13th International Conference on the Technology of Plasticity (ICTP 2021): Characterization of Plasticity and Ductile Fracture of Metals under Proportional and Non-proportional Loading II
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 10:20 AM
July 27, 2021
Room: Virtual: Room D
Location: Virtual
Session Chair: Fusahito Yoshida, CEM Institute Corporation
Work Hardening and Fracture Strain Measurement of Hardened SKD11 Steel Using Shear Punching Test: Takashi Matsuno1; Kouta Nakagiri1; Hiroto Shouji2; Mitsuru Ohata2; 1Tottori University; 2Osaka University
This study identified the work-hardening parameters and fracture strain of a hardened die-steel (SKD11). Due to the brittle behavior of SKD11 in tensile tests, a shear punching test was used as the low stress-triaxiality suppresses material fracture. Furthermore, a minute punch-die clearance was used to increase the compression stress due to material deformation. SKD11 steel sheets of 1.0 mm thickness were successfully deformed, and the punching force and stroke were recorded for inverse analysis using the finite element analysis (FEA). Subsequently, FEA of the shear punching test was repeated to optimize the parameters of Swift’s work-hardening law. Consequently, the Swift parameters were derived to ensure that the measured values of the punching force and stroke correspond with the numerically simulated curve. The fracture strain was identified as the maximum equivalent plastic strain at the punch stroke of specimen rupture.
Anisotropic Plasticity and Ductile Fracture of Titanium Alloy Sheet at Elevated Temperature: Characterization and Modeling: Heng Li1; Heng Yang1; 1Northwestern Polytechnical University
Heat assistant approach is promising to promote the formability of hard-to-form materials such as titanium alloy sheets. However, under thermal-mechanical coupling effects, the non-uniform deformation related anisotropic plasticity, damage and fracture of the material may be complicated and urgently need to be fully understood and accurately described. Thus, the experiments along different loading directions under various temperatures are conducted, and a yield-fracture locus in the stress plane is attempted to be plotted, revealing the distinct anisotropic yield and fracture evolution of the alloy during various thermal-mechanical loading conditions. Then, considering the effects of temperature on anisotropy plasticity and damage, a heat related discontinuous plasticity-fracture model is established and numerically implemented into FE simulation to smoothly present the evolution of plasticity and fracture behaviors. The comparison between the experimental results and numerical ones verifies the proposed model for describing the anisotropy in plasticity and ductile fracture under various thermal-mechanical loading conditions.
Effect of Anisotropy Evolution on Several Sheet Metal Forming Processes: Fusahito Yoshida1; 1CEM Institute Corporation
Most of sheet-metal forming simulations assume that the anisotropy of a sheet is fixed constant throughout the forming process. However, some materials show apparent anisotropy evolution with increasing plastic deformation. This paper presents a framework of description of anisotropy evolution, where an anisotropic yield function, which varies continuously varies with plastic strain, is defined as an interpolation between two yield functions at two discrete levels of plastic strain. The effect of anisotropy evolution was examined for several types of sheet metal forming processes, such as hydraulic bulging, conical-cup drawing, and cruciform-shaped drawing, by performing these experiments on a mild steel and type-5000 aluminum sheets together with the corresponding finite element (FE) simulations. From the comparison of FE simulations with the experimental results, it was concluded that the description of anisotropy evolution is essential for accurate simulation.
New Methods for Fracture Detection of Automotive Steels: Jacqueline Noder1; Clifford Butcher1; 1University of Waterloo
The VDA 238-100 tight-radius bend test has received significant attention from industry over the past decade because it provides a proportional plane strain – plane stress state until fracture. It will be demonstrated that the adoption of the vertical punch force as the unique metric for failure detection can lead to false positives. The punch force will reduce at large bend angles due to the mechanics of the test even in the absence of material failure. Two novel detection methods based on the nominal principal stress and the plastic work were evaluated on six different steel grades with a nominal ultimate tensile strength of approximately 590 MPa. For performance ranking of materials with the same strength level, the plastic work metric is found to be sufficiently sensitive to distinguish between various 590 MPa steel grades since the material hardening rate is directly embedded.