Mechanical response, texture evolution, and fracture of a rare-earth-containing magnesium alloy sheet, ZEK100, at different strain rates and temperatures: Experiments and modeling
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Date
2019-01-01
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Mechanical Engineering
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Engineering, Mechanical
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Access limited to the UMBC community. Item may possibly be obtained via Interlibrary Loan thorugh a local library, pending author/copyright holder's permission.
This item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.
Abstract
Magnesium alloys have been at the forefront as possible alternatives to conventional materials such as aluminum and steel for their high specific-strength. However, magnesium alloys exhibit anisotropy, tension-compression asymmetry, and quasi-brittle fracture at ambient temperature, which is exacerbated at high strain rates. It is well known that alloying with rare-earth elements can improve the low uniaxial ductility in comparison with conventional magnesium alloys. Therefore, the mechanical response and texture evolution of a rare-earth-containing magnesium alloy sheet, ZEK100, are investigated under different loading conditions to characterize the anisotropy, tension-compression asymmetry, strain rate sensitivity and thermomechanical response. A reduced-order crystal plasticity model that defines extension twinning, basal <a> slip, and non-basal slip as the deformation mechanisms, is used to model the experimental results and to give an insight in the active deformation mechanism. In addition, the fracture behavior of ZEK100 is also investigated at different stress states and strain rates. A variety of sample geometries loaded along different processing directions are used to achieve different stress states and deformation mechanisms. Surface strain maps for all the specimens are measured using the digital image correlation (DIC) technique to quantify the strain at fracture. ZEK100 exhibits larger strain at fracture across the gage section of the test specimens aligned with the transverse direction (TD) than specimens aligned with the rolling direction (RD); however, the opposite is shown for the local strain measurements at fracture. Therefore, the crystal plasticity model is used to simulate each loading condition to understand the anisotropic ductile fracture behavior of ZEK100. Using the stress states and deformation mechanisms from the simulations, a novel anisotropic criterion is developed which is an extension of the Hosford-Coulomb (HC) fracture model. The new anisotropic criterion accounts for the role of different deformation mechanisms on the anisotropic fracture response of ZEK100.