Papers by Keyword: GTN Model

Abstract: Carbon fiber reinforced plastic (CFRP) is applied in various fields such as automobile and aerospace industry due to high specific strength and rigidity than metals. However, since its ductility is poor, there are problems that it is difficult to perform press forming and the production cost increases. In recent years, studies on improving the ductility of CFRP for realizing press forming are gradually increasing. Experiments to obtain the mechanical properties of CFRP are costly and time consuming. Although there are several test standards in the compression test for CFRP, none of them evaluates mesoscale compression characteristics, and it is difficult to capture the deformation of internal fibers and resins when the sheet is subjected to forming. Therefore, establishing an analytical model that expresses the deformation of CFRP by evaluating mesoscale mechanical characteristics would be important to meet the increasing demand for the press forming of CFRP sheets. In this research, by modeling and analyzing CFRP sheets in microscale, the influence of the interaction between resin and fiber within a CFRP during plastic deformation was evaluated. The carbon fiber was modeled to observe its kink behavior based on an orthotropic elastic material model. The epoxy resin was regarded as a ductile material and a Gurson-Tvergaard-Needleman (GTN) model was applied, which represent a viscoelastic plastic material considering damage by void generation, growth and coalescence. Simulations were performed by changing the GTN parameters, and this paper explains the influence of each parameter on formability based on the analysis result.

Abstract: The plastic behavior of the Ti-6Al-4V alloy includes several features as strength differential effect, anisotropy and yield strength sensitivity to temperature and strain rate. Monotonic tensions in the three orthogonal directions of the material are performed to identify the Hill '48 yield criterion. Monotonic compression and plane strain tensile tests are also included in the experimental campaign to identify the orthotropic yield criterion of CPB06. An assessment of the two models is done by comparing the yield loci and the experimental data points for different levels of plastic work. A first approach of the damage modelling of the Ti-6AL-4V alloy is investigated with an extended Gurson-Tvergaard-Needleman damage model based on Hill '48 yield criterion. Finite element simulations of the experiments are performed and numerical results allows checking force-displacement curves until rupture and local information like displacement and strain fields. The prediction ability of the Hill '48, CPB and extended Gurson models are assessed on simple shear and notched tensile tests until fracture.

Abstract: Edge cracking is a commonly observed phenomenon in cold rolling process, but researchers appear to be far from fully understanding its failure mechanism due to the complex stress conditions of steel strip under the rolling condition. In this research, the shear modified GTN damage model coupled with Nahshon-Hutchinson shear damage mechanism was applied to investigate the damage and fracture behavior of steel strip in cold rolling. The results show that the shear modified GTN damage model is competent to predict the damage and fracture behavior of steel strip in cold rolling. By comparison to the cold rolling experiment, it presents that the prediction of edge crack occurrence of the shear modified GTN damage model is more accurate than that of the original GTN damage model.

Abstract: To study the failure process of metal structure with meso-defects, RVE (representative volume element) with various initial meso-defects were analyzed by using ABAQUS software, the parameter f (void volume fraction) of GTN damage model was regarded as the criterion of structural damage. The result shows that f increased more obvious with volume of defects for spherical defects with the same shape but different size. When the radius of defects is less than 0.15mm, the influence of defects’ volume on increases of f is clear enough. When the radius is greater than 0.15mm, the effects is diminishing. For ellipsoidal defects with the same volume but different aspect ratio, when the long axis perpendicular to the direction of load, the increased trend of f according to plastic deformation more obvious along with aspect ratio of defects. Apparently, as aspect ratio approaches infinity, f would have the fastest growth. Consequently, the bigger defect volume and aspect ratio, the more conducive for damage evolution of the metal structure.

Abstract: To characterize the degradation of material at low triaxiality, the shear modified GTN damage model proposed by Nahshon and Hutchinson (2008) was introduced in this study. The details of the numericalimplementation and validation of the model was conducted. And the shear modified parameter was determined by the comparisons of experimental and simulation results of the shear test. Then, the damage model was employed to simulate the cold rolling process, and the results showed that the shear modified GTN model can reveal the damage behavior and predict edge crackingof ductile materials in cold rolling.

Abstract: In this paper the behavior of crack propagation of the strip steel is investigated by using the Gurson-Tvergaard-Needleman (GTN) damage model. The damage parameters used in the damage model are determined by tension experiments and SEM observation. With the aid of finite element method the influences of rolling ruduction and tension on crack propagation are systematically analyzed. The numerical results show that the GTN damage model is available to prediction the initiation and propagation of edge cracks during rolling forming process and the simulation results agrees well with the experimental results.

Abstract: The ability to predict the forming severity with respect to crack and failure is essential to analysis of sheet metal forming process. The forming limit diagram (FLD) is commonly used to gauge the formability of sheet metal. In this article, forming limit diagrams of cold rolled carbon steel (JIS-SPCC), which widely used to produce the parts of automobile, are obtained by performing experiment and FE simulation with the Nakajima-test. By using the GTN (Gurson-Tvergaard -Needleman) damage mechanical model, a failure criterion based on void evolution was examined in this FE simulation. The parameters of GTN model are determined through comparison of experimental and numerical result with Nakajima-test. These parameters acceptably can be used in GTN model using given material. In application case, the reliability of the GTN model for failure criterion in simulation with automotive part was confirmed.

Abstract: Silicon steels tend to develop edge cracks during cold rolling, which need to be removed and cause rupture of the steel in the rolling mill. Hence, it is necessary to understand the formation of edge cracks. The damage distribution and the initiation and propagation of edge cracks occur around the notch tip during cold rolling process was investigated by using GTN damage model. The damage parameters f₀, f_c and f_F are determined by tension experiments and SEM observation. The influence of various rolling parameters on damage distribution and crack length was simulated by using ABAQUS. The numerical results show that the GTN damage model is available to prediction the initiation and propagation of edge cracks during rolling process. Parametric study carried out in this present work reveals that the possible occurrence of edge cracks is higher at larger reduction, higher friction coefficient, smaller roll radius and stronger unit tension. The simulation and experimental results have a good agreement .

Abstract: Powder Metallurgy (PM) component properties are influenced by the pore morphology, size, size-distribution and pore content [1]. Structural alloy Astaloy LH mechanical properties are characterized for density range 6.3 to 7.1 g/cm3. Porosity characterization of the material is also done using ASTM standard. In the first phase, an attempt is made to predict the tensile property using Gurson-Tvergaard-Needleman (GTN) model and FEM. The prediction is verified with tensile test results. It is observed that after fine tuning the parameters in the model, the prediction is found to be close to experimental values.

Abstract: In this study we characterize the fracture toughness of ST37-2 thin metal sheet. The toughness of this material is obtained by using the essential work concept on DENT (Double Edge Notched Test) specimens. These tension tests, show the linearity of the maximal force , the maximal displacement and the final displacement versus the ligament length . These results are confirmed numerically using the Gurson, Tvergaard and Needleman (GTN) micromechanical model. The simulations are carried out using Abaqus software package. A good correlation is obtained between the numerical value of and the essential work of fracture .