<p>Material hardening response plays a crucial role in the constitutive modeling and numerical simulations of metal materials undergoing large deformation. For example, simulation of the ductile failure of sheet metals usually requires a hardening response that goes far beyond the uniform strain limit in a conventional uniaxial tension test. A simple shear test such as the pure torsion tests for tubular specimens can allow the uniform strain to develop up to a much higher level without the occurrence of strain localization, thus providing an alternative to characterize the material hardening response to large strains. As an attempt to facilitate the material property characterization of sheet metals, this work investigates the material hardening and failure of AA6061-T6 sheets using a newly designed shear specimen mounted on a universal testing machine. To delay the onset of strain localization on the edges of the simple shear specimen and thus allow a larger strain to develop in the test section, a series of numerical simulations are first conducted to investigate the stress and strain state in some critical locations, such as the center of the test section and the upper and lower edges of the specimen. Based on the numerical results, a set of optimal geometric parameters such as the gauge width and length of the specimen are determined. The newly designed shear specimen is mounted on a universal testing machine and the Digital Image Correlation (DIC) technique is adopted to measure the strain field in the gauge section. After the simple shear stress-strain relationship is established from the tests, the material hardening response is identified based on the principle of plastic work equivalence, which is found to go up to a maximum uniform strain of 0.8, much higher than the limit strain of uniaxial tension test (order of 0.1). For comparison purpose, a set of simple shear tests of AA6061-T6 sheets based on two representative simple shear specimens from the literature are conducted using the same experimental setup. The two shear specimens fail at the strain level that ranges between 0.5 and 0.6, lower than the limit strain of 0.8 obtained in our specimen. This comparison shows the better performance of our newly designed simple shear specimen in the material hardening identification of this sheet metal. Meanwhile, the comparison also reflects the influence of specimen geometry on the identified failure strain under simple shear loading condition, which further points to the importance of appropriate specimen design in establishing the failure locus for sheet metals under different stress states.</p>

Identification of the Material Hardening and Failure of an Aluminum Alloy Sheet via a Simple Shear Test

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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