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INTRODUCTION

UNLIKE many traditional engineering materials, bulk metallic glasses (BMGs) have been developed as a scientific curiosity rather than for a specific need.[1] Therefore, this class of materials is yet to find widespread engineering applications. The excellent mechanical properties of BMGs such as high strength (1.4 GPa for Pt-based BMGs to above 4 GPa for FeCo-based BMGs),[2] high elastic limits ~2 pct, and wide range of fracture toughness 10 to 100 MPa
m1=2 [1] have been widely recognized. The deformation behavior of BMGs under nanoindentation,[3] microindentation,[4] flexural loads,[5] and uniaxial compression[6] and tension[7] has also been well studied in the literature. Although the inelastic deformation is known to occur in the form of shear bands, the nature of these shear band patterns is yet to be fully explored under a wide variety of loading scenarios. Improvements in the processing technology of BMGs have rapidly progressed in the last few decades from being able to make thin ribbons to large rods of diameter beyond 10 mm.[8,9] Innovative manufacturing methods and technologies are being adopted to make usable components from these BMGs for aerospace engineering and defense applications. Machining using a single-point tool is often one of the popular manufacturing methods to shape BMGs into complex parts. GHATU SUBHASH, Professor, is with the Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611-6250. Contact e-mail: subhash@ufl.edu HONGWEN ZHANG, Postdoctoral Candidate, is with the Department of Materials Science and Engineering, Michigan Technological University, Houghton, MI 49931. This article is based on a presentation made in the symposium entitled ‘‘Dynamic Behavior of Materials,’’ which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee. Article published online September 13, 2007 2936—VOLUME 38A, DECEMBER 2007

However, research into this particular aspect of BMGs is scarce, probably due to the limitations in the geometrical size of the specimens that can be obtained. Fundamental insights into the behavior of BMGs under machining conditions can be obtained by modeling their response under single-point loads. Such studies are well documented on metals[10] and brittle materials,[11] where, as a first step, the interaction between a singlepoint tool and a workpiece is modeled as an indentation event with the indenter penetrating the specimen in the normal direction while being dragged in the lateral direction. Typical static indentation experiments impose only normal loads. Extension of these experiments to single-point scratch loads allows for superposition of both normal and tangential loads. This loading scenario is expected to mimic the interaction of a single-point tool with the work piece during a machining operation and can provide insig