Parameters Of Gurson-Tvergaard-Needleman Model Research Articles

Application of the GTN model to predict the forming limit diagram of IF-Steel

Forming limit diagrams (FLDs) are extensively used in industries, particularly the auto industry. The establishment of these diagrams using a predictive approach can lead to reduction in both cost and time. In the present work, Gurson-Tvergaard-Needleman (GTN), a porosity-based model, was used to predict the FLD of an interstitial-free steel via finite element simulation. Optimum values of the GTN model were obtained by applying a response surface methodology (RSM) based on central composite design. Results show that RSM is a good method for an appropriate determination of the GTN model parameters, such as initial void volume fraction, effective void volume fraction, critical void volume fraction, and final void volume fraction. Furthermore, the experimental FLD of the specimen steel was considerably predicted using the obtained GTN model parameters.

Application of response surface methodology to drive GTN model parameters and determine the FLD of tailor welded blank

Tailor welded blanks (TWBs) have found great usage in auto industries; however there are some drawbacks, low formability and weld line movement, which hinder their applications. Prediction of their formability through forming limit diagrams (FLDs) enables one to consider the effects of forming parameters on forming behavior of TWBs. Different numerical approaches have been applied to predict the experimental FLD of these blanks. In the present research Gurson–Tvergaard–Needleman (GTN) model was applied as failure criterion. The parameters of GTN model were firstly derived for both thin and thick monolithic blanks of studied TWB by application of response surface methodology. Then experimental method of obtaining FLD was simulated and FLD of transversely welded TWB was predicted using Abaqus software. The results indicate that the FLD of studied TWB is lower than those related to the parent sheets and there is an appropriate agreement between the predicted and experimental FLDs of the studied TWB.

Forming Limit Stress Diagram Prediction of Aluminum Alloy 5052 Based on GTN Model Parameters Determined by In Situ Tensile Test

The conventional forming limit diagram (FLD) is described as a plot of major strain versus minor strain. However, FLD is dependent on forming history and strain path. In the present study, a forming limit stress-based diagram (FLSD) has been adopted to predict the fracture limit of aluminum alloy (AA) 5052-O1 sheet. Nakazima test is simulated by plastic constitutive formula derived from the modified Gurson-Tvergaard-Needleman (GTN) model. An in situ tensile test with scanning electron microscope (SEM) is proposed to determine the parameters in GTN model. The damage evolution is observed and recorded, and the parameters of GTN model are identified through counting void fraction at three damage stages of AA5052-O1. According to the experimental results, the original void volume fraction, the volume fraction of potential nucleated voids, the critical void volume fraction, the void volume fraction at the final failure of material are assigned as 0.002 918, 0.024 9, 0.030 103, 0.048 54, respectively. The stress and strain are obtained at the last loading step before crack. FLSD and FLD of AA5052-O1 are plotted. Compared with the experimental Nakazima test and uniaxial tensile test, the predicted results show a good agreement. The parameters determined by in situ tensile test can be applied to the research of the forming limit for ductile metals.

Identification of GTN model parameters by application of response surface methodology

A reliable prediction of ductile failure in metals is still a wide-open matter of research. Among different models, Gurson-Tvergaard-Needleman (GTN) has been used extensively. One major issue is the accurate identification of GTN model parameters, which it is not possible to perform experiments for their evaluation. In the present paper a novel inverse procedure aimed to estimate the material parameters of the GTN porosity-based plastic damage model by means of RSM method is represented. The results showed good agreement between experimental and predicted forming limit diagrams when determined GTN parameters were utilized. FE-simulation by means of Abaqus software used to predict FLDs. © 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11

Homogenization-based continuum plasticity-damage model for ductile failure of materials containing heterogeneities

This paper develops an accurate and computationally efficient homogenization-based continuum plasticity-damage (HCPD) model for macroscopic analysis of ductile failure in porous ductile materials containing brittle inclusions. Example of these materials are cast alloys such as aluminum and metal matrix composites. The overall framework of the HCPD model follows the structure of the anisotropic Gurson–Tvergaard–Needleman (GTN) type elasto-plasticity model for porous ductile materials. The HCPD model is assumed to be orthotropic in an evolving material principal coordinate system throughout the deformation history. The GTN model parameters are calibrated from homogenization of evolving variables in representative volume elements (RVE) of the microstructure containing inclusions and voids. Micromechanical analyses for this purpose are conducted by the locally enriched Voronoi cell finite element model (LE-VCFEM) [Hu, C., Ghosh, S., 2008. Locally enhanced Voronoi cell finite element model (LE-VCFEM) for simulating evolving fracture in ductile microstructures containing inclusions. Int. J. Numer. Methods Eng. 76(12), 1955–1992]. The model also introduces a novel void nucleation criterion from micromechanical damage evolution due to combined inclusion and matrix cracking. The paper discusses methods for estimating RVE length scales in microstructures with non-uniform dispersions, as well as macroscopic characteristic length scales for non-local constitutive models. Comparison of results from the anisotropic HCPD model with homogenized micromechanics shows excellent agreement. The HCPD model has a huge efficiency advantage over micromechanics models. Hence, it is a very effective tool in predicting macroscopic damage in structures with direct reference to microstructural composition.