New biaxial experiments for metallic flat specimens to develop damage and failure models

Prof. Michael Brünig, Professor of Structural Mechanics, has successfully acquired the project "Neue zweiaxiale Experimente für metallische Flachproben zur Entwicklung von Schädigungs- und Versagensmodellen" (New biaxial experiments for metallic flat specimens for the development of damage and failure models) at the DFG.

Duration: 2016 - 2021
Sponsor: DFG research grant

Current developments in lightweight construction place very high demands on the materials used. In the case of lightweight construction materials that are subject to multidimensional stresses in particular, detailed knowledge of their properties must be available in order to be able to make a reliable prediction of the safety of components. For this purpose, biaxial experiments with newly developed specimens and corresponding numerical simulations were carried out in order to gain detailed insights into the damage and failure mechanisms of ductile metals. Based on the results obtained, a damage and failure model was further developed that can be used for a wide range of stress states. It is known from experimental observations that in the case of tension-dominated loads, the damage is primarily caused by the growth of pores and their amalgamation, while in the case of shear and compression-dominated loads, the damage is primarily caused by microshear cracks. It is therefore extremely important to be able to understand and analyze the entire damage process in the material used up to the point of ultimate failure in order to develop a realistic, accurate and efficient numerical simulation model. To analyze the damage and failure processes that depend on the stress state, new experiments were developed in which the cross-shaped specimens can be loaded in two directions with different load ratios. In order to create the desired stress states, special geometries had to be designed in the central sample area. For this purpose, three different specimens (Z, X0 and H specimen) were selected, with which a wide range of stress states in critical specimen areas, in which damage and failure are expected, could be covered by varying the load conditions. At the same time, a continuum damage model was further developed, whereby in particular the functions that depend on the stress state and describe the damage could be determined. This made it possible to numerically simulate the behavior of the test specimens observed in the experiments. Using the numerically obtained data, a crack criterion based on critical damage variables could be developed, which allows the failure of components to be predicted. During the processing of the two funding periods of the project, the efficient interaction of experiments and numerical simulations became clear, which enables a comprehensive analysis of the deformation, damage and failure behavior of materials and components.