Deformation and fracture behavior of beams composed of alumium foam core and ceramic Al 2 O 3 under monolithic bending
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I. INTRODUCTION
WITH the development of various new processing techniques, metallic foams with low density, high strength, and energy absorption capability have been produced with lower cost and good consistency. They have been found to be good candidates as structural and functional materials. Aluminum foam is touted as one of the possible sound and impact energy absorbing materials for panels and sheets in the industrial, aerospace, and automotive fields. Many basic characteristics of monolithic aluminum foam, such as the Young’s modulus, plastic collapse stress, fracture toughness, and fatigue behavior, have been described in Evans et al.’s[1–5] and Ashby et al.’s[6–12] series of publications. Through theoretical analysis of honeycomb structure[4,5,13,14] and experiments of aluminum alloy foams,[1–3,6–10,15–17] it has been suggested that the relative density (defined as ratio of bulk foam density bf to cell wall density cf) plays a key role in the mechanical response of aluminum foams. The Young’s modulus, strength, and fracture toughness depend on in an exponent law type of relationship. During deformation, densification is a special macrodeformation mechanism for the aluminum foam under compressive loading. The concept of J.B. SHA, Research Fellow, is with the High Temperature Materials Group, National Institute for Materials Science, Ibaraki, 305-0047, Japan. Contact e-mail: [email protected] T.H. YIP, Assistant Professor, is with the School of Materials Engineering, Nanyang Technological University, Singapore 639798. Manuscript submitted July 29, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
densification strain, D, was introduced to characterize the deformation behavior. At the end of uniform deformation, densification by cell wall bending was generated gradually throughout the specimen. Densification begins when the compressive stress drops to a minimum value; the stress then rises smoothly with the progress of densification, i.e., compressive strain.[4,5,7,11] In practice, the potential exists for the aluminum foam applications in industries as the core of sandwich or multilayer beams with solid face sheets. The purpose of sandwich or multilayer beams design is to avoid the low stiffness of monolithic foam. Considering the service future in structure and energy absorption areas, the mechanical responses of these sandwich and multilayer beams are a priority worth investigating. Mechanical behaviors of sandwiches composed of aluminum foam core and aluminum alloy face sheets have been reported.[18,19,20] These beams fail into three modes: face yield, indentation (ID), and core shear. Mechanism maps showing failure domains of each mode have also been discussed and constructed for two aluminum alloy face sheets by Bart-Smith et al.[18] and Chen et al.[19] These maps identify regions of dominant failure, with ratios of core thickness to support span and face sheet thickness to support span as the coordinates. The map directly displays the tight influence of the geometrical parameters of the b
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