Abstract
Theoretical and experimental studies are presented to characterize the anisotropic plastic response under torsion loading of two nominally identical aluminum Al6061-T6 extruded round bars. Theoretical models are developed using isotropic (Von Mises 1913) and anisotropic (Barlat 1991) yield criteria, along with isotropic strain hardening formulae, to model post-yield behavior under simple torsion loading. For the case of simple shear loading, incremental plasticity theory is used to determine the theoretical elastic, plastic, and total shear strains. A set of experiments are performed to calibrate Barlat’s 1991 yield function. Several specimens are extracted at different orientations to the longitudinal direction of each round Al6061-T6 bar and tested under uniaxial tension and simple torsion to optimally determine all anisotropic (Barlat 1991) yield function parameters. During loading, Stereo Digital Image Correlation (DIC) is used to quantify surface deformations for the torsion experiments and a baseline tension specimen to identify and correct measurement anomalies. Results show the isotropic yield model either underestimates or overestimates the experimental shear strains for both extrusions. Conversely, results using the Barlat 1991 anisotropic yield criteria are in excellent agreement with experimental measurements for both extrusions. The presence of significant differences in the anisotropic parameters for nominally similar extrusions confirms that plastic anisotropy is essential for the accurate prediction of mechanical behavior in longitudinally extruded Al6061-T6 bars.
Highlights
Aluminum alloys are used extensively in a wide range of industries, including automobile, aerospace, transportation, and civilian infrastructure, with the material undergoing various processes such as rolling, extrusion, and forging to manufacture a component [1,2,3]
Inspection of the results shows that the model using the Barlat anisotropic yield function is in very good agreement with experimental measurements, with differences less than 5% for both specimens
The elastic, plastic, and total shear strain components are obtained (a) theoretically through computational modeling using both the Von Mises and Barlat Yld91 yield criteria with incremental plasticity, and (b) experimentally using StereoDIC for extruded, thin-walled tubular specimens subjected to applied torsional loads
Summary
Aluminum alloys are used extensively in a wide range of industries, including automobile, aerospace, transportation, and civilian infrastructure, with the material undergoing various processes such as rolling, extrusion, and forging to manufacture a component [1,2,3]. Tardif and Kyriakides [28] performed 3D finite element simulations using both anisotropic (Yld2004-3D) and isotropic The authors employ incremental plasticity with the conjugate work principle to develop the theoretical equations for predicting the elastic, plastic, and total strains due to the application of simple torsional shear stress for both isotropic and anisotropic yield criteria, (e.g., Von Mises [8] and Barlat Yld91 [17]), resulting in separate theoretical models (All six Barlat Yld anisotropic yield criteria parameters for each of the Al6061-T6 materials are determined through (1) uniaxial tension experiments on specimens extracted from different directions in each extrusion, and (2) a simple torsion experiment for a longitudinal cylindrical specimen).
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