Application of an Advanced GTN Model

Conference (2012)

On the numerical integration of an advanced Gurson model

in International Journal for Numerical Methods in Engineering (2011), 85(8), 1049-1072

This article is focused on a new extended version of Gurson's model (J. Eng. Mater. Technol. 1977; 99:2–15), its numerical integration scheme and its consistent tangent matrix being within an FE code ... [more ▼]

This article is focused on a new extended version of Gurson's model (J. Eng. Mater. Technol. 1977; 99:2–15), its numerical integration scheme and its consistent tangent matrix being within an FE code. First, this new advanced Gurson model is proposed, which is an extension of the original to take into account plastic anisotropy and mixed (isotropic+kinematic) hardening. In this paper, only the growth phase of cavities is considered (the nucleation of new voids is ignored). Second, a new numerical algorithm for the integration of this new Gurson model is presented. The algorithm is implicit in all variables and is unconditionally stable. This algorithm is generic and could be used for other anisotropic yield functions and other hardening laws. Third, the consistent tangent matrix is computed in an explicit way by exact linearization of the constitutive equations. To check its efficiency and robustness, the proposed integration algorithm is compared, under some simplified assumptions and choices, with the algorithms of Aravas (Int. J. Numer. Meth. Engng 1987; 24:1395–1416) and Kojic (Int. J. Numer. Meth. Engng 2002; 53(12):2701–2720). The performance of the developed consistent modulus, compared to other techniques for the computation of the tangent matrix is assessed. The paper ends with numerical simulations of tensile tests on homogeneous and notched specimens. [less ▲]

Investigation of the Efficiency of the Ti555 Compared with TA6V Alloy in the Case of an Aeronautic Application

in Proceedings of the 12th World Conference on Titanium (2011)

Investigation of the efficiency of the Ti555 compared with TA6V alloy in the case of an aeronautic application

in The 12th World Conference on Titanium Ti-2011 (2011)

Numerical modeling of damage evolution of DP steels on the basis of X-ray tomography measurements

in Mechanics of Materials (2011)

In order to couple the damage evolution and the stress state of DP steel grades, a new advanced GTN (Gurson-Tvergaard-Needleman) model was developed and implemented into a finite element code. This model ... [more ▼]

In order to couple the damage evolution and the stress state of DP steel grades, a new advanced GTN (Gurson-Tvergaard-Needleman) model was developed and implemented into a finite element code. This model is an extension of the original one. It takes into account the plastic anisotropy and the mixed (isotropic+ kinematic) hardening of the matrix. Two different methods to compute the void volume fraction were developed and used within the constitutive equations. The first method is new and allows the accurate modeling of the observations of damage initiation and growth in DP steels measured using high-resolution X-ray absorption tomography (Bouaziz et al., 2008; Maire et al., 2008). The second method is classic and assumes the additive decomposition of the total void volume fraction into a nucleation and a growth part. A parametric study is carried out to assess the effect of the kinematic hardening on some mechanical parameters such as the equivalent plastic strain, the triaxiality and the porosity. The numerical predictions are favorably compared to the experimental results. [less ▲]

Simulation of bending process of hardening metallic sheets using damage model. Part II: Numerical investigations

in Materials Science & Engineering : A (2010), 528(1), 442-448

In the first part of this paper, the theoretical aspects and the algorithmic developments related to the construction of the PBST (Pure Bending Simulation Tool) were provided. In this second part, this ... [more ▼]

In the first part of this paper, the theoretical aspects and the algorithmic developments related to the construction of the PBST (Pure Bending Simulation Tool) were provided. In this second part, this tool is used to simulate the pure bending process. The sensitivity of the bendability prediction to certain mechanical properties and phenomena (such as initial porosity and hardening parameters) is investigated by means of a parametric study. The efficiency and the performance of this tool (in terms of accuracy and computation time) compared to the FE method are shown through various numerical simulations. [less ▲]

Effect of a decrease in sample dimensions on plasticity: application to the micro-forming of nickel

in Steel Research International (2010), 81(9), 1173-1177

The mechanical behavior of polycrystalline nickel is investigated in tension as a function of the dimensions. Experimental tests and finite element simulations with a crystalline plasticity code are ... [more ▼]

The mechanical behavior of polycrystalline nickel is investigated in tension as a function of the dimensions. Experimental tests and finite element simulations with a crystalline plasticity code are carried out for samples with thicknesses ranging between 12.5 μm and 3.2 mm and grain size around 100 μm. Results show three different kinds of behavior depending on the number of grains across the thickness due to the apparition of stress and dislocation density gradients. Bulge tests are then used to study the formability of nickel polycrystals with thickness lower than 400 μm. [less ▲]

Comparison of mechanical efficiency of two microstructures of Ti5553 alloy in the case of bolted flanges submitted to tensile loading

in Steel Research International (2010), 81(9), 1148-1152

A combination of numerical and experimental methods is used to compare the efficiency of two microstructures of Ti5553 titanium alloy in an industrial test case. The test case consists in two parts of ... [more ▼]

A combination of numerical and experimental methods is used to compare the efficiency of two microstructures of Ti5553 titanium alloy in an industrial test case. The test case consists in two parts of sectors of aircraft engine stators linked together by an Inconel bolt and submitted to tensile loading. The efficiency of these microstructures is evaluated by using finite element (FE) models. The chosen FE models take into account elasto-visco-plastic material behaviors, contact with friction (bolt heads/flanges and flange/flange), and the initial bolt tightening. The parameters of the elasto-visco-plastic (EVP) material law are adjusted from experimental results extracted from tensile tests performed on Inconel, and Ti5553 alloys. Viscous properties are observed at different strain rates. The studied alloy is assumed to be plastically isotropic. In order to compare the fracture resistance of both microstructures, a micro-mechanical (damage based) rupture model ([4]) is used as a FE post-processing step. [less ▲]

The Role of Void Evolution on the bendability of Steel Sheets

in Oñate, E.; Owen, D. R. J. (Eds.) Computational plasticity X. Fundamentals and applications (2009, September)

In the present contribution, an advanced Gurson model is developed and implemented in the Lagamine finite element code[1. This model is used to simulate the bending process and to predict the bendability ... [more ▼]

In the present contribution, an advanced Gurson model is developed and implemented in the Lagamine finite element code[1. This model is used to simulate the bending process and to predict the bendability of the studied sheet. [less ▲]

Study of the formability of steels

in Proceedings of the International ESAFORM Conference 2009 (2009)

In the present contribution, a new advanced Gurson model [1] is developed. This new model is an extension of the initial one, to the plastic anisotropy and the mixed (isotropic+ kinematic) hardening of ... [more ▼]

In the present contribution, a new advanced Gurson model [1] is developed. This new model is an extension of the initial one, to the plastic anisotropy and the mixed (isotropic+ kinematic) hardening of the fully dense matrix. The nucleation and the growth phases are considered by integrating the empirical laws developed by Bouaziz et al. [2] in this new model. These laws, identified on the basis of X-ray microtomography results, display the triaxiality effect on the nucleation and the growth of cavities. This advanced Gurson model is implemented into a finite element code by using an implicit-explicit integration scheme. FE simulations study the behavior of a sample submitted to tensile test and assess the influence of nucleation and growth laws on the formability of this sample. [less ▲]