Researchers from China University of Petroleum-Beijing assessed the fracture behavior of anisotropic sheet metal under various stress states
Rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform. Ductile fracture of metallic materials involves void nucleation and void growth to coalescence. Therefore, anisotropic ductile fracture behavior is an important challenge in the forming of aluminum alloy plates. Although anisotropic ductile fracture behavior has been studied in several papers, the impact of stress states and plasticity anisotropy on ductile fracture is less understood.
Now, a team of researchers from China University of Petroleum-Beijing used coupling Hill48’s criterion to develop a novel damage model to assess the fracture behavior of anisotropic sheet metal under various stress states at the 0°, 45°, and 90° directions. Hill48’s criterion is a yield criteria for anisotropic plastic deformations developed by Rodney Hill an applied mathematician. The team also established0 the finite element method (FEM) analysis models. A hybrid experimental–numerical approach was used to focus the impact of the stress state and plasticity anisotropy on the ductile fracture behavior of 7050-T7451 aluminum alloy plate. To calibrate damage models, the team also assessed the force–displacement responses and predictive ability of the damage model established for anisotropic materials. To assess the impact of various stress states and plasticity anisotropy on the fracture process, the team analyzed the damage and strain evolutions.
The team found that diffuse and localized necking types have significant impact on the fracture processes at the 0°, 45°, and 90° directions. Diffuse necking governs most significantly at the 45° direction and in case of 0° and 90° directions, localized necking held dominance. Decrease in the stress concentration leads to reduction in the impact of the two necking types. In the fracture process, stress triaxiality plays a vital role but not a dominant role for notched tension specimens. However, stress triaxiality plays a major role for flat-grooved tension specimens. The impact of plasticity anisotropy leads to some variations in stress triaxiality and damage in the center. The research was published in the journal MDPI Metals on May 23, 2019.