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Description
The Portevin-Le Chatelier (PLC) effect is a propagative instability phenomenon appearing in metals, for example in steel and aluminum alloys at elevated and room temperature, respectively. It is characterized by serrations (repetitive changes from hardening to softening) visible in load-displacement diagrams and by traveling strain rate bands that can be observed in the sample. At the atomic level, dislocations are stopped by defects or solute atoms, causing their pile up with stresses going up. When a sufficient load is applied, the dislocations are freed and the stress drops. The cycle is then repeated and the phenomenon is called Dynamic Strain Aging (DSA). Lueders bands are another propagative instability phenomenon appearing in metals, characterized by a plastic front that moves through the sample right after yielding. The strains first localize in a shear band during a transient softening stage. At the edge of the shear band, a plastic front is formed and it then moves through the sample while a plateau is visible in the load-displacement diagram. When the plastic front reaches the end of the sample, hardening starts and the sample then exhibits uniform deformation.
Both the Lueders bands and PLC effect can be observed during a tensile test of aluminum alloy AW5083. Such tests have been performed on bone-shape samples for three strain rates at room temperature. After the initial elastic deformation, a small stress drop is visible, followed by a short plateau characteristic for Lueders bands, and saturation hardening with serrations indicating the PLC effect. On DIC images the elastic deformation followed by localization in a single band is first visible. Next, the plastic front is formed and moves. In the hardening process, when the PLC effect is activated, shear bands start to appear and disappear at different places in the sample.
A large strain thermo-visco-plastic Estrin-McCormick model, i.e. a phenomenological description of DSA, is used to simulate the behavior combining Lueders bands and the PLC effect. Different yield functions, both isotropic and anisotropic, are used in the formulation to determine the most suitable one. Computations are performed in AceGen and AceFEM packages for Wolfram Mathematica. The identification of the parameters of the model is part of future research.
ACKNOWLEDGMENT:
The work is supported within Weave-UNISONO call by the German Research Foundation (DFG grant 527828607) and by the National Science Centre, Poland \linebreak (NCN grant 2023/05/Y/ST8/00006).
