Papers by Keyword: Ductile Fracture Criterion

Abstract: In the metal plastic forming process, ductile fracture is an important factor influencing the forming properties of materials, and the ductile fracture criterion can effectively predict the moment and location when the material fracture. When using the ductile fracture criterion predicts the fracture of materials, the material constants expressed in integral form is an important index that affect the prediction accuracy. At present, the method to determine the material constants in the ductile fracture criterion is mostly combined with basic test. Therefore, the method to determine the material constants in ductile fracture criterion is introduced in this paper. These methods are divided into numerical calculation methods, finite element simulation method and the M-K theory model method.

Abstract: Blanking process has high productivity compared with other cutting processes. Because of this feature, the blanking process is used for the manufacture of automobile parts, electronic parts and so on. However, the blanking process is the process that leads to fracture. When the cutting surface are used as the functional surface, such as gears or cams, the precision of cutting surface is important and it can be improved by applying appropriate process conditions. The appropriate process conditions have been determined by repeating many experiments and this process is very inefficient. Owing to this background, the determination of the optimal process condition by numerical method such as the finite element method (FEM) is expected. In the previous studies, blanking process analyses of round blanking process which were modeled as 2D axisymmetric problem have been carried out and the cutting surface that coincided well with the experimental result was obtained. However, the blanking shape was not taken into consideration and they were not considering whether it can be applied to complicated shape expected to be applied in the future. In this study, blanking process analysis of quadrilateral blanking process was modeled as 2D plane strain problem and the applicability of various ductile fracture criteria was examined by comparing numerical results with experimental results based on shear length. As a result, there was little difference in the applicability of Cockcroft and Latham, Ayada, Brozzo ductile fracture criterion to the prediction of shear length under the current conditions.

Abstract: The FEM simulation results of deep drawing process are carried out to create training cases for the artificial neural network (ANN), and then the well-trained ANN(s) is used to predict the formability of aluminum alloy A1100-O sheets. The OYANE’ s ductile fracture criterion equation [J. Mech. Work. Technol. 4 (1980), pp. 65-81] was implemented to predict the formability of deep drawing process. This ductile fracture criterion is introduced and evaluated from the histories of stress and strain calculated by means of finite element analysis in order to get the ductile fracture value (I). The resolution of the results of ductile fracture criterion equations is carried out via a VUMAT user material, using ABAQUS/Explicit finite element code. From the calculative results of FEM simulation with the changing of various parameters, the formability predictions using ANN methodology was investigated by comparing with random case studies of FEM results and shown good agreements

Abstract: Sing point incremental forming (SPIF) limit is much higher than the traditional processes. Currently, there are still no systematic theories and criterions to predict the limit. In this paper, the Oyane ductile fracture criterion is introduced to predict the forming limit of SPIF based on the stress-strain data by the finite element simulations. The predicted fracture initiation sites and the forming limit curve are consistent with the experiment results; further, the forming characteristic, stress state, local temperature are the main reasons of the higher forming limit in SPIF.

Abstract: This paper is concerned with hole flangeability of steel sheet, which is evaluated by experiment and finite element analysis with respect to the hole processing condition. The hole flangeability of a material as a forming limit needs to be verified to predict and prevent the undesirable fracture during a flanging process. Hole expanding tests are carried out to identify the effect of hole processing conditions on the hole expanding ratio (HER), which is an indicator of the hole flangeability. Specimens with two different hole conditions are prepared: one is produced with punching process; and the other is reamed after punching to get smoother hole surface. Experimental results show that the facture mechanism and the HER are quite different with respect to the hole conditions. Thorough investigation of those effects is carried out with tensile tests of a specimen with notches. From the experiments, the fracture strain is obtained with different hole conditions and is used to determine the material constants of a new proposed ductile fracture criterion which is applied to finite element analyses of the hole flanging process for prediction of the HER. The experimental results are confirmed and reevaluated by the finite element analysis with the ductile fracture criterion.

Abstract: This paper investigates the characteristics of a hydro-mechanical punching process. The hydro-mechanical punching process is divided into two stages: the first stage is the mechanical half piercing in which an upper punch goes down before the initial crack is occurred; the second stage is the hydro punching in which a lower punch goes up until the final fracture is occurred. Ductile fracture criteria such as the Cockcroft et al., Brozzo et al. and Oyane et al. are adopted to predict the fracture of a sheet material. The index value of ductile fracture criteria is calculated with a user material subroutine, VUMAT in the ABAQUS
Explicit. The hydrostatic pressure retards the initiation of a crack in the upper region of the blank and induces another crack in the lower region of the blank during the punching process. The final fracture zone is placed at the middle surface of the blank to the thickness direction. The result demonstrates that the hydro-mechanical punching process makes a finer shearing surface than the conventional one as hydrostatic pressure increases.