Many experiments indicated the remarkable dependence of the strength and failure behavior of anisotropic ductile metals on the loading direction and on the stress state. These influences have to be taken into account in accurate material models and in the numerical simulation of complex loading processes predicting the safety and lifetime of aerospace structures. Therefore, the present paper discusses the effect of loading direction and stress state on the damage and failure behavior of the anisotropic aluminum alloy EN AW-2017A. Experiments and corresponding numerical analysis with the newly developed, biaxially loaded X0 specimen have been performed and the influence of different load ratios is examined. The formation of strain fields in critical parts of the X0 specimen is monitored by digital image correlation. Different failure modes are visualized by scanning electron microscopy of fracture surfaces. Stress states are predicted by finite element calculations and they are used to explain damage and fracture processes at the micro-level. The experimental–numerical analysis shows that the loading direction and the stress state remarkably affect the evolution of the width and orientation of localized strain fields as well as the formation of damage processes and fracture modes. As a consequence, characterization of anisotropic metals is highly recommended to be based on an enhanced experimental program with biaxial tests including different load ratios and loading directions.

The damage and failure behavior of anisotropic ductile metals depends on the material direction and on the stress state. Consequently, these effects have to be taken into account in material modeling and the corresponding numerical simulation, and also have to be experimentally investigated in a controlled and well-reproducible manner. In this context, the present paper focused on new biaxial experiments with the anisotropic aluminum alloy EN AW-2017A. Experiments with the newly developed, biaxially loaded H-specimen were performed with a focus on shear and shear-compression stress states. The formation of strain fields in critical parts of the H-specimen was monitored by digital image correlation, and fracture surfaces were visualized by scanning electron microscopy. Stress states were predicted by corresponding numerical simulations and they facilitated the comprehension of the damage and fracture processes at the micro level. The experiments with shear-compression stress states were realized with a special down-holder to avoid buckling, which enabled a well-controlled study in this generally difficult-to-access range. Furthermore, the anisotropic characterization of ductile sheet metals can be realized by an enhanced experimental program with a wide range of load ratios and loading directions.

The paper analyzes the damage and failure behavior of anisotropic ductile sheet metals through a combined approach of experimental and numerical analyses. An anisotropic continuum damage model considering the effect of plastic anisotropy on evolution of anisotropic ductile damage is presented. The Hoffman yield criterion is used to account for the strength-differential effect. Additionally, generalized anisotropic stress invariants are introduced to characterize the stress state of the anisotropic ductile metal. Experiments utilizing biaxial specimens under different stress triaxialities and loading directions are performed. Digital image correlation technique is used to determine the local strain fields in the critical regions of the specimens. Similarly, the fractured surfaces are examined with the help of scanning electron microscopy. Furthermore, numerical analysis on the microscale has been carried out to transfer microstructural details to the macroscale, capturing aspects such as micro-defects, matrix properties, and their evolution. The experimental and numerical results are then compared to understand various damage mechanisms and the role of plastic anisotropy in the damage and fracture behavior of anisotropic ductile metals.

It is experimentally observed that the failure in ductile metals is mainly due to the nucleation, growth, and coalescence of micro‐voids as well as micro‐shear‐cracks. Furthermore, plastic anisotropy has significant role in damage and failure behavior of ductile metals. Finite element simulations of unit cell provide a basis to understand different mechanisms on micro‐scale, for example, changes in shape and size of single voids and defects as well as localization of plastic strains. This contribution deals with the numerical analysis of unit cell containing spherical void subjected to symmetrical boundary conditions taking material anisotropy into account. Elastic isotropic behavior is described by Hooke's law while Hoffman yield criterion considering the strength‐differential effect is used to model the anisotropic plastic behavior. Generalized anisotropic stress invariants, generalized stress triaxiality, and generalized Lode parameter are introduced to characterize the stress state in the anisotropic ductile metal. The effect of plastic anisotropy on the damage behavior of the aluminum alloy EN AW‐2017A is studied in detail by performing a series of numerical simulations covering a wide range of stress triaxialites and Lode parameters. Stress triaxility and Lode parameter are controlled and kept constant during the entire loading process. The numerical results are then used to discuss general mechanisms of damage and failure process in ductile metals.