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RISS 인기검색어
- 검색키워드
- 저자 : Thai-Hoan Pham (검색결과 11 건)
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Pham, Thai-Hoan,Kim, Seung-Eock Elsevier 2017 Construction & building materials Vol.155 No.-
<P><B>Abstract</B></P> <P>The volume fraction (<I>f</I>) and properties of microstructural phases, the mechanical properties in the weld zone, and their relevance of commonly used steel, SM520, were investigated by using instrumented indentation. The volume fraction and properties of microstructural phases in fusion zone (weld metal –WM), heat-affected zone (HAZ), and base metal (BM) of the weld zone were identified by applying the statistical analysis for observed frequency density of hardness (<I>H</I>), elastic modulus (<I>E</I>), and yield strength (<I>σ<SUB>y</SUB> </I>) spectra from nano-indentation tests. The mechanical properties distributed across the weld zone were determined from the micro-indentation tests. Two different stiffness ferrite types can be characterized in each individual weld zone from the analysis of <I>H</I> and <I>E</I> results, while two different strength ferrite types can be identified in WM from the analysis of the <I>σ<SUB>y</SUB> </I> spectrum obtained from nano-indentations. The results from micro-indentations exhibited that the <I>E</I>, <I>H</I>, <I>σ<SUB>y</SUB> </I>, and <I>n</I> values in the HAZ decrease in the direction from WM to BM region and all the average values of <I>E</I>, <I>H</I>, <I>σ<SUB>y</SUB> </I>, and <I>n</I> in HAZ are higher than those in BM. The relevance of <I>f</I>, <I>E</I>, <I>H</I>, and <I>σ<SUB>y</SUB> </I> of microstructural phases and <I>E</I>, <I>H</I>, and <I>σ<SUB>y</SUB> </I> in the weld zone and was also discussed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nano- and micro-indentations were performed on the weld zone of SM520 steel. </LI> <LI> Compositions and properties (<I>E</I>, <I>H</I>, and <I>σ<SUB>y</SUB> </I>) of microstructural phases in weld zone are identified. </LI> <LI> Mechanical properties across the weld zone were estimated from micro-indentation and FE analysis results. </LI> <LI> Compositions and properties of microstructural phases relevant to mechanical properties in the weld zone. </LI> </UL> </P>
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Identification of the plastic properties of structural steel using spherical indentation
Pham, Thai-Hoan,Phan, Quang-Minh,Kim, Seung-Eock Elsevier 2018 Materials science & engineering. properties, micro Vol.711 No.-
<P><B>Abstract</B></P> <P>In this paper, a method for identification of the plastic properties of structural steels that exhibit a plastic plateau in their stress-strain curve from spherical indentation was proposed based on the results from extensive dimensional analyses and finite element (FE) simulations. Three explicit relationships, which related the properties of structural steel to the response from spherical indentation, were established. Considering that elastic modulus of structural steel was priori known since it can be extracted from the conventional methods, the plastic parameters of steel including yield strength (<I>σ</I> <SUB> <I>y</I> </SUB>), the strain hardening exponent (<I>n</I>), and the ratio (<I>α</I>) between the strain at beginning-point of strain hardening (<I>ε</I> <SUB> <I>st</I> </SUB>) and the yield strain ( <I>ε</I> <SUB> <I>y</I> </SUB>) can be determined from a spherical indentation load-depth (<I>P-h</I>) curve using three proposed dimensionless functions. The spherical indentation process was simulated by using a finite element program, and a large number of analyses with different combinations of steel properties were conducted. From the FE analyses results, the functions were established from regression analyses, and a reverse algorithm was suggested. Spherical indentation, tensile tests, reverse analyses were carried out on three different structural steels (SS400, SM490, and SM520) to validate the proposed algorithm.</P>
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Pham, Thai-Hoan,Kim, Seung-Eock Elsevier Sequoia 2017 Materials science & engineering Structural materia Vol.688 No.-
<P><B>Abstract</B></P> <P>This study describes a method that allows estimation of the equi-biaxial residual stress (<I>σ</I> <SUB> <I>R</I> </SUB>), yield strength (<I>σ</I> <SUB> <I>y</I> </SUB>), the strain hardening exponent (<I>n</I>), and the ratio (<I>α</I>) between strain at starting-point of strain hardening (<I>ε</I> <SUB> <I>st</I> </SUB>) and yield strain (<I>ε</I> <SUB> <I>y</I> </SUB>) of structural steel from the load-depth curve of one sharp indentation test. In this method, the relationships between the structural steel properties, residual stress, and the characteristics of the indentation loading-unloading curves were established in the form of dimensionless functions via extensive finite element (FE) analyses. Based on the FE analysis results of the indentation process with a large number of different material properties combinations, the effects of residual stress and plastic parameters on the indentation response were investigated, and a reverse algorithm for estimating four unknown quantities (<I>σ</I> <SUB> <I>R</I> </SUB>, <I>σ</I> <SUB> <I>y</I> </SUB>, <I>n</I>, and <I>α</I>) of steel from an indentation test was proposed. A stress-applying apparatus that allows the introduction of a compressive or tensile stress to the sample by applying a compressive or tensile force and maintaining the stress after releasing the force was also developed in this study. Indentation and tensile tests of structural steels (SS400 and SM490) were carried out and the proposed algorithm was validated through both numerical analyses and experimental results.</P>
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Safety assessment of an underground tunnel subjected to missile impact using numerical simulations
Duc-Kien Thai,Duy-Liem Nguyen,Thanh-Tung Pham,Thai-Hoan Pham 사단법인 한국계산역학회 2021 Computers and Concrete, An International Journal Vol.27 No.1
This work presents a safety assessment of an underground tunnel subjected to a ballistic missile attack employing the numerical approach. For the impact simulation, a box shaped reinforced concrete (RC) structure with a cross section dimension of 8.0×10.0 m under a soil layer that was attacked by a SCUD missile was modeled using finite element (FE) software LS-DYNA. SCUD missile is one of a series of tactical ballistic missiles developed by Soviet Union during the Cold War, which is adopted for a short-range ballistic missile. The developed FE simulation for the penetration depth of the missile impacting into the soil structure was verified from the well-known formula of the penetration prediction. The soil-structure interaction, the soil type, and the impact missile velocity effects on the penetration depth of the missile into the different soil types were investigated. The safety assessment of the underground tunnel was performed with regard to the different depths of the underground tunnel. For each missile velocity and soil type, a specific depth called the unsafe depth was obtained from the analysis results. The structure beneath the soil beyond this depth remains safe. The unsafe depth was found to be increased with the increasing missile velocity.
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Thu Thuy Thai,Anh Truc Trinh,Gia Vu Pham,Thi Thanh Tam Pham,Hoan Nguyen Xuan 한국부식방식학회 2020 Corrosion Science and Technology Vol.19 No.1
In this paper, the efficiency and the inhibition mechanisms of cobalt salts (cobalt nitrate and cobalt-exchangesilica Co/Si) for the corrosion protection of AA2024 were investigated in a neutral aqueous solution byusing the electrochemical impedance spectroscopy (EIS) and polarization curves. The experimental measurementssuggest that cobalt cation plays a role as a cathodic inhibitor. The efficiency of cobalt cation was importantat the concentration range from 0.001 to 0.01 M. The formation of precipitates of oxides/hydroxides ofcobalt on the surface at low inhibitor concentration was confirmed by the Scanning Electron Microscopy/EnergyDispersive X-Ray Spectroscopy (SEM/EDS) analysis. EIS measurements were also conducted for the AA2024surface covered by water-based epoxy coating comprising Co/Si salt. The results obtained from exposurein the electrolyte demonstrated the improvement of the barrier and inhibition properties of the coating exposedin the electrolyte solution for a lengthy time. The SEM/EDS analysis in artificial scribes of the coatingafter salt spray testing revealed the release of cobalt cations in the coating defect to induce the barrierlayer on the exposed AA2024 substrate.
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Thu Thuy Thai,Anh Truc Trinh,Thi Thanh Tam Pham,Hoan Nguyen Xuan 한국부식방식학회 2023 Corrosion Science and Technology Vol.22 No.2
In this study, cobalt oxide (Co3O4) and cobalt-doped magnetite (CoFe2O4) nanoparticles were synthesizedby a hydrothermal method. They were then used as corrosion inhibitors for corrosion protection ofAA2024-T3 aluminum alloys. These obtained nanoparticles were characterized by x-ray diffraction, fieldemissionscanning electron microscopy, and Zeta potential measurements. Corrosion inhibition activities ofCo3O4 and CoFe2O4 nanoparticles were determined by performing electrochemical measurements for bareAA2024-T3 aluminum alloys in 0.05 M NaCl + 0.1 M Na2SO4 solution containing Co3O4 or CoFe2O4nanoparticles. Corrosion protection for AA2024-T3 aluminum alloys by a water-based epoxy with or withoutthe synthesized Co3O4 or CoFe2O4 nanoparticles was investigated by electrochemical impedance spectroscopyduring immersion in 0.1 M NaCl solution. The corrosion protection of epoxy coating depositedon the AA2024-T3 surface was improved by incorporating Co3O4 or CoFe2O4 nanoparticles in the coating. The corrosion protection performance of the epoxy coating containing CoFe2O4 was higher than that of theepoxy coating containing Co3O4.
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Nguyen, Ngoc-Vinh,Pham, Thai-Hoan,Kim, Seung-Eock Elsevier 2019 Mechanics of materials Vol.137 No.-
<P><B>Abstract</B></P> <P>In this study, a series of experiments, which consist of constant strain rate indentation, and optical microscope examination, and finite element analysis were performed to investigate the strain rate-dependent behaviors of the mechanical properties of SS400 structural steel. The microstructures of SS400 steel was characterized using optical microscope examination. The influences of strain rate indentation on the characteristics of the loading/unloading curves were presented and the results showed a higher applied load, a higher loading curvature, and a higher loading work for a higher strain rate level. The strain rate-dependent behaviors of indentation hardness (<I>H</I>), yield strength (<I>σ<SUB>y</SUB> </I>), and work hardening (<I>n</I>) were investigated. When the strain rate level increased, both <I>H</I> and <I>σ<SUB>y</SUB> </I> strongly increased, while work hardening showed an almost linear increase. The strain rate-dependent behaviors of material properties were validated through the experimental and the numerical verifications. The strain rate sensitivity (SRS) value of 0.056 ± 0.02 was reported for SS400 steel and was highly consistent with the general trend reported for several types of structural steel in the literature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The pile-up phenomena occurred at all strain rate indentation levels, while the pop-in events can be observed to be more pronounced at low strain rate. </LI> <LI> The results showed higher applied load, higher loading curvature, higher total work, and higher contact stiffness for higher strain rate condition. </LI> <LI> The strain rate sensitivity of 0.056 ± 0.03 was well reported for SS400 steel. </LI> <LI> As the strain rate increased, indentation hardness yield stress strongly increased, while work hardening showed an almost linear increase. </LI> <LI> The strain rate-dependent behaviors of both yield stress and work hardening were validated through the experimental and numerical verifications. </LI> </UL> </P>
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Nguyen, Ngoc-Vinh,Pham, Thai-Hoan,Kim, Seung-Eock Elsevier 2019 Materials science & engineering. properties, micro Vol.744 No.-
<P><B>Abstract</B></P> <P>In this study, a series of experiments consisting of low-cycle fatigue, constant loading rate indentation, creep indentation experiments, optical microscopy examination, and transmission electron microscopy were performed to investigate the strain rate sensitivity behavior of SS400 structural steel under cyclic loading conditions. 400 indentations were conducted in the displacement control mode at different strain rate indentations varied from 0.02 s<SUP>−1</SUP> to 0.2 s<SUP>−1</SUP> and the effects of strain rate indentation on mechanical properties were investigated on four fatigue failure specimens. An analytical method was used to estimate mechanical properties of the structural steel from the loading/unloading curves. The results indicated that the yield strength and the strain hardening exponent strongly depended on both the strain rate indentation and the strain amplitude. Yield strength and strain hardening exponent tended to increase when the strain amplitude increased. The strain rate sensitivity (SRS) was also determined from the yield strength and the creep indentation data, and the dependency of the strain rate sensitivity on the strain amplitude level was examined. The results showed that the strain rate sensitivity exhibited decrease almost linearly when the strain amplitude increased from 0.4% to 1.0%. The results of the present study were used to assess and understand the strain rate sensitivity behavior of SS400 structural steel during low-cycle fatigue.</P>
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