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Reverse Bending을 통한 CTOD 시험 예비균열 형상균일화에 관한 연구
정세환,박동환,김현수,신상범,박태종,Jeong, Sehwan,Park, Dong-Hwan,Kim, Hyeon-Su,Shin, Sang-Beom,Park, Tae-Jong 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.2
This study investigates the appropriate range of reverse bending load for the CTOD test of thick weld by observing improvement of pre-crack shape and determination of the limit applicable load. In order to do it, the effect of the amount of the reverse bending load on the maximum deviation of the pre-crack length was investigated by the extensive tests, and the variation of plastic zone size in way of the crack tip under reverse bending load were evaluated by FEA. With the results obtained by the experiments and FEA, the proper range of reverse bending load was suggested. The effectiveness of the reverse bending method was verified by examining the pre-crack straightness after CTOD tests of thick weld specimens with various thickness and strength.
정세환(Sehwan Jeong),허훈(Hoon Huh),이재익(Jae-Yik Lee) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
This paper is concerned with the material properties of API steel plates for off-shore structures. Strain rate and temperature dependency on the material properties are investigated. Tensile tests have been performed with the variation of strain rate from 0.001/sec to 200/sec and the variation of the environmental temperature from -40℃ to 200℃. Differences in material properties through thickness direction of the steel plates are also investigated. Tensile specimens are obtained from two layers which are obtained from two different locations in a steel plate. One layer is collected in the middle and the other layer is collected near outer surface of the steel plate. Thermo-mechanical responses of the specimens of two layers are quantitatively compared and micro-structures are observed.
정세환(Sehwan Jeong),허훈(Hoon Huh),방건웅(Gun Woong Bahng),김창근(Chang Geun Kim),채균식(Kyun Shik Chae) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
The crashworthiness of auto?body structures is one of the important issues in the automotive industry. The crash analysis with finite element methods has been conducted in order to evaluate the crashworthiness of auto?body structures. In the car crash, auto?body structures undergo deformation with a wide range of strain rate from 0.001/sec to 500/sec. Since the material properties of steel sheets depend on the rate of deformation, in order to ensure the impact characteristics of auto?body structures accurately, the dynamic behavior of sheet metals must be examined and applied to the finite element model appropriately. This research is concerned with standard uncertainty evaluation of tensile properties of auto-body steel sheets in wide range of strain rate from 0.001/sec to 100/sec. Stress-strain relations of an auto-body steel sheet were obtained with quasistatic and high speed tensile tests. Uncertainty components in both testing methods are summarized and standard uncertainties of each input quantities are evaluated. An analytic model is established in order to calculate combined standard uncertainty of the measurand. The measurand is true stress with respect to true strain and the input quantities are load and displacement data during the tensile test and initial dimensions of specimen such as thickness, width and length. Uncertainties which come from signal processing and deviation of measured values in repetitive tests are also considered.
정세환(Sehwan Jeong),허훈(Hoon Huh),최민국(Min Kuk Choi),채균식(Kyun Shik Chae),김창근(Chang-Geun Kim) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
This research is concerned with the standard uncertainties in the tensile properties of auto-body steel considering strain rate effects and effects of uncertainties of tensile properties on crash analyses. A procedure to obtain plastic true stress data and analytic uncertainty model are established. Uncertainty sources in the high-speed tensile test are summarized. Standard uncertainties in measuring input quantities such as load, length, thickness, and width of the specimens are calculated, as are their associated sensitivity coefficients. Uncertainty induced by the FFT smoothing process used to reduce unnecessary signal in acquired data is also considered. Image analysis using a high-speed camera is performed in order to measure the length of the specimen during the high-speed tensile test. Combined standard uncertainty is then evaluated for the true stress data of an auto-body steel sheet at intermediate strain rates. Crash analysis of a square tube is performed with measured true stress data considering standard uncertainties. In the analyses, maximum and minimum values of true stress data in the range of expanded uncertainty are applied into the analyses. Finally, effects of the uncertainties on the crash analyses are quantitatively evaluated.
정세환(Sehwan Jeong),허훈(Hoon Huh),박연규(Yon-Kyu Park),김창근(Chang-Geun Kim) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
The crashworthiness of auto?body structures is one of the important issues in the automotive industry. The crash analysis with finite element methods has been conducted in order to evaluate the crashworthiness of auto?body structures. In the car crash, auto?body structures undergo deformation with a wide range of strain rate from 10?3/sec to 500/sec. Since the material properties of steel sheets depend on the rate of deformation, in order to ensure the impact characteristics of auto?body structures accurately, the dynamic behavior of sheet metals must be examined and applied to the finite element model appropriately. This research is concerned with standard uncertainty evaluation of dynamic material properties of steel sheets for auto?body structures. Analytic model of combined standard uncertainty for the dynamic tensile properties is established. The measurand is true stress with respect to true strain and the input quantities are load and displacement data during the tensile test and initial dimensions of specimen such as thickness, width and length. Uncertainty factors come from signal processing and repetition in the high speed tensile tests are also considered. Standard uncertainty and sensitivity coefficient of each input quantity are evaluated according to the ISO guide (GUM: Guide to the expression of Uncertainty in Measurement).
개선된 자동차용 강판 동적인장물성 측정에서의 표준불확도평가
최민국(Min Kuk Choi),정세환(Sehwan Jeong),허훈(Hoon Huh),김창근(Chang Geun Kim),채균식(Kyun Shik Chae) 한국자동차공학회 2013 한국자동차공학회 부문종합 학술대회 Vol.2013 No.5
Evaluation of the crashworthiness is one of the important issues in the automotive industry. In order to evaluate the crashworthiness of auto-body structure, finite element methods has been conducted for crash analysis. Generally, strain rates distribution of auto-body structure in the car crash is ranging from 0.001/s to 500/s. Since the material properties of steel sheets depend on the strain rates, the dynamic behavior of sheet metals must be examined and applied to the finite element model appropriately. This paper is concerned with the evaluation of standard uncertainty of modified measurement of high speed tensile properties of auto-body steel sheets. Obtaining procedure of the true stress?true strain data at intermediate strain rates is properly designed for the experiment and data acquisition compared with previous procedure. Standard uncertainty of the true stress is evaluated considering sources of uncertainties of input quantities and their associated sensitivity coefficients. A combined standard uncertainty is evaluated from not only the uncertainties of the input quantities but also the influence factor for the true stress. The results show that the standard uncertainty evaluation procedure has been successfully applied to high speed tensile properties.
동적하중을 받는 기능성 고폭화약조성 시뮬런트 재료물성 연구
박정수,염기선,박충희,정세환,이근득,허훈,Park, Jungsu,Yeom, Kee Sun,Park, Chunghee,Jeong, Sehwan,Lee, Keundeuck,Huh, Hoon 한국군사과학기술학회 2013 한국군사과학기술학회지 Vol.16 No.6
This paper is concerned with the material properties of functional high explosive(FHX) simulant at various strain rates ranging from $10^{-4}/sec$ to $10^1/sec$. Material properties of FHX at high strain rates are important in prediction of deformation modes of FHX in a warhead which undergoes dynamic loading. Inert FHX stimulant which has analogous mechanical properties with FHX was utilized for material tests due to safety issues. Uniaxial tensile tests at quasi-static strain rates ranging from $10^{-4}/sec$ to $10^{-2}/sec$ and intermediate strain rates ranging from $10^{-1}/sec$ to $10^1/sec$ were conducted with JANNAF specimen using a tensile testing machine, INTRON 5583, and developed high speed material testing machine, respectively. Uniaxial compressive tests at quasi-static strain rates and intermediate strain rates were conducted with cylindrical specimen using a dynamic materials testing machine, INSTRON 8801. And cyclic compressive loading tests were performed with various strain rates and strains. Deformation behaviors were investigated using captured images obtained from a high-speed camera.
박충희(Chunghee Park),정세환(Sehwan Jeong),허훈(Hoon Huh),박정수(Jungsu Park) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
This paper deals with mechanical properties of PBX(polymer bonded explosives) simulant at various strain rates ranging from 10?⁴/sec to 10?²/sec. Mechanical properties of PBX at high strain rates are important in prediction of deformation behaviors of PBX in a warhead system which undergoes severe dynamic loading. Inert PBX stimulant which has analogous mechanical properties with PBX was utilized for material tests due to safety issues. Uniaxial tensile tests at quasi-static strain rates were conducted at strain rates ranging from 10?⁴/sec to 10?²/sec using a tensile testing machine, INTRON 5583. Results of these tests were compared with those of uniaxial compressive tests conducted at quasi-static strain rates. Deformation behaviors of PBX simulant were investigated using captured images obtained from a high-speed camera.
허훈(Hoon Huh),송정한(Jung-Han Song),정세환(Sehwan Jeong),하지웅(Jiwoong Ha),임성준(Sung Jun Lim),최민국(Min Kuk Choi) 한국자동차공학회 2013 한국자동차공학회 학술대회 및 전시회 Vol.2013 No.11
The formability and crash worthiness of auto-body structures have been an important issue in the automotive industry because of the safety of passengers and usage of AHSS. This paper explains about the high speed mechanical property, failure load of welding and fracture model at a wide range of strain rate from 0.001/s to 200/s. Those properties and model can be directly applied to finite element analysis to evaluate the formability and the crashworthiness of auto-body structures. This paper introduces the acquisition procedure of the high speed tensile properties of auto-body steel sheets and the evaluation procedure of the standard uncertainty of the tensile properties as well as the effects of strain rate on the fracture locus and the failure load of spot and laser welding of auto-body steel sheets. Since a fracture model is indispensible for accurate assessment of the crashworthiness of an auto-body, a fracture model newly reported is also explained with derivation and application