Design of non-conventional biaxial tensile-shear tests for the structural characterization and ductile damage assessment of ductile engineering materials

Abstract

The paper focuses on the development and optimization of a non-conventional specimen geometry for mechanical testing of ductile materials under shear-tension loading conditions. This is of major importance, being well known from literature works, that material final failure is strongly dependent on the stress state and that the information about the material ultimate resistance is crucial in virtually any kind of machine design related safety assessment. More in detail, in this study an effective way to load the samples with a combination of shear and tension is devised, selecting and optimizing a proper specimen geometry and designing the related gripping system. The goal is to obtain stress states in test runs different as much as possible one with the other, with specimens easy to be machined, and using just a standard universal testing machine. This would make the biaxial tests available to a broad group of end users, even industrial.The state of the art of specimens for biaxial tests available in literature was used as starting point to design a novel simplified geometry and the dedicated gripping system. Numerical simulations of the prospective biaxial experiments were performed, ranging from pure shear to pure tension, to optimize the new geometry, improve its effectiveness and evaluate the material stress states and strain to fracture at the critical points that can be obtained from the tests. This local information proved to be sufficient to calibrate different damage models using the single proposed test, with proper combinations of shear to tension loads.