70계열 알루미늄합금 용접부의 피로균열진전 거동과 피로수명 예측에 관한 연구

옹장우,김재훈,정근춘 忠南大學校 産業技術硏究所 1988 산업기술연구논문집 Vol.3 No.1

It has been important to determine life cycle and stress range for the each welded metal under high cycle load control test conditions. In this study, fatigue crack propagation rate for 7017, 7020, 7039 and 5083 alluminum welded alloy was compared with stress intensity factor range linear elastic fracture mechanics. Compact tension specimens were used and crack growth rate da/dN and stress intensity factor range ΔK were analyzed concerning to the R value of 0.1 and 0.3. In order to find out the value of ΔK, ΔK-inceasing test method was applied by the standard fatigue testing method describes in ASTM E647-81. From the result, the stable crack propagation region of 7017, 7020, 7039 and 5083 alluminum welded alloy was applicable to the Paris equation da/dN = C(ΔK)m (C and m are material constants). Constant m decreases and constant C increases with increasing of stress ratio R. Without dependence on materials, the fatigue life and the propagation rate increase, while the gradients of crack propagation rate decrease, whith increasing stress ratio. Fatigue life was observed roughly in the order of 7020 > 5083 > 7017 > 7039, independently on crack propagation direction and stress ratio. The fatigue life is longer when the crack propagation direction of specimen and welded bead are parallel to each other than transverse. The crack propagation rate and the gradient of it are larger in the case of parallel specimen than transverse. The minimum crack length of fatigue life can be estimated through the knowledge of maximum equivalent crack length obtained by using nondestructive test.

탄소섬유 복합재료의 AE 특성에 관한 연구

옹장우,이영신,심봉식,지용관,주영상 대한기계학회 1989 대한기계학회논문집 Vol.13 No.1

This study was carried out to measure the mechanical properties and the acoustic emission (AE) characteristics of the carbon fiber reinforced composites of several types of the stacking sequence. AE signals were detected during the tensile tests. The number of ringdown counts, total ringdown counts were plotted together with the load-displacement curves. The tensile load-displacement behavior of specimen is compared and discussed based on the measured AE properties in relation to the failure mechanism. With the increase of load, AE signals increased. This showed that failure had being propagated by matrix deformation and cracking, delamination, fiber debonding and breakage. Felicity ratio has been obtained by observation of ;the Kaiser effect according to the variation of load ratio. The reloading tests showed that the felicity ratio decreased obviously when the load ratio or damage increased. These AE characteristics are hopeful to be employed as the criteria to evaluate the failure processes of composites. 본 연구에서는 카본/에폭시 프리프렉으로부터 제작된 적층판을 사용하여 인장시험시 발생하는 AE특성과 파괴거동을 비교 검토하고 이들을 통하여 탄소섬유 복합재료의 파손특성과 AE법의 유용성을 규명하고자 한다.

고강도 알루미늄합금의 피로균열의 하한계 및 안정 전파거동

옹장우,진근찬,김종배,김재훈,하태수 대한기계학회 1988 대한기계학회논문집 Vol.12 No.2

본 연구에서는 항공기, 압력용기 및 지상운송차량 등에 고강도와 용접성이 요구되는 고강도 알류미늄합금 7017T651, 7020T651 및 5083 H115에 대해 균열진전 하한계특성 및 안정 균열진전 하한계특성에 미치는 영향을 고찰 하고자 한다. The threshold fatigue crack growth and the stable crack propagation behaviors were studied in 7017 T 651, 7020 T 651 and 5083 H 115 aluminum alloys. The threshold (.DELTA. K $_{th}$) fatigue crack growth can be expressed by the equation .DELTA. $K_{th}$) = .DELTA. $K_{tho}$(1-R)$^{r}$ , where R is stress ratio, .DELTA. $K_{tho}$ is .DELTA. K at R = 0 and r is material constant. The stable crack growth rate against stress intensity factor range .DELTA. K exhibits the trilinear form with two transitions and results of investigation on crack closure phenomena showed that the crack opening stress intensity factor $K_{op}$ is approximately equal to R $K_{max}$. + .DELTA. K $_{th}$.th/.

알루미늄 合金 異材熔接部의 變形率測定

옹장우,전제춘,오상진 대한기계학회 1986 대한기계학회논문집 Vol.10 No.5

The strain distribution on a welded aluminum alloy transition joint produced by a static tensile load has been measured using a moire method combined with photoelastic coating method. The test specimens were made of aluminum alloy 6061-T6 and 2014-T6 butt welded with ER-4043 filler metal, and were post welded heat treated (solid solution heat treatment 502.deg. C 70min.) and precipitated (artificial aging 171.deg. C 600min.) to cause an abrupt change of mechanical properties between the base metals and weld metal. The photoelastic epoxy rubber was cemented on the specimen grating which had been reproduced on the specimen surface by using an electropolishing. The measurements were compared with strains computed by Finite Element Analysis. The following results were abtained. (1) The maximum strain were distributed along the center line in the transverse directiion of the weld metal. (2) The strain gradient along the fusion line increased approaching the V-groove tip and the maximum value was observed at a quarter of width from the V-groove tip. (3) The moire method combined with photoelastic coating was proved very useful for real time strain measurement in the welded aluminum alloy transition joint. 본 연구에서는 알루미늄 합금인 알루미늄 2014와 6061의 이재를 V형 맞대기 이음을 한 후 정적인장하중을 가하여 모아레법에 광탄성 피복법을 조합한 방법에 의 해 변형율을 실시간(real time)에서 측정하고 유한요소법으로 해석한 결과와 비교검 토하였다.

構造용高炭素鋼材 의 高溫 低 사이클 피勞擧動 에 關한 硏究

옹장우,김재훈 대한기계학회 1982 대한기계학회논문집 Vol.6 No.2

This study was undertaken to determine tensile properties and low-cycle fatigue behavior of 0.6%C high carbon steel used of structural purposes at temperatures up to 500.deg.C. In the low-cycle fatigue test the upper limit was decided by elongation(i.e. the total strain range), while the lower limit was defined by the load (i.e. zero load). The following results were obtained. Both, the ultimate tensile strength and low-cycle fatigue resistance attain the maximum values near 250.deg.C. Above this temperature the values decrease rapidly as the temperature increases. The low-cycle fatigue resistance decreases whenever there is an increase of the total strain range. Because the hardness of cycle fatigued specimen correlates cyclic hardening and cyclic softening, therefore the hardness of cycle fatigued specimen is smaller than that of the nonfatigued specimen at room temperature and 500.deg.C but much larger than the hardness of the nonfatigued specimen near 250.deg.C.

微小格子 를 利용한 304스테인레스鋼 의 피勞 크랙 進展擧動 에 관한 硏究

옹장우,임용호 대한기계학회 1982 대한기계학회논문집 Vol.6 No.3

The fatigue crack propagation behavior or non-heat-treatment and thermally aged type 304 stainless steel was investigated on the basis of linear elastic fracture mechanics. This Study was concentrated on the relations between the crack propagation rate and the stress intensity factor range. The following results are obtained : The precision measurement and observation of fatigue crack propagation behavior is studied with moire grating. The effect of thermally aged type 304 stainless steel is investigated under small load. In the equation da/dN=c(.DELTA. k)/SUP m/, factor m of thermally aged steel is a little higher than non-heat-treatmented steel and its limit is m=1.35-4.2.

휴반용 분무기의 Nozzle에 관한 연구(IV) (중거리용 Nozzle예 있어서 구경과 압력의 특성)

옹장우,이상우 한국농공학회 1975 한국농공학회논문집 Vol.17 No.3

This study was conducted to examine the effects of the change of cap hole diameter and pressure on the travelling distance and the sprayed particle size for the medium range nozzle. The results of this study are summarized as follows; 1) The effective travelling distance was about from 1 meter to 8 meters and centro-position of the travelling distance was about 3 or 5 meters. 2) Main effect of change of cap hole diameter for the travelling distance was a slight convex quadratic curve. 3) Main effect of change of pressure increased linearly, its increasing rate about 1.6 was large. 4) Sizes of sprayed particles were less than 250${\mu}$ generally and the sizes decreased according to the increasing of travelling distance. 5) Changes of diameter of sprayed particles by cap hole diameter increased in accordance with increasing of cap hole diameter. 6) Changes of diameter of sprayed particles by the groove depth of swirl plate was very slight.

모아레法 을 活용 比較한 오우스테나이트系 SUS 27 의 크리이프擧動

옹장우,이훈주 대한기계학회 1983 대한기계학회논문집 Vol.7 No.1

This study practiced to observe the creep behavior at specific temperature on Austentic SUB 27 stainless steel by Moire method. The results obtained from this study are summarized as follows; In tensile experiment, tensile strength and yielding strength decrease as the temperature increases. Yielding strength is equivalent to 60-70% of tensile strength. Reduction of Area and Elongation show minimum values at 300.deg. C. The results of Moire method using Moire heating resisting grid coincide with LVDT result. Therefor, It is proved that the Moire method has great merit in strain measurement of a creep behavior. In homologous at temp. 0.2 or less, creep behavior is very small amount. But, in more than 0.3, creep behavior is very active. Creep rate increase as temperature increase and creep rate is proportional to .alpha. values of experimental equation.

복합조직강의 저 및 고사이클 피로특성에 관한 실험적 연구(I) - 저사이클 피로특성 -

옹장우,성낙원 대한기계학회 1986 대한기계학회논문집 Vol.10 No.4

본 연구에서는 SM20C를 모재로 하여 입경의 크기가 다른 3종의 복합조직강을 제작 동일한 분위기에서 저 및 고사이클 전영역에 걸쳐 피로특성을 검토하고져 한다. 제일보는 그 중 저사이클특성에 대한 보고이다. 일반적으로 저사이클 피로현상은 재 료가 탄소성 상태하에서 전위, 미소크랙, 보이드(void) 등의 인자가 복합적으로 작용 하여 발생함으로 변형률속도, 제어파형, 온도, 시험방법 및 분위기에 따라 많은 영향 을 받는다. 따라서 본 연구에서는 두가지 실험방법을 사용, 응력-변형율거동을 검토 복합조직강의 피로특성과 입경크기가 피로거동 및 강도에 미치는 영향을 비교 고찰하 였다.

機械設計工學敎育科 敎科課程改善에 관한 硏究 : 機械製圖를 中心으로 With emphasis on the curriculum of the mechanical drawing

邕章祐,李永臣,梁均懿,柳盛淵 충남대학교 공업교육연구소 1981 論文集 Vol.4 No.1

This investigation aims at identifying some problems encountered with the mechanical drawing education in the Department of Mechanical Design Engineering of the College of Ind. Educ, and suggesting solutions to the problems associated. The study is based on the analysis of the mechanical drawing program and text materials currently applied to the department. The following recommendations are made; 1) Drawing theory and basic related theory should be more emphasized than before. 2) A systematic approach is recommended in the curriculum process. a) Teaching program should be revised taking into account the student level. b) Training level and subject should be adjusted. c) Job sheets and text-books for drawing exercise should be developed. d) Effective evaluation method should be established. e) The audio-visual media, e.g, OHP and section model should be actively utilized. f) Teaching assistants are required in drawing classes. 3) It takes at least 400 hours to educate the mechanical drawing satisfactorily.