AIAA JOURNAL Vol. 44, No. 6, June 2006 Crushing of a Textile Core Sandwich Panel Justin Caulfield ∗ and Anette M. Karlsson † University of Delaware, Newark, Delaware, 19716 and David J. Sypeck ‡ Embry-Riddle Aeronautical University, Daytona Beach, Florida 32114 A class of textile core sandwich structure is investigated with respect to their ability to absorb transverse com- pressive load. To this end, experimental observations are compared to numerical simulations for cores made from precrimped woven wire cloth laminated together via transient liquid-phase bonding. The experimental observa- tions show that this structure exhibits key properties for being a promising load-absorbing structure, for example, impact and blast protection. Matching numerical simulations show that the behavior can be captured with sim- ulations and that a relatively simplified scheme can be used. The simulations also suggest sensitivity to the local topology in absorbing energy, as well as explaining the somewhat unexpected deformation behavior observed exper- imentally. Multifunctionality, owing to the accessible open space between cells, coupled with attractive compressive behavior is achieved. Nomenclature d = diameter of the truss (wire diameter) E = Young’s modulus of the material comprising the trusses G c = shear modulus of the truss core R = radius of the truss, d /2 r = radius of the connecting element in the woven structure w = opening width (distance between wires) ¯ ρ core = relative density of the truss core σ Y = yield strength of the material comprising the trusses σ c Y = compressive strength of the truss core τ c Y = shear strength of the truss core I. Introduction L IGHTWEIGHT metallic materials based on topologically con- figured cellular trusslike cores and dense face sheets have recently been demonstrated to provide several advantages over com- peting concepts, such as cores made from more traditional materi- als such as hexagonal honeycombs or stochastic foams. 1−5 Panels with a stochastic cellular core are not particularly weight efficient. 6 However, panels with periodic truss cores, for example, tetrag- onal and pyramidal topologies, exhibit superior thermostructural characteristics 3 and are at least as weight efficient as the best com- peting concepts, for example, honeycombs, especially for curved panels. 6,7 The mechanical benefit from topologically configured cores lies in the ability for individual truss members within the core to absorb external core loads initially as local tensile or compres- sive truss loads only, with no bending of the trusses. When realized, core properties are related to relative density in a substantially linear way 1−5 : G c / E = A ¯ ρ core , τ c Y  σ Y = B ¯ ρ core , σ c Y  σ Y = C ¯ ρ core (1) Received 13 April 2005; presented as Paper 2005-1843 at the AIAA/ ASME/ASCE/AHS/ASC 46th Structures, Structural Dynamics, and Mate- rials Conference, Austin, TX, 18–21 April 2005; revision received 7 Octo- ber 2005; accepted for publication 25 October 2005. Copyright c  2005 by Anette M. Karlsson. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0001-1452/06 $10.00 in correspondence with the CCC. ∗ Research Assistant, Department of Mechanical Engineering. † Assistant Professor, Department of Mechanical Engineering. Member AIAA. ‡ Assistant Professor, Department of Aerospace Engineering. where A, B, and C are a function of truss architecture, load orien- tation, and node design. Because of the open space between cells, topologically config- ured cores provide opportunities for multifunctionality of a struc- ture. For example, a sandwich panel designed for its traditional task (transferring bending moment as coupled pairs in the face sheets and shear stress in the core) could also function as an impact and blast protection device by absorbing loads striking perpendicular to the panel plane. Long, flat stress–strain curves with plastic collapse occurring at a constant (plateau) stress are desired. For trusslike core structures with open interconnected porosity, the aligned chan- nels also provide the needed space for flow of a cooling medium within the structure. This might be advantageous for components subjected to elevated temperatures, for example, hypersonic vehicle airframes, power electronics heat sinks, etc. 5 For a topologically configured core to achieve multifunctional goals at optimum me- chanical performance, it is important that the material properties of the base are good, that the nodes (the joints of the trusses) are well designed (to avoid introducing local bending moments into the trusses), and that the trusses adhere nearly perfectly to the face sheets and adjoining trusses. 8−10 However, manufacturing of topologically configured cores with these characteristics can be a challenge from both an economic and technical standpoint. 11 An alternative and compromise in design criteria and manufactur- ing techniques for topologically configured materials, for example, honeycombs and cast trusslike structures, involves metallic sand- wich panels with textile cores (Fig. 1). 11 This relatively inexpensive approach to fabricating miniature metal trusstype structures 11,12 is based on a recognition that high structural quality porous metal ob- jects have already been made for many years by taking wrought metal wires and weaving them into bundles. Woven wire cloth, braided cables, and knitted metal fabrics are good examples of this. 13 The textile approaches used to create such articles are very well established and relatively inexpensive. Furthermore, a host of base metal choices are available. Virtually all metals can be drawn into wire and then woven, braided, or knitted into a variety of fil- ament arrangements, such as dutch weave, hexagonal mesh, three- dimensional weave, crimped mesh, and triaxial weave. 13 However, conventional metal textiles are unsuited for most multifunctional applications because the metal contacts are not normally bonded and the articles are thin (exceptions include three- dimensional woven articles). By lamination, many of these short- comings can be overcome. 11,12 Several base metal types and core architectures have been produced. 12 The aligned porosity provides the open space needed for other functionalities (heat exchange, fuel storage space, conduits for wiring and piping, etc.). 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