Plastic instability of mechanical bulging process for Zircaloy-4 cladding tube based on localized necking criterion

2020 ◽  
Vol 109 (1-2) ◽  
pp. 289-298
Author(s):  
Daw-Kwei Leu
Keyword(s):  
Plastic Instability ◽  
Localized Necking ◽  
Necking Criterion

Damage-coupled FLD of Sheet Metals for Warm Forming and Nonproportional Loading

2011 ◽  
Vol 20 (8) ◽  
pp. 1243-1262 ◽  
Author(s):  
M. Jie ◽  
C. L. Chow ◽  
X. Wu
Keyword(s):  
Evolution Equation ◽  
Damage Evolution ◽  
Strain Softening ◽  
Forming Limit ◽  
Sheet Metals ◽  
Nonproportional Loading ◽  
Damage Evolution Equation ◽  
Localized Necking ◽  
Loading Paths ◽  
Necking Criterion

A method of forming limit prediction for sheet metals at high temperatures and under nonproportional loading is presented. The method takes into account the strain-softening behaviors of the material at elevated temperatures. A localized necking criterion based on an isotropic damage-coupled acoustic tensor is developed and employed to determine the forming limits of strain-softening materials. The damage evolution equation is developed within the thermo-mechanical framework. A closed-form expression of the forming limit strains is derived by coupling the damage evolution equation into the localized necking criterion. A computer program, incorporating the incremental theory of plasticity, the damage evolution equation and the localized necking criterion, is developed to compute the forming limit strains under several nonproportional loading paths. A series of the uniaxial tensile tests is performed to measure the relevant mechanical properties of AA6061 at the elevated temperature of 450°C. The material damage variables are determined from the measured elastic modulii from a series of loading and unloading paths. The damage evolution equation of AA6061 at 450°C is formulated based on the test data. The computed limit strains are compared with the test results under various loading paths and a good agreement is observed. It is found that the critical damage value is independent on the stress states and loading paths. It may be concluded that the application of the material damage as a reliable criterion of localized necking including the nonproportional loading cases.

Study on Instability and Forming Limit of Sheet Metal under Stretch-Bending

2014 ◽  
Vol 611-612 ◽  
pp. 84-91 ◽  
Author(s):  
Bo Hou ◽  
Emin Semih Perdahcıoğlu ◽  
A.H. van den Boogaard ◽  
Daniela Kitting
Keyword(s):  
Tensile Stress ◽  
Sheet Metal ◽  
Stress Gradient ◽  
Sheet Thickness ◽  
Forming Limit ◽  
Localized Necking ◽  
Stretch Bending ◽  
Element Simulation ◽  
Deformation Stages ◽  
Necking Criterion

Under stretch-bending conditions, a significant tensile stress gradient through sheet thickness is induced, especially for a small punch radius. The traditional instability theories were developed assuming a uniform tensile stress / strain distribution through thickness; hence, may lead to unreliable prediction of stretch-bending formability. In this study, the instability behavior of sheet metal under stretch-bending is analyzed via FE-simulation of an Angular Stretch-Bend Test (ASBT). In order to reflect the influence of bending, contact normal stress etc., solid elements are used in the simulation. Three deformation stages are identified: (a). stable deformation; (b). strain localization through sheet thickness; (c). localized necking. Based on the instability characteristics, a localized necking criterion is proposed for predicting forming limits of sheet metal under stretch-bending. By combining the proposed criterion and solid element simulation, good agreement between numerical and experimental results is indicated. This work provides a new approach for predicting stretch-bend formability with sufficient accuracy and convenience.

Limit dome height and failure location of stainless steel tailor-welded blanks

2007 ◽  
Vol 221 (12) ◽  
pp. 1497-1506 ◽  
Author(s):  
M Jie ◽  
C H Cheng ◽  
C L Chow ◽  
L C Chan
Keyword(s):  
Numerical Simulation ◽  
Stainless Steel ◽  
Dome Height ◽  
Forming Limit ◽  
Forming Limits ◽  
Limit Dome Height ◽  
Localized Necking ◽  
Tailor Welded Blanks ◽  
Necking Criterion ◽  
Failure Location

Forming limits of stainless steel tailor-welded blanks (TWBs) are investigated through both testing and numerical simulation. Limit dome height (LDH) tests were performed for 1.2/1.0 mm TWBs with 0°, 90°, 45° weldment orientations and various blank widths. Numerical simulation of the LDH test was conducted with LSDYNA. Since TWB is, in reality, a structure, the forming limits of TWBs in terms of the LDH and failure location should be characterized rather than the conventional forming limit diagrams (FLDs). A localized necking criterion based on the vertex theory was employed to identify the failure sites of TWBs. The localized necking criterion was compiled into a computer program, which processed the output data from LSDYNA. The LDHs and failure locations were computed for various combinations of blank thickness and weldment orientation. The predicted LDH and failure locations were compared with the test results and found to be satisfactory.

Prediction on Localized Necking in Sheet Metal Forming: Finite Element Simulation and Plastic Instability in Complex Industrial Strain Paths

2007 ◽  
Vol 344 ◽  
pp. 825-832 ◽  
Author(s):  
Augusto Barata da Rocha ◽  
Abel D. Santos ◽  
Pedro Teixeira
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Sheet Metal ◽  
Numerical Models ◽  
Plastic Instability ◽  
Linear Strain ◽  
Localized Necking ◽  
Element Simulation ◽  
Non Linear ◽  
Strain Paths

The use of Finite Element Simulation allows accurate predictions of stress and strain distributions in complex stamped parts. The onset of necking is strongly dependent on the strain paths imposed to the parts and therefore the prediction of localized necking can be a difficult task. Numerical models of plastic instability have been used to predict such behavior and recent and more accurate constitutive models have been applied in these calculations. In many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries, the optimization of sheet metal processes, through the use of numerical simulations, has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving. This paper makes an analysis of the evolution of strain gradients in stamped parts. The combination of Finite Element Analysis with a Plastic Instability Model, developed to predict localized necking under complex strain paths, shows that it is possible to predict failure with precision. Several constitutive laws are used and comparisons are made with experiments in stamped benchmark parts. Considering non linear strain paths, as detected in stamped parts, more accurate failure predictions are achieved. The work described in this paper shows the need to include a post processor analysis of failure, capable of predicting the behavior of the material under non linear strain paths. Taking this phenomenon into account, it is shown that it is possible to increase the accuracy of the onset of localized necking prediction.

Localized Necking Criterion for Strain-Softening Materials

2005 ◽  
Vol 127 (3) ◽  
pp. 273-278 ◽  
Author(s):  
C. L. Chow ◽  
M. Jie ◽  
X. Wu
Keyword(s):  
Strain Softening ◽  
Strain Ratio ◽  
Closed Form Expression ◽  
Forming Limit ◽  
Left Hand ◽  
Localized Necking ◽  
Softening Behavior ◽  
Necking Criterion ◽  
Acoustic Tensor ◽  
The Right

The paper presents the development of a localized necking criterion based on the singularity of acoustic tensor. This criterion is applicable to materials exhibiting strain-softening behavior. The tensor form of the criterion is deployed in simple mathematical expressions, based on which the forming limit diagrams (FLDs) of strain-softening materials can be determined. At the left-hand side of a FLD, or the negative strain ratio region, a closed-form expression of localized band inclination is derived as a function of the strain-ratio value. At the right-hand side of a FLD, or the positive strain ratio regions, the localized band is assumed to be perpendicular to major strain according to the MK [Marciniak and Kuczynski (1967)] model. On both sides of the FLD, the localized necking criteria are analytically expressed by elements of tangent modulus matrix. For the sake of illustration of the proposed criterion, a special case of localized necking employing associative and isotropic plasticity is presented. The material chosen for the illustration is AA-6061 at an elevated temperature. The proposed criterion is also applicable to the formability of other metals at high temperatures and other strain-softening materials such as rocks.

On the Theories of Sheet Metal Necking and Forming Limits

1978 ◽  
Vol 100 (3) ◽  
pp. 303-309 ◽  
Author(s):  
A. S. Korhonen
Keyword(s):  
Sheet Metal ◽  
Present State ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Strain Path ◽  
Plastic Instability ◽  
Stretch Forming ◽  
Theoretical Limit ◽  
Forming Limits ◽  
Localized Necking

The history and the present state of the theory of sheet metal forming limits are reviewed. The theory of necking and plastic instability (Swift-Hill and Marciniak-Kuczyn´ski models) is discussed and theoretical limit strains are calculated. The influence of the strain path on the theoretical limit strains is discussed with computational examples. At the present no theory can fully explain the localized necking in stretch forming.

Sign in / Sign up

Export Citation Format

Share Document