13th International Conference on the Technology of Plasticity (ICTP 2021): Characterization of Plasticity and Ductile Fracture of Metals under Proportional and Non-proportional Loading IV
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
Thursday 10:20 AM
July 29, 2021
Room: Virtual: Room A
Location: Virtual
Session Chair: Junying Min, Tongji University
Strength Prediction Model for Line Pipe Steels Subject to Multiple Deformation Paths: Hongjin Choi1; Soo-Chang Kang2; Jinwoo Lee3; Myoung-Gyu Lee1; 1Seoul National University; 2POSCO; 3KIMS
Manufacturing a line pipe includes complex forming steps: decoiling, leveling, and roll forming. The mechanical properties of final formed pipe are evaluated from samples taken out of the pipe, which needs additional bending deformations for standard tensile tests. In this process, materials are subject to complex deformation paths, represented by cyclic bending superimposed with tensile deformation. The material under loading path changes exhibits anisotropic hardening like Bauschinger effect and transient response, and what’s more they are orientation dependent. Therefore, understanding the evolution of mechanical properties of pipe steels during the forming process is important to design coil strength targeting the final pipe strength. In this study, a distortional anisotropic hardening model, which captures the Bauschinger and cross-hardening/softening effects, is applied to predict the mechanical responses under multiple deformation paths. Specifically, identification of model parameters, finite element modeling, and quantitative validations by predicting proof strength after pipe forming are presented.
Experimental Implementation of SS 316L Cruciform Testing to Achieve Various Deformation Paths: Elizabeth Mamros1; Sarah Mayer1; Jinjin Ha1; Brad Kinsey1; 1University of New Hampshire
By following varying deformation paths, e.g., a linear path to a final equibiaxial strain value versus bilinear deformation with uniaxial loading followed by nonequal biaxial loading, the same final strain state can be achieved. However, the stress state that the material is subjected to is considerably different due to the varying deformation. This is of interest in a growing field of stress superposition to improve formability and final part properties in metal forming applications. For example, this work may be applicable to forming patient-specific, trauma fixation hardware with differing strength and weight reduction requirements in various regions. In this paper, equibiaxial experimental tests were performed on a custom fabricated cruciform machine with the goal of investigating martensitic phase transformations in stainless steel 316L subjected to varying deformation paths. A novel cruciform specimen geometry was designed in collaboration with the National Institute of Standards and Technology to achieve large strain values in the gauge region to promote martensitic transformations. Digital Image Correlation was utilized to measure surface strains in-situ. A scanning electron microscope was used to measure the amount of martensitic transformation in the samples.
Plasticity and Ductile Fracture of Ultra-high Strength Steel Sheets under Complex Stress State: Experiments and Modeling: Fei Han1; 1Baosteel
As one of the means of light-weight, more and more ultra-high strength steel has been applied to car body. The plasticity, damage and fracture behavior of UHSS under complex stress state is the key to accurate simulation of forming process and crash. The newly developed high elongation QP steel and press-hardening steel of Baosteel were tested under different loading conditions, including shear, uniaxial tension, plane strain tension and biaxial tension. With the help of digital image correlation technology, the development of plastic strain under various stress states was analyzed. Based on the testing results and numerical simulation, the parameters of plasticity and fracture model of UHSS were obtained. The validity of the model was verified by comparing the stamping and crash test results of component made by QP and PHS steel. The research results will provide guidance for parts design and structural design in the application of UHSS.
Design of a New Cruciform-like Specimen for Combined Tension and Shear of Metal Sheets: Minki Kim1; Jinjin Ha1; Yannis Korkolis1; 1The Ohio State University
This paper is concerned with design of a new cruciform-like specimen to measure plastic flow under combined tension and shear loading conditions for AA6013-T4 aluminum sheet. The specimen design borrows from the “smiley face”, which is commonly used for the simple shear experiment, but has four arms, as a cruciform specimen: two arms are used to induce shearing, while the other two induce tension. The details of the geometry are optimized by FEA to promote deformation uniformity in the cross section. Experiments are performed using an in-plane biaxial testing machine, with 5 different force ratios between tension and shear, so that combined stress states in (σ11, σ22, σ12) 3D-stress space are probed. Based on the results, the Yld2000-2D anisotropic yield function is calibrated by least-square optimization, and the influence of shear stress on the yield function parameter calibration is evaluated by comparing yield surfaces identified by different calibration approaches.
Stress-based Ductile Fracture Criterion for Nonlinear Strain Paths with Model Calibration: Jeong Whan Yoon1; 1KAIST
A shear specimen is optimized by minimizing the variation of stress triaxiality in the shear zone. In the optimization, Hill48 and Yld2000-2d (Barlat et al., 2003) criteria and Hill48 with non-associated flow rule are employed to model the anisotropic deformation. Isotropic fracture behavior is modeled by both linear model and nonlinear model considering different triaxiality conditions. It is observed that the mean stress model shows significant difference in the compression area compared to Mohr Coulomb-based normal stress model and a new isotropic model with the mean stress term shows a good correlation for AA 6k21. The criterion is applied for drawing, redrawing and expansion for a beverage can which has complex nonlinear strain paths. Effect of kinematic hardening on fracture is also investigated. It has been shown that the proposed stress-based fracture model predicts the failure stroke accurately.