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노치 ( Notch )를 가진 試片의 有限要素法에 의한 彈塑性 極限 荷重解析
이택순,김동섭,황평,Lee, Taik-Soon,Kim, Dong-Sub,Hwang, Pyung 대한기계학회 1983 대한기계학회논문집 Vol.7 No.4
Many papers have shown limit loads of v-notched tension specimens in plane stress by the elastic-plastic finite element method. But they are always higher than the theoretical maximum loads. The present approach tries to find the reasons and formulates correction factor applicable to any notch shape using virtual work principle with triangular elements. The corrected limit loads are in good agreement with theoretical upper bound solutions and they are little influenced by mesh size and specimen length, which make the computing time save.
TMCP 고장력강 용접 부의 하한계 피로균열진전 특성평가
이택순(Taik-Soon Lee),오대석(Dae-Sek Oh),이휘원(Hwi-Won Lee) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.3
Recently developed TMCP steels, which were manufactured by controlled rolling followed by accelerated cooling process, were examined to study their characteristics and weldability. Accelerated cooling type TMCP steel’s hardness test result exhibited high value on weld zone. On the contrary, base metal and HAZ exhibited comparatively the similar value. On this experiment result Softening of HAZ is not occurred. in the heat affected zone, grain size repression be caused by chemical composition properties which a small quantity Al-Ti-B-N. Changing stress ratio near-threshold fatigue crack propagation experiments were carried out. According to this result, crack propagation velocity of the HAZ exhibited slower than the base metal and near-threshold value had increased at the HAZ. Finally accelerated cooling type TMCP steels were exhibited excellent mechanical properties in both strength and toughness.
多重 過荷重에 의한 Al 7075-T6 合金의 疲勞龜裂 成長遲延現狀에 관한 硏究
李澤淳(Taik-Soon Lee),李侑泰(You-Tae Lee) 한국해양공학회 1992 韓國海洋工學會誌 Vol.6 No.1
Aircraft structures and engineering structures are always subject to variable amplitude loads. Variable amplitude loads include some kind of loading history ; for example, constant amplitude load, single peak overload and block overload etc. Crack growth under variable amplitude loading exhibits retardation effect.<br/> In this study, the 4 point bending fatigue test was performed by hydrolic servo fatigue testing machine on 7075-T6 Al-alloy.<br/> The retardation effect of overload ratio and numbers of overload cycle was quantitatively studied.<br/> 1) Change of retardation effect against increment of overload ratio is more evident when the multiple overload is applied than single overload is done.<br/> 2) The number of overload cycle is very important factor about the crack growth retardation effect when the overload ratio is more than 1.75 ; that is not when the overload ratio is less than 1.75.<br/> 3) Overload affected zone size increased gradually by increment of crack growth retardation effect.<br/> 4) Crack driving force is more greatly reduced when the crack tip branched off two direction than it sloped to one direction.
이택순(Taik-Soon Lee),이휘원(Hwi-Weon Lee),김영철(Young-Chul Kim) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.3
The corrosion fatigue test were carried out to evaluate the fatigue characteristics of accelerated cooled (ACC) TMCP high tensile strength steels and weld joint with high heat input by one side one run submerged arc welding.<br/> In this paper, the fatigue crack growth behaviors were investigated with the center crack tension specimen of base metal and heat affected zone in substitute sea water and air, respectively.<br/> Main results obtained are summarized as follows:<br/> 1. The fatigue crack growth rates in sea water faster than those in air environment for the different heat input values, crack growth rate of base metal is very fast and effect of heat input is not remarkable.<br/> 2. In HAZ (82kJ/㎝, 116kJ/㎝), the crack branching phenomena were observed in both air and sea water environment,<br/> 3. In SEM observation, the corrosion effect on base metal was larger than that on HAZ in corrosion environment.
이문철(Moon-Chul Lee),최영근(Young-Geun Choi),이택순(Taik-Soon Lee) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.1
The use of advanced composite materials has grown in recent years in aerospace and other structures. Out of various kinds of repairing methods the one selected for this study is an idealized case which simulates a situation where a damaged laminate has been repaired by drilling a hole and thereafter plugging the hole with reinforcement. Two types of reinforcement are investigated ; adhesively bonded plug reinforcement or snug-fit unbonded plug in the hole. For each case of reinforcement, four different sizes of hole diameter and three types of reinforcing material (steel, aluminum, plexiglass) are employed for investigation.<br/> The experiment are mainly forced on the evaluation of ultimate strength of laminate with reinforced hole in comparison to its counterpart with the open hole.
SMC 복합재료와 Carbon/Epoxy 복합재료의 파괴인성평가
최영근(Young-Geun Choi),이유태(You-Tae Lee),이택순(Taik-Soon Lee) 한국해양공학회 1993 韓國海洋工學會誌 Vol.7 No.1
In composite materials, the fracture perpendicular to the fiber direction usually shows a non-linear behavior accompannying blunting and plastic deformation around the crack tip.<br/> In this study, the fracture thoughness in random short fiber SMC composite material and Carbon/Epoxy composite material is estimated by the A.M.(Area Method) and the G.L.M.(Generalized Locus Method) which can determine a stable total energy release rate(GT) not only in highly elastic material but also in highly non-linear materials.
Swaging에 의한 Autofrettage 加工의 有限要素解析
李澤淳,金東燮,李輝遠 영남대학교 공업기술연구소 1984 연구보고 Vol.12 No.1
Elastic-Plastic stress analysis has been carried out on an auto-frettage processed cylinder by mechanical push swaging. The analysis using finite element method was based on the incremental stress-strain relationship at the von-Mises yielding criterion and Prandtl-Reuss hypothesis in a axially symmetric plain stress condition. By this method, not only permanent enlargement of inner bore diameter but also residual stress distribution was calculated as a function of mandrel diameter. In consequence, enlargement of an autofrettage processed cylinder has good agreement between theoretical and experimental results. Thus, in autofrettage process the bore size and residual stress can be predicated using this method.
有限要素法에 의한 Butt 熔接部 殘留應力의 熱彈塑性解析
李澤淳 嶺南大學校 工業技術硏究所 1985 연구보고 Vol.13 No.1
It is well known that welding thermal stress and resulting residual stress influence the strength of welded structre, causing brittle fracture and cracking. During welding, a limited portion of the welded joint is heated up to a very high temperature and cooled down to room temperature. These condition produce thermal stress, which causes distorsion and residual stress of structure. In the thermal cycle, the temperature distribution change with time and it effects the mechanical properties of the metals. In order to perform a reliable theoretical analysis, it is necessary to obtain an accurate informations on the entire histories of material properties during thermal cycle. With the help of thermal elasto-plastic theory method, the author developed a method of finite element analysis of thermal and residual stresses induced in butt weld under a moving electrode in the course of first bead.