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

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.

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Effect of Yield Surface Curvature on Necking and Failure in Porous Plastic Solids

Journal of Applied Mechanics ◽

10.1115/1.3171801 ◽

1986 ◽

Vol 53 (3) ◽

pp. 491-499 ◽

Cited By ~ 65

Author(s):

R. Becker ◽

A. Needleman

Keyword(s):

Plane Strain ◽

Volume Fraction ◽

Kinematic Hardening ◽

Constitutive Models ◽

Ductile Failure ◽

Isotropic Hardening ◽

Void Coalescence ◽

Potential Surfaces ◽

Plane Strain Tension ◽

Path Dependent

The effect of material path dependent hardening on neck development and the onset of ductile failure is analyzed numerically. The calculations are carried out using an elastic-viscoplastic constitutive relation that has isotropic hardening and kinematic hardening behaviors as limiting cases and that accounts for the weakening due to the growth of micro-voids. Final material failure is incorporated into the constitutive model by the dependence of the plastic potential on void volume fraction. Results are obtained for both axisymmetric and plane strain tension. Failure is found to initiate by void coalescence at the neck center in axisymmetric tension and within a shear band in plane strain tension. The increased curvature of flow potential surfaces associated with the kinematic hardening solid leads to somewhat more rapid diffuse neck development than occurs for the isotropic hardening solid. However, a much greater difference between the predictions of the two constitutive models is found for the onset of ductile failure.

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An Approach for Predicting the Initiation of Ductile Fracture in Plane Strain Rolling

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.827.379 ◽

2019 ◽

Vol 827 ◽

pp. 379-384

Author(s):

Elena Lyamina ◽

Alexander Pirumov ◽

Yeong Maw Hwang

Keyword(s):

Ductile Fracture ◽

Plane Strain ◽

Fracture Criterion ◽

Ductile Fracture Criterion ◽

Axis Of Symmetry ◽

Workability Diagram

The paper extends Orowan’s method to the prediction of ductile fracture in plane strain rolling. In general, any uncoupled ductile fracture criterion can be used in conjunction with the solution found. However, the present paper focuses on a ductile fracture criterion based on the workability diagram. It is assumed that the initiation of fracture occurs at the axis of symmetry.

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Prediction of ductile fracture for Al6016-T4 with a ductile fracture criterion: Experiment and simulation

International Journal of Damage Mechanics ◽

10.1177/1056789519865771 ◽

2019 ◽

Vol 29 (8) ◽

pp. 1199-1221 ◽

Cited By ~ 2

Author(s):

Saijun Zhang ◽

Yanchun Lu ◽

Zhaohui Shen ◽

Chi Zhou ◽

Yanshan Lou

Keyword(s):

Ductile Fracture ◽

Metal Forming ◽

Fracture Criterion ◽

Stress Triaxiality ◽

Yield Function ◽

Isotropic Hardening ◽

Ductile Fracture Criterion ◽

Fracture Locus ◽

Hardening Law ◽

Tension Tests

The key point in this paper is the prediction of the onset of ductile fracture with a newly proposed ductile fracture criterion in various stress state ranging from shear to uniaxial tension. A series of tension tests with different material orientations are carried out up to fracture. The anisotropic Drucker yield function with an isotropic hardening law is identified to describe the elastic–plastic behaviors of Al6016-T4 aluminum alloy. The uncoupled ductile fracture criterion is calibrated and then utilized to construct the fracture locus of Al6016-T4, which is implemented into the ABAQUS/Explicit to validate the prediction of ductile fracture criterion by comparing experimental results to numerical ones. The validation demonstrates that the ductile fracture criterion can accurately predict the onset of ductile fracture for Al6016-T4 in medium stress triaxiality ranging from 0.1 to 0.44 where most ductile fracture occurs in sheet metal forming.

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Strain-Path Effects on the Formability Behavior of Interstitial-Free Steel

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.651-653.126 ◽

2015 ◽

Vol 651-653 ◽

pp. 126-131

Author(s):

Jetson Lemos Ferreira ◽

José Osvaldo Amaral Tepedino ◽

Marco Antonio Wolff ◽

Luciano Pessanha Moreira

Keyword(s):

Uniaxial Tension ◽

Plane Strain ◽

Strain Path ◽

Steel Sheet ◽

Interstitial Free ◽

If Steel ◽

Biaxial Stretching ◽

Nominal Thickness ◽

Strain Paths ◽

If Steel Sheet

In this work, the formability behavior of Interstitial-Free (IF) steel sheet, grade DC07 with 0.65 mm of nominal thickness, was evaluated by means of both linear and bi-linear strain-paths to define the Forming Limit Curve (FLC) at the onset of necking according to ASTM E22182 standard. In the first strain-path, flat-bottomed punch with 200 mm diameter and 10 mm corner die radius was adopted together with counter-blanks of an IF steel sheet grade DC07 with 0.80 mm nominal thickness in order to yield two equal amounts of plastic work under uniaxial tension and under equibiaxial stretching strain-paths. Afterwards, Nakajima’s 100 mm hemispherical punch stretching procedure and bulge tests were adopted to determine the FLC of both as-received and strained DC07 blanks with the help of an automated digital image correlation system to define the linear and bi-linear limit strains. Increasing the straining level (5 and 10%) of the first strain-path in uniaxial tension improved the limit strains of the DC07 steel sheet between the plane-strain intercept (FLC0) and the biaxial stretching region of the FLC. On the other hand, blanks which were firstly pre-strained in equibiaxial stretching mode (4.8 and 9%) provided better formability in the FLC drawing region and reduced limit strains in plane-strain and biaxial stretching regions.

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Finite Plane Strain Bending under Tension of Isotropic and Kinematic Hardening Sheets

Materials ◽

10.3390/ma14051166 ◽

2021 ◽

Vol 14 (5) ◽

pp. 1166

Author(s):

Stanislav Strashnov ◽

Sergei Alexandrov ◽

Lihui Lang

Keyword(s):

Plane Strain ◽

Kinematic Hardening ◽

Tensile Force ◽

Plastic Region ◽

Equivalent Plastic Strain ◽

Isotropic Hardening ◽

Finite Plane ◽

Present Solution ◽

Bending Under Tension ◽

Elastic Unloading

The present paper provides a semianalytic solution for finite plane strain bending under tension of an incompressible elastic/plastic sheet using a material model that combines isotropic and kinematic hardening. A numerical treatment is only necessary to solve transcendental equations and evaluate ordinary integrals. An arbitrary function of the equivalent plastic strain controls isotropic hardening, and Prager’s law describes kinematic hardening. In general, the sheet consists of one elastic and two plastic regions. The solution is valid if the size of each plastic region increases. Parameters involved in the constitutive equations determine which of the plastic regions reaches its maximum size. The thickness of the elastic region is quite narrow when the present solution breaks down. Elastic unloading is also considered. A numerical example illustrates the general solution assuming that the tensile force is given, including pure bending as a particular case. This numerical solution demonstrates a significant effect of the parameter involved in Prager’s law on the bending moment and the distribution of stresses at loading, but a small effect on the distribution of residual stresses after unloading. This parameter also affects the range of validity of the solution that predicts purely elastic unloading.

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Numerical study of chip formation and cutting force in high-speed machining of Ti-6Al-4V bases on finite element modeling with ductile fracture criterion

International Journal of Material Forming ◽

10.1007/s12289-021-01617-9 ◽

2021 ◽

Author(s):

Mehmet Aydın

Keyword(s):

Finite Element ◽

Finite Element Modeling ◽

Ductile Fracture ◽

Cutting Force ◽

Chip Formation ◽

High Speed ◽

Fracture Criterion ◽

Numerical Study ◽

High Speed Machining ◽

Ductile Fracture Criterion

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Comparison of Modified Mohr–Coulomb Model and Bai–Wierzbicki Model for Constructing 3D Ductile Fracture Envelope of AA6063

Chinese Journal of Mechanical Engineering ◽

10.1186/s10033-021-00549-4 ◽

2021 ◽

Vol 34 (1) ◽

Author(s):

Jianye Gao ◽

Tao He ◽

Yuanming Huo ◽

Miao Song ◽

Tingting Yao ◽

...

Keyword(s):

Ductile Fracture ◽

Fracture Criterion ◽

Fracture Strain ◽

Stress Triaxiality ◽

Ductile Fracture Criterion ◽

Forming Process ◽

Tension Tests ◽

Wide Range ◽

Round Bar ◽

Fracture Envelope

AbstractDuctile fracture of metal often occurs in the plastic forming process of parts. The establishment of ductile fracture criterion can effectively guide the selection of process parameters and avoid ductile fracture of parts during machining. The 3D ductile fracture envelope of AA6063-T6 was developed to predict and prevent its fracture. Smooth round bar tension tests were performed to characterize the flow stress, and a series of experiments were conducted to characterize the ductile fracture firstly, such as notched round bar tension tests, compression tests and torsion tests. These tests cover a wide range of stress triaxiality (ST) and Lode parameter (LP) to calibrate the ductile fracture criterion. Plasticity modeling was performed, and the predicted results were compared with corresponding experimental data to verify the plasticity model after these experiments. Then the relationship between ductile fracture strain and ST with LP was constructed using the modified Mohr–Coulomb (MMC) model and Bai-Wierzbicki (BW) model to develop the 3D ductile fracture envelope. Finally, two ductile damage models were proposed based on the 3D fracture envelope of AA6063. Through the comparison of the two models, it was found that BW model had better fitting effect, and the sum of squares of residual error of BW model was 0.9901. The two models had relatively large errors in predicting the fracture strain of SRB tensile test and torsion test, but both of the predicting error of both two models were within the acceptable range of 15%. In the process of finite element simulation, the evolution process of ductile fracture can be well simulated by the two models. However, BW model can predict the location of fracture more accurately than MMC model.

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