compliant Cellular Materials with Graded Stiffness(2006) Gupta, Guarav; Tan, JunJay; Seepersad, Carolyn ConnerTypically, cellular materials are designed for structural applications to provide stiffness or absorb impact via permanent plastic deformation. Alternatively, it is possible to design compliant cellular materials that absorb energy via recoverable elastic deformation, allowing the material to spring back to its original configuration after the load is released. Potential applications include automotive panels or prosthetic applications that require repeated, low-speed impact absorption without permanent deformation. The key is to arrange solid base material in cellular topologies that permit high levels of elastic deformation. To prevent plastic deformation, the topologies are designed for contact between cell walls at predetermined load levels, resulting in customized, graded stiffness profiles. Design techniques are established for synthesizing cellular topologies with customized compliance for static or quasi-static applications. The design techniques account for cell wall contact, large scale deformations, and material nonlinearities. Resulting cellular material designs are fabricated with selective laser sintering, and their properties are experimentally evaluated.