Papers by Hyeong-yeon Lee
Transactions of The Korean Society of Mechanical Engineers A, Dec 31, 2021
High-temperature mechanical behaviors of Type 316L stainless steel (SS), which is considered as o... more High-temperature mechanical behaviors of Type 316L stainless steel (SS), which is considered as one of the major structural materials of Generation-IV nuclear reactors, were investigated through the tension and creep tests at elevated temperatures. The tension tests were performed under the strain rate of 6.67×10-4 (1/s) from room temperature to 650 o C, and the creep tests were conducted under different applied stresses at 550 o C, 600 o C, 650 o C, and 700 o C. The tensile behavior was investigated, and the modeling equations for tensile strengths and elongation were proposed as a function of temperature. The creep behavior was analyzed in terms of various creep equations: Norton's power law, modified Monkman-Grant relation, damage tolerance factor(λ), and Z-parameter, and the creep constants were proposed. In addition, the tested tensile and creep strengths were compared with those of RCC-MRx. Results showed that creep exponent value decreased from n=13.55 to n=7.58 with increasing temperature, λ = 6.3, and Z-parameter obeyed well a power-law form of Z=5.79E52(σ/E) 9.12. RCC-MRx showed lower creep strength and marginally different in creep strain rate, compared to the tested results. Same creep deformation was operative for dislocation movement regardless of the temperatures.
Annals of Nuclear Energy, 2016
Abstract Flow mixing characteristics inside a wire-wrapped 37-pin bundle were measured using a wi... more Abstract Flow mixing characteristics inside a wire-wrapped 37-pin bundle were measured using a wire-mesh sensing system. The subchannel flow mixing within a sodium-cooled fast reactor (SFR) core subassembly is an important phenomenon to predict temperature distributions for the core thermal design and safety analysis. To identify the mixing characteristics experimentally, a dedicated test facility including the wire-mesh sensor system and tracing liquid injection system was developed. The conductivity fields at the end of a 37-pin bundle were visualized in several different flow conditions which are corresponding to 20–115% flow of the prototype reactor nominal flow based on the Reynolds number. A CFD preliminary analysis under pre-determined boundary conditions was also performed to verify the design parameters and range of various operating values of the current mixing test. The experimentally identified mixing characteristics were compared with the CFD results, which show reasonable agreements with each other. The current experimental work includes the uncertainty evaluation by performing the separated test for the elementary parameters.
ASTM International eBooks, Sep 16, 2009
This publication is a Validated Methods, Reference Methods and Measurements Report by the Joint R... more This publication is a Validated Methods, Reference Methods and Measurements Report by the Joint Research Centre, the European Commission's in-house science service. It aims to provide evidence-based scientific support to the European policy-making process. The scientific output expressed does not imply a policy position of the European Commission. Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use which might be made of this publication.
This study presents assessment of creep crack growth rates (CCGRs) for the base metal (BM), weld ... more This study presents assessment of creep crack growth rates (CCGRs) for the base metal (BM), weld metal (WM), and heat affected zone (HAZ) of Gr. 91 weld joint, which was prepared by a shield metal arc weld (SMAW) method. A series of tensile, creep, creep crack growth (CCG) tests were performed for the BM, WM, and HAZ at the identical temperature of 550°C. The CCGR laws for the BM, WM and HAZ were constructed and compared in terms of a C*-fracture parameter. In addition, the CCGR law tested for BM was compared to that of RCC-MRx code. For a given value of C*, the WM and HAZ were almost similar in the CCGR, but they were significantly faster than the BM. This reason was closely attributed to the higher creep rate in the WM and HAZ than the BM. Currently elevated temperature design (ETD) code in French, RCC-MRx was found to be non-conservative in the CCGR when compared with the present investigation.
대한기계학회 춘추학술대회, Nov 1, 2014
High-temperature tensile behavior for Grade 91 (Gr. 91) steel for use of a sodium-cooled fast rea... more High-temperature tensile behavior for Grade 91 (Gr. 91) steel for use of a sodium-cooled fast reactor (SFR) structure was investigated, and full-range stress-strain curves were described in terms of RCC-MRx procedures (French SFR code) and four constitutive equations: power-law form, logarithmic form, exponential form, and modified form (powerlaw + exponential). To do this, a series of high-temperature tensile data was obtained from the tensile tests performed with a strain rate of 6.67 x10-4 (1/s) at R.T to 650oC. On the basis of experimental tensile data, full-range stress-strain curves were designed by RCC-MRx procedures. In addition, a modified constitutive equation in terms of a combination of power-law form and exponential form were proposed to well describe the full-range stress-strain curves, and the suitable equation in the four equations was investigated by fitting to the experimental curves. Results showed that the stress-strain curves designed by RCC-MRx were in accordance with the experimental curves at all of the temperature ranges, and a proposed modified equation was found to be superior in modeling of the stress-strain curves to the other equations. It can be conveniently used in modeling full-range stress-strain curves without calculation procedures in RCC-MRx code.
Transactions of The Korean Society of Mechanical Engineers A, 2015
The material properties of crack growth models at an elevated temperature were derived from the r... more The material properties of crack growth models at an elevated temperature were derived from the results of numerous crack growth tests for Mod.9Cr-1Mo (ASME Grade 91) steel specimens under fatigue loading and creep loading at an elevated temperature. These crack growth models were needed for defect assessment under creep-fatigue loading. The mathematical crack growth rate models for fatigue crack growth (FCG) and creep crack growth (CCG) were determined based on the test results, and the models were compared with those of the French design code RCC-MRx to investigate the conservatism of the code. The French design code RCC-MRx provides an FCG model and a CCG model for Grade 91 steel in Section III Tome 6. It was shown that the FCG model of RCC-MRx is conservative, while the CCG model is non-conservative compared with the present test data. Thus, it was shown that further validation of the property was required. Mechanical strength tests and creep tests were also conducted, and the test results were compared with those of RCC-MRx.
ABSTRACT For a design application of Alloy 617, the isochronous stress-strain curves (ISSC) shoul... more ABSTRACT For a design application of Alloy 617, the isochronous stress-strain curves (ISSC) should be constructed at a specified temperature. The ISSCs can be constructed using Young's modulus, average tensile hardening rule, and creep strain laws. To develop the ISSCs, it is necessary to determine the total strain composed of the elastic, plastic, and creep strains. To determine the total strain, the RCC-MR code and Blackburn's methods are described in detail. In addition, to practically determine the tensile elastic and plastic strain components of Alloy 617, a new method is proposed and applied in addition to these two methods. Results show that in the elastic regime, these three methods were identical in the tensile curves, and in the plastic regime, the Blackburn's equation was higher in the stress-strain curves than the RCC-MR code. Two methods revealed some differences in the analyzed curves, but a new method seemed to be better because it lay midway between the two methods. However, in spite of this difference in the plastic regime, it is suggested that these three methods can be utilized to calculate the elastic and plastic strain of Alloy 617. The reason for this is that the creep stress conditions, which are generally tested at 800°C, 850°C, 900°C, and 950°C of Alloy 617, correspond to a lower elastic regime rather than the plastic regime.
International Journal of Pressure Vessels and Piping, Feb 1, 2021
Abstract The present paper provides engineering estimates for plastic J-integral and crack openin... more Abstract The present paper provides engineering estimates for plastic J-integral and crack opening displacement (COD) of a non-idealized axial through-wall crack (TWC) in pipes based on detailed 3-dimensional finite element (FE) analyses. The behaviors of plastic J-integral and COD of a non-idealized axial TWC in typical pressurized pipes in nuclear power plants were systematically investigated. The FE model and analysis procedure employed in this study were verified by comparing the present FE results with the limited existing solutions for pipes with an idealized axial TWC. Based on the FE results, the new plastic influence functions, h1 and h2, which include the effect of a non-idealized TWC on plastic J-integral and COD, are provided as tabular solutions. By employing the plastic influence functions, plastic J-integral and COD of a non-idealized axial TWC along crack front can be directly predicted based on GE/EPRI method. In the present paper, plastic J-integral and COD estimates based on the reference stress concept have also been suggested. Finally, the estimated results were compared with elastic-plastic FE results by using actual stress-strain data and Ramberg-Osgood constants for TP 316 stainless steel. In addition, the engineering estimates proposed in this study were extended to estimating the creep fracture mechanics parameters at elevated temperature. Based on Norton and RCC-MRx creep models, C*-integral and creep COD rate values predicted from the present engineering solutions were validated by comparing with creep FE results. The results provided in this paper demonstrate that the present estimates can be applied to calculating plastic J-integral and COD, C*-integral, and creep COD rate of a non-idealized axial TWC.
A web-based design evaluation program is developed for the elevated temperature design (ETD) anal... more A web-based design evaluation program is developed for the elevated temperature design (ETD) analysis according to the RCC-MRx for Generation IV and fusion reactor systems. The program, named 'HITEP_RCC-MRx,' is composed of two modules: 'HITEP_RCC-DBA,' which computerizes the design-by-analysis (DBA) for class 1 components according to RB-3200 procedures, and 'HITEP_RCC-PIPE,' which computerizes the design-by-rule (DBR) analysis for class 1 piping according to RB-3600 procedures. Each module performs three major design evaluations on load-controlled stress, inelastic strain and creep-fatigue damage in a reliable and efficient way. The program is verified with a number of components and piping systems in sodium test facilities subjected to high temperature loading for the DBA module and the DBR module, respectively. Since HITEP_RCC-MRx is programmed with web-based language, it can operate on a smartphone as well as on a personal computer once it is connected to an internet or WIFI. Comparisons of the ETD codes of RCC-MRx and ASME Section III Subsection NH are made in terms of the programmability and reproduction of the evaluation results. A new creep model proposed for Grade 91 steel is incorporated in the program for comparison of creep behaviors between the creep models of RCC-MRx and the new Garofalo creep model for Grade 91 steel. Comparisons for verification between the evaluation results from HITEP_RCC-MRx and direct calculations using Excel confirm that the HITEP_RCC-MRx performs ETD evaluations in an efficient and reliable way.
대한기계학회논문집.C, Sep 1, 2016
The material properties of heat resistant materials at power plants are affected by thermal aging... more The material properties of heat resistant materials at power plants are affected by thermal aging as operating time is accumulated. In this study, the influence of thermal aging on yield strength, tensile strength and fracture behavior for Mod.9Cr-1Mo (ASME Grade 91) steel which is a material widely adopted for Generation IV nuclear energy system has been investigated and analyzed. Service exposed Gr.91 steel materials sampled from a piping system of an ultra-supercritical (USC) plant in Korea with accumulated operation time of 73,716 hours were used for material testing. The test results of the service exposed material specimens were compared with those of the virgin Gr.91 steel specimens. Those test data were compared with the material properties of ASME code and RCC-MRx code. Conservatisms of the material properties in the design codes have been quantified based on the comparisons of those from virgin and service exposed material specimens.
The present paper provides predictive creep deformation model for Gr. 91 steel at 600 °C. To cove... more The present paper provides predictive creep deformation model for Gr. 91 steel at 600 °C. To cover primary-secondary creep regions, two types of creep models, i.e. Garofalo’s and RCC-MRx models were considered in the present study, where the parameters of Garofalo’s model were characterized based on experiment results, and the parameters of RCC-MRx model were determined by the values given in the RCC-MRx code. Furthermore, each creep model were developed based on CREEP (user creep subroutine invoked in ABAQUS) codes for applying to finite element (FE) simulations using commercial code. Then, FE analyses for creep deformation were performed by using the developed CREEP codes (for Garofalo’s and RCC-MRx models), and the results were compared with experiment data. As results, Garofalo’s model provides more accurate results than RCC-MRx model.
Transactions of The Korean Society of Mechanical Engineers A, 2000
2021 28th International Conference on Nuclear Engineering, Oct 19, 2021
An integrated software platform of elevated temperature design evaluation for pressure boundary c... more An integrated software platform of elevated temperature design evaluation for pressure boundary components and piping subjected to high-temperature operation in the creep range has been developed. The software of ‘HITEP’ platform is capable of performing high-reliability design evaluations according to two nuclear grade design rules of ASME BPVC Section III Subsection HB and RCC-MRx, and one non-nuclear grade the Section VIII Division 2 Code Case 2843-2. The program modules were verified with a number of example problems. The HITTEP platform can be used for a reliable and efficient elevated temperature design of pressure boundary components and piping systems in generation IV nuclear systems, supercritical thermal power plants and oil refinery plants subjected to high-temperature operation in the creep range.
본 연구에서는 프랑스의 RCC-MR A16 절차에 기초하여 Mod.9Cr-1Mo 강(ASME Grade 91) 구조의 크리프-피로 균열 개시 및 성장 평가법을 확장 개발하였다... more 본 연구에서는 프랑스의 RCC-MR A16 절차에 기초하여 Mod.9Cr-1Mo 강(ASME Grade 91) 구조의 크리프-피로 균열 개시 및 성장 평가법을 확장 개발하였다. 현재의 A16 지침은 오스테나이트 스테인리스강에 대해서만 크리프-피로 균열 개시 및 성장 평가법을 제시하고 있지만, 현재 초초임계(USC) 화력발전소는 물론 미래형 원자로 시스템의 구조재료로서 폭넓게 채택되고 있는 Mod.9Cr-1Mo 강에 대한 지침은 제시하지 않고 있다. 본 연구에서는 FMS(페리틱-마르텐사이트강)에 대한 크리프-피로 균열 개시 및 성장 평가법을 제시하고 있고, 구조물에 대한 크리프-피로 균열 거동 평가를 수행하였다. 평가결과는 구조시험을 수행한 결과 얻은 관찰 이미지와 비교하였다.
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Papers by Hyeong-yeon Lee