Browsing by Subject "honeycomb structures"
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Item Additively Manufactured Conformal Negative Stiffness Honeycombs(University of Texas at Austin, 2017) Debeau, D.A.; Seepersad, C.C.This study investigates the static and dynamic mechanical performance of conformal negative stiffness honeycomb structures. Negative stiffness honeycombs are capable of elastically absorbing a static or dynamic mechanical load at a predefined force threshold and returning to their initial configuration after the load is released. Most negative stiffness honeycombs rely on mechanical loading that is orthogonal to the base of the structure. In this study, a more three dimensional design is presented that allows the honeycomb to conform to complex surfaces and protect against impacts from multiple directions. The conformal designs are additively manufactured in nylon and stainless steel and subjected to quasi-static mechanical loading and dynamic mechanical impact tests that demonstrate their impact protection capabilities.Item A Comparison of Modeling Methods for Predicting the Elastic-Plastic Response of Additively Manufactured Honeycomb Structures(University of Texas at Austin, 2018) Sharma, Raghav; Le, Thao; Song, Jiaxu; Harms, Ethaniel; Sowa, Daniel; Grishin, Alex; Bhate, DhruvValid and accurate models describing the mechanical behavior of additively manufactured cellular materials are crucial to enabling their implementation in critical-to-function parts. Broadly speaking, the modeling approaches commonly used in the literature fall into three categories. Each of these differs in the level of discretization at which the cellular behavior is modeled: at the level of each material point, at the level of the unit cell or at the level of a connecting member that constitutes a unit cell. Each of these three approaches relies on different characterization techniques and the way in which the resulting data is leveraged in the development of the model. In this work, we critically examine all three modeling approaches using FEA and compare their accuracy in the prediction of the elastic and plastic behavior of experimentally characterized hexagonal honeycomb structures made with Fused Deposition Modeling, and discuss the pros and cons of each method.Item Determination of a Shape and Size Independent Material Modulus for Honeycomb Structures in Additive Manufacturing(University of Texas at Austin, 2017) Le, Thao; Bhate, Dhruv; Parsey, John M.; Hsu, Keng H.Most prior work on modeling cellular structures either assumes a continuum model or homogenizes “effective” cell behavior. The challenge with the former is that bulk properties do not always represent behavior at the scale of the cellular member, while homogenization results in models that are shape specific and offer little insight into practical design matters like transitions between shapes, partial cells or skin junction effects. This paper demonstrates the strong dependence of measured properties on the size of the honeycomb specimen used for experimental purposes and develops a methodology to extract a material modulus in the presence of this dependence for three different honeycomb shapes. The results in this paper show that the extracted modulus for each shape converges as the number of cells in the specimen increases and further, that the converging values of the material moduli derived from the three shapes are within 10% of each other.Item A Validated Methodology for Predicting the Mechanical Behavior of Ultem-9085 Honeycomb Structures Manufactured by Fused Deposition Modeling(University of Texas at Austin, 2016) Bhate, D.; Van Soest, J.; Reeher, J.; Patel, D.; Gibson, D.; Gerbasi, J.; Finfrock, M.ULTEM-9085 has established itself as the Additive Manufacturing (AM) polymer of choice for end-use applications such as ducts, housings, brackets and shrouds. The design freedom enabled by AM processes has allowed us to build structures with complex internal lattice structures to enhance part performance. While solutions exist for designing and manufacturing cellular structures, there are no reliable ways to predict their behavior that account for both the geometric and process complexity of these structures. In this work, we first show how the use of published values of elastic modulus for ULTEM-9085 honeycomb structures in FE simulation results in 40- 60% error in the predicted elastic response. We then develop a methodology that combines experimental, analytical and numerical techniques to predict elastic response within a 5% error. We believe our methodology is extendable to other processes, materials and geometries and discuss future work in this regard.