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Macroseismic and Microseismic Events Declustering for Korea Peninsula
Ekaputra Rhajendra,Eric Yee,Minyoung Kang,Changkyu Lee,Soojin Jung,Euihyun Jung 대한토목학회 2023 대한토목학회 학술대회 Vol.2023 No.10
This research focuses on declustering the earthquake catalog by removing non-independent events, such as foreshocks and aftershocks. The Gardner and Knopoff (GK) method, known for its simplicity and efficiency, is used for declustering. However, the GK method may inadvertently remove more events than necessary and cannot handle complex cascading event sequences. The results showed that approximately 71% of the earthquake catalog consisted of independent events. Nonetheless, there were limitations in the data distribution and gaps in information for events outside a specific magnitude range. Further analysis is required to assess the usability of macroseismic events and analyze ground motion prediction equations using a refined catalog. This project emphasizes the significance of declustering and considering event independence in seismic hazard analysis for the Korean Peninsula.
I. M. W. Ekaputra,WOO GON KIM,박재영,김선진,Eung-Seon Kim 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.7
In this study, the Q * parameter was characterized to evaluate the Creep crack growth rate (CCGR) of type 316LN stainless steel. Creep crack growth (CCG) data were obtained by CCG tests under different applied loads at 600°C. An additional CCG test was conducted at 550°C to investigate the possible temperature dependence of the stress intensity factor. An equation using the Q * parameter for evaluating CCGR was proposed, and this parameter was characterized and compared with the typical C * fracture parameter, which is commonly used. The Q * parameter exhibited good linearity of the data, exhibiting no nonlinearity-induced dual value at the early stage. The Q * parameter was suitable for characterizing the CCGR regardless of different applied loads and types of steels. In addition, fracture microstructures near the crack revealed a typical intergranular fracture mode, and this fracture was dominantly propagated along the grain boundary. The cracks were developed by the growth and interlinking of cavities, which were attributed to the precipitates forming along the grain boundary.
Evaluation of Work Hardening Parameters in Modelling the Plastic Flow Behavior for Alloy 617
I.M.W. Ekaputra,Woo-Gon Kim(김우곤),Jae-Young Park(박재영),Seon-Jin Kim(김선진),Seon-Eung Kim(김응선) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
This paper attemps to investigate the work hardening parameters used in modelling the plastic flow of true stress and true plastic strain behavior for alloy 617. The tensile tests were conducted at the strain rate of 5.55×10<SUP>-4</SUP> s<SUP>-1</SUP> under wide range of temperatures (RT ~ 950 ℃). Several equations or flow relationships such as Hollomon, Ludwik, Swift, Ludwigson, and Voce were proposed to investigate the plastic flow behavior. The result showed that the work hardening parameters of Ludwigson can describe the plastic flow behavior adequately, since these parameters yielded the smallest error quantification in fitting line under all temperature ranges as low, intermediate, and high. At the intermediate temperatures, an anomalous work hardening behavior appeared like a plateaus. It was considered as a dynamic strain aging (DSA) phenomenon, where the serrated plastic-flow phenomenon occured due to the interaction between solute atoms and mobile dislocation. In addition, the anomalous behavior was also observed from the graph of yield strength and/or ultimate tensile strength under various temperature ranges.
Derivation of Q* Parameter for Evaluating Creep Crack Growth Rate of Modified 9Cr-1Mo Steel
I.M.W. Ekaputra,Woo-Gon Kim(김우곤),Jae-Young Park(박재영),Seon-Jin Kim(김선진),Min-Hwan Kim(김민환),Yong-Wan Kim(김용완) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
The concept of the Q* parameter was first proposed by Yokobori et al. The Q* parameter is defined as the exponent of the exponential function in the thermal activation process equation. In this study, the creep crack growth (CCG) behavior of the modified 9Cr-1Mo steel is evaluated using the Q* parameter. The CCG tests were carried out under various loads at 550oC and 600oC. The K and C* parameters have been used to characterize the CCGR of modified 9Cr-1Mo steel. The results show that the K parameter exhibits the largest scatter data, and there is no systematic trend in each series of tests, while C* showed a narrower scattering of data of CCGR than the K parameter. However, C* decreased during the early stage of crack growth and subsequently increased, i.e., a dual value due to the nose appearance, and it did not distinguish among the series of data under various loads at 550oC and 600oC clearly in a one linear line. The Q* parameter was able to evaluate the CCG by a simple monotical linear function without a dual value owing to nose existing in the early stage, and it exhibited an increase or decrease regardless of the testing conditions. The Q* was regarded as an independent parameter that is not depending on stress and temperature, whereas the C* was regarded as a dependent parameter depending on the creep stress and temperature.
Influence of Dynamic Strain Aging on Tensile Deformation Behavior Of Alloy 617
I. M. W. Ekaputra,김우곤,박재영,김선진,김응선 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.6
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°C to 950°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°C to 700°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°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
Evaluation of Q* Parameter for Characterizing Creep Crack Growth Rate of Type 316LN Stainless Steel
I.M.W. Ekaputra,Woo-Gon Kim,Jae-Young Park,Seon-Jin Kim,Min-Hwan Kim,Yong-Wan Kim 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
This study evaluated the CCGR (creep crack growth rate) of type 316LN stainless steel using the Q<SUP>*</SUP> parameter. In a previous investigation, the Q<SUP>*</SUP> parameter was applied for modified 9Cr-1Mo steel under various applied loads and temperatures. It is obvious that the Q<SUP>*</SUP> parameter can be depicted as an independent parameter that was able to distinguish the curves under various applied loads and temperatures. Furthermore, the Q<SUP>*</SUP> parameter for type 316LN SS exhibited a similar characteristic as modified 9Cr-1Mo steel. This showed a simple monotical linear function without a dual value due to nose in the early stage of the CCG curve. The relationship between type 316LN SS and modified 9Cr-1Mo steel can also be performed clearly in the graph by the parallel movement of the curves. The type 316LN SS showed a higher Q<SUP>*</SUP> value than the modified 9Cr-1Mo steel, but it has the same slope value. Meanwhile, the CCGR characteristics were not expressed when using the C<SUP>*</SUP> parameter, which was located at the same band. The Q<SUP>*</SUP> parameter was found to be a powerful parameter that not only is able to characterize the CCGR under various applied loads and temperatures, but also under various type of steels. In addition after the CCG tests of type 316LN SS, a fracture micrograph exhibited an intergranular fracture mode.