scholarly journals Hole-Expansion: Sensitivity of Failure Prediction on Plastic Anisotropy Modeling

2021 ◽  
Vol 5 (2) ◽  
pp. 28
Author(s):  
Jinjin Ha ◽  
Yannis P. Korkolis
Keyword(s):  
Stress State ◽  
Uniaxial Tension ◽  
Plane Strain ◽  
Biaxial Tension ◽  
Plastic Anisotropy ◽  
Yield Function ◽  
Hydraulic Press ◽  
Image Correlation ◽  
Hole Expansion ◽  
Plane Strain Tension

The influence of yield function parameters on hole-expansion (HE) predictions are investigated for an anisotropic AA6022-T4 aluminum sheet. The HE experiment is performed in a fully-instrumented double-action hydraulic press with a flat-headed punch. Full strain fields are measured by a stereo-type digital image correlation (DIC) system. The stress state gradually changes from uniaxial to plane-strain tension to biaxial tension in the radial direction. Besides HE, the plastic anisotropy of AA6022-T4 is characterized by uniaxial tension and plane-strain tension experiments. Uniaxial tension is considered as the most important, since it is the stress state along the hoop direction in the hole. For the finite element (FE) simulation, the Yld2000-2d non-quadratic anisotropic yield function is used with two different parameter sets, calibrated by: (1) uniaxial tension only (termed Calib1) and, (2) both uniaxial and plane-strain tension (Calib2). The strain field predictions show a good agreement with the experiments only for Calib2, which takes into account plane-strain as well uniaxial tension. This indicates the importance of biaxial modes, and in particular plane-strain tension, for the adopted yield function to produce accurate HE simulations.

Modeling of Necking/Shear Failure of Aluminum Sheet Metals With Consideration of Void Nucleation and Growth

2001 ◽  
Author(s):  
W. Y. Chien ◽  
J. Pan ◽  
S. C. Tang
Keyword(s):  
Plane Strain ◽  
Shear Failure ◽  
Failure Strain ◽  
Void Nucleation ◽  
Sheet Material ◽  
Plastic Anisotropy ◽  
Rate Sensitivity ◽  
Sheet Metals ◽  
Plane Strain Tension ◽  
Aluminum Sheets

Abstract Failure of two aluminum sheets, AA5754 and AA6111, under stretching conditions is analyzed using a combined plane stress and plane strain approach. The sheet material is modeled by an elastic-viscoplastic constitutive relation that accounts for material plastic anisotropy, material rate sensitivity, and the softening due to the nucleation, growth, and coalescence of microvoids. Failure processes of sheet metals are modeled under plane strain tension. Also, failure strains are determined under bending conditions when the necking mode is suppressed. The results are consistent with experimental observations where the failure strain of the aluminum sheets increases significantly under bending conditions. The results indicate that when a considerable amount of necking is observed under stretching conditions, failure strains under bending conditions are higher.

scholarly journals Prediction of Strain Path Changing Effect on Forming Limits of AA 6111-T4 Based on A Shear Ductile Fracture Criterion

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 546
Author(s):  
Silin Luo ◽  
Gang Yang ◽  
Yanshan Lou ◽  
Yongqian Xu
Keyword(s):  
Ductile Fracture ◽  
Uniaxial Tension ◽  
Plane Strain ◽  
Strain Path ◽  
Fracture Criterion ◽  
Kinematic Hardening ◽  
Isotropic Hardening ◽  
Ductile Fracture Criterion ◽  
Plane Strain Tension ◽  
Strain Paths

Strain path changing is a phenomenon in the stamping of complex panels or multiple-step stamping processes. In this study, the influence of the strain path changing effect was investigated and assessed for an aluminum alloy of 6111-T4 with a shear ductile fracture criterion. Plastic deformation of the alloy was modeled by an anisotropic Drucker yield function with the assumption of normal anisotropy. Then the shear ductile fracture criterion was calibrated by the fracture strains at uniaxial tension, plane strain tension and equibiaxial tension under proportional loading conditions. The calibrated fracture criterion was utilized to predict forming limit curves (FLCs) of the alloy stretched under bilinear strain paths. The analyzed bilinear strain paths included biaxial tension after uniaxial tension, plane strain tension and equibiaxial tension. The predicted FLCs of bilinear strain paths were compared with experimental results. The comparison showed that the shear ductile fracture criterion could reasonably describe the effect of strain path changing on FLCs, but its accuracy was poor for some bilinear paths, such as uniaxial tension followed by equibiaxial tension and equibiaxial tension followed by plane strain tension. Kinematic hardening is suggested to substitute the isotropic hardening assumption for better prediction of FLCs with strain path changing effect.

Serrated Flow and Surface Markings in Aluminum Alloys

1998 ◽  
Vol 120 (1) ◽  
pp. 48-56 ◽  
Author(s):  
Ming Li ◽  
Daniel J. Lege
Keyword(s):  
Plane Strain ◽  
Continuum Mechanics ◽  
Materials Science ◽  
Imaging System ◽  
Biaxial Tension ◽  
Infrared Thermal Imaging ◽  
Serrated Flow ◽  
Plane Strain Tension ◽  
Mechanics Analysis ◽  
Thermal Imaging System

Serrated flow and associated progressive surface markings severely restrict the application of some aluminum sheet alloys for automotive body exteriors. This paper attempts to approach the phenomenon from the localization theory of continuum mechanics as well as from the classical atomistic and dislocation considerations. Plane strain tension tests were conducted for a commercial Al-Mg alloy (5182-O) at different strain rates and temperatures, and the local temperature changes were measured by an infrared thermal imaging system. Continuum mechanics analysis provided the insight into the myth that band surface markings never appear under biaxial tension strain states. In addition, continuum mechanics analysis shed light on the observation that PLC bands were not seen on the surface of plane strain tension specimens even though the stress-strain curves exhibited serrations. Finally, it is emphasized that only by combining the efforts of continuum mechanics at the macroscale and materials science at the microscale, can a complete understanding of the phenomenon be reached.

Shear band development in polycrystals

1993 ◽  
Vol 443 (1919) ◽  
pp. 547-562 ◽  
Keyword(s):  
Shear Band ◽  
Strain Rate ◽  
Plane Strain ◽  
Simple Shear ◽  
Biaxial Tension ◽  
Short Interval ◽  
Rate Sensitivity ◽  
Band Model ◽  
Plane Strain Tension ◽  
Deformation State

Shear band localizations are studied using a band model involving two polycrystalline aggregates; one representing the material inside the potential band and the other the material outside. Each of these aggregates is assumed to be homogeneously deformed and conditions of compatibility and equilibrium are enforced across the band interfaces. The aggregate constitutive response is obtained from a generalized Taylor polycrystal model, in which each grain is characterized in terms of an elastic–viscoplastic continuum slip constitutive relation, so that no ambiguity arises concerning the choice of active slip systems. Because of the material rate sensitivity a shear band bifurcation is ruled out at achievable strain levels, but localization occurs from the growth of an initial inhomogeneity. Results are presented for imposed loading histories of plane strain tension, biaxial tension and simple shear, both for an initially isotropic aggregate and for an aggregate that has undergone a pre-strain in plane strain compression. Depending on the material properties, the initial conditions and the imposed deformation state, either (i) localization, in the sense of a very high strain rate concentration in the band, takes place; or (ii) the band strain rate increases rapidly for a short interval and then saturates; or (iii) the initial inhomogeneity does not induce a large strain rate concentration in the band. The initial pre-strain promotes earlier localization in plane strain tension and in simple shear. In biaxial tension, localization occurs earlier for the pre-strained material if the initial imperfection is large, but tends to saturate for smaller imperfections. The effects of variations in imperfection amplitude and material strain rate sensitivity are illustrated.

Use of Plane-Strain Tension and Shear Tests to Evaluate Yield Surfaces for AA1050 Aluminium Sheet

2014 ◽  
Vol 794-796 ◽  
pp. 596-601
Author(s):  
Kai Zhang ◽  
Bjørn Holmedal ◽  
Odd Sture Hopperstad ◽  
Stéphane Dumoulin
Keyword(s):  
Experimental Data ◽  
Plane Strain ◽  
Yield Function ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Shear Tests ◽  
Anisotropic Plasticity ◽  
Type Iii ◽  
Plane Strain Tension ◽  
Force Displacement

Plane-strain tension and shear tests were carried out for a fully annealed AA1050 sheet. The tests were simulated numerically with a commercial finite element method (FEM) code using an anisotropic plasticity model including the Yld2004-18p yield function, the associated flow rule and isotropic hardening. The advanced yield function was calibrated by three different methods: using uniaxial tension data combined with FC-Taylor model predictions of the equibiaxial yield stress and r-value, using 201 virtual yield points in stress space, and using a combination of experimental data and virtual yield points (i.e., a hybrid method). The virtual stress points at yielding were provided by the recently proposed Alamel model with the so-called Type III relaxation (Alamel Type III model). FEM simulations of the tests were then made with parameters of Yld2004-18p identified by these three methods. Predicted force-displacement curves were compared to the experimental data, and the accuracy of the parameter identification methods for Yld2004-18p was evaluated based on these comparisons.

scholarly journals Parameter Estimation and Application of Anisotropic Yield Criteria for Cylindrical Aluminum Extrusions: Theoretical Developments and StereoDIC Measurements

2021 ◽  
Vol 11 (20) ◽  
pp. 9701
Author(s):  
Farzana Yasmeen ◽  
Michael A. Sutton ◽  
Xiaomin Deng ◽  
Megan Ryan ◽  
Anthony P. Reynolds
Keyword(s):  
Plastic Anisotropy ◽  
Experimental Studies ◽  
Longitudinal Direction ◽  
Theoretical Models ◽  
Yield Function ◽  
Shear Loading ◽  
Image Correlation ◽  
Yield Model ◽  
Yield Criteria ◽  
Shear Strains

Theoretical and experimental studies are presented to characterize the anisotropic plastic response under torsion loading of two nominally identical aluminum Al6061-T6 extruded round bars. Theoretical models are developed using isotropic (Von Mises 1913) and anisotropic (Barlat 1991) yield criteria, along with isotropic strain hardening formulae, to model post-yield behavior under simple torsion loading. For the case of simple shear loading, incremental plasticity theory is used to determine the theoretical elastic, plastic, and total shear strains. A set of experiments are performed to calibrate Barlat’s 1991 yield function. Several specimens are extracted at different orientations to the longitudinal direction of each round Al6061-T6 bar and tested under uniaxial tension and simple torsion to optimally determine all anisotropic (Barlat 1991) yield function parameters. During loading, Stereo Digital Image Correlation (DIC) is used to quantify surface deformations for the torsion experiments and a baseline tension specimen to identify and correct measurement anomalies. Results show the isotropic yield model either underestimates or overestimates the experimental shear strains for both extrusions. Conversely, results using the Barlat 1991 anisotropic yield criteria are in excellent agreement with experimental measurements for both extrusions. The presence of significant differences in the anisotropic parameters for nominally similar extrusions confirms that plastic anisotropy is essential for the accurate prediction of mechanical behavior in longitudinally extruded Al6061-T6 bars.

scholarly journals Plane strain tension fracture at high strain rate

2021 ◽  
Vol 250 ◽  
pp. 01020
Author(s):  
Morwan Adlafi ◽  
Bertrand Galpin ◽  
Laurent Mahéo ◽  
Christian C. Roth ◽  
Dirk Mohr ◽  
...  
Keyword(s):  
Stress State ◽  
High Strain Rate ◽  
Strain Rate ◽  
Plane Strain ◽  
High Strain ◽  
Tension Stress ◽  
Outer Diameter ◽  
Strain Rates ◽  
High Strain Rates ◽  
Plane Strain Tension

Under plane stress conditions, most micromechanical and phenomenological models predict a minimum in ductility for plane strain tension stress state. Therefore, the stress state of plane strain tension plays a crucial role in many forming and crash applications and the reliable measurement of the strain to fracture for plane strain tension is particularly crucial when calibrating modern fracture initiation models. Recently, a new experimental technique has been proposed for measuring the strain to fracture for sheet metal after proportional loading under plane strain conditions. The basic configuration of the new setup includes a dihedral punch which applies out-of-plane loading onto a Nakazima-type of discshaped specimen with two symmetric holes and an outer diameter of 60 mm. In the present work, the applicability of the test is extended to high strain rates. High strain rates of about 100/s to 200/s are obtained using a drop weight tower device with an original sensor for load measurements. Quasi static tests are also performed for comparison, keeping the same specimen geometry, image recording parameters and set-up. The effective strains at fracture are compared from quasi-static to high strain rate loading for three different materials, i.e one aluminium alloy and two steels.

scholarly journals Plasticity and Formability of Annealed, Commercially-Pure Aluminum: Experiments and Modeling

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4285
Author(s):  
Jinjin Ha ◽  
Johnathon Fones ◽  
Brad L. Kinsey ◽  
Yannis P. Korkolis
Keyword(s):  
Yield Criterion ◽  
Pure Aluminum ◽  
Plastic Anisotropy ◽  
Rate Sensitivity ◽  
Hydraulic Press ◽  
Image Correlation ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Commercially Pure ◽  
Strain Paths

The plasticity and formability of a commercially-pure aluminum sheet (AA1100-O) is assessed by experiments and analyses. Plastic anisotropy of this material is characterized by uniaxial and plane-strain tension along with disk compression experiments, and is found to be non-negligible (e.g., the r-values vary between 0.445 and 1.18). On the other hand, the strain-rate sensitivity of the material is negligible at quasistatic rates. These results are used to calibrate constitutive models, i.e., the Yld2000-2d anisotropic yield criterion as the plastic potential and the Voce isotropic hardening law. Marciniak-type experiments on a fully-instrumented hydraulic press are performed to determine the Forming Limit Curve of this material. Stereo-type Digital Image Correlation is used, which confirms the proportional strain paths induced during stretching. From these experiments, limit strains, i.e., the onset of necking, are determined by the method proposed by ISO, as well as two methods based on the second derivative. To identify the exact instant of necking, a criterion based on a statistical analysis of the noise that the strain signals have during uniform deformation versus the systematic deviations that necking induces is proposed. Finite element simulation for the Marciniak-type experiment is conducted and the results show good agreement with the experiment.

Effects of Strain-Rate and Deformation Mode on Strain-Induced Martensite Transformation of AISI 304L Steel Sheet

2016 ◽  
Vol 835 ◽  
pp. 216-221
Author(s):  
Alexandre de Melo Pereira ◽  
Marcelo Costa Cardoso ◽  
Luciano Pessanha Moreira
Keyword(s):  
Strain Rate ◽  
Plane Strain ◽  
Strain Curve ◽  
Deformation Mode ◽  
Image Correlation ◽  
Temperature Deformation ◽  
Uniaxial Tensile ◽  
Aisi 304L ◽  
Plane Strain Tension ◽  
Uniaxial Tensile Testing

Metastable austenitic stainless steels are prone to strain-induced martensitic transformation (SIMT) during deformation at room temperature, as in the case of sheet metal forming processes. SIMT is influenced by chemical composition, grain size, temperature, deformation mode or stress state and strain-rate effects. In this work, uniaxial and plane-strain tension tests were performed in AISI 304L sheet to evaluate the SIMT as a function of strain-rate. Feritscope and temperature in-situ measurements were performed during the uniaxial tensile testing. Digital image correlation (DIC) technique was employed to determine the in-plane surface strains of the plane-strain tension specimen. From the uniaxial tensile and plane-strain tension results, the yield stress increased with the strain-rate in the small strain range whereas a cross-effect in the stress-strain curve is exhibited in the large strain domain. This effect is attributed to the specimen heat generation, which inhibits the SIMT phenomenon. Conversely, plane-strain deformation mode displayed a higher SIMT rate and an improved work-hardening behavior in comparison to the uniaxial tensile straining.

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