An Investigation on the Fatigue Fracture of P/M Al-SiC Nanocomposites
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TRODUCTION
THE evaluation of mechanical properties of nanostructured and ultrafine-grained materials has been researched intensively in recent years.[1] As reviewed in Reference 2, a number of studies have also been devoted to investigate the mechanical properties of nanocomposites. With regard to metal matrix nanocomposites, Al-SiC is probably the most intensively studied material system due to its unique combination of properties.[2,3] It is known that the uniform distribution of nanoparticles throughout the metal matrix enhances the elastic modulus and strength of the material, while the ductility decreases mainly due to dislocation interaction with the non-shearable nanoparticles.[4–6] Meanwhile, a literature survey shows that evaluation of mechanical properties has mostly been limited to tensile and hardness tests. Recently, the high-temperature deformation of Al matrix nanocomposites under compression (upsetting)[7–9] and time-dependent tensile (creep) loads has been noted.[10]
H. GHASEMI YAZDABADI, Graduated MSc Student, and A.K. EKRAMI, Professor, are with the Department of Materials Science and Engineering, Sharif University of Technology, P.O. Box 113659466, Tehran, Iran. H.S. KIM, Professor, is with the Department of Materials Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, South Korea. A. SIMCHI, Professor, is with the Department of Materials Science and Engineering, Sharif University of Technology, and also with Institute for Nanoscience and Nanotechnology, Sharif University of Technology, Contact e-mail: [email protected] Manuscript submitted June 30, 2012. Article published online February 1, 2013 2662—VOLUME 44A, JUNE 2013
Although fatigue fracture is the most common source of failures of engineered materials and accounts for >80 pct of damage in practical applications,[11] the fatigue behavior of nanocomposites has been investigated very limitedly. One of the authors recently reported fatigue properties of Cu-Al2O3 nanocomposites under a shear mode by a rotating bending test[12] and showed that the presence of alumina nanoparticles enhances the high cycle fatigue (HCF) strength. Cyclic hardening at the low cycle fatigue (LCF) range ( 0.1) was applied to reindex the data points. Low-angle grain boundaries (LAGBs) were defined at misorientations in the range of 2 to 15 deg (white colored in IPFs), while grains with higher angles were considered as high-angle grain boundaries (HAGBs). C. Tensile and Fatigue Testing Flat dog bone-shaped samples were prepared by a wire-arc discharge of the forged billets along the extrusion direction according to ASTM E466 standard (Figure 1). Mechanical polishing was performed to gain a mirror-like surface. Tensile tests were done using an automated mechanical testing machine (Zwick Z250, Germany) at a constant strain rate of 2 9 103 s1. The fatigue tests were performed on a SCHENCK model servo hydraulic machine equipped with a 10 kN load cell. The cyclic loadings were performed in a pull-pull mode with minimum to maximum stress r
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