Necking Prediction in Tube Hydroforming by Stress-Based Forming Limit Diagrams

2011 ◽  
Vol 462-463 ◽  
pp. 284-288
Author(s):  
A. Jaamialahmadi ◽  
Mehran Kadkhodayan
Keyword(s):  
Tube Hydroforming ◽  
Yield Function ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Equilibrium Equations ◽  
Forming Limit Diagrams ◽  
Fea Simulation ◽  
Yield Loci ◽  
The Hill ◽  
Practical Forming

Path-independent stress based forming limit diagrams for anisotropic materials along with the Hill 48 yield function; power law strain hardening and isotropic hardening are derived. Bifurcation analyses via solving equilibrium equations of a pointed vertex on subsequent yield loci are utilized. The presented practical forming limit diagrams (FLSDs) show more acceptable agreements with experimental data compared with those obtained by other methods. A typical neck detection macro in APDL is developed by FEA simulation for a free bulge tube hydroforming to confirm the significant simplicity and straightforwardness of the mentioned FLSD.

Numerical Determination of Sheet Metal Forming Limit Based on a New Combined Model of M-K Theory and Shear Localization Criterion

2013 ◽  
Vol 330 ◽  
pp. 821-825
Author(s):  
L.C. Chan
Keyword(s):  
Sheet Material ◽  
Yield Function ◽  
Shear Localization ◽  
Alloy Sheet ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Combined Model ◽  
Limit Model ◽  
K Theory ◽  
Localization Criterion

A combined forming limit model of M-K theory and shear localization criterion is proposed in this paper to study the formability of 6016-T4 Aluminum alloy sheet, with the sheet material modeled by the Yld2000-2d yield function and two isotropic hardening models. The forming limit curve (FLC) of the material can be predicted well using the M-K model in the right region, and using the shear localization criterion in the left region. The critical plane strain of the material was computed using the M-K model and then used to determine the shear localization criterion. In fact, the combined model takes advantage of both of these theories. As a consequence, the results obtained from the proposed combined necking model seem to agree satisfactorily with those of the experiments.

A New Description of Yield Loci Based on Polycrystal Plasticity for High Strength Steels

2009 ◽  
Vol 410-411 ◽  
pp. 543-553
Author(s):  
Yu Guo An ◽  
Henk Vegter ◽  
Louisa Carless
Keyword(s):  
High Strength Steels ◽  
High Strength ◽  
Yield Function ◽  
Mechanical Tests ◽  
Stress Factors ◽  
Shear Mode ◽  
Polycrystal Plasticity ◽  
Yield Loci ◽  
Constraint Model ◽  
The Hill

Recently, many flexible constitutive equations have been proposed for sheet forming simulations. However, various mechanical tests are required to determine the many material parameters needed for such models. In the present work, effort has been made to investigate the correlation between the polycrystal plasticity based yield loci and those determined from mechanical tests, in order to define yield functions easily and accurately with minimum amount of experimental work. The results for different materials indicate that, in many cases, the Hill’48 deviates significantly from the measured yield loci. The yield loci derived from measured texture and polycrystal plasticity perform better than the Hill’48 yield function in general. Based on the two yield loci derived from the Taylor full constraint model and the Pancake model, a new combined model is proposed. The new model uses the averaged biaxial points of the two models but keeps the shape of the yield loci derived from the Taylor full constraint model in the stretching regime. The stress factors in the uniaxial and shear mode are calculated by averaging the stress factors of the two models. The proposed new description has been validated using several steel grades.

On the Improvement of Formability and the Prediction of Forming Limit Diagrams at Fracture by Means of Constitutive Modelling

2012 ◽  
Vol 504-506 ◽  
pp. 29-34 ◽  
Author(s):  
Yalin Kiliclar ◽  
Marcus Engelhardt ◽  
Ivaylo N. Vladimirov ◽  
Michael P. Pietryga ◽  
Hermann von Senden genannt Haverkamp ◽  
...  
Keyword(s):  
High Speed ◽  
Materials Science ◽  
Kinematic Hardening ◽  
Deformation Gradient ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Forming Process ◽  
Element Analysis ◽  
Forming Limits ◽  
Forming Limit Diagrams

Sheet metal forming processes are well-established in production technology for the manufacturing of large quantities. To increase the formability, the processing limit of a single forming process can be enhanced by a combination of quasi-static and high-speed forming process. The forming limits for both operations for the aluminum alloy EN AW 6082 T6 obtained via simulations and experiment are investigated in a research cooperation between the Institute of Materials Science (IW) and the Institute of Applied Mechanics (IFAM). Significant changes in forming limits with higher strain rates are indicated by the experimental results. Here, the forming limit curves move to the lower right hand side. The processes are simulated and the FLD at fracture are predicted by means of finite element analysis. The constitutive model is based on the multiplicative split of the deformation gradient. It is coupled with ductile damage and combines nonlinear kinematic and isotropic hardening. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. The coupling of damage and viscoplasticity is carried out following the well-known concept of effective stress and the principle of strain equivalence. Using these powerful tools the simulation of dynamic effects and the prediction of forming limit diagrams at fracture shows good correlation with the experiments.

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.

Fundamental Concepts for “Corner” Forming Limit Diagrams and Closed-Form Formulas for Planar Tube Hydroforming Analysis

2005 ◽  
Vol 128 (4) ◽  
pp. 874-883 ◽  
Author(s):  
L. M. Smith ◽  
J. J. Caveney ◽  
T. Sun
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Closed Form ◽  
Tube Hydroforming ◽  
Experimental Results ◽  
Forming Limit ◽  
The Finite Element Method ◽  
Forming Limit Diagrams ◽  
Form Approach ◽  
Good Agreement

A family of closed-form formulas for calculating minimum corner-fill radii in planar sections of tube hydroformed products is introduced. Corner forming limit diagrams relating the limiting major strain to the minimum corner-fill radius are introduced. The theory accounts for friction effects and accommodates regular shaped polygon die sections. This effort represents an exploration into a method for design and analysis of tube hydroforming processes without employing the finite element method and while using a closed form approach for capturing friction effects. Good agreement with experimental results is observed.

Optimization of Tube Hydroforming Process Using Probabilistic Constraints on Failure Modes

2011 ◽  
Vol 62 ◽  
pp. 21-35 ◽  
Author(s):  
Anis Ben Abdessalem ◽  
A. El Hami
Keyword(s):  
Failure Modes ◽  
High Reliability ◽  
Thickness Distribution ◽  
Tube Hydroforming ◽  
Forming Limit Diagram ◽  
Plastic Instability ◽  
Probabilistic Constraints ◽  
Forming Limit ◽  
Reliability Based Design ◽  
Hydroforming Process

In metal forming processes, different parameters (Material constants, geometric dimensions, loads …) exhibits unavoidable scatter that lead the process unreliable and unstable. In this paper, we interest particularly in tube hydroforming process (THP). This process consists to apply an inner pressure combined to an axial displacement to manufacture the part. During the manufacturing phase, inappropriate choice of the loading paths can lead to failure. Deterministic approaches are unable to optimize the process with taking into account to the uncertainty. In this work, we introduce the Reliability-Based Design Optimization (RBDO) to optimize the process under probabilistic considerations to ensure a high reliability level and stability during the manufacturing phase and avoid the occurrence of such plastic instability. Taking account of the uncertainty offer to the process a high stability associated with a low probability of failure. The definition of the objective function and the probabilistic constraints takes advantages from the Forming Limit Diagram (FLD) and the Forming Limit Stress Diagram (FLSD) used as a failure criterion to detect the occurrence of wrinkling, severe thinning, and necking. A THP is then introduced as an example to illustrate the proposed approach. The results show the robustness and efficiency of RBDO to improve thickness distribution and minimize the risk of potential failure modes.

The bending dependency of forming limit diagrams

2018 ◽  
Vol 12 (5) ◽  
pp. 815-825 ◽  
Author(s):  
Felix M. Neuhauser ◽  
Oscar Terrazas ◽  
Niko Manopulo ◽  
Pavel Hora ◽  
Chester Van Tyne
Keyword(s):  
Forming Limit ◽  
Forming Limit Diagrams
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