• Ocean Systems Engineering
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• 제8권4호
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• pp.409-426
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• 2018

This paper presents the strengthening of tubular joint by wrapping Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). In this study, total number of layers, stacking sequence and length of wrapping are the different parameters involved when fiber reinforced polymers (FRP) composites are used for strengthening. For this, parameters where varied and results were compared with the reference joint. The best stacking sequence was identified which has the highest value in ultimate load with lesser deflections. For determining the best stacking sequence, numerical investigation was performed on CFRP composites; length of wrapping and number of layers were fixed. Later, the studies were focused on CFRP and GFRP strengthened joint by varying the total number of layers and length of wrapping. An attempt was done to propose a parametric equation from multiple regression analysis, which can be used for CFRP strengthened joints. Hashin failure criteria was used to check the failure of composites. Results revealed that FRP was having a greater influence in the load bearing capacity of joints, and in reducing the deflections and stresses of joint under axial compressive loads. It was also seen that, CFRP was far better than GFRP in reducing the stresses and deflection.

• Steel and Composite Structures
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• 제38권6호
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• pp.637-656
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• 2021

The component-based method is widely used to analyze the initial stiffness of joint in steel structures. In this study, an analytical component model for determining the column face stiffness of square or rectangular hollow section (SHS/RHS) subjected to tension was established, focusing on endplate connections. Equations for calculating the stiffness of the SHS/RHS column face in bending were derived through regression analysis using numerical results obtained from a finite element model database. Because the presence of bolt holes decreased the bending stiffness of the column face, this effect was calculated using a novel plate-spring-based model through numerical analysis. The developed component model was first applied to predict the bending stiffness of the SHS column face determined through tests. Furthermore, this model was incorporated into the component-based method with other effective components, e.g., bolts under tension, to determine the tensile stiffness of the T-stub connections, which connects the SHS column, and the initial rotational stiffness of the joints. A comparison between the model predictions, test data, and numerical results confirms that the proposed model shows satisfactory accuracy in evaluating the bending stiffness of SHS column faces.

• International Journal of Korean Welding Society
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• 제2권2호
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• pp.7-13
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• 2002

A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies" Requirements for Approval of $CO_2$ Laser Welding Procedures" Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to $-50^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.ximum hardness.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.222-228
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• 2002

A comparison of the welding performance of ship hull structural steels has been made. The weldability of steels especially designed for laser processing was compared to that of conventional hull and structural steels with plate thicknesses up to 12 mm. Autogenous laser beam welding was used to weld butt joints as well as skid and stake welded T-joints. The welds were assessed in accordance with the document "The Classification Societies′ Requirements for Approval of $CO_2$ Laser Welding Procedures". Small imperfections in the weld only grew slightly in root bend tests and they only had a minor influence on the fatigue properties of laser fillet welded joints. In Charpy impact tests, the 27 J transition temperature of the weld metal and HAZ ranged from below -60 to -5$0^{\circ}C$. The amount of martensite in the weld metal depended on the carbon equivalent of the steel with the highest amounts and highest hardness levels in conventional EH 36 (389 HV 5). Thermomechanically rolled steels contained less martensite and showed a correspondingly lower maximum hardness.

• 한국해양공학회지
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• 제2권2호
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• pp.112-121
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• 1988

A study on friction welding of carbon steel bar (SM45C) to chrome molybedenum steel bar(SCM4) is examined experimentally through tensile test, hardness test, microstructure test and fatigue test. so, this paper deals with optimizing the welding concitions and analyzing various mechanical properties about friction welds of SM45C to SCM4 steel bars. The results obtained are summarized as follows; 1) For friction welded joints of SM45C to SCM4 steel bars, the total upset(U)increases linearly with an increase of heating time ($t_{1}$) till 6s. 2) The determined optimum welding conditions are heating time ($t_{1}$)2s, upsetting time($t_{2}$), 3s, heating pressure($p_{1}$), 4kgf/$mm^{2}$(39.2MPa), upsetting pressure($p_{2}$, 8kgf/mm$^{2}$(78.4MPa) and rotating speed(N), 2, 000rpm when the total upset(U) is 3.4mm, resulting in a computed relationship between the joint tensile strength .sigma.$_{t}$ (kgf/mm$^{2}$and the total upset U(mm); .sigma.$_{t}$ =$0.21U^{3}$ - $3.38U^{2}$ +17.03U + 66.00 3) As the elongation is increased more and more, the fracture position becomes away from weld interface and the fractures are similar to those of SM45C. Fracture is taken place on SM45C side. 4) The weld interface of two dissimilar materials is mixed strongly, and the heat affected zone is about 2.0mm at SM45C while about 2.7 mm at SCM4 side. Therefore, the welded zone and heat affected zone are very narrow, comparing with those of the joints welded by the other welding methods. 5) The fatigue strengths at N=10$^{6}$ cycles of SM45C, SCM4 and friction welded joints are 23kgf/$mm^{2}$, 33kgf/$mm^{2}$(220.5 MPa), and 22.5kgf/$mm^{2}$(220.5MPa) respectively, and fracture at friction welded joint takes place at the side of SM45C. 6) The hardness of the friction weld interface is 3 times higher than that of base metal. 7) Fatigue strength of friction welded joint is higher than that of base metal. 8) Notch sensitivity factor of friction welded joint is lower than that of base metal.

• Journal of Welding and Joining
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• 제16권5호
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• pp.48-55
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• 1998

This study was undertaken to investigate the friction welding of A2024-T6 aluminum alloy and SM45C carbon steel using insert metals. The relationships among the friction welding conditions, the tensile strength of joints, the hardness distribution of welds, the microstructure of welds and the tensile fracture surfaces were mainly investigated through this experiment. When the A6063-T5 aluminum alloy of insert metal was used, the maximum tensile strengh of joint was obtained. In this case, the maximum joint efficiency was 75.3 percent and in the case of unusing the insert metals, it was 37.7 percent. Optimal welding conditions were N=2000rpm, P$_1$=40MPa, P$_2$=140MPa, t$_1$=1.0sec and t$_2$=5sec.

• 한국보건간호학회지
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• 제14권1호
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• pp.122-130
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• 2000

This study was designed to investigate the effects of an aquatic exercise program on the physical function and depression among the community elderly. The subjects were 41 cases of aged over 65 who went to elderly college in Hawsung-Kun, Kyeongkee province. Seventeen of them were assigned to control group, while twenty four subjects to the experimental group. The period of data collection was from June., 1999 to November., 1999. The aquatic exercise program was developed by the author with the assistance of rehabilitation medicine doctor and physical therapist in the public health center. The program was carried out once a week for 6 months in regular swimming pool. Data were analyzed with t-test, $X^2$ test, ANCOVA. paired t-test using SAS 6.12. Results were obtained as follows: 1. The increments in the range of motion of the shoulder and knee joints in experimental group after exercise was significantly greater than those in the control group. 2. The physical pain score decreases significantly after the exercise in the experimental group only. 3. The experimental group revealed lower level of depression after exercise than the level before the exercise, whereas control group showed no significant changes in this level. These findings may indicate that the aquatic exercise program is effective in increasing the range of motion of shoulder and knee joints and also effective in decreasing pain, the level of depression. Accordingly. the aquatic exercise program can be adopted as an health promotion program for community elderly.

• Steel and Composite Structures
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• 제45권5호
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• pp.749-766
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• 2022

This paper investigates the seismic performance of exposed RCFST column-base joints, in which the high-strength steel bars (USD 685) are set through the column and reinforced concrete foundation without any base plate and anchor bolts. Three specimens with different axial force ratios (n = 0, 0.25, and 0.5) were tested under cyclic loadings. Finite element analysis (FEA) models were validated in the basic indexes and failure mode. The hysteresis behavior of the exposed RCFST column-base joints was studied by the parametrical analysis including six parameters: width of column (D), width-thickness ratio (D/t), axial force ratio (n), shear-span ratio (L/D), steel tube strength (f_y) and concrete strength (f_c). The bending moment of the exposed RCFST column-base joint increased with D, f_y and f_c. But the D/t and L/D play a little effect on the bending capacity of the new column-base joint. Finally, the calculation formula is proposed to assess the bending moment capacities, and the accuracy and stability of the formula are verified.

• Journal of Advanced Marine Engineering and Technology
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• 제17권4호
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• pp.38-48
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• 1993

A study on friction welding of stainless steel bar(SUS431) to chrome molybdenum steel bar(SCM21) was accomplished experimentally through analysis for relations among friction welding conditions, tension test, hardness test, microstructure test and acoustic emission test. The results obtained are summarized as follows ; 1. Through friction welding of SUS431 bar to SCM21 bar, the optimum welding condition by considering on strength and toughness was found to be the range of heating time of 3-5 sec when the number of rotating speed of 2000rpm, heating pressure of 10kg/$mm^2$, and upsetting time of 4 sec. 2. Quantitative ralationship was identified between heating time($T_1$, sec) and tensile strength (${\sigma},\;kgf/mm^2$) of the friction welded joint and the relation equation is $\sigma$=52.62$T_1{^{0.06}}$. 3. Through AE test, quantitative relationship was confirmed between heating time($T_1$, sec) and total AE(N, counts) during welding, and the relation is computed as follows ; N=30413.6$e^{0.06T1}$. 4. It was confirmed that the quantitative ralationship exists between the tensile strength of the welded joints and AE cumulative counts. And the relation is computed as the following ; ${\sigma}$=16.37(ln N)- 116.4. 5. When ONZ=36500-41500 counts by $OT_1Z$=3~5sec, it was identified by experiment that the range of welded joint tensile strength is 55.6-57.7kgf/$mm^2$/ whose joint efficiency is more than 100%, and it was experimentally confirmed that the real-time nondestructive quality(strength) evaluation for the friction welded joints could be possible by acoustic emission technique.

• 한국강구조학회 논문집
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• 제13권1호
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• pp.9-18
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• 2001

대스팬 철골구조물의 지붕구조로서 강관트러스가 많이 사용되고 있다. 강관트러스는 타 단면(H, L형강 등)에 비하여 구조역학적인 측면에서 유리하다고 할 수 있다. 그러나 지관의 압축력에 의하여 격점부에는 국부좌굴이 발생하고 이로 인하여 구조체 전체의 내력이 격점부의 지배를 받게 된다. 또한 강관 격점부에서의 내력 및 변형 성상은 거동이 복잡하여 정확한 거동을 예측하기 어려울뿐만 아니라 해석적으로 정밀해를 구하기 어렵다. 이 연구에서는 T형 격점부를 대상으로 지관과 주관의 직경비(d/D) 주관경과 두께비(D/T)에 관한 변수를 설정하여 일련의 실험을 진행하고 기초하여 단순한 링해석법을 이용하여 항복하중에 관한 실용해를 제안하였다. 또한 부가적으로 각국에서 제안된 항복하중에 관한 기존의 연구결과와도 비교, 검토하였다.