Modeling the Axial Mechanical Response of Amorphous Fe 45 Ni 45 Mo 7 B 3 Honeycombs
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TRODUCTION
HONEYCOMBS are lightweight cellular materials that are used in structural applications because of their efficient strength and propensity for mechanical energy absorption. There is a necessity to develop cellular structures with specific mechanical properties through the reexamination and optimization of the unit cell geometries.[1] The manufacturability of a particular geometry is also a factor. The double-walled hexagonal cell is a good example of a material property efficiency compromise to allow a more efficient manufacturing process. Honeycombs are anisotropic and most effective at bearing loads when applied in the out-of-plane (X3) direction. When used in sandwich cores, the throughthickness properties of honeycombs are important. Honeycombs formed using regular hexagonal unit cells are most commonly observed and applied; other cell shapes such as circle, rectangle, triangle, and Kagome (mixed) also exist.[2] Crystalline-base materials including aluminum, steel, polymers, and even Kevlar (DuPont,
BALAJI JAYAKUMAR, Graduate Student, and JAY C. HANAN, Associate Professor, are with the Mechanical and Aerospace Engineering, Oklahoma State University, Tulsa, OK 74106. Contact e-mail: [email protected] Manuscript submitted April 30, 2011. Article published online September 16, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
Wilmington, DE) have been used to make cellular structures. Their mechanical properties were well characterized even starting from the early 1990s.[3–5] In all the analytical models proposed to predict the mechanical behavior of honeycombs, the relative density of a cellular structure is the most critical property that governs its mechanical properties.[2,5–7] Analytical models for relative density and mechanical properties of cellular materials based on the square, triangle, rectangle, circle, and Kagome unit cells shapes are presented elsewhere.[8,9] With the discovery that metallic glasses have excellent strength and stiffness, it is natural to imagine methods to process cellular structures using these amorphous materials. Two important factors that have limited the use of metallic glasses in structural applications include the lack of ductility and limited time at temperature before crystallization.[10] Plastic deformation in amorphous materials takes place as an onset of shear bands; failure is not initiated by plastic yielding but by brittle fracture.[11] Foaming was the first technique to form closed- or open-form cellular structures from amorphous base materials.[12] Palladium-based foams (Pd43Ni10Cu27P20) were manufactured using thermoplastic forming to produce 86 pct porous foams capable of yielding plastically and inheriting a plastic strength of 250 to 600 MPa.[13] Control of porosity influences the mechanical properties of cellular structures. Existing analytical models support this claim and show that for the same density of the solid base material, the yield strength of honeycombs are 16 times greater compared with foams. 1:64 r q ¼ 0:31 ðfoamsÞ ½1 rS qS VOLUME 43A,
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