Papers by Keyword: Tension-Compression Test

Abstract: The results of computer and physical modeling of pipe steel hot rolling on a continuous rolling mill 2000 are presented. The moment of growth of austenite grains and the reasons for their growth are determined. The possibility of grinding the microstructure of the metal before controlled cooling, and the thermal deformation conditions conducive to grinding are investigated. It is shown that Nb (C,N) are not a factor in stopping the growth of austenite grains, but only inhibit the growth processes.

Abstract: In sheet metal formingprocess of automotive parts, springback effect is crucial, in particular, foradvanced high strength (AHS) steels. Most structural components of new vehiclesshow very complex shapes that require multi–step forming procedures.Therefore, finite element (FE)simulation has been often used to describe plasticdeformation behavior and springback occurrence of formed metal sheets.Recently, the kinematic hardening Yoshida–Uemorimodel has showed great capability for predicting elastic recovery of material. In this work, the AHSsteel grade JSC780Y wasinvestigated, in which tension–compressiontests were carried out. From resulted cyclic stress–strainresponses, material parameters were identified using different fitting methods.Determined model parameters were firstly verified by using simulations of 1–elementmodel. The most appropriate parameter set was thenobtained. Finally, a Hat-Shape forming test was performed and springback waspredicted and compared with experimental results.

Abstract: The roll levelling is a forming process used to remove the residual stresses and imperfections of metal strips by means of plastic deformations. The process is especially important to avoid final geometrical errors when coils are cold formed or when thick plates are cut by laser. In the last years, and due to the appearance of high strength materials such as Ultra High Strength Steels, machine design engineers are demanding a reliable tool for the dimensioning of the levelling facilities. In response to this demand, Finite Element Analysis is becoming an important technique able to lead engineers towards facilities optimization through a deeper understanding of the process.In this scenario, the accuracy and quality of the simulation results are highly dependent on the accuracy of the implemented material model. During roll levelling process, the sheet metal is subjected to cyclic tensile-compressive deformations, therefore a proper constitutive. model which considers the phenomena that occurs during cyclic loadings, such as the Bauschinger effec, work hardeningt and the transient behaviour, is needed. The prediction of all these phenomena which affect the final shape of the product are linked to the hardening rule.In the present paper, the roll levelling simulation of a DP1000 steel is performed using a combined isotropic-kinematic hardening formulation introduced by Chaboche and Lemaitre since its simplicity and its ability to predict the Bauschinger effect. The model has been fitted to the experimental curves obtained from a cyclic tension-compression test, which has been performed by means of a special tool developed to avoid the buckling of the specimen during compressive loadings. The model has been fitted using three different material hardening parameter identification methodologies which have been compared.

Abstract: Measurement of hardening under reversed uniaxial loading is because of its simplicity very effective mechanical test to achieve several important features of material behavior. In this paper is described special fixture which serves as a prevention of the sheet buckling during the cyclic tension-compression test. Result of the cyclic tension-compression test can consider several important features of the material behavior, which are necessary to be defined in the numerical simulation process. Experimental part of this paper consists of comparison results of strain path obtained from numerical simulation and real experiment. While in numerical simulation process was used material model describing isotropic hardening, real material behaved differently. Difference between strain paths also causes differences between results of springback values obtained in numerical simulation. New material models which include Bauschinger effect whether workhardening stagnation can diminish differences between results of an experiment and a numerical simulation and thus may also improve accuracy of the numerical simulation.

Abstract: Modeling sheet metal forming operations requires understanding of the plastic behavior of the sheet metal along the non-proportional strain paths. Measurement of hardening under reversed uniaxial loading is because of its simplicity very effective mechanical test to achieve several important features of material behavior. With the reversed uniaxial loading can be examined features as Bauschinger effect, work hardening stagnation, permanent softening etc., which are necessary to defined kinematic hardening in the numerical simulations. The biggest problem of uniaxial reversed loading is buckling of the sheet metal during the compression phase. In this article is described development of the simple fixture, used for the reversed uniaxial loading and results of tension-compression test for the steel DP 600 in various pre-strain levels are specified.

Abstract: Redistribution of residual stresses in a stamped sheet metal leads to the springback phenomenon. Springback phenomenon is well predicted for some mild steel materials, but not for steels with higher strengths. Nowadays, one of the most used tools to stamping optimization is usage of numerical simulations. In this paper was investigated sheet metal behavior under cyclic tension-compression test. Special fixture which serves as a buckling prevention of sheet metal in the compression phase of measuring stress-strain curve was designed. Obtained stress-strain curve was used to the definition of kinematic hardening model in numerical simulation. This model was verified with the real experiment in deep drawing process.

Abstract: After roll forming processes, metallic coils show several flatness imperfections and residual stresses that must be minimized when high quality components are manufactured by means of sheet metal forming processes. The equipments typically used for this purpose are roll leveling facilities. In the present work, a uniaxial cyclic tension-compression test has been used to determine the mechanical response of steel sheet under the different loading modes. After this, the Chaboche and Lemaitre nonlinear mixed hardening model has been fitted to the material behavior. This hardening model is able to reproduce some phenomena which occur during low cyclic deformation such as Bauschinger effect and workhardening. During the fitting of the model, the number of tension-compression cycles performed in the material characterization and the number of backstresses used for the model definition have been analyzed. Finally the influence of the material model in the roll leveling process results has been numerically analyzed. Different simulations have been performed by introducing initial defects with the objective of predicting residual stresses, residual curvatures, leveling force and torque force at the end of the process.

Abstract: This paper aims to investigate high temperature behavior of ZrO2 particle-dispersed Ni composites. The tension-compression tests under constant stress rates as well as creep tests including stress-dip tests were performed using a high-temperature material testing set up, which consists of an electric-hydraulic fatigue testing machine, electric furnace and extensometer with a laser sensor. ZrO2 particle-dispersed Ni composites were fabricated by using the powder metallurgical methods. The results obtained from the experimental study show that ZrO2 particles remarkably strengthen the composite and there exists a reasonable correlation between the tensioncompression stress-strain relation and the creep behavior. In addition, the creep behavior has been examined based on the micromechanical concept, which takes into account the diffusional mass flow at the interface between the particles and matrix. Some numerical analysis based on this concept demonstrates that even a little amount of ZrO2 particles can effectively increase the creep resistance of the composites