Interface Effects on the Fracture Mechanism of a High-Toughness Aluminum-Composite Laminate
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THE aluminum industry has a long record of improving the performance of aerospace alloys. This has resulted in the development and progressive application in commercial aircraft of very high-strength 7xxx alloys and high damage tolerance 2xxx and 6xxx alloys.[1–3] However, the big challenge still is to achieve high-strength and good damage-tolerance alloys for thick-section applications. Although the aluminum industry continues to develop higher-performance alloys, an additional and complementary avenue for improving the performance of airframes structures is becoming increasingly interesting: optimizing the use of materials. In this sense, it could be possible to improve the damage tolerance of metallic structures by modifying conventional-design configurations to take maximum profit from the strong points of aluminum alloys and de-emphasize their weaker points.[4–6] Laminated metal composites consist of alternating metal or reinforced metal layers that are bonded with ‘‘sharp’’ interfaces. Laminated metal composites can dramatically improve many properties, including toughness, fatigue behavior, impact behavior, wear, corrosion, and damping capacity; or provide enhanced formability or ductility.[7–14] From a mechanical viewpoint, optimizing the combination of strength, toughness, and interface bonding is the basis for lamination. C.M. CEPEDA-JIME´NEZ and J.M. GARCI´A-INFANTA, Postdoctoral Researchers, O.A. RUANO, Professor, and F. CARREN˜O, Staff Researcher, are with the Departamento de Metalurgia Fı´ sica, CENIM, CSIC, 28040 Madrid, Spain. Contact email: cm.cepeda@ cenim.csic.es M. POZUELO, Postdoctoral Researcher, is with the Department of Materials Science and Engineering, University of California, Los Angeles, CA 90095-1595. Manuscript submitted January 10, 2008. Article published online October 21, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A
The toughness and impact behavior in many respects are the most interesting issues from the viewpoint of their applicability. Hot rolling is capable of obtaining good bonds between layers, while refining the microstructure, thereby improving toughness.[15,16] The interfaces that may delaminate are responsible for the high impact and fracture resistance of the multilayer materials and contribute to increasing the extrinsic toughening by different mechanisms. Delamination in the layers ahead of the crack tip results in a reduction and redistribution of the local stress.[17,18] In the case of ultrahigh carbon steel-based composite laminates, it has been shown that interlayer delamination is the principal mechanism of crack arresting.[19,20] This process makes crack propagation through the composite very difficult. The main objective in this research is to study the influence of processing and thermal treatments on the microstructure and interfacial mechanical properties of an aluminum multilayer material with high specific strength and outstanding toughness. The second objective is the study of extrinsic mechanisms responsible for the toughness increase in the processed c
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