• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1995.06a
• /
• pp.100-123
• /
• 1995

The relationship between plastic deformation and crystal grain change in warm forging processes of SM100 carbon steel is studied. If the carbon steel is deformed in warm forging temperature (about recrystallization range), the crystal grain and cementite of the internal part are changed, so material properties are changed. Some experimental values, such as the elliptic degree of cementite, the grain size of cementitie and ferrite grain size, are investigated. When the plastic deformation proceeds, the elliptic degree of cementite becomes large, the grain size of cementite particle is small, and the size of ferrite grain appears fine by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging is calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result. At effective strain 0.3 dynamic recovery and dynamic recrystallization begin, over 2.5 the organization of material has better quality that is suitable for the following cold forming.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2000.03b
• /
• pp.183-190
• /
• 2000

Effective range of Hydraulic Hammer Compaction was studied by numerical analysis instead of empirical method. Numerical analyses were carried out with commercial FEM code, ABAQUS, and verified by comparing the numerical results with field tests of Hydraulic Hammer Compaction. Most of material properties were evaluated by data from laboratory and in-situ tests. Vertical effective range was estimated by distribution curve of plastic strain energy dissipated through soil layers under dynamic load and these results were in good agreement with field tests. Based on verification, the effects of governing properties of Hydraulic Hammer Compaction such as number of hit can be determined by numerical analyses. In addition, vertical effective range can also be determined by Menard's empirical equation using the external work at converging time of plastic strain energy in numerical analysis. This implies that the minimum energy of Hydraulic Hammer Compaction for improvement can be determined by Menard's equation.

• International Journal of Automotive Technology
• /
• v.5 no.4
• /
• pp.297-302
• /
• 2004

This paper presents the low cycle thermal fatigue of the engine exhaust manifold subject to thermo-mechanical cyclic loading. As a failure of the exhaust manifold is mainly caused by geometric constraints of the less expanded inlet flange and cylinder head, the analysis is based on the exhaust system model with three-dimensional temperature distribution and temperature dependent material properties. The result show that large compressive plastic deformations are generated at an elevated temperature of the exhaust manifold and tensile stresses are remained in several critical zones at a cold condition. From the repetition of these thermal shock cycles, maximum plastic strain range (0.454%) could be estimated by the stabilized stress-strain hysteresis loops. It is used to predict the low cycle thermal fatigue life of the exhaust manifold for the thermal shock test.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.2
• /
• pp.461-472
• /
• 1996

The relationship between plastic deformation and crystal grain change in warm forging processes of SM10C carbon steel is studied. If the carbon steel is deformed at warm forging temperature(about recrystallization range), material properties are changed due to microstructural chanre of the crystal grain and cementite of the internal part. Some experimental values are investigated in terms of the elliptic degree of cementite, the grain size of cementite and ferrite grain size. When plastic deformation proceeds, the elliptic degree of cementite becomes larger and the grain size of cementite particle becomes small. In addition, the size of ferrite grain becomes fines by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging was calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result, At the level of effective strain 0.3, dynamic recovery and dynamic recrystallization begin and at the level of over 2.5, the organization of material has better internal structure that is suitable for the following cold forming.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2004.03b
• /
• pp.730-737
• /
• 2004

In this paper, in order to examine cyclic hehavior characteristics and safety of underground flexible pipes for electric cables subject to cyclic vehicle load, FEM analysis and cyclic soil box test were carried out. As results of the test, it was revealed that the vertical displacement of the test was larger than that of FEM analysis because thermal effect arising from power cables made reduction of rigidity of the pipe so that large deformation of the pipe induced by the heat occured. Moreover, it was shown that the final vertical displacement under about 0.4 million times of the cyclic load test was not satisfied with elastic allowable displacement of the pipe, and long term stability of the pipe was not stable since behavior characteristics of the pipe exists plastic strain range pasted clastic strain range.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.05a
• /
• pp.240-243
• /
• 2003

Finite element analyses for bursting failure prediction in bulge forming under combined internal pressure and independent axial feeding are carried out. By means of the FEM combined with Oyane's ductile fracture criterion based on Hills quadratic plastic potential, the forming limit and bursting pressure level are investigated for a seamed tube that comprises of weldment, heat affected zone(HAZ) and base material parts. Especially, in order to determine the material property of HAZ tensile tests for the base material and the weld metal are executed based on iso-strain approach. Finally, through a series of bulge forming simulations with consideration of the weldment and HAZ it is concluded that the proposed method would be able to predict the bursting pressure and fracture initiation site more realistically, so the approach can be extended to a wide range of practical bulge forming processes.

• Journal of the Korean Society of Safety
• /
• v.22 no.1 s.79
• /
• pp.19-23
• /
• 2007

The aim of this study was to determine residual stresses in thermal barrier coatings(TBCs) by isothermal heating. Specimens were heated at the range of $1000{\sim}1600^{\circ}C$. A finite element method was used to determine the residual stresses. Finite element coupled heat transfer and elastic-plastic thermal stress analysis using a general purpose commercial FEM software ABAQUS. I obtained the stresses were not affected below the temperature of $1400^{\circ}C$ but affected over that of temperature.

• Transactions of Materials Processing
• /
• v.18 no.4
• /
• pp.354-360
• /
• 2009

Hot-forging process and die design were made for a large-scale compressor wheel of Ti-6Al-4V alloy by using the results of 2-D FEM simulation. The design integrated the geometry-controlled approach and the processing contour map based on the dynamic materials model and the flow stability criteria. In order to obtain the processing contour map of Ti-6Al-4V alloy, compression tests were carried out in the temperature range of $915^{\circ}C$ to $1015^{\circ}C$ and the strain rate range of $10^{-3}s^{-1}$ to $10s^{-1}$. In the die design of the compressor wheel using the rigid-plastic FEM simulation, forging dimensional accuracy, the capacity of the forging machine and defect-free forging were considered as main design factors. The microstructure of hot forged wheel using the designed die showed a typical alpha-beta structure without forging-defects.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.12
• /
• pp.44-55
• /
• 1994

This study is to apply the theory of fatigue fracture to solder joints under thermal cyclic loading and predict life of solder joint to failure. A 62Sn-36Pb-2Ag solder was used in this study. Tensile tests were preformed at temperatures of 15.dec. C, 50.dec. C and 85.dec. C in order to find terms of crack length "a". plastic strain range ""${\Delta}{\varepsilon}_p$" and temperature "T". Solder joint under thermal cyclic loading was analyzed by FEM. this FEM analysis together with the crack growth rate will provide the capability of the fatigue life prediction of solder joints and enhance the reliability od solder joint.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.46 no.4
• /
• pp.75-84
• /
• 2004

The evaluation technique of seismic performance on agricultural infrastructure based on dynamic numerical simulations, which Included a cyclic elasto-plastic and a viscoelastic-viscoplastic constitutive model to actual multi-layered ground conditions during large earthquake were performed by a liquefaction analysis in the present study. From the liquefaction analysis, it was verified that the models can give a good description of the damping characteristics and liquefaction phenomena of ground accurately during large event which induces plastic deformation in large strain range.