Prediction of limit strain in sheet metal-forming processes by 3D analysis of localized necking

2000 ◽  
Vol 42 (11) ◽  
pp. 2233-2248 ◽  
Author(s):  
Koichi Ito ◽  
Koichi Satoh ◽  
Moriaki Goya ◽  
Tohru Yoshida
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Limit Strain ◽  
3D Analysis ◽  
Localized Necking

A Generalized Mixed Kinematic-Isotropic Hardening Plastic Model Coupled With Anisotropic Damage for Sheet Metal Forming

2002 ◽  
Author(s):  
C. L. Chow ◽  
X. J. Yang
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Kinematic Hardening ◽  
Isotropic Hardening ◽  
Strain History ◽  
Anisotropic Damage ◽  
Plastic Model ◽  
Localized Necking ◽  
Element Simulation

The paper presents a generalized mixed isotropic-kinematic hardening plastic model coupled with anisotropic damage for sheet metal forming. A nonlinear anisotropic kinematic hardening is developed. For the predication of limit strains at localized necking in stamping under complex strain history, the model and its associated damage criterion for localized necking are established and implemented into LS-DYNA3D by compiling it as a user subroutine. The finite element simulation of LS-DYNA3D based on the present model is carried out. The location of localized necking for sheet metal forming has been successfully identified.

Modelling of Forming Limit Strains of AA5083 Aluminium Sheets at Room and High Temperatures

2016 ◽  
Vol 1135 ◽  
pp. 202-217 ◽  
Author(s):  
José Divo Bressan ◽  
Luciano Pessanha Moreira ◽  
Maria Carolina dos Santos Freitas ◽  
Stefania Bruschi ◽  
Andrea Ghiotti ◽  
...  
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Stress Rupture ◽  
Forming Limit ◽  
Limit Curve ◽  
Local Necking ◽  
Localized Necking

Present work analyses mathematical modelling to predict the onset of localized necking and rupture by shear in industrial processes of sheet metal forming of aluminium alloy 5083 such as biaxial stretching and deep drawing. Whereas the AA5083 sheet formability at room temperature is moderate, it increases significantly at high temperature. The Forming Limit Curve, FLC, which is an essential material parameter necessary to numerical simulations by FEM, of AA 5083 sheet was assessed experimentally by tensile and Nakajima testing performed at room and 400°C temperatures. Tensile test specimens at 0o, 45o and 90o to the direction of rolling (RD) and Nakazima type specimens at 0o RD of aluminium AA5083 were fabricated. Simple tensile tests at room and 400°C temperatures were performed to obtain the coefficients of plastic anisotropy and material strain and strain rate hardening behavior at different temperatures. Nakazima biaxial tests at room and high temperature, employing spherical punch were carried out to plot the limit strains in the negative and positive quadrant of the Map of Principal Surface Limit Strains, MPLS, of aluminium AA5083 sheet. The “Forming Map of Principal Surface Limit Strains”, MPLS, shows the experimental FLC which is the plot of principal true strains in the sheet metal surface (ε1,ε2), occurring at critical points obtained in laboratory formability tests or in the fabrication process of parts. Two types of undesirable rupture mechanisms can occur in sheet metal forming products: localized necking and rupture by induced shear stress. Therefore, two kinds of limit strain curves can be plotted in the forming map: the local necking limit curve FLC-N and the shear stress rupture limit curve FLC-S. Localized necking is theoretically anticipated to occur by two mathematical models: Marciniak-Kuczynski modelling, hereafter M-K approach, and D-Bressan modeling. Prediction of limit strains are presented and compared with the experimental FLC. The shear stress rupture criterion modeling by Bressan and Williams and M-K models are employed to predict the forming limit strain curves of AA5083 aluminium sheet at room and 400°C temperatures. As a result of analysis, a new concept of ductile rupture by shear stress and local necking are proposed. M-K model has good agreement with both D-Bressan models.

A Unified Bifurcation Analysis of Sheet Metal Forming Limits

2001 ◽  
Vol 123 (3) ◽  
pp. 329-333 ◽  
Author(s):  
Xinhai Zhu ◽  
Klaus Weinmann ◽  
Abhijit Chandra
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Yield Criterion ◽  
Strain Ratio ◽  
Thin Sheets ◽  
Dimensional Problem ◽  
Localized Necking ◽  
Extension Direction ◽  
Zero Extension

The purpose of this study is to determine analytically the orientations of localized necks occurring in sheet metal forming processes, and obtain the corresponding forming limit diagrams (FLDs). In addition to the force equilibrium condition as adopted by other researchers, we include the moment equilibrium in this study. The shear terms due to the perturbation are found to vanish inside the localized neck of a region of deformation. This simplifies the two-dimensional problem to a one-dimensional problem. Furthermore, it is found that there are only three possible orientations for the initiation of a localized neck, i.e., two principal directions and one zero extension direction (which applies only to negative strain ratio deformations). A special case study using the von Mises yield criterion is also presented in this paper. Predictions from our unified analysis matches with the results of Hill, R., 1952, “On Discontinuous Plastic States, With Special Reference to Localized Necking in Thin Sheets,” J. Mech. Phys. Solids, 1, pp. 19–30. For the negative strain ratio regime (left-hand side of the FLDs), and with the results of Storen, S., and Rice, R., 1975, “Localized Necking in Thin Sheets,” J. Mech. Phys. Solids, 23, pp. 421–441. For the positive strain ratio regime (right hand-side of the FLD). When the localized neck is assumed to be in the zero extension direction for the negative strain ratio deformation, deformation theory and flow theory of plasticity give the same limit strains, and a unified solution to the limit strain is obtained. This solution is independent of the specific yield criterion used.

Numerical and Experimental Study of Forming Limit Diagrams in Sheet Metal Forming and Seamed Tube Hydroforming

2013 ◽  
Vol 395-396 ◽  
pp. 914-919 ◽  
Author(s):  
Ren Tao Zhang ◽  
Xian Feng Chen ◽  
Hai Bo Su ◽  
Zhi Yong Chen
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Experimental Approach ◽  
Tube Hydroforming ◽  
Numerical Approach ◽  
Forming Limit ◽  
Forming Limit Diagrams ◽  
Localized Necking ◽  
Biaxial Stretching

The paper establishes the forming limit diagrams (FLDs) for QSTE340 seamed tube hydroforming and the mother sheet metal forming by numerical approach and experimental approach. A novel experimental approach is proposed to evaluate the formability for tube hydroforming under biaxial stretching through elliptical bulging.Then the Nakazima and three types of tube hydroforming tests are simulated with finite element (FE) program LS-DYNA. The failure criterion of thickness gradient criterion (TGC) is introduced. The FLDs for seamed tube hydroforming and the mother sheet metal forming are constructed. The comparison of results based on TGC with experimental data shows the TGC is an appropriate one to determine the onset of localized necking. Finally, the differences and relationships between the FLDs for the seamed tube hydroforming and the mother sheet metal forming are discussed.

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.

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