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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.
Creep Crack Growth Behavior at High Temperatures of Alloy 617
Woo-Gon Kim(김우곤),Jae-Young Park(박재영),I.M.W. Ekaputra,Seon-Jin Kim(김선진),Eung-Seon Kim(김응선) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Alloy 617 is a major candidate material for use of the intermediate heat exchanger (IHX) of a very high temperature reactor (VHTR) system, which is designed to be used for a 60 year lifetime at a high temperature. Creep crack growth (CCG) behavior as well as creep deformation, due to creep damage during the long service life at elevated temperatures, is very important. However, the CCG design data to meet the needs of the conceptual designers and/or to develop ASME design code of VHTR system are not available elsewhere. In this study, a series of experimental CCG data was obtained from the CCG tests performed under different applied loads at 800 and 850oC for Alloy 617. The CCG behavior was evaluated in terms of the C<SUP>*</SUP> fracture parameter, and the CCG laws for the two temperatures were proposed and fracture microstructures were observed and discussed.
인장 및 크리프 재료상수가 크리프 균열성장에 미치는 영향
박재영(Jae-Young Park),김우곤(Woo-Gon Kim),I.M.W.EKAPUTRA,김선진(Seon-Jin Kim),김응선(Eung-Seon Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
Time-dependent fracture mechanics parameter C<SUP>*</SUP> is well used to evaluate the creep crack growth (CCG) rate for creep-ductility material. Calculation of C<SUP>*</SUP> includes fully-plastic contribution to J-integrals (J<SUB>p</SUB>) and load-line displacement rate at creep condition (V<SUB>c</SUB>). These values are influenced by the material constants of D, m and n obtained in the tensile and creep tests. This study investigated the influence of the material constants to the CCG rate. The values for J<SUB>p</SUB>, V<SUB>c</SUB> and C* were calculated with the variations of D, m and n values using an experimental CCG data. Various plots on the influence of the material constants to the CCG rate were presented and the results were discussed.
Grade 91 강의 크리프 균열성장 거동에 대한 천이영역과 정상상태영역의 상관 관계
박재영(Jae-Young Park),김우곤(Woo-Gon Kim),I. M. W. Ekaputra,김선진(Seon-Jin Kim),김응선(Eung-Seon Kim) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.12
제 4 세대 원자로의 고온 구조재료로 사용되는 Grade 91 강의 크리프 균열성장 거동에 대한 천이영역과 정상상태영역에서의 상관 관계를 조사하였다. 이를 위해 600℃ 의 동일한 온도 및 동일한 하중조건에서 1/2” CT 시편을 사용하여 크리프 균열성장 시험 데이터를 얻었다. 크리프 균열성장 속도식은 C*-파괴매개변수를 사용하여 천이영역과 정상상태영역에서의 평가 식을 각각 도출하였다. C*와 da/dt 의 관계에서 천이영역의 크리프 균열성장 속도는 시험 데이터의 산포가 크지만 정상상태영역의 크리프 균열성장 속도와 비슷한 기울기로서 상관성이 있었으며 천이영역 균열성장속도는 정상상태 균열성장속도에 비해 약 5.6 배 낮았다. 본 결과를 이용하면 짧은 시간의 천이영역 균열성장속도로부터 장시간의 시험으로 얻을 수 있는 정상상태 균열성장속도를 예측할 수 있다. A correlation between the transient regime and steady state regime on the creep crack growth (CCG) for Grade 91 steel, which is used as the structural material for the Gen-IV reactor systems, was investigated. A series of CCG tests were performed using 1/2” CT specimens under a constant applied load and at a constant temperature of 600 °C. The CCG rates for the transient and steady state regimes were obtained in terms of C* parameter. The transient CCG rate had a close correlation with the steady-state CCG rate, as the slope of the transient CCG data was very similar to that of the steady state data. The transient rate was slower by 5.6 times as compared to the steady state rate. It can be inferred that the steady state CCG rate, which is required for long-time tests, can be predicted from the transient CCG rate obtained from short-time tests.