• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1306-1313
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• 2004

This paper addresses a theoretical approach to calculate the amount of the stored energy during high strain-rate deformations using atomistic level simulation. The dynamic behavior of materials at high strain-rate deformation are of great interest. At high strain-rates deformations, materials generate heat due to plastic work and the temperature rise can be significant, affecting various properties of the material. It is well known that a small percent of the energy input is stored in the material, and most of input energy is converted into heat. However, microscopic analysis has not been completed without construction of a material model, which can simulate the movement of dislocations and vacancies. A major cause of the temperature rise within materials is traditionally credited to dislocations, vacancies and other defects. In this study, an atomistic material model for FCC such as copper is used to calculate the stored energy.

• Structural Engineering and Mechanics
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• v.46 no.2
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• pp.231-244
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• 2013

An efficient method is proposed here to identify multiple damage cases in structural systems using the concepts of flexibility matrix and strain energy of a structure. The flexibility matrix of the structure is accurately estimated from the first few mode shapes and natural frequencies. Then, the change of strain energy of a structural element, due to damage, evaluated by the columnar coefficients of the flexibility matrix is used to construct a damage indicator. This new indicator is named here as flexibility strain energy based index (FSEBI). In order to assess the performance of the proposed method for structural damage detection, two benchmark structures having a number of damage scenarios are considered. Numerical results demonstrate that the method can accurately locate the structural damage induced. It is also revealed that the magnitudes of the FSEBI depend on the damage severity.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.459-466
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• 2006

The objective of this study is to improve the accuracy of damage detection using natural frequency and modal strain energy. The following approaches are used to achieve the goal. First, modal strain energy is introduced and newly GA-based damage detection technique using natural frequency and modal strain energy is proposed. Next, to verify efficiency of the proposed technique, damage scenarios for free-free beams are designed and the vibration modal tests as damage cases are conducted. Finally, feasibility of proposed technique is verified in comparison with a GA-based damage detection technique using natural frequency and mode shape.

• Structural Engineering and Mechanics
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• v.33 no.3
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• pp.325-337
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• 2009

Structural damage detection, damage localization and severity estimation of jacket platforms, based on calculating modal strain energy is presented in this paper. In the structure, damage often causes a loss of stiffness in some elements, so modal parameters; mode shapes and natural frequencies, in the damaged structure are different from the undamaged state. Geometrical location of damage is detected by computing modal strain energy change ratio (MSECR) for each structural element, which elements with higher MSECR are suspected to be damaged. For each suspected damaged element, by computing cross-modal strain energy (CMSE), damage severity as the stiffness reduction factor -that represented the ratios between the element stiffness changes to the undamaged element stiffness- is estimated. Numerical studies are demonstrated for a three dimensional, single bay, four stories frame of the existing jacket platform, based on the synthetic data that generated from finite element model. It is observed that this method can be used for damage detection of this kind of structures.

• Computers and Concrete
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• v.22 no.6
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• pp.563-572
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• 2018

Uniaxial compressive strength test and uniaxial compression creep one were produced on four groups of twelve concrete specimens with different hole number by RLW-2000 rock triaxial rheology test system. The relationships between horizontal holes and instantaneous failure stress, the strain, and creep failure stress, the strain, and the relationships between stress level and instantaneous strain, creep strain were studied, and the relationship between horizontal holes and failure mode was determined. The results showed that: with horizontal hole number increasing, compressive strength of the specimens decreased whereas its peak strain increased, while both creep failure strength and its peak strain decreased. The relationships between horizontal holes and compressive strength of the specimens, the peak strain, were represented in quadratic polynomial, the relationships between horizontal holes and creep failure strength, the peak strain were represented in both linear and quadratic polynomial, respectively. Instantaneous strain decreased with stress level increasing, and the more holes in the blocks the less the damping of instantaneous strain were recorded. In the failure stress level, instantaneous strain reversally increased, creep strain showed three stages: decreasing, increasing, and sharp increasing; in same stress level, the less holes the less creep strain rate was recorded. The compressive-shear failure was produced along specimen diagonal line where the master surface of creep failure occurred, the more holes in a block, the higher chances of specimen failure and the more obvious master surface were.

• Nuclear Engineering and Technology
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• v.48 no.6
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• pp.1387-1395
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• 2016

To investigate the dynamic strain aging (DSA) behavior of Alloy 617, high-temperature tensile tests were carried out with strain rates variations of $10^{-3}/s$, $10^{-4}/s$, and $10^{-5}/s$ from $24^{\circ}C$ to $950^{\circ}C$. Five flow relationships, Hollomon, Ludwik, Swift, Ludwigson, and Voce, were applied to describe the tensile true stress-strain curves, and the DSA region was defined. In describing the tensile curves, Ludwigson's equation was superior to the other equations, and the DSA region was adequately defined by this equation as plateaus at intermediate temperatures from $200^{\circ}C$ to $700^{\circ}C$. It was identified that Alloy 617 is dominated by three types of serrations, known as Types D, A+B, and C. The activation energy values for each serration type were obtained by the Arrhenius equation. By using the obtained activation energy values, the serrated yielding map and the DSA mechanism were drawn and manifested. In addition, the relationship between the tensile strength and strain rate at higher temperatures above $700^{\circ}C$ was found to be closely related to the amounts of slip lines. In the scanning electron microscope (SEM) fractographs, there was a significant difference at the low, intermediate, and high temperatures, but almost the same to the three strain rates.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.355-356
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• 2016

It is shown that the maximum value of exchange current is obtained where hydrogen adsorption energy is near 0. This enables to estimate catalytic efficiency of a material with hydrogen adsorption energy, which is relatively easier to calculate with density fuctional theory (DFT) method. Strain dependence of the adsorption energy was studied with DFT method and adsorption energy of 0.04 eV per hydrogen atom is obtained at 30% strain.

• Nuclear Engineering and Technology
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• v.53 no.7
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• pp.2304-2311
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• 2021

The dislocation density in strain-hardened Alloy 690 was analyzed using scanning transmission electron microscopy (STEM) to study the relationship between the local plastic strain and susceptibility to primary water stress corrosion cracking (PWSCC) in nuclear power plants. The test material was cold-rolled at various thickness reduction ratios from 10% to 40% to simulate the strain-hardening condition of plant components. The dislocation densities were measured at grain boundaries (GB) and in grain interiors of strain-hardened specimens from STEM images. The dislocation density in the grain interior monotonically increased as the strain-hardening proceeded, while the dislocation density at the GB increased with strain-hardening up to 20% but slightly decreases upon further deformation to 40%. The decreased dislocation density at the GB was attributed to the formation of deformation twins. After the PWSCC growth test of strain-hardened Alloy 690, the fraction of intergranular (IG) fracture was obtained from fractography. In contrast to the change in the dislocation density with strain-hardening, the fraction of IG fracture increased remarkably when strain-hardened over 20%. From the results, it was suggested that the PWSCC growth behavior of strain-hardened Alloy 690 not only depends on the dislocation density, but also on the microstructural defects at the GB.

• Journal of Microbiology and Biotechnology
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• v.26 no.9
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• pp.1570-1578
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• 2016

Commercial application of laccase is often hampered by insufficient enzyme stocks, with very low yields obtained from natural sources. This study aimed to improve laccase production by mutation of a Coriolopsis gallica strain and to determine the biological properties of the mutant. The high-yield laccase strain C. gallica TCK was treated with N-methyl-N-nitro-N-nitrosoguanidine and ultraviolet light. Among the mutants isolated, T906 was found to be a high-production strain of laccases. The mutant strain T906 was stabilized via dozens of passages, and the selected ones were further processed for optimization of metallic ion, inducers, and nutritional requirements, which resulted in the optimized liquid fermentation medium MF9. The incubation temperature and pH were optimized to be 30℃ and 4.5, respectively. The mutant strain T906 showed 3-times higher laccase activity than the original strain TCK under optimized conditions, and the maximum laccase production (303 U/ml) was accomplished after 13 days. The extracellular laccase isoenzyme 1 was purified and characterized from the two strains, respectively, and their cDNA sequence was determined. Of note, the laccase isoenzyme 1 transcription levels were overtly increased in T906 mycelia compared with values obtained for strain TCK. These findings provide a basis for C. gallica modification for the production of high laccase amounts.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.202-204
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• 2009

Erosion is a common failure mode of materials frequently encountered in plant and power industry. Although the erosion resistance of Fe-base alloy has been inferior to the other expensive materials, it is expected that the strain-induced martensitic transformation can impart high erosion resistance to Fe-base alloy. The key technology to develop Fe-base metal cored welding wire for erosion resistant overlay welding may include the strain-induced metallurgy for hardening rate control and the welding flux metallurgy for dilution control. Sophisticated studies showed that the strain-induced martensitic transformation behavior was related to the critical strain energy which was dependent on the alloy composition. Dilution and bead shape of overlay weld were proved to be affected by metal transfer mode during gas tungsten arc welding and elements in welding fluxes. It was considered that the highly erosion resistant Fe-base overlay weld could be achieved by precise control of alloy composition to have proper level of critical strain energy for energy absorption and welding flux formulation to have small amount of deoxidizing metallic elements for dilution.