Effects of ductile laminate thickness, volume fraction, and orientation on fatigue-crack propagation in Ti-Al 3 Ti metal
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I. INTRODUCTION
THE design of structural components through microstructural tailoring is no longer a paradigm shift; rather it has become an exciting avenue for interdisciplinary research leading to the development of unique materials systems— metal-intermetallic laminate (MIL) composites are novel examples of such an effort.[1] The aim of the present work is to use the excellent complementary properties of constituent materials to create a composite endowed with optimal, application-specific properties. The concept of ductile-phase toughening of brittle material, originally proposed by Kristic and Nicholson,[2] uses the work of plastic stretching of a ductile component embedded in a brittle matrix to increase energy dissipation, thus leading to increased toughness. Since the original work of Kristic, there have been considerable efforts to improve the toughness of brittle materials through ductile-phase reinforcements. Over the last decade, composites with different ductile reinforcement morphologies, which included particles, wires, and laminates, were developed, and the effect of these ductile reinforcements on the mechanical properties has been extensively RAGHAVENDRA R. ADHARAPURAPU, Graduate Student, KENNETH S. VECCHIO, Professor, and FENGCHUN JIANG, Research Scientist, are with the Department of Mechanical and Aerospace Engineering, Materials Science and Engineering Group, University of California, San Diego, LaJolla, CA 92093. Contact e-mail: [email protected] AASHISH ROHATGI, Research Scientist, is with Geo-Centers, Inc., Fort Washington, MD 20749-1340. Manuscript submitted June 10, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
investigated for aerospace and structural applications that required optimization in weight and enhanced toughness.[3–27] A systematic study of various factors affecting the composite properties has since been accomplished. These factors include the interfacial properties between phases involved that determine the extent of constraint on the ductile inclusions by the stiff brittle phase,[2,9,28–32] the effect of reinforcement morphology (shape and size), and the volume fraction of reinforcement.[3–9,11,12,15–21,33] The concept of laminating various metals and alloys resulting in composites that exploit unique properties of the constituent materials has been known for a very long time.[34] Nevertheless, in the development of structural intermetallic composites, the idea has been embraced as a potential new engineering concept. Over the past decade, a number of diverse brittle intermetallics and ceramics have been toughened with various ductile metal laminates.[15–20,23–27,35–62] A number of these laminate systems were originally conceived and developed with an aim of increasing crack propagation resistance in brittle components used for high-temperature aerospace applications.[63–66] In spite of such rapid progress toward understanding these novel materials, a review of the available literature indicates very few references that explored fatigue damage response of brittle/ductile
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