• Transactions of Materials Processing
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• v.8 no.2
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• pp.216-221
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• 1999

In this paper, an application-oriented approach to piercing analysis in automatic forging simulation by the rigid-viscoplastic finite element mehtod is presented. In the presented approach, the accumulated damage is traced and the piercing instant is determined when the accumulated damage reaches the critical damage value. A method of obtaining the critical damage value by comparing the tensile test result with the analysis one is given. The presented approach is verified by experiments and applied to automatic simulation of a sequence of 6-stage forging processes.

• Transactions of Materials Processing
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• v.23 no.3
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• pp.164-170
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• 2014

To predict the deformation and fracture during tube expansion using the finite element (FE) method, a material model is considered that incorporates the damage evolution due to the deformation. In the current study, a Rice-Tracey model was used as the damage model with inclusion of the hydrostatic stress term. Since OFHC Cu is not significantly affected by strain rate, a Hollomon flow stress model was used. The material parameters in each model were obtained by using an optimization method. The objective function was defined as the difference between the experimental measurements and FE simulation results. The parameters were determined by minimizing the objective function. To verify the validity of the FE modeling, cross-verification was conducted through a tube expansion test. The simulation results show reasonable agreement with the experiments. The design for a minimum diameter of expansion tube using the FE modeling was verified by a simplified tube expansion test and simulation results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.693-701
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• 2016

In this study, notch defects are evaluated using fracture mechanics. To understand the effects of notch defects, FE analysis is conducted to predict the limit load and J-integral for middle-cracked and single-edge cracked plates with various sizes of notch under tension and bending. As the radius of the notch increases, the energy release rate also increases, although the limit load remains constant. The values of fracture toughness($J_{IC}$) of SM490A are determined for various notch radii through FE simulation instead of conducting an experiment. As the radius of the notch increases, the energy release rate also increases, together with a more significant increase in fracture toughness. To conclude, as the notch radius increases, the resistance to crack propagation also increases.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.362-365
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• 2005

The hub hole is usually formed with a flanging process followed by a blanking process of a ]tole. Since the hole is made by blanking, the blanked surface is so rough that the formability in the region is rather poor. The emerging task is to identify the formability of the blanked region in the forming simulation and to relate the criterion to the real forming process by experiments. In this paper, hole expansion tests are carried out with respect to various hole conditions to verify the hole condition effect on the hole expansion ratio. The hole of specimens is made by machining or punching. In the case of punching, two different punching clearances are used for making the hole. From the results of test, fracture mechanism of the hole expansion is explained.

• Journal of Industrial Technology
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• v.24 no.A
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• pp.29-35
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• 2004

Fine blanking can be considered as a manufacturing process capable of producing sheet metal parts with completely smooth edges that may be hardly obtained by conventional shear-cutting procedures. This fact, together with the considerable economic advantages offered by this process, has been responsible for the rapid acceptance of fine blanking throughout the manufacturing industry all over the world, and the discovery of many new applications. This study was performed to investigate the effect of clearance and V-ring shape on the quality of sheared surface in a fine blanking process. The critical value needed to apply the normalized Cockcroft-Latham fracture criterion to the simulation of fine blanking is obtained by correlating the result of finite element analysis and that of experiment for the uniaxial tensile test. From finite element analysis of an axisymmetric fine blanking process, it has been found that punch load, die-roll depth, burnish zone size and shape of sheared surface are considerably influenced by clearance and V-ring shape.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.753-760
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• 2013

The hydrogen embrittlement of metallic materials is an important issue from the viewpoint of structural integrity. In this regard, the estimation of mechanical properties and fracture toughness under hydrogen conditions provides very important data. This study provides an experimental validation of the approach for simulating the small punch of Inconel 617 using finite element damage analysis, as recently proposed by the authors, and applies an inverse method for the determination of the constitutive tensile behavior of materials. The mechanical properties obtained from the inverse method are compared with those obtained from the tensile test and validated. The mechanical properties and fracture toughness are predicted by using the inverse method and finite element damage analysis.

• Journal of Powder Materials
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• v.22 no.5
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• pp.337-343
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• 2015

Powder compaction is a continually and rapidly evolving technology where it is a highly developed method of manufacturing reliable components. To understand existing mechanisms for compaction, parameter investigation is required. Experimental investigations on powder compaction process, followed by numerical modeling of compaction are presented in this paper. The experimental work explores compression characteristics of soft and hard ductile powder materials. In order to account for deformation, fracture and movement of the particles, a discrete-finite element analysis model is defined to reflect the experimental data and to enable investigations on mechanisms present at the particle level. Effects of important simulation factors and process parameters, such as particle count, time step, particle discretization, and particle size on the powder compaction procedure have been explored.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.128-133
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• 2004

This study has been focused on the development of shear forming process of grid for lead-acid battery. The grid plays an important role in the flow of electricity because the grid is a skeleton of the pasted plate. Therefore, it must be of the highest quality to prevent plate failures and then, battery failure, and ensure the best battery performance possible. The finite element analysis of the shear forming process is carried out and the result is compared with the experimental data. The influence of the numerical parameters such as clearance, velocity of punch and critical damage value on the simulation results turns out to be very considerable.

• Journal of the Korean Institute of Gas
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• v.25 no.1
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• pp.20-29
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• 2021

During multi-stage fracturing in a low permeable shale formation, stress interference occurs between the stages which is called the "stress shadow effect(SSE)". The effect may alter the fracture propagation direction and induce ununiform geometry. In this study, the stress shadow effect on the hydraulic fracture geometry and the well productivity were investigated by the commercial full-3D fracture model, GOHFER. In a homogeneous reservoir model, a multi-stage fracturing process was performed with or without the SSE. In addition, the fracturing was performed on two shale reservoirs with different geomechanical properties(Young's modulus and Poisson's ratio) to analyze the stress shadow effect. In the simulation results, the stress change caused by the fracture created in the previous stage switched the maximum/minimum horizontal stress and the lower productivity L-direction fracture was more dominating over the T-direction fracture. Since the Marcellus shale is more brittle than more dominating over the T-direction fracture. Since the Marcellus shale is more brittle than the relatively ductile Eagle Ford shale, the fracture width in the former was developed thicker, resulting in the larger fracture volume. And the Marcellus shale's Young's modulus is low, the stress effect is less significant than the Eagle Ford shale in the stage 2. The stress shadow effect strongly depends on not only the spacing between fractures but also the geomechanical properties. Therefore, the stress shadow effect needs to be taken into account for more accurate analysis of the fracture geometry and for more reliable prediction of the well productivity.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.550-555
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• 2006

In this study, effects of forming angle and friction coefficient on a initiation of the Mannesmann hole defect were analyzed by using a response surface method. The maximum effective plastic strain at center point of specimen is utilized for the prediction of the starting point of crack occurrence, which is suggested by the comparison of integrals of four different ductile fracture models between the histories of the effective plastic strain at center point. It was revealed that the principal stress at the center is the dominant element to the increase of the effective plastic strain. It was also verified by the simulation results from the comparison of experiment and simulation. It is provided that the forming angle of 25 degrees and the spreading angle of 1 degree can be a proper design condition without an occurrence of internal hole defect and an excessive slip.