Effect of Nonlinear Kinematic Hardening Constants on Cyclic Spherical Indentation Test

2010 ◽  
Author(s):  
A. Nayebi
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Applied Load ◽  
Kinematic Hardening ◽  
Hysteresis Loops ◽  
Indentation Test ◽  
Material Behavior ◽  
Spherical Indentation ◽  
Displacement Curve ◽  
Residual Displacements

In the last decade, instrumented indentation test has been widely used to determine the mechanical properties of different materials and especially for metals. The mechanical properties such as Young modulus, yield stress, hardening exponent, and stress-strain curve were determined with the help of the load–displacement curve of the continuous indentation test. The method consists of pushing an indenter in a material sample and the applied load and the indenter displacement are measured. In this research the load on the indenter was considered as cyclic and varied from zero to Fmax. Because of the Bauschinger effect, the hysteresis loops were formed. With the help of these hysteresis loops, nonlinear kinematic hardening parameters of the Armstrong–Freiderick (A-F) model can be determined. Spherical indenter was used and the sample was considered isotropic. The material behavior was modeled by the A-F rule. The test was modeled by the finite element method. An axi-symmetric mesh was used. The A–F model constants, C and γ, were varied to obtain their effects on the hysteresis loops. Maximum applied load was considered constant for different finite element modeling and the maximum and residual displacements were calculated from the simulations results. The normalized maximum and the residual displacements were increased as a function of the cycles. It was shown that these parameters value and their rate are dependent on the material model constants. These dependences were shown for different examples which can help to characterize the A-F model constants by the cyclic spherical indentation tests.

Characterization of mechanical properties of metallic foams by instrumented indentation test

2018 ◽  
Vol 115 (4) ◽  
pp. 405
Author(s):  
Ali Nayebi ◽  
Azam Surmiri
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Constitutive Model ◽  
Indentation Test ◽  
Metallic Foam ◽  
Spherical Indentation ◽  
Metallic Foams ◽  
Aluminum Foams ◽  
Inelastic Behaviour ◽  
Indentation Response

In this study, the spherical indentation tests with a spherical rigid indenter of 5 mm radius were used. The inelastic behaviour of metallic foam was considered as an isotropic crushable foam constitutive model of Deshpande and Fleck which has been shown experimentally that their model can be applied to aluminum foams. The spherical indentation test was modeled by finite element method. A 2D axisymmetric model was developed. Practically, the size of the indenter tip should be reasonably large compared to the size of the cells/pores in the specimen and the indentation depth should also be reasonably large so that the indentation response does reflect the averaged material behaviours, which are described by the aforementioned constitutive model. The applied load on the indenter versus its displacement was obtained under different metallic foam mechanical properties. Numerical results from the finite element simulations are used to obtain the dependence of the indentation response on the metallic foam material parameters which characterizes the plastic deformation of metallic foams. Finally, the stress–curves and the elastic modulus of different foams are obtained by the indentation curve, which is obtained by FEM.

Inverse Characterization of Nonlinear Anisotropic Mechanical Properties of Engineered Cardiovascular Tissues Using a Spherical Indentation Test

2007 ◽  
Author(s):  
M. A. J. Cox ◽  
R. A. Boerboom ◽  
C. V. C. Bouten ◽  
N. J. B. Driessen ◽  
F. P. T. Baaijens
Keyword(s):  
Mechanical Properties ◽  
Soft Tissues ◽  
Indentation Test ◽  
Tensile Tests ◽  
Material Behavior ◽  
Uniaxial Tensile ◽  
Spherical Indentation ◽  
Mechanical Conditioning ◽  
Indentation Tests

Over the last few years, research interest in tissue engineering as an alternative for e.g. current treatment and replacement strategies for cardiovascular and heart valve diseaes has significantly increased. In vitro mechanical conditioning is an essential tool for engineering strong implantable tissues [1]. Detailed knowledge of the mechanical properties of the native tissue as well as the properties of the developing engineered constructs is vital for a better understanding and control of the mechanical conditioning process. The typical highly nonlinear and anisotropic behavior of soft tissues puts high demands on their mechanical characterization. Current standards in mechanical testing of soft tissues include (multiaxial) tensile testing and indentation tests. Uniaxial tensile tests do not provide sufficient information for characterizing the full anisotropic material behavior, while biaxial tensile tests are difficult to perform, and boundary effects limit the test region to a small central portion of the tissue. In addition, characterization of the local tissue properties from a tensile test is non-trivial. Indentation tests may be used to overcome some of these limitations. Indentation tests are easy to perform and when indenter size is small relative to the tissue dimensions, local characterization is possible. Therefore, we propose a spherical indentation test using finite deformations.

Can indentation technique measure unique elastoplastic properties?

2009 ◽  
Vol 24 (3) ◽  
pp. 784-800 ◽  
Author(s):  
Ling Liu ◽  
Nagahisa Ogasawara ◽  
Norimasa Chiba ◽  
Xi Chen
Keyword(s):  
Critical Strain ◽  
Indentation Test ◽  
Strain Curve ◽  
Spherical Indentation ◽  
Plastic Behavior ◽  
Displacement Curve ◽  
Application Range ◽  
Indentation Technique ◽  
Elastoplastic Properties ◽  
Force Displacement

Indentation is widely used to extract material elastoplastic properties from measured force-displacement curves. Many previous studies argued or implied that such a measurement is unique and the whole material stress-strain curve can be measured. Here we show that first, for a given indenter geometry, the indentation test cannot effectively probe material plastic behavior beyond a critical strain, and thus the solution of the reverse analysis of the indentation force-displacement curve is nonunique beyond such a critical strain. Secondly, even within the critical strain, pairs of mystical materials can exist that have essentially identical indentation responses (with differences below the resolution of published indentation techniques) even when the indenter angle is varied over a large range. Thus, fundamental elastoplastic behaviors, such as the yield stress and work hardening properties (functions), cannot be uniquely determined from the force-displacement curves of indentation analyses (including both plural sharp indentation and deep spherical indentation). Explicit algorithms of deriving the mystical materials are established, and we qualitatively correlate the sharp and spherical indentation analyses through the use of critical strain. The theoretical study in this paper addresses important questions of the application range, limitations, and uniqueness of the indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material constitutive properties.

Shakedown Limit Load Determination for a Kinematically Hardening 90-Degree Pipe Bend Subjected to Constant Internal Pressure and Cyclic Bending

2007 ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Plastic Material ◽  
Kinematic Hardening ◽  
Limit Load ◽  
Material Behavior ◽  
Pipe Bend ◽  
Cyclic Bending ◽  
Perfectly Plastic ◽  
Shakedown Limit

A simplified technique for determining the shakedown limit load of a structure employing an elastic-perfectly-plastic material behavior was previously developed and successfully applied to a long radius 90-degree pipe bend. The pipe bend is subjected to constant internal pressure and cyclic bending. The cyclic bending includes three different loading patterns namely; in-plane closing, in-plane opening, and out-of-plane bending moment loadings. The simplified technique utilizes the finite element method and employs small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full cyclic loading finite element simulations or conventional iterative elastic techniques. In the present paper, the simplified technique is further modified to handle structures employing elastic-plastic material behavior following the kinematic hardening rule. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure accounting for the back stresses, determined from the kinematic hardening shift tensor, responsible for the translation of the yield surface. The outcomes of the simplified technique showed very good correlation with the results of full elastic-plastic cyclic loading finite element simulations. The shakedown limit moments output by the simplified technique are used to generate shakedown diagrams of the pipe bend for a spectrum of constant internal pressure magnitudes. The generated shakedown diagrams are compared with the ones previously generated employing an elastic-perfectly-plastic material behavior. These indicated conservative shakedown limit moments compared to the ones employing the kinematic hardening rule.

Energy-Consistent Finite Element Modelling of Ferromagnetic Hysteresis

2012 ◽  
Author(s):  
Christophe Geuzaine ◽  
Laurent Stainier ◽  
Francois Henrotte
Keyword(s):  
Finite Element ◽  
Magnetic Energy ◽  
Kinematic Hardening ◽  
Hysteresis Loops ◽  
Macroscopic Model ◽  
Dissipated Energy ◽  
Internal Variables ◽  
Incremental Formulation ◽  
Ferromagnetic Hysteresis ◽  
Electromagnetic Models

In this article we propose a macroscopic model for ferromagnetic hysteresis that is well-suited for finite element implementation. The model is readily vectorial and relies on a consistent thermodynamic formulation. In particular, the stored magnetic energy and the dissipated energy are known at all times, and not solely after the completion of closed hysteresis loops as is usually the case. The obtained incremental formulation is variationally consistent, i.e., all internal variables follow from the minimization of a thermodynamic potential. This variational approach is directly inspired from the kinematic hardening theory of plasticity, which opens the door for novel energy-consistent coupled mechanical/electromagnetic models.

Effect of Crystallographic Orientation on Nanoindentation Response of Fe3Si Single-Crystals

2018 ◽  
Vol 784 ◽  
pp. 44-48 ◽  
Author(s):  
Jaroslav Čech ◽  
Petr Haušild ◽  
Aleš Materna
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Shear Stress ◽  
Contact Area ◽  
Measured Data ◽  
Deformation Mechanisms ◽  
Spherical Indentation ◽  
Indentation Modulus ◽  
Slip Systems ◽  
Correct Interpretation

Deformation mechanisms and mechanical properties of Fe3(wt.%)Si single crystal in two different orientations were investigated by spherical indentation. For correct interpretation of measured data and better understanding of the deformation mechanisms under the contact area, finite element simulations were carried out and resolved shear stress in available slip systems was computed. Pop-in behavior, differences in hardness, indentation modulus and shapes of residual imprints were observed and associated with different activation of slip.

scholarly journals Analysis of Undrained Seismic Behavior of Shallow Tunnels in Soft Clay Using Nonlinear Kinematic Hardening Model

2020 ◽  
Vol 10 (8) ◽  
pp. 2834
Author(s):  
Mohsen Saleh Asheghabadi ◽  
Xiaohui Cheng
Keyword(s):  
Finite Element ◽  
Kinematic Hardening ◽  
Soft Clay ◽  
Hysteresis Loops ◽  
Stiffness Degradation ◽  
Triaxial Tests ◽  
Embedment Depth ◽  
Ground Acceleration ◽  
Cyclic Shear ◽  
Hardening Model

In this study, a soil–tunnel model for clay under earthquake loading is analyzed, using finite element methods and a kinematic hardening model with the Von Mises failure criterion. The results are compared with those from the linear elastic–perfectly plastic Mohr–Coulomb model. The latter model does not consider the stiffness degradation caused by imposing cyclic loading and unloading to the soil, whereas the kinematic hardening model can simulate this stiffness degradation. The parameters of the kinematic hardening model are calibrated based on the results of experimental cyclic tests and finite element simulation. Here, two methods—one using data from cyclic shear tests, and the other a new method using undrained cyclic triaxial tests—are used to calibrate the parameters. The parameters investigated are the peak ground acceleration (PGA), tunnel lining thickness, tunnel shape, and tunnel embedment depth, all of which have an effect on the resistance of the shallow tunnel to the stresses and deformations caused by the surrounding clay soils. The results show that unlike traditional models, the nonlinear kinematic hardening model can predict the response reasonably well, and it is able to create the hysteresis loops and consider the soil stiffness degradation under the seismic loads.

Determining engineering stress–strain curve directly from the load–depth curve of spherical indentation test

2010 ◽  
Vol 25 (12) ◽  
pp. 2297-2307 ◽  
Author(s):  
Baoxing Xu ◽  
Xi Chen
Keyword(s):  
Indentation Test ◽  
Strain Curve ◽  
Spherical Indentation ◽  
Displacement Curve ◽  
Large Set ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Constraint Factors ◽  
Engineering Stress ◽  
Depth Curve

The engineering stress–strain curve is one of the most convenient characterizations of the constitutive behavior of materials that can be obtained directly from uniaxial experiments. We propose that the engineering stress–strain curve may also be directly converted from the load–depth curve of a deep spherical indentation test via new phenomenological formulations of the effective indentation strain and stress. From extensive forward analyses, explicit relationships are established between the indentation constraint factors and material elastoplastic parameters, and verified numerically by a large set of engineering materials as well as experimentally by parallel laboratory tests and data available in the literature. An iterative reverse analysis procedure is proposed such that the uniaxial engineering stress–strain curve of an unknown material (assuming that its elastic modulus is obtained in advance via a separate shallow spherical indentation test or other established methods) can be deduced phenomenologically and approximately from the load–displacement curve of a deep spherical indentation test.

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