DUCTILE FRACTURE OF SS-304L MICROTUBE UNDER COMBINED AXIAL FORCE AND INTERNAL PRESSURE
The fracture behavior of the stainless-steel SS-304L is assessed by loading microtubes of 2.38 mm diameter under combined axial force and internal pressure, using a custom apparatus. The force/pressure ratio is controlled in the experiments, to generate different biaxial stress paths that are proportional or nearly proportional. The results from the experiments are used to calibrate the non-quadratic anisotropic yield function Yld2004-3D. Then, finite element (FE) models of the microtubes are created after incorporating the anisotropic material modeling framework, and compared with the experiments to establish their fidelity. The FE models are then used to probe the fracture behavior under the proportional loading. The failure modes of the microtubes are different depending on the stress state being axial- or hoop-stress-dominant. It is found that the structural instabilities that precede necking are different and appear at different levels of strain. The strains at the onset of fracture, as determined by probing the FE model, reveal significant fracture anisotropy, that can be possibly also attributed to the specimen geometry, beyond the material processing.