• Journal of the Korean Society for Heat Treatment
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• v.14 no.4
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• pp.228-234
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• 2001

The present study was an attempt for systematic data conversion between FDM and FEM in order to evaluate the thermal stress distribution during quenching process. It has been generally recognized that FDM is efficient in flow and temperature analysis and FEM in that of stress. But it induced difficulty and tedious work in analysis that one uses both FDM and FEM to take their advantages because of the discrepancy of nodes between analysis tools. So we proposed field data conversion procedure from FDM to FEM in 3-dimensional space, then applied this procedure to analysis of quenching process. The simulation procedure calculates the distributions of temperature and microstructure using FDM and microstructure evolution equations of diffusion and diffusionless transformation. FEM was used for predicting the distributions of thermal stress. The present numerical code includes coupled temperaturephase transformation kinetics and temperature-microstructure dependent material properties. Calculated results were compared with previous experimental data to verify the method, which showed good agreements.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.9
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• pp.815-824
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• 2015

In this study, we conducted the approximate multi-objective optimization of gap sizes of pressurized-water reactor (PWR) annular fuels. To determine the contacting tendency of the inner-outer gaps between the annular fuel pellets and cladding, thermoelastic-plastic-creep (TEPC)analysis of PWR annular fuels was performed, using in-house FE code. For the efficient heat transfer at certain levels of stress, we investigated the tensile, compressive hoop stress and temperature, and optimized the gap sizes using the non-dominant sorting genetic algorithm (NSGA-II). For this, response surface models of objective and constraint functions were generated, using central composite (CCD) and D-optimal design. The accuracy of approximate models was evaluated through $R^2$ value. The obtained optimal solutions by NSGA-II were verified through the TEPC analysis, and we compared the obtained optimum solutions and generated errors from the CCD and D-optimal design. We observed that optimum solutions differ, according to design of experiments (DOE) method.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.87-91
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• 2009

Welding is one of the most important joining processes and the effect of welding residual stresses in the structure has a great deal of influence on its quality. In this paper, recent development in computational welding mechanics, particularly calculation of welding residual stresses, is introduced. The hypoelastic formulation of finite element analysis for thermoelastic-plastic deformation is applied to welding processes to find residual deformations and stresses. Leblond's phase evolution equation coupled with the energy equation is employed to calculate the phase volume fraction; this plays an important role as a kinetics parameter affecting phase fraction effects in the mechanical constitutive equation of welded materials. Furthermore, transformation plasticity is taken into account for an accurate evaluation of stress. The influence of the phase transformation and the transformation plasticity on residual stress is investigated by means of numerical analyses using metallurgical parameters in Leblond's phase evolution equation that are adjusted with respect to various cooling rates in a CCT-diagram. Coding implementation is conducted by way of the ABAQUS user subroutines, UMAT.