• Journal of Welding and Joining
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• v.14 no.2
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• pp.36-45
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• 1996

Fatigue strength of the spot welded lap joint is considerably influenced by corrosive environments. Particularly, the chloride and the sulfide are most injurious to strength of the spot welded lap joint. Therefore, there is a need to evaluate its effect to corrosion fatigue strength for safe life design of spot welded structures. In order to evaluate their corrosion fatigue strength, corrosion fatigue tests on the spot welded lap joints of the uncoated and the coated high strength steel sheets were conducted in air and in 10% NaCl solution. Corrosion fatigue strength of the uncoated specimens were entirely lower than the coated one in NaCl solution, but those of the coated specimens in NaCl solution were lower than in air. And stress distribution in single spon welded lap joint subjected to tension-shear load was investigated by the finite element method. Using these results, we tried to evaluate corrosion fatgue strength of the various spot welded lap joints with maximum stress $\sigma_{max}$ at edge on loading side of the spot welded lap joint. We could find that corrosion fatigue strength could be quantitatively and systematically rearranged by $\sigma_{max}$.

• Structural Engineering and Mechanics
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• v.5 no.4
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• pp.433-450
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• 1997

The objective of this work is to predict the failure loads, associated maximum transverse displacements, locations and the modes of failure, including the onset of delamination, of thin, flat, square symmetric laminates under the action of uni-axial compression. Two progressive failure analyses, one using Hashin criterion and the other using Tensor polynomial criteria, are used in conjunction with the finite element method. First order shear deformation theory and geometric nonlinearity in the von Karman sense have been employed. Five different types of lay-up sequence are considered for laminates with all edges simply supported. In addition, two boundary conditions, one with all edges fixed and other with mixed boundary conditions for $(+45/-45/0/90)_{2s}$ quasi-isotropic laminate have also been considered to study the effect of boundary restraints on the failure loads and the corresponding modes of failure. A comparison of linear and nonlinear results is also made for $({\pm}45/0/90)_{2s}$ quasi-isotropic laminate. It is observed that the maximum difference between the failure loads predicted by various criteria depend strongly on the laminate lay-ups and the flexural boundary restraints. Laminates with clamped edges are found to be more susceptible to failure due to the transverse shear and delamination, while those with the simply supported edges undergo total collapse at a load slightly higher than the fiber failure load.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.173-178
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• 2005

In this paper, an efficient and robust analysis system for the flutter optimization of laminated composite wings has been developed using the coupled computational method based on the genetic algorithm. General three-dimensional doublet-lattice method is efficiently used to compute generalized aerodynamic forces of T-tail configuration in the frequency domain. Structural dynamic analyses of laminated composite T-tail models are conducted using finite clement method. The classical P-k flutter analysis technique is applied to effectively solve the aeroelastic governing equations in the frequency domain. Optimum design studies using genetic algorithm have been conducted in order to obtain maximum flutter stability of a composite T-tail configuration. The results show that flutter stability can be significantly increased using composite materials with proper optimum design concepts even for the same weight and shape condition. In the view point of engineering design, it is also importantly shown that the optimization of the vertical wing part is highly effective comparing to the optimization of horizontal wing part.

• Journal of Plant Biology
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• v.26 no.2
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• pp.53-71
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• 1983

Physicochemical properties of soil, mineral cyclings, production of plants, and relationship between sodium(Na) content and progresses of plant communities were studied in a coastal salt marsh in Incheon. Contents of Na, available phosphorus(A-P) and value of electric conductivity of soil decreased in order of Salicornia herbacea, Limonium tetragonum, Phragmites communis and Zoysia sinica communities, but contents of organic matter, total nitrogen(T-N) and calcium(Ca) of soil were vice versa. Specise diversity index decreased with increase of Na content of soil with correlation coefficient of -0.82. The aboveground biomass of plant communities were 2,981 g.dw/$m^2$ in P. communis, 1,471 g.dw/$m^2$ in Z. sinica, 189g.dw/$m^2$ in S. herbacea and 71 g.dw/$m^2$ L. tetragonum, respectively. Seasonal changes of contents of inorganic nutrients per unit land area coincided with those of biomass of plant communities, however, the maximum contents of K occured earlier than the maximum biomass. Amounts of inorganic nutrients absorbed by plant were directly proportion to its biomass and it was true to reverse in restored amounts of them to soil. In turnover times of nutrients of the communities, it took the shortest time for P but the longest for Ca and P. communis community took the shortest but L. tetragonum the longest. For example, in P. communis turover time of P took one year and that of Na 1,440 years. Lack of P element, therefore, was expected in this study area.

• Transactions of Materials Processing
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• v.27 no.3
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• pp.165-170
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• 2018

In order to increase the lifetimes of cold forging dies, insert rings are generally used. In this study, an insert ring and shrunk ring of the flange upsetting die were designed for the cold forging of an automotive wheel nut. The Stress distribution occurring in the die during forging was simulated using a commercial finite element analyzing program. The effects of the fitting interference and inclined angle of the insert ring on the compressive stress of the die inside were also investigated. The simulated data were compared with the real lifetimes of the forging dies. The maximum compressive stress acting on the edge of a forging die should have the most influence on die lifetime, an idea which could help develop the die design with the longest lifetime. The design of the most optimal forging die with the longest lifetime is made possible by analyzing the maximum inner pressure and principal stress between the shrunk ring and insert ring.

• Structural Engineering and Mechanics
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• v.6 no.2
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• pp.143-159
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• 1998

The objective of this present work is to estimate the failure loads, associated maximum transverse displacements, locations and the modes of failure, including the onset of delamination, of thin, square symmetric laminates under the action in-plane positive (+ve) shear load. Two progressive failure analyses, one using the Hashin criterion and the other using a Tensor polynomial criterion, are used in conjunction with finite element method. First order shear deformation theory along with geometric non-linearity in the von Karman sense have been employed. Variation of failure loads and failure characteristics with five type of lay-ups and three types of boundary conditions has been investigated in detail. It is observed that the maximum difference between failure loads predieted by various criteria depends strongly on the laminate lay-up and the flexural boundary restraint. Laminates with clamped edges are found to be more susceptible to failure due to transverse shear (ensuing from the out of plane bending) and delamination, while those with simply supported edges undergo total collapse at a load slightly higher than the fiber failure load. The investigation on negative (-ve) in-plane shear load is in progress and will be communicated as part-II of the present work.

• Journal of Korean Society of Rural Planning
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• v.25 no.3
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• pp.1-9
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• 2019

Population is important as a fundamental element of local industry and economy, and census data is essential to regional planning and policy making. Although there have been many researches on population and regional planning, there are few studies on population considering spatial unit. In this study, the population of three spatial scales were compared in order to establish the spatial unit suitable for the rural planning. The study area is Gangwon, Chungcheong-Nam, Chungcheong-Buk, Jeolla-Nam, Jeolla-Buk, Gyeonsang-Nam, Gyeonsang-Buk and Jeju province. Population were compared using statistical data analysis, GIS visualization, and spatial statistics. The mean, maximum, minimum, and variance of population were calculated and the coefficient of variation according to spatial unit was compared. The mean, maximum, minimum, and variance of population were calculated and the coefficient of variation according to spatial unit was compared. As the results, the census output area unit is difficult to interpret spatial analysis results. Administrative district unit has the limit that includes areas where the population does not live. The grid unit is well suited to the geographical characteristics but has many disadvantages of the grid with small population. Therefore, It is necessary to complement the limits of the Eup and Myeon-dong administrative district through the grid unit data.

• International Journal of Korean Welding Society
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• v.1 no.1
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• pp.51-57
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• 2001

Effect of the joint details on the stress distribution over a slot structure has been studied in order to improve its fatigue life using a finite element analysis. The joint details of interest are the radius and height of scallop at the stiffener as well as the mis-alignment between the stiffener and longitudinal member. For a slot structure currently used, the stiffener heel is subjected to the maximum stress for a given external load, where is a potential fatigue crack initiation site. The stresses at the stiffener heel and toe decrease both by increasing the scallop radius and more significantly by increasing the mis-alignment while no notable effect of the scallop height on it is appreciated. A proper combination of these factors makes it possible to reduce the stresses at the stiffener heel and In, theoretically, more than 50%. This is attributed to the modification of the stress distribution over the slot structure including the transition of the maximum stressed region from the stiffener heel to the slot surface of the transverse web. Such then results in a g[eat improvement of the fatigue life of the slot structure.

• Geomechanics and Engineering
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• v.35 no.4
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• pp.367-383
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• 2023

The present paper examines the natural frequency responses of the bi-directional (n_x-n_y, n_y-n_z and n_z-n_x) and multidirectional (n_x-n_y-n_z) functionally graded (FG) plate and curved structures with and without porosity. The even and uneven kind of porosity pattern are considered to observe the influence of porosity type and porosity index. The numerical findings have been obtained using a higher order shear deformation theory (HSDT) based isometric finite element (FE) approach generated in a MATLAB platform. According to the convergence and validation investigation, the proposed HSDT based FE model is adequate to predict free vibrational responses of multidirectional porous FG plates and curved structures. Further a parametric analysis is carried out by taking various design parameters into account. The free vibrational behavior of bidirectional (2D) and multidirectional (3D) perfect-imperfect FGM structure is examined against various power law index, support conditions, aspect, and thickness ratio, and for the curvature of curved structures. The results indicate that the maximum non-dimensional fundamental frequency (NFF) value is observed in perfect FGM plates and curved structures compared to porous FGM plates and curved structures and it is maximum for FGM plates and curved structures with uneven kind of porosity than even porosity.

• Structural Engineering and Mechanics
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• v.88 no.5
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• pp.463-480
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• 2023

The buckling-restrained braced frames with eccentric configurations (BRBF-Es) exhibit stable cyclic behavior and possess a high energy absorption capacity. Additionally, they offer architectural advantages for incorporating openings, much like Eccentrically Braced Frames (EBFs). However, studies have indicated that significant residual drifts occur in this system when subjected to earthquakes at the Maximum Considered Earthquake (MCE) hazard level. Consequently, in order to mitigate these residual drifts, it is recommended to employ self-centering systems alongside the BRBF-E system. In our current research, we propose the utilization of the Direct Displacement-Based Seismic Design method to determine the design base shear for a hybrid system that combines BRBF with an eccentric configuration and a self-centering frame. Furthermore, we present a methodology for designing the individual components of this composite system. To assess the effectiveness of this design approach, we designed 3-, 6-, and 9-story buildings equipped with the BRBF-E-SCF system and developed finite element models. These models were subjected to two sets of ground motions representing the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE) seismic hazard levels. The results of our study reveal that although the combined system requires a higher amount of steel material compared to the BRBF-E system, it substantially reduces residual drift. Furthermore, the combined system demonstrates satisfactory performance in terms of story drift and ductility demand.