Forming Limits Under Stretch-Bending Through Distortionless and Distortional Anisotropic Hardening

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Ji He ◽  
Bin Gu ◽  
Yongfeng Li ◽  
Shuhui Li
Keyword(s):  
Detailed Comparison ◽  
Forming Limit ◽  
Anisotropic Hardening ◽  
Hardening Model ◽  
Stretch Bending ◽  
Bending Process ◽  
Hardening Models ◽  
Out Of Plane ◽  
Forming Limit Curves ◽  
Insight Into

The necking behavior of sheet metals under stretch-bending process is a challenge for the forming limit prediction. State-of-the-art forming limit curves (FLCs) allow the prediction under the in-plane stretching but fall short in the case under out-of-plane loading condition. To account for the bending and straightening deformation when sheet metal enters a die cavity or slide along a radius, anisotropic hardening model is essential to reflect the nonproportional loading effect on stress evolution. This paper aims to revisit the M-K analysis under the stretch-bending condition and extend it to accommodate both distortionless and distortional anisotropic hardening behavior. Furthermore, hardening models are calibrated based on the same material response. Then the detailed comparison is proposed for providing better insight into the numerical prediction and necking behavior. Finally, the evolution of the yield surface and stress transition states is examined. It is found that the forming limit prediction under stretch-bending condition through the M-K analysis strongly depends on the employed anisotropic hardening model.

Void Nucleation Effects in Biaxially Stretched Sheets

1980 ◽  
Vol 102 (3) ◽  
pp. 249-256 ◽  
Author(s):  
C. C. Chu ◽  
A. Needleman
Keyword(s):  
Plastic Strain ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Hydrostatic Stress ◽  
Forming Limit ◽  
Stress Theory ◽  
Out Of Plane ◽  
Necking Criterion ◽  
Controlled Nucleation ◽  
Forming Limit Curves

The effects of void nucleation occurring during the deformation history on forming limit curves are considered for both in-plane and punch stretching employing a constitutive model of a porous plastic solid. Both plastic strain controlled and stress controlled nucleation processes are simulated by a two parameter void nucleation criterion. For in-plane stretching, plastic strain controlled nucleation can have, in certain circumstances, a significantly destabilizing effect on the forming limit curve. However, within the framework of plane stress theory which neglects the enhancement of the hydrostatic stress due to necking, a stress controlled nucleation process is not found to be significantly destabilizing. In punch stretching a ductile rupture criterion, which limits the maximum volume fraction of voids, as well as the appearance of a well defined thickness trough, is adopted as a localized necking criterion. Only plastic strain controlled void nucleation is considered here in out-of-plane stretching. The resulting forming limit curves have the same shape as those obtained previously with void nucleation neglected.

M–K Analysis of Forming Limit Diagram Under Stretch-Bending

2012 ◽  
Author(s):  
Ji He ◽  
Z. Cedric Xia ◽  
Shuhui Li ◽  
Danielle Zeng
Keyword(s):  
Sheet Metal ◽  
Deformation Theory ◽  
Plane Deformation ◽  
Forming Limit Diagram ◽  
Flow Theory ◽  
Forming Limit ◽  
Bending Effect ◽  
Stretch Bending ◽  
Right Hand ◽  
Bending Process

Since the Forming limit diagram (FLD) was introduced and developed by Keeler etc. about four decades ago, it has been intensively studied by researchers and engineers. Most work has been focused on the in-plane deformation which is considered as the dominant mode of the most forming processes. However the effect of out-of-plane deformation modes especially bending effect becomes important in accurate prediction of formability when thick sheet metal and smaller forming radii are encountered. Recent work on experiment research of stretch-bending induced FLD (BFLD) shows that it gives higher formability than conventional forming limit. In this paper, bending effect through the sheet metal thickness on right-hand side of FLD is studied. The Marciniak-Kuczynski (M-K) analysis is extended to include bending and models based on both flow theory and deformation theory are proposed. The radial return method is adopted as the frame to calculate the stress states from given strain and deformation history. The effect of bending and unbending process on the Right-Hand-Side FLD is investigated and compared. The obtained results show that the bending process slightly decreases the sheet metal formability on right-hand side in flow theory based model which is a discrepancy with the prediction of deformation theory based BFLD model. The insight gained from new proposed FLD prediction model in this paper provides an understanding of how the bending process effects on the FLD. This is important for the further research to reconsider the problems of how the bending effect evolves in forming process to enhance the conventional FLD and how to get a perfectly true theoretical explanation for this phenomenon.

scholarly journals Comparison of Constitutive Models for predicting the formability of SS 304 by tubular hydroforming process

2022 ◽  
Vol 12 (1) ◽  
pp. 0-0
Keyword(s):  
Constitutive Modeling ◽  
Constitutive Models ◽  
Tensile Tests ◽  
Forming Limit ◽  
Uniaxial Tensile ◽  
Hardening Models ◽  
Forming Precision ◽  
Hydroforming Process ◽  
Ss 304 ◽  
Forming Limit Curves

Finite Element (FE) simulation of sheet/tube forming precision depends mainly on the accuracy of the constitutive modeling. The present paper aim is to compare the constitutive models to fit the stress-strain curves. The accurate deformation behavior of the SS 304 tubes depends on the constitutive modeling of hardening behavior. Deformation data of the tensile specimens cut from tubular sample were collected by conducting Uniaxial tensile tests (UTT) at three different rolling directions. Five constitutive relationships were then recognized by fitting the true stress and strain data with the constitutive models of Hollomon, Power, Krupowsky, Voce and Ghosh, and the fitting accuracy were analyzed and compared. Effects of hardening models on Forming Limit Curves (FLC), pressure loading and bulge height of the hydroformed tube were then studied. The obtained FLC from the simulations were compared with experimental FLC to predict the accuracy of the hardening models.

scholarly journals Electrically Assisted Stretch Bending of Aluminum Extruded Profile

2018 ◽  
Vol 175 ◽  
pp. 03056
Author(s):  
Fengchao Cao ◽  
Yuansong Zeng ◽  
Baosheng Liu
Keyword(s):  
Electrical Power ◽  
Hydraulic Cylinder ◽  
Electrical Heating ◽  
Forming Limit ◽  
Stretch Bending ◽  
Electrically Assisted ◽  
Aluminum Profile ◽  
Tension Tests ◽  
Assembly Accuracy ◽  
Bending Process

Aluminum extruded profile is widely applied in aircraft frame parts whose forming quality is directly related to the assembly accuracy, aerodynamic shape and the service life of aircraft. However, it normally faces difficulties of large springback and low forming limit while forming at room temperature by stretch bending method. Here, electricity was applied in stretch bending process to heat aluminum profile aiming at improving the formability and reducing the springback by using electrically assisted stretch bending machine which is consisted of electrical power with the capability of 10000A and 40000kN stretching force for each hydraulic cylinder. In this research, a set of uniaxial tension tests was performed at different temperature to determine the relationship between the deformation behavior of aluminum profile and temperature. Then, a series of stretch bending tests were conducted to investigate the springback law of the aluminum profile. The corresponding stretch bending parts were obtained under different conditions. The experiment results show that, the plasticity of aluminum profile can be improved when the temperature rises, and the springback of aluminum profile can be reduced even more due to the electrical heating effect compared to the cold stretch bending process. Therefore, the forming accuracy of aluminum profile can be improved in electrically assisted stretch bending process.

M–K Analysis of Forming Limit Diagram Under Stretch-Bending

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Ji He ◽  
Z. Cedric Xia ◽  
Shuhui Li ◽  
Danielle Zeng
Keyword(s):  
Deformation Theory ◽  
Plane Deformation ◽  
Forming Limit Diagram ◽  
Flow Theory ◽  
Dominant Mode ◽  
Forming Limit ◽  
Thick Sheet ◽  
Bending Effect ◽  
Stretch Bending ◽  
Bending Process

Since the forming limit diagram (FLD) was introduced by Keeler, etc., five decades ago, it has been intensively studied by researchers and engineers. Most work has focused on the in-plane deformation which is considered as the dominant mode of the majority forming processes. However the effect of out-of-plane deformation becomes important in the accurate prediction of formability when thick sheet metals and/or smaller forming radii are encountered. Recent research on the stretch-bending induced FLD (BFLD) has been inconclusive. Some studies indicated that the bending effect will enhance a sheet metal's formability while others suggested otherwise. In this paper, we present an in-depth study of the through-thickness bending effect on the forming limits. The Marciniak–Kuczynski (M–K) analysis is extended to include bending, and models based on both flow theory and deformation theory of plasticity are proposed. The study is limited to the right-hand-side of FLD where the bending is along the major stretch direction. The radial return method is adopted as the framework to integrate constitutive equations. The results show that the bending process decreases the sheet metal formability with the flow-theory based model, while the opposite is true if the deformation theory based analysis is adopted. A detailed examination of the deformation histories from those two models reveals that the loading–unloading-reverse loading process during stretch-bending holds the key to the understanding of the conflicting results. The insight gained from the proposed FLD prediction model in this paper provides a new understanding of how the bending process affects the FLD, which can be used to predict and explain the localized necking phenomenon under the stretch-bending condition.

Research on springback characteristic in flexible multi-points 3D stretch-bending process

2021 ◽  
pp. 095440542110284
Author(s):  
Song Gao ◽  
Tonggui He ◽  
Qihan Li ◽  
Yingli Sun ◽  
Jicai Liang
Keyword(s):  
Simulation Model ◽  
High Efficiency ◽  
Vertical Direction ◽  
Factors Affecting ◽  
Stretch Bending ◽  
Element Simulation ◽  
Bending Process ◽  
Bending Radius ◽  
Aluminum Profiles ◽  
Bending Sequence

The problem of springback is one of the most significant factors affecting the forming accuracy for aluminum 3D stretch-bending parts. In order to achieve high-efficiency and high-quality forming of such kind of structural components, the springback behaviors of the AA6082 aluminum profiles are investigated based on the flexible multi-points 3D stretch-bending process (3D FSB). Firstly, a finite element simulation model for the 3D FSB process was developed to analyze the forming procedure and the springback procedure. The forming experiments were carried out for the rectangle-section profile to verify the effectiveness of the simulation model. Secondly, the influence of tension on springback was studied, which include the pre-stretching and the post-stretching. Furthermore, the influences of the bending radius and bending sequence are revealed. The results show that: (1) The numerical model can be used to evaluate the effects of bending radius and process parameters on springback in the 3D FSB process effectively. (2) The pre-stretching has little effect on the horizontal springback reduction, but it plays a prominent role in reducing the springback in the vertical direction. (3) The increase of bending deformation in any direction will lead to an increase of springback in its direction and reduce the springback in the other direction. Besides, it reduces the relative error in both directions simultaneously. This research established a foundation to achieve the precise forming of the 3D stretch-bending parts with closed symmetrical cross-section.

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