Regular, low density cellular structures - rapid prototyping, numerical simulation, mechanical testing
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Regular, low density cellular structures - rapid prototyping, numerical simulation, mechanical testing J. Stampfl1 , M.M. Seyr2 , M.H. Luxner2 , H.E. Pettermann2 , A. Woesz3 , P. Fratzl3 1 TU Wien, Institute of Materials Science and Testing, Vienna, Austria 2 TU Wien, Institute of Lightweight Design and Structural Biomechanics, Vienna, Austria 3 Max Planck Institute of Colloids and Interfaces, Dept. of Biomaterials, Potsdam, Germany
ABSTRACT Cellular solids form the basis of many biological and engineering structures. Most models use the relative density and the mechanical properties of the bulk material as the main parameter for the prediction of the mechanical properties of such structures. In this work the influence of the architecture of periodic cellular solids on the mechanical properties is investigated numerically and experimentally. Using computer aided design, structures with 8x8x8 base cells are designed and fabricated. The physical prototypes which are tested experimentally are made from thermosetting and thermoplastic polymers by employing Rapid Prototyping (RP) techniques. Various RP techniques are compared regarding their suitability for the fabrication of cellular materials. For numerical simulation of the cellular structures, linear Finite Element analysis is employed. Three-dimensional models are set up using higher order beam elements. In a first step, the structure is treated as an infinite medium and homogenization via a ’periodic micro-field approach’ is used. The entire elastic tensors for different relative densities are evaluated, from which the directional dependencies of the Young’s moduli are derived. In a second step, simulations of finite structures are performed for direct comparison with experiments. Samples consisting of several basic cells are modeled which leads to a better correspondence to the experimental setup. Finite structures of different numbers of cells are modeled to study the influence of the sample size. The experimental and numerical results correspond very well and form a consistent picture of the problem. The multi-disciplinary approach leads to a comprehensive view of effects which govern the mechanical behaviour of the investigated cellular structures. RAPID PROTOTYPING OF CELLULAR MATERIALS Rapid Prototyping (RP) offers the possibility to fabricate cellular structures with defined internal and external geometry [1]. Furthermore, recently developed techniques enable the fabrication of complex structures with very small feature resolution. Microstereolithography for instance enables the user to fabricate parts with feature resolutions in the range of 5-10 µm [2, 3]. In the course of this work, RP techniques have been used to fabricate polymeric cellular structures whose mechanical properties (strength, stiffness) were investigated experimentally. Cellular structures exhibit multiple undercut features. The utilized process must be able to shape such features. In the course of this work, two RP processes were utilized: Stereolithography (SLA) and selective la
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