13th International Conference on the Technology of Plasticity (ICTP 2021): Rob Wagoner Honorary Symposium I
Program Organizers: Glenn Daehn, Ohio State University; Libby Culley, The Ohio State University; Anupam Vivek, Ohio State University; Jian Cao, Northwestern University; Brad Kinsey, University of New Hampshire; Erman Tekkaya, TU Dortmund; Yoshinori Yoshida, Gifu University
Tuesday 9:15 AM
July 27, 2021
Room: Virtual: Room A
Location: Virtual
Session Chair: Hojun Lim, Sandia National Laboratories
Forming Limit Results Comparing the Bragard Technique with a Statistical, Deformation-history Analysis: Michael Stout1; Javier Signorelli1; Analía Roatta1; 1Instituto de Física Rosario, CONICET, Universidad Nacional Rosario
We designed a laboratory scale, Marciniak and Kuczynski, testing device to record the deformation history from limit-strain experiments and used this equipment to test a commercially designated Zn20 sheet and a drawing-quality steel. Reference limit strains were calculated with the Bragard analysis, norm ISO 12004-2, and we compared these results to a time-history approach based on Pearson’s correlation coefficient. The Bragard analysis uses the deformations outside of the necking instability to calculate the strain limits, while the time-history approach studies the deformation history within the plastic instability. For the highly rate-sensitive Zn20 the Bragard standard is conservative for all strain states. For the moderately strain-rate sensitive steel, results from the two techniques were nearly identical in balanced-biaxial tension. However, the Bragard analysis is again conservative for plane-strain and uniaxial-tension deformations. Our results indicate that the Bragard and temporal analysis should be combined to obtain the optimal forming-limit diagram.
Cancelled
Constitutive Hardening Model Development for Materials with Evolving Microstructural Phase Constituents: Kavesary Raghavan1; Jun Hu1; Erik Pavlina1; Xiaohua Hu2; Jiahao Cheng2; Xin Sun2; 1AK Steel; 2Oak Ridge National Laboratory
Next generation advanced high strength steels and metastable austenitic stainless grades show considerable evolution in their microstructural phase constituents due to transformation of austenite into martensite during deformation. The austenite to martensite transformation depends on strain rate, temperature, deformation mode and intrinsic composition dependent austenite stability. In this study, we examine stress strain behavior at different strain rates (0.001/s – 1000/s) for representative advanced high strength third generation austenite containing Q&P steels and metastable austenitic stainless steels. Applicability of several constitutive hardening models, both phenomenological and based on transformation modeling, are explored to describe the experimental stress-strain data.
Investigating Plastic Anisotropy of Al7079 Using Crystal Plasticity Simulations: Hojun Lim1; Sharlotte Kramer1; Edmundo Corona1; Amanda Jones1; Benjamin Reedlunn1; Taejoon Park2; Farhang Pourboghrat2; 1Sandia National Laboratories; 2The Ohio State University
Processing techniques used to produce polycrystalline metal alloys often result in preferred crystal orientations with associated plastic anisotropy. While various anisotropic plasticity models are used to predict final shapes and prevent catastrophic failure, more predictive models require multiple mechanical tests at various orientations and stress states to fit many model parameters. In order to efficiently characterize and predict plastic anisotropy without extensive mechanical tests, crystal plasticity finite element method (CPFEM) simulations using initial microstructural data from EBSD and XRD measurements are performed and compared with experiments. Tensile tests of Al7079 at various directions are performed to obtain stress-strain response and r-values. It is shown that CPFEM model incorporating the texture and grain morphology of Al7079 captures anisotropic mechanical behavior and r-values reasonably well. In addition, various factors that may influence the accuracy of the anisotropy prediction are investigated.
Simulated Microstructure Effects on Macroscopic Mechanical Properties Based on Multiscale Crystal Plasticity: Yoshiteru Aoyagi1; Ryota Kobayashi1; David McDowell2; 1Tohoku University; 2Georgia Institute of Technology
Multiaxial stress state causes complex deformation in sheet metal forming. Sheet metals produced by severely rolling show mechanical anisotropy depending on the strong rolling texture. While crystal plasticity simulations considering actual microstructure information has attracted attention with developing of microscopic observation of metals using the electron backscattered diffraction pattern (EBSD) method. However, a uniaxial tensile test generally determines mechanical properties used for the crystal plasticity simulation by neglecting the mechanical anisotropy. In this study, crystal plasticity simulation on severely rolled metals is carried out to investigate the effects of microstructures of metals on mechanical properties. Yield surfaces are predicted by crystal plasticity analyses based on the microstructure observed using EBSD method and stress-strain curves obtained by uniaxial and biaxial tensile tests. Extreme value distributions of mechanical properties estimate the effects of the microstructures.
Relating Microstructure to Deformation in Al Alloys via Multiscale Electron Microscopy: Josh Kacher1; Yung Suk Jeremy Yoo1; 1Georgia Institute of Technology
Ductile fracture is an inherently multiscale processes, ranging from nanoscale crack nucleation mechanisms to collective dislocation interactions ranging across hundreds of microns. Understanding these processes requires multiscale characterization approaches that reflect the nature of the processes. A key factor in these multiscale approaches is the ability to quantify data in such a way that information can be passed between the length scales. In this talk, I will discuss the application of multiscale electron microscopy techniques to understanding fracture in Al 6xxx alloys under different loading conditions. Heat treatable Al alloys provide an especially interesting case study as they are composed of a range of secondary particles, including distributed intermetallic particles, dispersoids on the order of single microns, and precipitates, as well as heterogeneities inherent to polycrystalline materials. Results will be discussed in terms of ductile fracture processes and the general applicability of multiscale electron microscopy to understanding deformation and failure.
Descriptions of Several Cyclic Plasticity Phenomena Based on Y-U Model: Elastic-plastic Transition, Closure of Stress-strain Loop and Ratcheting: Fusahito Yoshida1; 1CEM Institute Corporation
For numerical simulation of springback, an accurate description of stress-strain response in the elastic-plastic transition region, specifically unloading process, is of vital importance. This paper describes its constitutive modeling based on the Yoshida-Uemori (Y-U) kinematic hardening law, along with the description of nonlinear unloading-reloading stress-strain behavior. For modeling of nonlinear unloading, it is treated as the nonlinear elasticity, which is directly associated with the plastic-strain dependent chord modulus. Cyclic plasticity modeling for the subsequent small-scale plastic region is discussed. Furthermore, the descriptions of closure of a cyclic stress-strain hysteresis loop and ratcheting are presented. For the above modeling, no additional material parameters are needed. The model was validated by comparing the numerical simulation of stress-strain responses with the corresponding experimental observations in advanced high-strength steel sheets.
Advancing the Accuracy of Computational Models for Double-sided Incremental Forming: Newell Moser1; Dohyun Leem2; Shuheng Liao2; Kornel Ehmann2; Jian Cao2; 1National Institute of Standards and Technology; 2Northwestern University
Double-Sided Incremental Forming (DSIF) is a rapid-prototyping manufacturing process for metal forming that, for low-volume production, is competitively energy-efficient. However, controlling DSIF for arbitrary designs with respect to accuracy and formability is an ongoing challenge. These challenges arise due to a lack of understanding (and control) of the underlying deformation mechanisms in DSIF. And so, there is a need for high-fidelity simulations of DSIF that unravel these underlying complexities. Moreover, DSIF pushes the limits of today’s finite element formulations due to true strains that approach one, finite rotations, nonlinear contact, and triaxial stress states that range across multiple length scales. To confidently develop a finite element model of DSIF, an extensive verification and validation process must be considered, which is the objective of this study. Differing finite element types, boundary conditions, and amounts of artificial acceleration are compared, and recommendations based on efficiency and accuracy are summarized.
New Generation Press Hardening Steels with Tensile Strength of 1.7-2.0GPa and Enhanced Bendability: Jianfeng Wang1; Qi Lu1; Xiaochuang Xiong1; Hongliang Yi1; 1General Motors China
Press hardened components are widely used in a vehicle's body structure to increase safety and reduce mass for improved fuel economy. The commercial steel grade is the boron-containing 22MnB5 with 0.22-0.24 in wt% carbon, which can achieve a tensile strength of 1.5GPa. As vehicle lightweighting increasingly becomes a design imperative for automotive industry, it is desired to utilize press hardened components with strength exceeding 1.5Gpa by increasing carbon to 0.30-0.35 in wt%. However, increased carbon content often reduces fracture resistance under bending. This paper investigates bendability of two new press hardening steels. The first steel, with a tensile strength of 2.0Gpa, is coated with aluminum silicon to avoid oxidation and scaling during the hot stamping process. The second steel, with a tensile strength of 1.7Gpa, does not have any pre-coating and yet it is oxidation resistant at hot stamping temperature. Mechanisms of achieving enhanced bendability are also discussed.
A Critical Review on the CPFEM Models Accounting for Gain Boundary Hardening Effect and Some Developments toward Simplification of the Wagoner Super-Dislocations (SD) Model: Yao Shen1; Ran Chen1; Guisen Liu1; 1Shanghai Jiao Tong University
Grain boundary hardening effect is an important but difficult topic in crystal plasticity finite element method (CPFEM). CPFEM Models accounting for grain boundary effect are critically reviewed from 3 aspects: 1) The key gradients in the model, 2) Comparison to the simple two-phase composite model, 3) Comparison to the "real or ideal" slip profile evolution. Based on these critical reviews, the Wagoner super-dislocations (SD) model for grain boundar hardening is developed with an emphasis on its simplification. Performance of the simplified model is evaluated.