Material Behavior Characterization via Multi-Directional Deformation of Sheet Metal: Session II
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.
Monday 2:30 PM
February 24, 2020
Room: Theater A-1
Location: San Diego Convention Ctr
Session Chair: Kester Clarke, Los Alamos National Laboratory
2:30 PM Invited
Evolution of Local Formability Concepts for Advanced High Strength Steels (AHSS): Brandon Hance1; 1U. S. Steel
Over the past five years, awareness of local formability has increased dramatically as advanced high strength steels (AHSS) gain prominence in automotive body-in-white applications. In this presentation local formability and global formability are defined, and the established and emerging measures of each are illustrated. The foundational and progressive development of a formability classification and rating system for AHSS is reviewed. With various case study examples, concepts such as the Local/Global Formability Map, the Formability Index and the Edge Thinning Limit are highlighted. Furthermore AHSS performance levels (i.e. GEN1, GEN1+ and GEN3) are re-defined in the context of a newly-developed AHSS Performance Index, where strength, global formability and now, local formability, are included. Finally performance targets for future AHSS grade development are proposed, and the possible extension of intrinsic local formability concepts to automotive crashworthiness are discussed.
3:10 PM Invited
Industry Perspective on the Mechanical Characterization of Next Generation Steels: Erik Pavlina1; Jun Hu1; Kavesary Raghavan1; 1AK Steel
Next generation sheet steels are multi-phase materials that often contain a metastable phase or constituent that transforms as a result of deformation. Such transformation is influenced by material factors and external conditions (for example, deformation rate or deformation mode), and this transformation should be considered when developing and applying anisotropic hardening models. Additionally, OEMs are increasingly requesting mechanical property data beyond that obtained from quasi-static uniaxial tensile tests, such as high rate mechanical properties. This presentation addresses the issues of next generation materials characterization from the perspective of an industrial producer of sheet steels. Industrial successes and challenges in the area of advanced mechanical characterization are highlighted. Transformation kinetics, high strain rate testing, tension-compression testing, and fracture, among other topics, are discussed.
3:50 PM
An Investigation into Improved Elongation-to-fracture in AHSS via Continuous Bending Under Tension: Rishabh Sharma1; Camille Poulin2; Marko Knezevic2; Michael Miles1; David Fullwood1; 1Brigham Young University; 2University of New Hampshire
Continuous bending under tension (CBT) can achieve strains well above the uniaxial tension forming limit curve. In this study, optimal CBT processing conditions lead to an increase in elongation-to-failure of 4.3 and 3 times the uniaxial tension value, respectively, for quenched and partitioned and TRIP aided bainitic ferrite 1180 steels. A macro- and micro- scale investigation revealed several insights into the forming process. Digital image correlation was used to map strains on the surface of the sample, and a combination of electron backscatter diffraction (EBSD) and high-resolution EBSD was used to map microstructure evolution (including retained austenite transformation rate) and development of geometrically necessary dislocations in interrupted CBT samples. The retained ductility of the interrupted CBT samples was measured in uniaxial tension. The study indicates slower strain hardening than uniaxial tension while delaying plastic instability. The transformation rate of the RA is slower and evenly distributed across the entire deformation.
4:10 PM Break
4:35 PM
Development of a Lean Duplex TRIP Steel with a Superior Formability: Peijun Hou1; Yuan Li1; Jun-Sang Park2; Dongchul Chae3; Chanho Lee1; Yang Ren2; Ke An4; Hahn Choo1; 1University of Tennessee; 2Argonne National Laboratory; 3POSCO Technical Research Laboratory; 4Oak Ridge National Laboratory
Fundamental mechanisms responsible for the cracking phenomenon in advanced high strength steel alloys subjected to deep-drawing processes have been investigated using in-situ neutron diffraction and synchrotron x-ray diffraction. Despite high hardening rate and tensile ductility, the transformation-induced plasticity (TRIP) steels are susceptible to cracking mainly due to residual-stress concentration. In this study, a lean duplex TRIP steel with superior resistance to cracking has been developed by manipulating the residual-stress partitioning and plastic anisotropy. The evolutions of lattice strain, texture, and the martensitic transformation kinetics were studied to understand the constitutive behaviors of TRIP steel and lean duplex TRIP steel during uniaxial deformation. Subsequently, distributions of residual stresses and martensite phase fraction were mapped in deep-drawn steel cups. By investigating the effects of the martensitic transformation, duplex microstructure, and texture on the residual-stress partitioning and plastic anisotropy, their influences on the stress concentration and cracking behavior is elucidated.
4:55 PM
Experimental Studies into the Role of Cyclic Bending during Stretching of Dual-phase Steel Sheets: Marko Knezevic1; Camille Poulin1; 1University of New Hampshire
Continuous-bending-under-tension (CBT) has been conceived as a mechanical test or a forming process imparting cyclic bending during stretching of a metallic sheet or strip in order to increase its elongation to fracture (ETF) relative to simple tension (ST). This paper evaluates the behavior in CBT of four dual-phase (DP) automotive advanced high strength steels, DP 590, DP 780, DP 980, and DP 1180. In doing so, the process parameter space defined in terms of crosshead velocity applying the tensile force, and roller depth imposing the amount of bending to the specimen has been explored to maximize the ETF of these materials. The optimal parameters improve ETF of the materials over five times. Microstructural characterization of the materials revealed high integrity of the sheets deformed to large plastic strains under CBT due to a favorable distribution of deformation as opposed to localized flow followed by necking and fracture in ST.
5:15 PM
Damage Detection of Sheet Metal via Multi-directional Deformation: Brahmananda Pramanik1; John Becker1; Jared Schmidlin1; Wednesday Rehm1; 1Montana Tech
The accurate diagnosis of hidden damage within a sheet metal component (SMC) is the focus of the current research. Vibration test approach is ever challenging and needs serious attention. There is relatively less research on developing non-destructive structural-damage diagnosis technique by analyzing the vibrational mode shapes of the SMC at the operational frequency range. An engineering structure can be modeled as Multi-Degree-Of-Freedom (MDOF) vibration system which has a definite natural frequency corresponding to the degree of freedom. This research collected frequency data, damping parameters, and mode shape data of two typical 2D plates resembling an SMC; one was pristine and other was with known damage. The mode shapes of both plates were compared using an in-house developed MATLAB routine. The two-dimensional coordinate locations of the discrepancy on the mode shapes were considered to determine the location of the damage. Finally, the method was evaluated with a previously unknown damaged specimen.