Tension-compression Tests Research Articles

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.

Jointed Pipeline Response to Large Ground Deformation

AbstractThe performance of segmental pipelines under large ground deformation is strongly influenced by the axial pullout and compressive load capacity of their joints, as well as by the limits on joint rotation during permanent and transient ground deformation. Although ductile iron (DI) pipelines with push-on joints are commonly used in water distribution systems, experimental data and numerical simulation related to their performance under large ground movements are lacking. This paper reports on a series of specially designed four-point bending experiments and finite-element (FE) simulations to characterize 150-mm (6-in.) diameter DI push-on joints. The results were used to develop a relationship between rotation and metal binding as a function of axial pullout, as well as to determine the magnitudes of rotation and moment that initiate joint leakage. FE simulations were performed to investigate the deformation associated with joint leakage. Uniaxial tension and one-dimensional compression tests were ...

Mechanism based nonlinear constitutive model for composite laminates subjected to large deformations

A nonlinear constitutive model for composite laminates is developed with the focus on the distinction among inducing mechanisms. It is shown, that the effect of fiber rotation and damage is essential in consideration of large deformations. The evolution of yielding is described by two independent hardening curves either for in-plane shear or transverse normal load. A method for the experimental determination of the hardening curves is proposed based on uniaxial tests. To ensure the applicability to structural parts, the numerical model is validated by a large number of various angle-ply tension and off-axis compression tests, fabricated of the same carbon/epoxy IM7-8552 material. Extra wide specimen geometry was used for the conducted angle-ply tension tests to prevent delamination failure. The implemented model shows excellent correlation even at very large shear strains of up to 14%.

Warm PreStress effect on highly irradiated reactor pressure vessel steel

This study investigates the Warm Prestress (WPS) effect on 16MND5 (A508 Cl3) RPV steel, irradiated up to a fluence of 13·1023n.m-2 (E>1MeV) at a temperature of 288°C, corresponding to more than 60years of operations in a French Pressurized Water Reactor (PWR). Mechanical properties, including tensile tests with different strain rates and tension–compression tests on notched specimens, have been characterized at unirradiated and irradiated states and used to calibrate constitutive equations to describe the mechanical behavior as a function of temperature and fluence. Irradiation embrittlement has been determined based on Charpy V-notch impact tests and isothermal quasi-static toughness tests. Assessment of WPS effect has been done through various types of thermomechanical loadings performed on CT(0.5T) specimens. All tests have confirmed the non-failure during the thermo-mechanical transients. Experimental data obtained in this study have been compared to both engineering-based models and to a local approach (Beremin) model for cleavage fracture. It is shown that both types of modeling give good predictions for the effective toughness after warm prestressing.

Measurement and modeling of simple shear deformation under load reversal: Application to advanced high strength steels

In this paper, the stress–strain behavior under load reversal of advanced high strength steel (AHSS) sheet samples was measured using a modified simple shear (SS) apparatus. The forward–reverse loading behavior was characterized for three different grades of AHSS; namely, DP, TRIP and TWIP steels. For comparison purpose, compression–tension (CT) tests were also carried out for the same materials. For all the cases, a typical complex anisotropic hardening behavior, including the Bauschinger effect, transient strain hardening with high rate and permanent softening, was observed during load reversal. No premature localization and sheet buckling occurred in these experiments, which have been major technical hurdles in CT tests. For example, an engineering shear strain of over 40%, which corresponds to an effective strain of roughly 0.2, at reversal was achieved for DP980 although the uniform elongation of this material in uniaxial tension is only 5%. A recently developed distortional hardening model (HAH) was employed to reproduce the SS stress–strain curves. Using the coefficients determined with these SS data, the CT behavior was predicted with the HAH model and compared with experimental results. This complementary study indicated that the constitutive model determined from the SS flow curves satisfactorily reproduced the CT hardening behavior. As an application, finite element simulations of springback were carried out for 2D draw-bending of a strip sheet.

Complex modulus and complex Poisson’s ratio from cyclic and dynamic modal testing of asphalt concrete

The complex moduli and complex Poisson’s ratio of two cylindrical asphalt concrete specimens have been determined through modal testing in this paper. These results have been compared to cyclic tension–compression measured complex moduli and complex Poisson’s ratio of asphalt concrete specimens with different dimensions. The modal testing has been performed by measuring frequency response functions of the specimens using an impact hammer and an accelerometer. The material properties have been characterized by matching finite element computed frequency response functions to the measurements. The results of the different specimens show that the modal test systematically give a slightly higher absolute value of the complex moduli compared to the cyclic testing. The differences are most likely a result of the different strain levels applied in the two test methods. However, the modal and cyclic tension–compression testing resulted in similar values of the complex Poisson’s ratio for the two different asphalt concrete mixtures despite the different applied strain levels.

Effects of Hardening Models on CUO Forming and Springback Simulation of High Strength Line Pipes

The UOE process is an effective approach for manufacturing the line pipes used in oil and gas transportation. During the UOE process, a steel plate is crimped along its edges, pressed into a circular pipe with an open-seam by the successively U-O forming stages. Subsequently, the open-seam is closed and welded. Finally, the welded pipe is expanded to obtain a perfectly round shape. In particular, during the O-forming stage the plate is suffered from distinct strain reversal which leads to the Bauschinger effect, i.e., a reduced yield stress at the start of reverse loading following forward strain. In the finite element simulation of plate forming, the material hardening model plays an important role in the springback prediction. In this study, the mechanical properties of API X90 grade steel are obtained by a tension-compression test. Three popular hardening models (isotropic hardening, kinematic hardening and combined hardening) are employed to simulate the CUO forming process. A deep analysis on the deformation and springback behaviors of the plate in each forming stage is implemented. The formed configurations from C-forming to U-forming are almost identical with three hardening models due to the similar forward hardening behaviors. Since the isotropic hardening model cannot represent the Bauschinger effect, it evaluates the higher reverse stress and springback in the O-forming stage which leads to a failure prediction of a zero open-seam pipe. On the contrary, the kinematic hardening model overestimates the Bauschinger effect so that predicts the larger open-seam value. Specifically, the simulation results using the combined hardening model show good agreement in geometric configurations with the practical measurements.

Reclaimed asphalt pavement and additives’ influence on 3D linear behaviour of warm mix asphalts

This paper presents results of laboratory tests on nine types of specimens consisting of different hot and warm mix asphalts produced with a reclaimed asphalt pavement. Linear viscoelastic behaviour was investigated using tension–compression tests on cylindrical specimens on a wide range of temperatures (from −25°C to +45°C) and frequencies (from 0.03 to 10 Hz). Complex moduli, E*, and complex Poisson's ratios, ν*, were determined in two perpendicular material directions. Differences between measured ν* reveal a negligible anisotropy in the horizontal confection plane. The time–temperature superposition principle was verified with good approximation, with the same shift factor values, in one-dimensional and three-dimensional conditions. The same values of shift factor were also obtained for all specimens that contain bitumen with identical crude oil origin. Experimental results were modelled using the 2S2P1D model previously developed at the University of Lyon/ENTPE. In this paper, a new representation of results using normalised curves is proposed. These curves show identical properties for the different materials, which have the same origin of bitumen and aggregate. Finally, the performance of tested materials was compared.

Analysis and modeling of 3D complex modulus tests on hot and warm bituminous mixtures

This paper presents the results of laboratory testing of hot and warm bituminous mixtures containing Reclaimed Asphalt Pavement (RAP). Complex modulus measurements, using the tension–compression test on cylindrical specimens, were conducted to determine linear viscoelastic (LVE) behavior. Sinusoidal cyclic loadings, with strain amplitude of approximately 50⋅10−6, were applied at several temperatures (from −25 to +45 °C) and frequencies (from 0.03 Hz to 10 Hz). In addition to axial stresses and strains, radial strains were also measured. The complex modulus E∗ and complex Poisson’s ratios ν∗ were then obtained in two perpendicular directions. Measured values in these two directions do not indicate anisotropy on Poisson’s ratio. The time-temperature superposition principle (TTSP) was verified with good approximation in one-dimensional (1D) and three-dimensional (3D) conditions for the same values of shift factor. Experimental results were modeled using the 2S2P1D model previously developed at the University of Lyon/ENTPE. In addition, specific analysis showed that eventual damage created during complex modulus test is very small and is equivalent to the effect of an increase of temperature of about 0.25 °C.

Validation of Kinematic Hardening Parameters from Different Stress States and Levels of Plastic Strain with the Use of the Cyclic Bending Test

The recent development of new lightweight sheet metal materials, like advanced high-strength steels or aluminium alloys, in combination with an increasing component complexity provides new challenges to the numerical material modelling in the FEM based process design. An auspicious approach to improve the quality of the numerical results – most notably in springback analysis – is the modelling of the so called Bauschinger effect achieved through implementation of kinematic hardening models. Within this paper the influence of the stress state and the level of pre-strain on the numerical simulation result of the advanced high strength steel DP-K45/78+Z will be analysed. For this purpose, a parameter identification of the kinematic hardening law according to Chaboche and Rousselier is performed at different pre-strains on the basis of experimental data from tension-compression tests as well as cyclic shear tests. Finally, the identified parameters are validated in a comparison between numerical and experimental results of a cyclic bending test.

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.

Effects of mean stress and fibre volume content on the fatigue-induced damage mechanisms in CFRP

The effect of the load type (tension and compression) in quasi-static and of the applied mean stress in fatigue tests on the mechanical behaviour and on the damage mechanisms in unidirectional (UD) carbon/epoxy laminates has been studied in combination with the influence of fibre volume content. Results show that the fibre volume content increases the mechanical properties in tension–tension fatigue tests for all tested angles 0°, 45° and 90°. The tensile damage mechanisms of off-axis specimens depend on the fibre volume content and change from matrix cracking and matrix–fibre debonding to fibre-pull out with an increasing amount of fibres as investigated in detail in a previous work. In tension–compression tests, higher fibre volume contents are only beneficial in fatigue tests at angles of 0° and 45°. Fatigue strengths of UD 90° specimens in tension–compression tests are not significantly improved by the fibre volume content which can be ascribed to breakage of entire fibre bundles and crushed fibres on the fracture surfaces.

Three‐dimensional analysis of fatigue tests on bituminous mixtures

AbstractA tension–compression test on cylindrical specimens was used to study the three‐dimensional behaviour of bituminous mixtures during fatigue tests. The tests were carried out at 10 °C, 10 Hz at constant strain amplitude mode. The axial strain, radial strain and axial stress were measured using a prototype apparatus developed at the University of Lyon/“Ecole Nationale des TPE” (ENTPE). In addition to axial stress and strain analysis, the measurements of the radial strain made it possible to obtain the complex Poisson ratio and the volumetric strains during the tests. The results showed good correlations between the volumetric strains and global damage. The effects of the change of temperature due to viscous dissipation on the volumetric strain and on the complex modulus were also analysed.

Effect of Blast Furnace Slag on Mechanical Properties of Glass Fiber Polymer Composites

The use of polymer fibre reinforced Composite materials is finding applications day by day in engineering fields such as aero-space, automotive, aircrafts constructions, etc. Glass fibre polymer composites are reinforced with granulated blast furnace slag (GBFS) ball milled to size of 5nm in different weight fractions, i.e. (0%, 5%, 10% and 15%) and fabricated by using hand lay-up technique. These fabricated slabs are cut into required dimensions and the tests for mechanical properties like Tension test, Compression test, Flexural test Impact test and Hardness test were performed. Tension test, compression test and Flexural test were performed on Computerized Universal Testing Machine (UTM), Impact test was performed for Izod and Charpy specimens and Hardness test was performed on Brinell's Hardness Testing Machine. From the experimental results obtained, it was noticed that the mechanical properties were enhanced when the blast furnace slag percent was increased and also among these percentages of blast furnace slag, the specimen having 15% was possessing highest properties.

J0410301 応力経路変化を伴う金属薄板変形挙動とその材料モデル

The elasto-plastic deformation behaviors of an IF steel sheet during stress path changes were investigated by performing nonproportional tension-compression tests. To evaluate the developed constitutive models in describing nonproportional deformation behaviors, numerical simulations of stress-strain responses were conducted for the same stress paths as the experiments. From the comparisons of experiment and calculations, it was found that the proposed constitutive model can describe well every deformation behaviors of an IF steel sheet during stress path changes.

Cyclic Test of DP600 Steel under Tension-Compression Load for Different Pre-Strain Levels

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.

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.

STRUCTURE AND MECHANICAL CHARACTERISTIC OF CATTLE HORNS

In order to investigate the structure and mechanical characteristics of cattle horns, the microstructures of the keratin shell and bone core were examined by scanning electron microscopy, and a series of mechanical tests were performed by the tension-compression test machine and pendulum impact test machine. Results showed that the keratin shell was a laminated structure stacked by keratin protein slices, and the bone core was a light-weight porous material with pores randomly distributed in the longitudinal direction. The ultimate tensile strength of the keratin shell diminished gradually from distal to middle to proximal parts with the values of 162, 125 and 85 MPa, respectively. The ultimate compressive strength of keratin shell and bone core in the longitudinal direction was higher than that in the transverse. The moisture could cut down significantly the mechanical characteristics of keratin shell and bone core. The shock toughness of the keratin shell was 4.9 J/cm2, which was 7 times as large as that of the bone core. It can be concluded that cattle horn is a graded biological material with outstanding mechanical characteristics. The moisture, location and direction of the sampling have a significant effect on the mechanical characteristics of cattle horns. Compared with the bone core, the keratin shell has a better crashworthiness performance.

Characterization of strain-softening behavior and failure mechanisms of composites under tension and compression

A methodology is presented to directly measure the damage properties and strain softening response of laminated composites by conducting over-height compact tension (OCT) and compact compression (CC) tests. Through the use of digital image correlation (DIC) technique, and analysis of the measured surface displacement/strain data, the strain-softening response of composites is constructed. This method leads to a direct determination of the Mode I translaminar fracture properties with the assumption that the shear stress is negligible around the damage zone and the crack growth occurs in the symmetric opening mode. Using this methodology, and by correlating the observed failure mechanisms with the strain-softening curves, the interaction of failure mechanisms leading to the final failure and also the distinction between the tensile and compressive failure mechanisms can be studied. The effectiveness of the method in accurate identification of the damage parameters is demonstrated through sectioning and deplying techniques. As a consistency check and further verification of the method, the obtained strain-softening curves are fed into a numerical damage mechanics model and successfully used to simulate the detailed response of the very same OCT and CC specimens from which the strain-softening curves were extracted.