Effects of lamination and changes in layer thickness on fatigue-crack propagation of lightweight laminated metal composi
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I.
INTRODUCTION
DISCONTINUOUSLY reinforced aluminum alloys (DRAs) are candidate materials for applications in which high specific stiffness and specific strength are required. Moreover, DRAs can be processed using conventional techniques such as extrusion, forging, and rolling, which makes them cost effective for various applications. However, the relatively low fracture toughness of these composites compared to monolithic materials has prevented their more widespread use. For this reason, several investigators have used extrinsic toughening approaches to improve the fracture toughness of DRAs.[1–26] In particular, the lamination of DRAs with more ductile/tough layers is one approach which has exhibited significant improvements under static loading conditions. However, many of the applications which require high fracture toughness also require good fatigue-crack propagation resistance. Unfortunately, much less work has been conducted on the fatigue-crack growth resistance of the layered/laminated materials. Although some fatigue work conducted in the crack-divider orientation has been conducted by Huffman et al. [27,28] on 6090/SiC/25p-5182, the improved laminate toughness was accompanied by superior fatigue-crack-growth resistance but a lower fatigue threshold. Other work by Chawla and Liaw[29] on roll-bonded pure aluminum and AISI 304 stainless steel laminates tested in the crack-divider orientation revealed that the crack growth rates in the laminates were slower than those exhibited by its components. Very little
HALA A. HASSAN, formerly Graduate Student, Department of Materials Science and Engineering, Case Western Reserve University, is Assistant Professor, Department of Design and Production Engineering, Ain Shams University, Cairo, Egypt. J.J. LEWANDOWSKI, Leonard Case Professor of Engineering, Department of Materials Science and Engineering, Case Western Research University, Cleveland, OH 44106, is Overseas Fellow, Churchill College, Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB2 3QZ United Kingdom. Contact e-mail: [email protected] M.H. ABD EL-LATIF, Professor, is with the Department of Design and Production Engineering, Ain Shams University. Manuscript submitted June 30, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
work has been conducted on laminated metal composites (LMCs) tested in the crack-arrestor orientation, and that is the focus of this investigation. II.
EXPERIMENTAL PROCEDURES
A. Materials The LMC which was chosen for this study was 6090/SiC/25p-6013, produced by diffusion bonding. Both the DRA and Al layers were produced via powder metallurgy.[30,31] Laminates with different DRA/Al layer thicknesses were investigated for a 50/50 volume-fraction ratio of the DRA and Al layers. In this case, a 50/50 laminate contains an equivalent volume fraction of DRA and Al layers. The DRA and aluminum alloy layers were stacked together in a vacuum hot press which was maintained at 1 ⫻ 10⫺6 Torr, and the layers were pressed at 450 °C under an axial pressure of
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