“…This is consistent with the behaviour curves where softening occurs in the final part of the deformation. This phenomenon caused that the flow stress to be lower with respect to the quasi-static tests [18]. In the literature, constitutive models are typically based on isothermal flow curves.…”
is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. During forging and machining manufacturing processes, the material is subject to large strains at high strain rates which provoke local heating and microstructural changes. Modelling of these phenomena requires precise knowledge of the stress-strain constitutive equations for a large range of strains, strain rates and temperatures. An experimental study of the rheology of both hyper-and hypo-eutectoid steels (with different microstructures) over a temperature range from 20 1C to 1000 1C and with strain rates from 10 À2 to 10 5 s À1 has been undertaken. These tests were performed in compression on cylindrical specimens and in shear using hat-shaped specimens. Both a GLEEBLE 3500 thermomechanical testing machine and a Split-Hopkinson Pressure Bar apparatus were used. From these tests, three deformation domains have been identified as a function of the material behaviour and of the changes in the deformed microstructure. Each domain was characterized by its behaviour, including the competition between hardening and softening, strain rate sensitivity on the flow stress and the softening phenomenon (i.e. recrystallisation or recovery, etc.). Finally, based on thermodynamical considerations, the conditions of thermoplastic instability (i.e. shear bands, twinning, heterogeneities, etc.) and microstructural changes are highlighted using process maps of the dissipated power repartition.
“…This is consistent with the behaviour curves where softening occurs in the final part of the deformation. This phenomenon caused that the flow stress to be lower with respect to the quasi-static tests [18]. In the literature, constitutive models are typically based on isothermal flow curves.…”
is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. During forging and machining manufacturing processes, the material is subject to large strains at high strain rates which provoke local heating and microstructural changes. Modelling of these phenomena requires precise knowledge of the stress-strain constitutive equations for a large range of strains, strain rates and temperatures. An experimental study of the rheology of both hyper-and hypo-eutectoid steels (with different microstructures) over a temperature range from 20 1C to 1000 1C and with strain rates from 10 À2 to 10 5 s À1 has been undertaken. These tests were performed in compression on cylindrical specimens and in shear using hat-shaped specimens. Both a GLEEBLE 3500 thermomechanical testing machine and a Split-Hopkinson Pressure Bar apparatus were used. From these tests, three deformation domains have been identified as a function of the material behaviour and of the changes in the deformed microstructure. Each domain was characterized by its behaviour, including the competition between hardening and softening, strain rate sensitivity on the flow stress and the softening phenomenon (i.e. recrystallisation or recovery, etc.). Finally, based on thermodynamical considerations, the conditions of thermoplastic instability (i.e. shear bands, twinning, heterogeneities, etc.) and microstructural changes are highlighted using process maps of the dissipated power repartition.
“…This was e.g. pointed out by El-Magd [15], who used the evolution of the stress triaxiality from the central element to establish the failure locus. A similar approach is used in the present paper.…”
Abstract. The overall goal of this work-in-progress is to try to establish the fracture locus (i.e. the equivalent strain to fracture as a function of the stress triaxiality factor) for the high-strength AA7075-T651 aluminium alloy. Experiments on several specimen geometries enabled us to reach stress triaxialities in the range from ı* = 0 for shear tests to ı* = 1.4 for notched specimen tensile tests. For shear tests, failure occurred by strong strain localization. However, local stresses and strains can not be deduced directly from these tests. Consequently, Digital Image Correlation (DIC) was used to extract the local strain fields to failure. In parallel, numerical simulations of the tests were run using the non-linear finite element code LS-DYNA to extract the evolution of the local stress triaxiality during straining. Based on a combination of both experimental and numerical data, the failure locus of the material can be constructed.
“…This was confirmed by taking two values of friction as 0.0 and 0.05 but no considerable difference was noticed in the simulation results.Projectile is modeled with hexahedral meshing. The behavior of the target plate is simulated using Johnson-Cook model [15][16][17][18] and the material constants. Numerical simulations are performed using fine mesh of different mesh sizes for the target plate.…”
Section: Problem Description and Model Validationmentioning
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