Papers by Keyword: Flow Stress

Abstract: The localization of plastic deformation was examined for polycrystalline aluminum samples having grain sizes in the range from 8·10^-3to 10 mm. It is found that the length of localized deformation autowaves is determined by the grain size of material. The localized plastic flow patterns emergent in the polycrystalline aluminum samples are found to be connected to the Hall-Petch relation. Two types of flow stress dependencies of grain size are distinguished.

Abstract: Aluminum foams are porous metallic materials which possess an outstanding combination of physical and mechanical properties such as: a high rigidity with a very low density. In this present research work, a study on the upsetting of an aluminum foam (with a density = 0.73 g/cm³) is carried out by employing different compression velocity values. From the results obtained, it is possible to determine the material flow stress for its subsequent use in finite element simulations (FEM). Once the material flow stress has been determined, it will be employed in order to analyze the conformability of several parts by FEM.

Abstract: The stress-strain curves, mechanical behaviors, and Johnson-Cook model of 4Cr13 stainless steel were investigated at both the strain rates from 0.001s-1 to 7000s-1 and the temperatures from 293K to 673K based on the electronic universal testing machine and the split Hopkinson bar. The results showed that 4Cr13 stainless steel was very sensitive to the temperature and the strain rate. The temperature sensitivity factor decreased with increasing the temperature, and the strain rate sensitivity factor increased with increasing the strain rate. Both the temperature sensitivity factor and strain rate sensitivity factor decreased with increasing strain. The flow stress increased with strain rate and strain, but decreased with temperature. The J-C model prediction had a good agreement with the experimental stress-strain in the wide range of temperatures and strain rates. The Johnson-Cook model gave the foundation for finite element analysis during the cutting process.

Abstract: The hot deformation behavior of Mg-3.5Zn-0.6Y-0.5Zr alloy was investigated by compressive tests of strain rate ranges of 0.002~1 s^-1 and deformation temperature ranges of 300~450 °C using a Gleeble 1500D thermal simulator. The flow stresses in different deformation conditions are measured. The results show that flow stress is significantly affected by both deformation temperature and strain rate, the flow stress increases with increase in strain rate and decreases in deformation temperature during the hot compression process. The constitutive equation established on the basis of data of activation energy and stress exponent is a hyperbolic sine function.

Abstract: Cu-Ag alloy is using for Cu Cladding Al Contact Wire, it was formed by continuous extrusion. The flow stress behavior of Cu-Ag alloy for Cu cladding Al contact wire was studied by hot compression experiments using Gleeble-1500 hot simulation machine. The flow stress mathematical models of the Arrhenius relationship of the hyperbolic sine function are established including hot deformation activation energy, deformation temperature and strain rate. The results may be using in numerical simulation for forming.

Abstract: Use VDBF-250 vacuum hot pressing sintering furnace TiC10/Cu-Al₂O₃ composite was prepared by vacuum-pressed sintering. In the cold isotatic pressing machine for sintering state sample was cold isostatic pressing and detection performance. Using the Gleeble-1500D simulator, the high-temperature plastic deformation behavior of TiC10/Cu-Al₂O₃ composite was investigated at 450850°C with the strain rate of 0.0011s¹ and total strain of 0.7 the dynamic recrystallization behavior of the composite was studied. The results show that the density, microhardness and electrical conductivity of the composite are 98.53%, 161HV and 48.7%IACS. After the isostatic cool pressing, The comprehensive performance of the material were improved. The softening mechanism of the dynamic recrystallization is a feature of high-temperature flow stressstrain curves of the composites, and the peak stress increases with the decrease of deformation temperature or the increase of strain rate, and Belong to temperature and strain rate sensitive material.

Abstract: The hot compression tests on a Gleeble-1500D thermal mechanics simulator were carried out under the strain rate range of 1~ 0.005s-1 at the temperature range of 873-1373K in order to evaluate the constitutive equation of 5Cr21Mn9Ni4N valve steel. All of the flow stress curves exhibit a single peak stress, after which the stress is followed by a steady state regime. The results indicate that the deforming behavior is strongly depending on the strain rate and the deforming temperature. According the experimental data, the hyperbolic law is used to develop the constitutive equations. In the constitutive equations, the effect of the deforming temperature and the strain rate are represented by the Zener-Hollomam parameter. And the flow stress curves are coinciding with the constitutive equation of .

Abstract: Thanks to their properties, microalloyed steels have found numerous applications in virtually all branches of industry. Forging plants, which supply various forged parts for automotive industry, are under substantial pressure to cut costs and reduce production times. One of potential sources of savings is reducing the forging temperature. This step requires that the deformation behaviour of feedstock materials is mapped accurately. The C38ML material was chosen for the present experiment and tested in compression in a plastometer. Test temperatures ranged from 700 °C to 1100 °C at deformation rates between1 mm/s and 100 mm/s. Data from plastometer tests were converted into a model compatible with the DEFORM simulation software. The model was employed for optimising the forging process in terms of forming tool speeds. Another approach to finding this valuable information consists in using various simulation programmes. In the present experiment, measured deformation curves were compared with those obtained using the JMatPro software. Finally, reference forgings were made in a hydrostatic forging press in trials of the new manufacturing procedure and their properties were measured

Abstract: In the paper a flow stress model based on internal variables is shortly presented. The multiplicative model contains three parts. In the model, the normalized dislocation density ρ_m was considered, as a strain function only, independently to the strain rate and the temperature. Influence of varying processing conditions (the strain rate and the temperature) is introduced as a factor. The first one is a model of so called master curve. It is an internal variable model based on dislocation density and its output value strongly depends on strain and very weakly on temperature and strain rate. The second factor introduces varying deformation conditions. Changes of flow stress do not occur instantly with the change of deformation conditions, but it requires some strain for transition. The third part considers influence of recrystallization. The results of the model parameters identification and verification in varying deformation conditions are presented in this paper.

Abstract: Dynamic recrystallization (DRX) is widely used in industrial hot working processes to control the microstructure and properties of the workpiece and to keep the forming forces low. For the analysis and design of metal forming processes powerful simulation methods, must notably the Finite Element (FE) method, have been developed. Various models are available that consider the coupled evolution of microstructure and flow stress during hot deformation processes. Some of these models have been implemented into FE codes and are widely available now. However, for the implementation of flow stress models incorporating DRX into an FE formulation, special smoothness requirements exist that are not automatically fulfilled by the available flow stress models. This work reviews some conditions that a flow stress model incorporating DRX has to fulfill in order to be consistently embedded into an FE code for large plastic deformation. A specific Sellars-type model is analyzed for consistency with these conditions. It is shown that the use of a classical JMAK equation for the DRX kinetics within these models is problematic for Avrami exponents smaller than or equal to 3, for which the flow stress model is not sufficiently smooth. DRX kinetics based on the work of Cahn are proposed to remedy the differentiability issues.