United States Department of Transportation
i
Aluminum 2024-T351 Input Parameters for *MAT_224 in LSDYNA, Part 2: Additional Tests to Determine Plastic Heating and Ductile Fracture Behavior Under Combined Loading
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2022-08-01
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[PDF-2.26 MB]
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Edition:Final report
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Abstract:A team consisting of The Ohio State University (OSU), George Mason University (GMU), National Aeronautics and Space Administration Glenn Research Center (NASA-GRC), and the Federal Aviation Administration (FAA) Aircraft Catastrophic Failure Prevention Research Program (ACFPP) collaborated to develop a new material model in LS-DYNA for Aluminum 2024-T351. An initial set of reports were produced as DOT/FAA/AR-13/25 P1-3. This supplemental report describes additional experiments designed and conducted to answer questions that arose during the *MAT_224 card development process. The additional tests were organized into three groups: 1) Dynamic tension tests to study the conversion of plastic work into heat at high strain rates, 2) tests conducted to determine the fracture strain of 2024-T351 aluminum under a specific state of compression and shear, and 3) tests conducted to determine the material fracture strain under a certain three-dimensional stress state (inplane biaxial tension and through thickness compression). To study conversion of plastic work to heat, tension tests on miniature dog-bone coupons were conducted at strain rates ranging from 1E-4 s-1 to 6000 s-1. During the tests, full-field strain and temperature were measured on opposite sides of the sample using high speed Digital Image Correlation (DIC) and a Telops high speed thermal infrared (IR) camera, respectively. Both strain and temperature data were superposed on a common coordinate system using MATLAB-based image processing techniques; average Taylor-Quinney (Beta) parameters were then determined. To further characterize the fracture strain dependence on stress state, an additional stress state was measured via a combined compression and shear (torsion) test using an axial-torsional hydraulic load frame. The new stress state had the highest ratio of compressive to torsional stress tested to date. To study the effect of the in-plane biaxial tension plus through thickness compression on the fracture strain of Aluminum 2024-T35, a new punch test with a backing plate was designed and conducted. These new tests were based on ASTM E643-15 Standard Test Method for Ball Punch Deformation of Metallic Sheet Material. The standard tests were modified such that the ratio of the die diameter to the punch diameter was dramatically increased and in two cases, a ductile copper backing plate was added behind the aluminum test specimen, providing out-of-plane compression. Three types of tests were conducted: 1) unbacked, 2) backed test with thin copper plate and 3) backed test with thick copper plate. These tests were designed to ensure that the stress triaxiality ranged from -2/3 to 0.113 while maintaining a near constant Lode parameter of -1. Tests conducted for backed experiments included both monotonic tests to failure and sequential loading-unloading tests to analyze strain evolution and failure morphology. Fracture strains for the backed experiments were determined to be substantially higher than those from unbacked (biaxial tension only) tests.
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