Cyclic Tension-compression Tests Research Articles

Comparison of 15Mo3 Strain Curves Obtained for Strain-Controlled Cyclic Bending and Tension-Compression Tests

The paper presents a comparison of the fatigue life curves based on test of 15Mo3 steel under cyclic, pendulum bending and tension-compression. These studies were analyzed in terms of a large and small number of cycles where strain amplitude is dependent on the fatigue life. It has been shown that commonly used Manson-Coffin-Basquin model cannot be used for tests under cyclic bending due to the impossibility of separating elastic and plastic strains. For this purpose, some well-known models of Langer and Kandil and one new model of authors, where strain amplitude is dependent on the number of cycles, were proposed. Comparing the results of bending with tension-compression it was shown that for smaller strain amplitudes the fatigue life for both test methods were similar, for higher strain amplitudes fatigue life for bending tests was greater than for tension-compression.

A model-reduction approach to the micromechanical analysis of polycrystalline materials

The present study is devoted to the extension to polycrystals of a model-reduction technique introduced by the authors, called the nonuniform transformation field analysis (NTFA). This new reduced model is obtained in two steps. First the local fields of internal variables are decomposed on a reduced basis of modes as in the NTFA. Second the dissipation potential of the phases is replaced by its tangent second-order (TSO) expansion. The reduced evolution equations of the model can be entirely expressed in terms of quantities which can be pre-computed once for all. Roughly speaking, these pre-computed quantities depend only on the average and fluctuations per phase of the modes and of the associated stress fields. The accuracy of the new NTFA-TSO model is assessed by comparison with full-field simulations on two specific applications, creep of polycrystalline ice and response of polycrystalline copper to a cyclic tension-compression test. The new reduced evolution equations is faster than the full-field computations by two orders of magnitude in the two examples.

Deformation Characteristics of Advanced High Strength Steel under Cyclic Bending and Reversed Bending

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.

Comparison of Three Methods for Material Hardening Parameter Identification under Cyclic Tension-Compression Loadings: Roll Levelling Case Study

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.

Springback prediction and reduction in deep drawing under influence of unloading modulus degradation

Springback is considered as one of the major problems in deep drawing of high-strength steels (HSS) and advanced high-strength steels (AHSS) which occurs during the unloading of part from the tools. With an ever increasing demand on the automotive manufactures for the production of lightweight automobile structures and increased crash performance, the use of HSS and AHSS is becoming extensive. For the accurate prediction of springback, unloading behavior of dual phase steels DP600, DP1000 and cold rolled steel DC04 for the deep drawing process is investigated and a strategy for the reduction of springback based on variable blankholder force is also presented. Cyclic tension compression tests and LS-Opt software are used for the identification of material parameters for Yoshida-Uemori (YU) model. Degradation of the Young’s modulus is found to be 28 and 26 and 14 % from the initial Young’s modulus for DP600, DP1000 and for the DC04 respectively for the saturated value. A finite element model is generated in LS-DYNA based on the kinematic hardening material model, namely Yoshida-Uemori (YU) model. The validation of numerical simulations is also carried out by the real deep drawing experiments. The springback could be predicted with the maximum deviation of 1.1 mm for these materials. For DP1000, the maximum springback is reduced by 24.5 %, for DP600 33.3 and 48.7 % for DC04 by the application of monotonic blankholder force instead of a constant blankholder force of 80 kN. It is concluded that despite the reduction of Young’s modulus, the springback can be reduced for these materials by increasing the blankholder force only in last 13 % of the punch travel.

Experimental and Numerical Investigation of Sheet Metal Behavior under Cyclic Tension-Compression Loading

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.

An Investigation of Springback in Sheet Metal Forming of High Strength Steels

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.

Bauschinger Effect Exhibited in Advanced High Strength Steel Sheets under Cyclic Tension and Compression Tests

The Bauschinger effect exhibited in the advanced high strength steel sheets was examined by conducting cyclic tension-compression tests. The experimental device for performing the cyclic tension and compression tests with a single sheet specimen was developed in the present study. The experimental apparatus consists of a novel constraint jig that could prevent the sheet specimen from buckling during the compression test. The efficiency of the developed clamping device was validated by both the finite element analysis and the cyclic tension and compression tests conducted in the present study. The test results reveal that the advanced high strength steel exhibits significant Bauschinger effect. It is also confirmed that the finite element prediction of springback present in the stamping of advanced high strength steel sheets is more consistent with the experimental results if the Bauschinger effect is considered.

Uniaxial ratchetting of extruded AZ31 magnesium alloy: Effect of mean stress

The uniaxial ratchetting of extruded AZ31 magnesium alloy was investigated in the cyclic tests with different mean stresses and at room temperature. The prescribed mean stresses and corresponding stress amplitudes were chosen to make the different plastic deformation mechanisms such as dislocation slipping, twinning and detwinning occur individually or simultaneously during the cyclic deformation of the AZ31 magnesium alloy with a hexagonal close packed crystal structure, and then the effect of mean stress on the uniaxial ratchetting of the magnesium alloy was discussed. It is seen that ratchetting occurs in the AZ31 magnesium alloy during the stress-controlled cyclic loading, but different evolution features are observed in the uniaxial ratchetting tests with different mean stresses. Different ratchetting behaviors are determined by the different deformation mechanisms of extruded AZ31 magnesium alloy occurring in the tensile and compressive parts of cyclic loading. A sigmoidal stress–strain hysteresis loop of the magnesium alloy presented in the cyclic tension–compression tests with some suitable mean stresses and stress amplitudes is caused by the twinning/detwinning deformation mechanism, which should be reasonably considered in constructing a cyclic constitutive model to describe the uniaxial ratchetting of magnesium alloys.

Bauschinger Effect During Unloading of Cold-rolled Copper Alloy Sheet and its Influence on Springback Deformation after U-bending

Tension, cyclic tension-compression and partial unloading tests for two types of cold rolled brass sheet (i.e. JIS C2600R-H, C2600R-1/2H) were carried out in order to investigate cyclic plasticity and unloading behavior, and to determine the plastic dependency on Young's modulus. The Young's moduli for the pre-strained materials were determined in different two ways. For the first case, unlading stress-strain data from σ0 to 0.0MPa was used, and data from σ0 to (σ0 - 2Y0) was used for the second case, where σ0 and Y0 denote 90% of the stress at the beginning of unloading and the initial yield stress used in a constitutive equation, respectively. The saturated Young's moduli were significantly different on C2600R-H sheet, but similar plastic strain dependency on Young's modulus relationship was found on C2600R-1/2H sheet. Subsequently, U-bending experiments and the corresponding finite element simulations using several combinations of plastic strain dependent Young's moduli and isotropic and kinematic hardening rules were conducted. The simulation results indicated that Young's moduli measured using σ0 to (σ0 - 2Y0) data with elasto-plastic unloading is the best choice for springback simulation of the cold rolled sheets.

Експериментальне визначення ефекту Баушингера і пошкоджуваності матеріалу

Present paper is devoted to an experimental determination of the Bauschinger effect and material damage which occur at elastic-plastic deformation. The series of cyclic tension-compression tests of flat samples made from aluminum alloy D16 were conducted. Given a phenomenon of buckling at compres-sion stage the flat samples were cut according to both ATSM standard and preliminarily conduction of the buckling analysis. Based on the experimental data a mathematical model of plasticity is developed in the way of improvement of the nonlinear kinematic hardening model by introducing of an additional function of previously accumulated plastic strain. For better correlation with experimental results the Mises plasticity criterion written in the form of the Baltov and Sawczuk’s model was modified by intro-ducing of a function which is intended to describe decrease of the yield stress during plastic deforma-tion. In order to model a reduction of the young’s module at unloading stage of the cyclic tension-compression test a material damage parameter was introduced according to the effective stress concep-tion. Numerical simulation of the cyclic tension-compression testing which accompanied experimental investigation has shown good coincidence with experiment results.

Modeling of Bauschinger Effect During Stress Reversal

It is widely known that the constitutive model of Bauschinger effect is one of key points to conduct the accurate sheet metal stamping. In the present research, the elasto‐plasticity behaviors of thin sheet metals were investigated by conducting in‐plane cyclic tension–compression tests in the different angle from the pre‐strained direction. In order to evaluate the accuracy of constitutive models for describing the above mentioned elasto‐plasticity behaviors, including the Bauschinger effect, some numerical experiments were conducted for the corresponding stress paths calculations by using three kinds of constitutive models: the isotropic hardening model (hereafter IH model), Yoshida–Uemori model (hereafter Y–U model), and the modified Yoshida–Uemori kinematic hardening model (hereafter modified Y–U model). From the comparisons, it is found that the author's present constitutive model shows a good agreement with the experimental stress–strain responses.

Yoshida–Uemori material models in cyclic tension–compression tests and shear tests

Demands for energy conservation and impact resistance have made high-strength steel a crucial material in sheet metal parts for the automotive industry. However, during metal stamping, the springback associated with high-strength steel plates is significantly greater than for mild steel. This makes numerical simulation and prediction in stamp forming extremely difficult. The Yoshida–Uemori material model comprehensively describes the Bauschinger effect and work hardening stagnation that occur in metal during cyclic large plastic deformation, making it an important model for the simulation of high-strength steel stamp forming. This study employed cyclic tension–compression tests and shear tests to explore the construction of a Yoshida–Uemori model and verify its accuracy using numerical simulation.

Influence of the Number of Tensile/Compression Cycles on the Fitting of a Mixed Hardening Material Model: Roll Levelling Process Case Study

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.

Analysis of Fatigue Test for Bituminous Mixtures

AbstractIn this study, cyclic tension-compression tests on cylindrical specimens are performed in order to investigate fatigue characteristics of bituminous mixtures. Sinusoidal loading is applied ...

Thermo-mechanical FE model with memory effect for 304L austenitic stainless steel presenting microstructure gradient

The main purpose of this study is to determine, via a three dimensions Finite Element analysis (FE), the stress and strain fields at the inner surface of a tubular specimen submitted to thermo-mechanical fatigue. To investigate the surface finish effect on fatigue behavior at this inner surface, mechanical tests were carried out on real size tubular specimens under various thermal loadings. X-ray measurements, Transmission Electron Microscopy observations and micro-hardness tests performed at and under the inner surface of the specimen before testing, revealed residual internal stresses and a large dislocation microstructure gradient in correlation with hardening gradients due to machining. A memory effect, bound to the pre-hardening gradient, was introduced into an elasto–visco-plastic model in order to determine the stress and strain fields at the inner surface. The temperature evolution on the inner surface of the tubular specimen was first computed via a thermo-elastic model and then used for our thermo-mechanical simulations. Identification of the thermo-mechanical model parameters was based on the experimental stabilized cyclic tension–compression tests performed at 20°C and 300°C. A good agreement was obtained between numerical stabilized traction–compression cycle curves (with and without pre-straining) and experimental ones. This three dimensional simulation gave access to the evolution of the axial and tangential internal stresses and local strains during the tests. Numerical results showed: a decreasing of the tangential stress and stabilization after 40 cycles, whereas the axial stress showed weaker decreasing with the number of cycles. The results also pointed out a ratcheting and a slightly nonproportional loading at the inner surface. The computed mean stress and strain values of the stabilized cycle being far from the initial ones, they could be used to get the safety margins of standard design related to fatigue, as well as to get accurate loading conditions needed for the use of more advanced fatigue analysis and criteria.

Determination of thermal properties of asphalt mixtures as another output from cyclic tension-compression test

This paper describes investigation into the change of temperature of asphalt mixtures during cyclic tests on cylindrical specimens. Tension-compression tests were performed at different strain amplitudes (from 55 μm/m to 133 μm/m). Temperature is measured at the surface and inside the specimen. From the analysis of the experimental results, the thermal conductivity (k) and the convection heat transfer coefficient (h) were determined during the steady temperature phase. The specific heat coefficient (C) of the material was determined during the transient temperature phase. This parameter is also indentified using a finite element simulation of the heat process. A thermal conductivity of 1.35 W/(m.°C) and a specific heat of 820 J/(kg.°C) were found for the asphalt mixtures used in this research. These values are quite realistic when compared to values proposed in the literature that are obtained using the traditional thermo-physical measurements. Furthermore, the thermal parameters obtained from FP2C, a device used for the identification of thermal properties of materials, confirm the results.

Elasto-plasticity Behavior of IF Steel Sheet with Planar Anisotropy and Its Macro-meso Modeling

Elasto-plasticity behavior of an IF steel sheet was investigated by performing uniaxial tension tests in three directions (0°, 45° and 90° to the rolling direction of the sheet), in-plane cyclic tension compression test and bi-axial tension test. The sheet has strong planar anisotropy (r0 = 2.15, r45 = 2.12 and r90 = 2.89) but very weak flow stress directionality. Equi-biaxial flow stress is as large as 1.23 times of the uniaxial flow stress. These elasto-plasticity deformation characteristics, as well as the Bauschinger effect and cyclic hardening behavior, are well described by a macro-plasticity model (Yoshida-Uemori model incorporating with the 4th-order anisotropic yield function). Further, the simulation of elasto-plasticity stress strain responses of the sheet were conducted by two types of crystal plasticity models, i.e., Taylor hypothesis based model and CPFEM, using the crystallographic orientation distribution data measured by neutron diffraction method. The models capture most of the above-mentioned deformation characteristics qualitatively, but the predicted anisotropy and the Bauschinger effect are weaker than those of the real material. The CPFEM gives more realistic results than the Taylor model.

OS0303 マグネシウム合金板の面内繰返し実験観察とそのモデル化

To investigate the deformation behavior of a magnesium sheet, the finite element calculation was carried out under tension and in-plane cyclic tension-compression test. From the experimental data, the twin deformation was observed during the tensile deformation after uniaxial compression. For the accurate description of the above mentioned twin deformation, we have developed the constitutive equation of twining behavior. From the comparison, it is found that the developed constitutive equations can calculate stress-strain response accurately.

Evaluation of advanced anisotropic models with mixed hardening for general associated and non-associated flow metal plasticity

The main objective of this paper is to develop a generalized finite element formulation of stress integration method for non-quadratic yield functions and potentials with mixed nonlinear hardening under non-associated flow rule. Different approaches to analyze the anisotropic behavior of sheet materials were compared in this paper. The first model was based on a non-associated formulation with both quadratic yield and potential functions in the form of Hill’s (1948). The anisotropy coefficients in the yield and potential functions were determined from the yield stresses and r-values in different orientations, respectively. The second model was an associated non-quadratic model (Yld2000-2d) proposed by Barlat et al. (2003). The anisotropy in this model was introduced by using two linear transformations on the stress tensor. The third model was a non-quadratic non-associated model in which the yield function was defined based on Yld91 proposed by Barlat et al. (1991) and the potential function was defined based on Yld89 proposed by Barlat and Lian (1989). Anisotropy coefficients of Yld91 and Yld89 functions were determined by yield stresses and r-values, respectively. The formulations for the three models were derived for the mixed isotropic-nonlinear kinematic hardening framework that is more suitable for cyclic loadings (though it can easily be derived for pure isotropic hardening). After developing a general non-associated mixed hardening numerical stress integration algorithm based on backward-Euler method, all models were implemented in the commercial finite element code ABAQUS as user-defined material subroutines. Different sheet metal forming simulations were performed with these anisotropic models: cup drawing processes and springback of channel draw processes with different drawbead penetrations. The earing profiles and the springback results obtained from simulations with the three different models were compared with experimental results, while the computational costs were compared. Also, in-plane cyclic tension–compression tests for the extraction of the mixed hardening parameters used in the springback simulations were performed for two sheet materials.