Mechanical and Microstructural Characterization of Aluminum 6061 Processed by Plane Stress Local Torsion
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ENHANCED mechanical properties and performance of structural components can be achieved by severe plastic deformation (SPD) processing of materials through plastically deforming materials to very large strains. A brief review of SPD methods for grain refinement can be found elsewhere.[1] SPD processes generally involve bulk deformation. This can be a disadvantage as it consumes high energy. Within a part or a component that is under loading during service in a structure, only small volumes of the material within specific areas are prone to early failure. Fastener holes and their surrounding areas are just one of many possible examples where a component is vulnerable to failure due to stress concentration in the vicinity of the hole. It has been shown that a crack emanating from a hole often results in the failure of components in structures. Therefore, localized improvement of the material’s strength for a critical application is mandatory. The local reinforcement of the material is characterized by variations in the structure and mechanical properties of the material similar to functionally graded materials[2] or those obtained by a method called
AMIR HOSSEIN SHAMDANI, Research Support Officer, is with the Institute of Railway Technology, Monash University, PO Box 31, Clayton, VIC 3800, Australia. SHAHIN KHODDAM, Visiting Academic, is with the Institute of Frontier Materials, Deakin University, Waurn Ponds, Geelong, VIC 3216, Australia. Contact e-mail: [email protected] Manuscript submitted February 18, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
‘‘OPTICA’’ to improve the wear resistance of ductile iron by locally optimizing the microstructure.[3] Localized severe plastic deformation (LSPD) processes such as surface mechanical attrition treatment,[4] high-pressure tube twisting,[5] and plane stress local torsion (PSLT)[6] have been proposed and studied recently. LSPD processes can enhance the mechanical properties of the material locally and improve the global performance of the component. Local torsion is a process that has similarities with the PSLT process and has been dealt with in the literature.[7–9] Analytical studies of local torsion date back to the investigations on the elastic—perfectly plastic and rigid—plastic response of an infinite disk with a circular hole loaded by pressure and twisting along the interior surface of the hole.[7] Finite and infinitesimal deformation of an axisymmetric disk of a nonuniform thickness with a circular hole under hole expansion and torsion was also studied.[8] In these works, a comprehensive analytical solution of combined expansion and twisting of holes under different assumptions was presented. The studies included mathematical modeling without dealing with the experimental implementation of local torsion. A special test known as Andrade shear test, comparable to the local torsion process, was applied to copper and aluminum Andrade disks[9] to investigate the rupture life of the two materials by determining their constitutive characteristics at an elevated t
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