• Transactions of Materials Processing
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• v.3 no.2
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• pp.167-177
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• 1994

Most of bulk metal forming processes may be limited by ductile fracture such as surface or internal cracks developing in the workpiece. It is important to identify the conditions within the deforming workpiece which may lead to fracture, and then it is possible to modify the forming processes to produce sound and reliable product. This paper suggests the scheme to simultaneously accomplish prediction of fracture initiation and analysis of deformation in metal forming processes. The Cockcroft-Latham criterion which is successfully applied to a variety of loading situations is used in the present investigation to estimate whether fracture occurs during the deformation process. The numerical predictions and experimental results of two types of metal forming process are compared, axisymmetric extrusion and simple upsetting. The proposed scheme has successfully predicted the fracture initiation found experimentally.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.183-191
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• 1994

This paper suggests the scheme to simultaneously accomplish prediction of fracture initiation and analysis of deformation in metal forming processes. the Cockcroft-Latham criterion is used to estimate whether fracture occurs during the deformation process. The numerical predictions and experimental results of simple upsetting are compared. The proposed scheme successfully predicted the fracture initiation found experimentally.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.347-350
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• 2003

The metal forming behavior and defect formation in Ti-6Al-4V tube during hot backward extrusion were investigated. To predict the forming-defects such as shear band, inner cracks or surface cracks, dynamic material model(DMM) including Ziegler's instability criterion and modified Cockcroft-Latham fracture criterion(C-L model) were used. These models were coupled to the internal variables generated from FE analysis. The chilling effect and friction indicated a great influence on the deformation mode of the tube and the formation of surface cracks. The simulation results for the backward extrusion were compared with the experimental observations.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10b
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• pp.22-25
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• 2003

The forming limits are studied for cold upsetting of high strength aluminium alloy in the present paper. Different geometry ratio and frictional conditions are investigated in the forgeability test to evaluate the forming limits and also to obtain the various strain paths. The critical fracture value can be obtained by integrating along the strain path till free surface crack initiation. To predict the damage evolution of cold upsetting, the computer-aided evaluation of forming limits is obtained by using the finite-element software DEFORM-3D and the modified Cockcroft-Latham criterion. The predicted theoretical limit strains agree quite well with the experimental results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.391-394
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• 2008

Durability of product is an important technical parameter of a current interception device (CID) filter. This parameter is influenced by several factors, such as: environment condition, external force, shape of device, heat and so on. In this study, the effect of the geometry of the device on durability was carried out. The effect of shape on durability of device is presented by force-carrying capacity that a device can sustain a maximum external force. Studied parameters of the CID filter's geometry include clearance, thickness, and corner radius. Fracture criterion of Cockcroft and Latham was also used to predict the maximum force-carrying capacity of device.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.3
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• pp.94-101
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• 1996

This paper presents an investigation of the ability of the scheme to simultaneously accomplish both prediction of fracture initiation and analysis of deformation in cold forged products. The Cockcroft-Latham criterion which is successfully applied to a variety of loading situations is used in the present investigation to estimate if and where surface and internal fracture occur during the deformation process. The numerical predictions and experimental results of two types of fundamental cold metal forming process taken into account are compared. Finite element simulation combined with fracture criterion has successfully predicted the site of surface or internal fracture initiation and corresponding to level of deformation observed experimentally.

• Transactions of Materials Processing
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• v.21 no.4
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• pp.258-264
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• 2012

The forming failure of AZ31 alloy sheet during deep drawing processes was predicted by the FEM and ductile fracture criteria. Uniaxial tensile tests of round-notched specimens and FE simulations were performed to calculate the critical damage values for three ductile fracture criteria. The critical damage values for each criterion were expressed as a function of strain rate at various temperatures. In order to determine the best criterion for failure prediction, Erichsen cupping test under isothermal conditions at $250^{\circ}C$ were conducted. Based on the plastic deformation histories obtained from the FE analysis of the Erichsen cupping tests and the critical damage value curves, the initiation time and location of fracture were predicted under bi-axial tension deformation. The results indicate that the Cockcroft-Latham criterion had good agreement with the experimental data. In addition, the FE analysis combined with the criterion was applied to another deep drawing process using an irregular shaped blank and these additional results were verified with experimental tests.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.201-205
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• 1996

This paper suggests the scheme to simultaneously accomplish prediction of fracture initation and geometrical configuration of deformation in metal forming processes using the artificial neural network. A three-layer neural network is used and a back propagation algorithm is adapted to train the network. The Cockcroft-Latham criterion is used to estimate whether fracture occurs during the deformation process. The geometrical configuration and the value of ductile fracture are measured by finite element method. The prediction of network and numerical results of simple upsetting are compared. The proposed scheme has successfully predicted the geometrical configuration and fracture initiation.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.9
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• pp.102-108
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• 2000

A finite element analysis has been performed to investigate the effect of v-ring indenter on the sheared surface in the fine blanking of a pawl which is a part of the automotive safety belt and is made of S45C sheet. In the present analysis the Cockcroft and latham fracture criterion and the element kill method are used in order to simulate the blanking operation successfully. The simulation results are obtained for various positions and heights of the v-ring indenter. And the theoretical results are compared with available experimental results. It is shown that this FEM simulation result can be useful for predicting the optimal fine blanking condition of real products.

• Transactions of Materials Processing
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• v.9 no.2
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• pp.152-158
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• 2000

A finite element analysis has been performed to investigate the effect of die clearance on shear planes in the fine blanking of a part of automobile safety belt. For the analysis, S45C is selected as an material, which is used in manufacturing the part of automobile safety belt, and Cockcroft-Latham fracture criterion is applied. Effect of die Clearance on die-roll width, die-roll depth, burnish zone, and fracture zone has been investigated in the finite element analysis by a rigid-plastic FEM code, DEFORM-2D. From the analysis, it has been found that die-roll depth and depth of the shear plane increase with increasing die clearance. And the burnish zone decreases with increasing die clearance, but the variation of fracture zone is opposite to that of burnish zone because the increase in die clearance requires less fracture energy. Theoretical predictions are compared with experimental results. There is a good agreement between theory and experiment.