Anisotropic fracture behavior of the 3rd generation advanced high-strength - Quenching and Partitioning steels: Experiments and simulation

Advanced high-strength steels (AHSS) have revolutionized the automotive industry by reducing weight without compromising crashworthiness. The new third-generation steels, such as quenching and partitioning (QP) steels, offer exceptional strength and ductility. However, despite the extensive strength-ductility studies, there is a wide knowledge gap in the literature on the fracture behavior of QP steels under a large range of stress states and loading conditions for material forming operations. This study aims to systematically investigate the fracture behavior of QP1000 sheet metal through a combination of experimental and numerical approaches. In addition to the classic fracture dependency on stress states, we particularly focus on the anisotropic behavior in terms of both plasticity and fracture. Mechanical tests with digital image correlation are performed along three loading directions covering stress states from simple shear to plane-strain tension. The evolving non-associated Hill48 (enHill48) model is employed to describe anisotropic plasticity, while the fracture behavior is represented by a partially coupled anisotropic fracture model and a fully anisotropic fracture model. It is concluded that the investigated QP steel shows moderate anisotropic plasticity behavior yet strong fracture anisotropy, which intensifies with the increase of stress triaxiality. The partially coupled anisotropic fracture model, which has shown success for materials with minor anisotropic plasticity, fails to describe the anisotropic fracture and a fully anisotropic model provides significantly improved predictive capability.