Papers by Keyword: Bauschinger Effect

Abstract: In the production of the large-diameter thick-walled steel pipes (with a diameter of 1020-1420 mm and with a wall thickness of up to 32-48 mm from the high-strength steels of the strength class K50-K65) under the SMS Meer technology for the main gas-and-oil pipelines, the steel sheet is bent several times sequentially during the technological transitions from one press to another. At the elastoplastic alternating-sign bends of the sheet, the yield strength of the bending moment of the sheet changes from one bend to another, which causes great difficulties for the metallurgical technologists when they calculate the curvature of the tube’s wall and the final diameter of the pipe. To solve this problem, we propose the new analytical method for calculating the bending moment and curvature of a steel sheet under the low-cycle alternating-sign bending.

Abstract: There are materials whose forward flow curve is practically independent of plastic strain (perfect plasticity) but the Bauschinger effect reduces the elastic range with flow reversal. A new model that is capable of describing such behavior of material under plane stress conditions has been recently proposed. An important class of structures in which the state of stress can often be accurately approximated by plane stress conditions is thin hollow discs. It is therefore of interest to use the new model for determining the distribution of residual stresses in thin discs subject to various loading conditions, followed by unloading. This paper presents a solution for the residual stresses and strains in a hollow hyperbolic disc loading by external pressure, followed by unloading.

Abstract: The Yoshida-Uemori combined kinematic and isotropic hardening model is widely applied to numerical prediction of spring-back during sheet metal forming process. With the experimental plastic behavior of aluminum alloy AA5182-O sheet under single cyclic loading, the semi-analytical method was presented to calibrate the parameters of Yoshida-Uemori hardening model. Meanwhile, an inverse identification method was suggested by parameter optimization for minimizing the error between the experimental and predicted results. By comparing the two methods, the Yoshida-Uemori hardening model identified by inverse method is found to be more accurate for description of the Bauschinger effect than the one identified by semi-analytical method, especially for transient softening phenomenon.

Abstract: In this study, the Bauschinger effect in ultrafine-grained pure aluminum rods (A1070) was investigated. The samples were produced by multipass equal-channel angular pressing (ECAP) with ‘route BC’, which is known to give nearly equiaxial-shaped crystal grains. Dumbbell-shaped specimens with a circular cross section were machined from the samples subjected to ECAP to carry out uniaxial tensile and compressive tests, which were followed by reversal of the loading direction at a prestrain of 1%. The influence of the grain size on the intensity of the Bauschinger effect was investigated. The Bauschinger effect is interpreted to be a manifestation of internal stresses produced near the grain boundaries by the accumulation of dislocations. On the basic of our experimental results, the roles of the grain boundaries, which are usually at least partially considered as barriers to dislocation motion, are reconsidered.

Abstract: Bauschinger effect is significant for metal forming, particularly for aluminum. A material constitutive model especially for multi-stage sheet metal forming is presented in this paper, which is improved based on Yoshida-Uemori(Y-U) model assumes that there exists different coefficient on equivalent back stress and boundary surface between stages. The prediction of this model is validated through real tension and compression test. Compared to other hardening rules, it can be shown that a more accurate result can be predicted by this model. This model is also successfully applied to be used in the numerical simulation of a multi-stage manufacturing process of an A-pillar, the experimental result demonstrates the advantage of this model in springback analysis in multi-stage simulation over other constitutive model.

Abstract: In this research effect of the pipe forming on strength properties of rolled metal was investigated. Deformed state of metal during pipe processing was analyzed and tests with specimens from plate were performed. Analysis of the experimental data was exploited to evaluate effect of the strain on yield stress in each stage of the pipe forming and specimen flattening. The model for estimation of mechanical properties of the rolling mill product based on the required mechanical properties of the pipe was created.

Abstract: This paper presents the yielding surface isotropic hardening study of the aluminum alloy 7050 T7451 submitted to monotonic loadings, considering the nonlinear constitutive model proposed by Voce. The stress state imposed characterizes a behavior whose plastic deformations cannot be neglected. The analysis depends on the segregation between the isotropic and the kinematic hardening that composes the material’s behavior during its transient life. Monotonic and cyclic tension-compression tests have been realized in order to allow the Bauschinger Effect understanding. The results have been compared to FEM simulations in order to validate the model.

Abstract: The identification of the material models which are used in the finite element analysis for the forming operation and springback are very important in terms of accurate predictions. The aim of this paper is to characterize both the anisotropy and the hardening of the ultra-high strength steel such as martensitic steel (MS steel) in order to identify material parameters of constitutive equation, which able to reproduce the mechanical behavior. Uniaxial tensile tests were carried out for characterizing the anisotropic plastic behavior of the MS steel. Cyclic tests under tension-compression load were also carried out for characterizing the Bauschinger effect during reverse deformation. Yoshida-Uemori hardening model associated with orthotropic yield criterion Hill’s 1948 is used to represent the in-plane mechanical behavior of the martensitic steel. The resented results show a very good agreement between model predictions and experiments: flow stresses during loading and reverse loading are well reproduced.

Abstract: The use of new materials, e.g. aluminum and magnesium alloys, in the automotive and aviation sector is becoming increasingly important to reach the global aim of reduced emissions. Especially magnesium alloys with their low density offer great potential for lightweight design. However, magnesium alloys are almost exclusively formable at elevated temperatures. Therefore, material characterization methods need to be developed for determining the mechanical properties at elevated temperatures. In particular, cyclic tests at elevated temperatures are required to identify the isotropic-kinematic hardening behavior, which is important for numerically modeling the springback behavior. In this contribution, a characterization method for determining the cyclic behavior of the magnesium alloy AZ31B at an elevated temperature of 200 °C is presented. The setup consists of a miniaturized tensile specimen and stabilization plates to prevent buckling under compressive load. The temperature in the relevant area is introduced with the help of conductive heating. Moreover, the complex kinematic model according to Chaboche and Rousselier is identified, to map the transient hardening behavior of AZ31B after load reversal, which cannot be modeled with a single Bauschinger coefficient.

Abstract: In the present study, the Bauschinger effect exhibited in the advanced high strength steel under cyclic bending and reversed bending deformation was examined by both the experimental approach and the finite element analysis. The cyclic tension-compression tests were first conducted for the DP590 steel sheet to determine the material constants required in the Yoshida-Uemori model used in the finite element simulations. Since the deformation mode occurred in the reversed bending tests is similar to that presented in the sheet metal passing across the draw bead or die corner, a three-point reversed bending test apparatus was also developed and the experiments were conducted in the present study. The reversed bending test results clearly demonstrate that the Bauschinger effect presents in the reversed bending process. It confirms that the cyclic reversed bending tests can be applied to examine the Bauschinger effect exhibited in the sheet metal forming process. The finite element analysis was also performed to simulate both the U-hat bending and cyclic reversed bending processes. The comparison of the simulation results with the experimental data reveals that the finite element predictions in both springback and reversed bending load are more accurate if the Yoshida-Uemori model is adopted. It implies that consideration of the Bauschinger effect is necessary in the sheet metal forming if a reversed loading path is present during the forming process.