Material Behavior Characterization via Multi-Directional Deformation of Sheet Metal: Session III
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Daniel Coughlin, United States Steel Corp; Kester Clarke, Los Alamos National Laboratory; Piyush Upadhyay, Pacific Northwest National Laboratory; John Carsley, Novelis, Inc.
Tuesday 8:30 AM
February 25, 2020
Room: Theater A-1
Location: San Diego Convention Ctr
Session Chair: John Carsley, Novelis, Inc.
8:30 AM Invited
Modeling Anisotropic Plasticity Under Complex Loading Conditions: Effects of Loading Path Changes on Flow Stress, Springback and Formability of Sheet Metals: Myoung-Gyu Lee1; Hongjin Choi1; Jinwoo Lee2; Hyuk Jong Bong2; 1Seoul National University; 2Korea Institute of Materials Science
Sheet metals often exhibit complex mechanical responses, which include anisotropy, path dependent flow stress, and strength differential. For example, advanced high strength steels (AHSS) show significant anisotropic hardening under load reversals, and Mg alloys present strong strength differentials between tension and compression. Therefore, accurate constitutive models and numerical technique are required to improve the fidelity of forming simulations employed during process designs. In this presentation, recent efforts on developing new distortional plasticity based anisotropic hardening models and identifying their model parameters are introduced. The constitutive models predict the flow stress evolutions under different loading histories such as Bauschinger effect and stress overshooting under load reversal and cross loading, respectively, and the strength differentials in Mg alloys under tension and compression. For validations, predicted springback of AHSS and Mg alloy sheets, and flow stresses after multi-stage loading of rather thick steel sheets are compared with corresponding experimental data.
9:10 AM Invited
Modeling of Hole-expansion of Prestrained Sheets
Using Distortional Hardening: Yannis Korkolis1; Jinjin Ha1; 1Ohio State University
The hole-expansion of AA6022-T4 is investigated with respect to prestraining effect, and is simulated by the Yld2000-2D yield function combined with the HAH distortional hardening model. The experiment is performed in two steps: first, 8% of uniaxial prestraining is accomplished; then, hole-expansion is conducted by a flat-headed punch. Digital image correlation (DIC) provides the in-plane strain contours throughout the loading. The anisotropy of the material is clearly visible in these contours, which are non-axisymmetric. For the case of non-prestrained sheets, the strain evolution can be captured very accurately by isotropic hardening and the Yld2000-2D yield function. For the case of prestrained sheets, it is experimentally observed that the location of failure shifts from ~45o to RD. It is shown that the current version of the HAH model is deficient in capturing the evolution of the thickness contours, and in predicting the shift in the location of failure.
9:50 AM
Effects of Y Concentration on Mechanical Response of Mg-Y Alloys: Xin Wang1; Jiaxiang Wang2; Kehang Yu1; Timothy Rupert1; Subhash Mahajan3; Enrique Lavernia1; Irene Beyerlein2; Julie Schoenung1; 1University of California Irvine; 2University of California, Santa Barbara; 3University of California, Davis
The addition of rare earth elements has led to promising enhancement of the room temperature ductility of Mg. Further improvements in the mechanical properties of Mg alloys, however, will require a fundamental understanding of the effects of alloying elements on deformation mechanisms. The mechanical behavior of four basal-textured Mg-Y sheet alloys, with compositions of Mg-0.2Y, Mg-0.6Y, Mg-1Y and Mg-3Y (wt%), was studied in both tension and compression along the rolling direction, and in compression along the normal direction. The multi-directional deformation stress-strain curves and texture evolution were correctly reproduced by Visco-Plastic Self-Consistent (VPSC) modeling by incorporating twin-affected dislocation trapping rates. The combination of experiments and modeling yields a more comprehensive understanding of the effects of Y concentration on the activities of slip and twinning modes, which were further validated by transmission electron microscopy (TEM).
10:10 AM Break
10:30 AM
A New Yield Criterion Accounting for Anisotropy and Anisotropic Asymmetry from Near Isotropy to Triclincity: Zachary Brunson1; Aaron Stebner1; 1Colorado School of Mines
With the ever-increasing drive for light-weighting structures in every industry from aerospace and automotive to wind and solar power, structural materials with anisotropic and asymmetric behavior are becoming more popular, including heavily textured materials such as sheet metal. Since an accurate and efficient description of the elastic limit is necessary to describe both the deformation during manufacturing and the final component strength, we propose two new yield criteria for anisotropic and anisotropically asymmetric solids. Extending the 2006 and 2008 orthotropic yield criteria of Cazacu, Plunkett, and Barlat to allow for anisotropy in both the strengths and strength differential effects (asymmetry) allows for modelling of asymmetry in shear, a reduction in the number of coefficients, and applications to lower symmetry materials (i.e. triclinic). This presentation explores the world of anisotropic and asymmetric yield criteria, introducing two new yield criteria with non-isotropic asymmetry and providing experimental case studies for various applications.
10:50 AM
Microstructure Control for Enhanced Multi-step Formability: Menglei Jiang1; Cemal Cem Tasan1; 1Massachusetts Institute of Technology
In metallic materials, deformation history can be erased by carrying out thermal treatments, through recovery, recrystallization, or phase transformation processes. The ductility of a strain-hardened metal can thus be regained, even after severe deformation processes. In principle, such treatments can be employed to improve the forming or stamping limits of sheet metal. However, resulting increases in processing costs and the material behavior uncertainty, reduce the use of thermal treatments, even in multi-step forming operations. Here, we present a study of the behavior of metallic material during interrupted forming and annealing processes. Combining electron microscopy based microstructure mapping, digital image correlation based strain mapping, and finite element modeling, we discuss potential materials design strategies, that would maximize the multi-step formability of sheet metal.
11:10 AM
Production of Commercially Pure Aluminum Strips via a Single-Step, Machining-based Technique: Mohammed Naziru Issahaq1; Kevin Trumble1; Srinivasan Chandrasekar1; 1Purdue University
Commercially pure aluminum sheets and strips are conventionally produced through cold rolling. This process is a multi-step deformation technique that imposes relatively low incremental plastic strains on the strips. This work explores an alternative technique that imposes high strains in a single-step, machining-based deformation to produce the sheets and strips. However, the commercially pure aluminum alloys have high ductility in the as-cast or annealed (O-temper) condition, and often exhibit “gummy” behavior during machining. The ductile flow mode of these alloys renders the production of extremely thicker strips with uneven free surfaces. By varying the rake angle and cutting speeds, a process map will be demonstrated to enhance the selection of appropriate cutting conditions necessary to produce strips with improved surface finish comparable to the conventional cold rolling processes. The microstructure and texture are also shown to be distinctly different from strips produced by conventional cold rolling.