Machine-learning based temperature- and rate-dependent plasticity model: Application to analysis of fracture experiments on DP steel

A non-quadratic pressure-sensitive constitutive model under non-associated flow rule with anisotropic hardening: Modeling and validation

Anisotropic fracture of advanced high strength steel sheets: Experiment and theory

Optimising the strength-ductility-toughness combination in ultra-high strength quenching and partitioning steels by tailoring martensite matrix and retained austenite

A basic ductile fracture testing program is carried out on specimens extracted from TRIP780 steel sheets including tensile specimens with a central hole and circular notches. In addition, equi-biaxial punch tests are performed. The surface strain fields are measured using two- and three-dimensional digital image correlation. Due to the localization of plastic deformation during the testing of the tensile specimens, finite element simulations are performed of each test to obtain the stress and strain histories at the material point where fracture initiates. Error estimates are made based on the differences between the predicted and measured local strains. The results from the testing of tensile specimens with a central hole as well as from punch tests show that equivalent strains of more than 0.8 can be achieved at approximately constant stress triaxialities to fracture of about 0.3 and 0.66, respectively. The error analysis demonstrates that both the equivalent plastic strain and the stress triaxiality are very sensitive to uncertainties in the experimental measurements and the numerical model assumptions. The results from computations with very fine solid element meshes agree well with the experiments when the strain hardening is identified from experiments up to very large strains.

Hybrid experimental–numerical analysis of basic ductile fracture experiments for sheet metals

Anisotropic fracture modeling of sheet metals: From in-plane to out-of-plane

The quenching and partitioning (QP) steels have received much attention due to its high strength and good ductility, which results from deformation induced martensitic transformation (DIMT). However, due to the stress state, temperature and strain rate dependent DIMT behavior, the DIMT related flow behavior of QP steels might be more complex than other advanced high strength steels (AHSS) without martensitic transformation. During forming process of such materials (non-linear loading process), effects of DIMT behavior and DIMT related flow behavior on springback prediction are still unknown. In this paper, we focused on the martensitic transformation behavior of QP steels under complex loading (linear loading and cyclic loading). The X-ray diffraction and digital image correlation techniques were performed to monitor the retained austenite evolution and strain history of the specimen, respectively. Then, flow behaviors of QP sheets steels subjected to complex loading are analyzed and compared with DP980 sheets steels (without DIMT). Finally, modified Yoshida and Uemori model calibrated by two different cyclic loading tests, i.e., tension-compression test and cyclic shear test, are adopted in this study to investigate the stress state dependent DIMT effect on springback prediction. The results show, for QP steels, the DIMT is stress state dependent. Accordingly, compared with DP steels, its flow behavior exhibits remarkable stress state sensitivity. Due to these special DIMT behavior and flow behavior of QP steels, its springback prediction should be treated differently compared with DP steels.

The deformation induced martensitic transformation and mechanical behavior of quenching and partitioning steels under complex loading process

Cyclic Sheet Metal Test Comparison and Parameter Calibration for Springback Prediction of Dual-Phase Steel Sheets

The necking behavior of sheet metals under stretch-bending process is a challenge for the forming limit prediction. State-of-the-art forming limit curves (FLCs) allow the prediction under the in-plane stretching but fall short in the case under out-of-plane loading condition. To account for the bending and straightening deformation when sheet metal enters a die cavity or slide along a radius, anisotropic hardening model is essential to reflect the nonproportional loading effect on stress evolution. This paper aims to revisit the M-K analysis under the stretch-bending condition and extend it to accommodate both distortionless and distortional anisotropic hardening behavior. Furthermore, hardening models are calibrated based on the same material response. Then the detailed comparison is proposed for providing better insight into the numerical prediction and necking behavior. Finally, the evolution of the yield surface and stress transition states is examined. It is found that the forming limit prediction under stretch-bending condition through the M-K analysis strongly depends on the employed anisotropic hardening model.

Bin Gu

Papers

Anisotropic fracture of advanced high strength steel sheets: Experiment and theory

Anisotropic fracture modeling of sheet metals: From in-plane to out-of-plane

The deformation induced martensitic transformation and mechanical behavior of quenching and partitioning steels under complex loading process

Cyclic Sheet Metal Test Comparison and Parameter Calibration for Springback Prediction of Dual-Phase Steel Sheets

Forming Limits Under Stretch-Bending Through Distortionless and Distortional Anisotropic Hardening