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Kweon, Hyeong Do,Kim, Jin Weon,Song, Ohseop,Oh, Dongho Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.2
Knowing a material's true stress-strain curve is essential for performing a nonlinear finite element analysis to solve an elastoplastic problem. This study presents a simple methodology to determine the true stress-strain curve of type 304 and 316 austenitic stainless steels in the full range of strain from a typical tensile test. Before necking, the true stress and strain values are directly converted from engineering stress and strain data, respectively. After necking, a true stress-strain equation is determined by iteratively conducting finite element analysis using three pieces of information at the necking and the fracture points. The Hockett-Sherby equation is proposed as an optimal stress-strain model in a non-uniform deformation region. The application to the stainless steel under different temperatures and loading conditions verifies that the strain hardening behavior of the material is adequately described by the determined equation, and the estimated engineering stress-strain curves are in good agreement with those of experiments. The presented method is intrinsically simple to use and reduces iterations because it does not require much experimental effort and adopts the approach of determining the stress-strain equation instead of correcting the individual stress at each strain point.
권형도(Hyeong Do Kweon),남덕우(Deok Woo Nam),서정수(Jung Soo Suh) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.4
Natural frequencies of the extension shaft assembly (ESA) of the control element drive mechanism (CEDM) for the advanced power reactor plus (APR+) have been determined by analyzing data obtained from a test and performing a numerical modal analysis. Axial acceleration time history signals of the ESA were obtained from an operational sequence of the CEDM, which produces impact force the same as that of impact tests onto the ESA. FFT analysis for the signals resulted in four natural frequencies. A modal analysis was performed to confirm the reliability of the results from the data analysis. Four natural frequencies for axial mode also resulted from the modal analysis. Maximum difference between two results is within 9%, therefore, the natural frequencies of the ESA from the data analysis are reliable.
배관내 열성층이 피크응력강도에 미치는 영향에 관한 연구
권형도(Hyeong-Do Kweon),이강용(Kang-Yong Lee),김종성(Jong-Sung Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Thermal stratification in piping may lead to considerable additive global bending moments and local peak stresses. Numerical analysis is carried out to assess the effect of thermal stratification in piping on peak stress intensity according to ASME Code, Section Ⅲ, NB-3200 under various conditions considering three parameters. As the temperature difference between top and bottom at inner side of piping increases, peak stress intensity increases linearly. On the other hand, peak stress intensity decreases with the increase of boundary layer thickness. Moreover the increase of thermal stratification length causes the increase of peak stress intensity until it approaches to a sustainable value.
인장시험과 유한요소해석을 통한 SA-508 저합금강의 진응력-진변형률 곡선 결정 방법
권형도(Hyeong Do Kweon),허은주(Eun Ju Heo),이도환(Do Hwan Lee),김진원(Jin Won Kim) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
It is essential to determine true stress-strain curve of a material for plastic properties input to a numerical analysis. A simple methodology for determining the true stress-strain curve of SA-508 Grade 3 Class 1 low alloy steel using limited information from a general tensile test with finite element analysis is proposed in this paper. Before necking, it is reasonable to simply convert measured engineering stress-strains to true stress-strains under uniform deformation. After necking, it is difficult to know true stress-strains due to nonuniform deformation without any specialized measurement techniques. Five post-necking strain hardening models are taken into account, which are Linear, Swift, Ludwick, Hollomon-Linear, and Hollomon-Linear-Constant equations. The equations can be decided using tensile test results that are true stress-strain value at the maximum load point, corrected true stress-strain value at the fracture point, and Considere Instability Condition. Hollomon-Linear and Hollomon-Linear-Constant models showed that the engineering stress-strains resulted from the finite element analysis best agree with the experimental results.
간선임도와 작업임도를 고려한 복합임도망의 적정밀도 산정
권형근 ( Hyeong Keun Kweon ),이준우 ( Joon Woo Lee ),이학준 ( Hak Jun Rhee ),지병윤 ( Byeng Yun Ji ),정도현 ( Do Hyun Jung ) 한국임학회 2016 한국산림과학회지 Vol.105 No.1
본 연구는 효율적인 임내도로망 구축을 위한 정책적 기초자료를 제공하고자 산림청 산하 5개소의 임도시설시범단지를 대상으로 복합임도망의 적정밀도를 산정하였다. 그 결과, 복합임도망의 적정밀도는 10.1~15.9 m/ha이었으며, 단일 규격의 간선임도망은 8.4~12.4 m/ha로 나타났다. 이를 기준으로 임도개설비용을 추정해보면, 단일규격의 간선임도망에 비해 약 1~8% 낮게 측정된 반면, 임도밀도는 20~30%가량 증가하였다. 또한, 대상지의 생산예정재적과 집재비용이 증가함에 따라 복합임도망의 적정밀도도 증가하였으며, 특히 고규격의 간선임도 밀도가 급격히 증가하였다. 한편, 경사가 급한 지역일수록 저규격의 작업임도 밀도가 상대적으로 증가하는 경향을 보였다. This study was conducted to provide the basic policy information for establishing efficient forest-road networks. Synthetic forest-road networks that consist of main and spur roads and forest-road networks with only main road (hereafter called “main-road network”) were planned for the five forest-road experimental districts of Korea Forest Service in this study. Road density of the synthetic forest-road networks was calculated and compared with the road density of the main-road networks. The results showed that the optimum road density of the synthetic forest-road networks was 10.1~15.9 m/ha, and the road density of the main-road networks was 8.4~12.4 m/ha. The construction cost of the synthetic forest-road networks was estimated about 1~8% lower than the main-road networks, while the road density was 20~30% greater than the main-road networks. As timber volume and hauling cost increased, the optimum road density of the synthetic forest-road networks increased, within which the road density of highstandard main road rapidly increased. On the other hand, the spur road density increased with slope gradient.
지병윤 ( Byoung Yun Ji ),권형근 ( Hyeong-keun Kweon ),황진성 ( Jin Seong Hwang ),정도현 ( Do Hyun Jung ) 한국임학회 2016 한국산림과학회지 Vol.105 No.4
본 연구는 임도사업의 계획과 유지관리 단계에서 임도 관리자 집단의 의식성향을 파악하여 체계적인 임도정책 수립을 위한 기초자료를 제공하기 위하여 수행하였다. 임도의 계획과 유지관리에 대한 설문조사 결과, 임도 노선의 계획시 고려사항으로는 육림작업, 산지재해 예방, 목재수확 등의 항목에서 높은 중요도를 보였으며, 간선임도에 대한 선호도가 가장 높게 나타났다. 또한 임도 유지관리 작업의 적절성에 대해서는 두 집단 모두 인력 및 예산부족으로 인한 어려움(92.9%)이 있다고 응답하였다. 임도의 개설로 우려되는 주요 피해형태로는 사면붕괴로 인한 인명피해, 사유지 통행에 대한 분쟁 등의 순으로 나타났으며, 현재 실행하고 있는 임도 유지·관리작업의 주요 내용으로는 배수시설의 정비와 노면정비가 높게 나타났다. 임도시설에 대한 주요 보완사항으로는 배수시설, 비탈면 녹화와 안정에 대한 응답이 높게 나타났다. This study was conducted to provide the basic policy information for systematic forest road planning and maintenance management by surveying two different administrator groups. The survey results showed that the high priorities of forest road planning were silviculture, disaster prevention, and timber harvesting, and main forest road type was preferred for future use. Also 92.9% of the respondents expressed difficulties due to insufficient manpower and budget. The expected damage types due to forest road construction were threat-tolife by slope failure and dispute on crossing private land. The current main maintenance tasks on forest roads included drainage and road surface maintenance works. Main forest road facilities that should be needed after the construction were installation of additional drainage structures, and slope revegetation and stabilization.