• Journal of the Korean Operations Research and Management Science Society
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• v.23 no.3
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• pp.49-62
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• 1998

In the ring loading problem, traffic demands are given for each pair of nodes in an undirected ring network with n nodes and a flow is routed in either of the two directions, clockwise and counter-clockwise. The load of a link is the sum of the flows routed through the link and the objective of the Problem is to minimize the maximum load on the ring. In the ring loading problem with integer demand splitting, each demand can be split between the two directions and the flow routed in each direction is restricted to integers. Recently, Vachani et al. ［INFORMS J. Computing 8 (1996) 235-242］ have developed an Ο(n$^3$) algorithm for solving this integer version of the ring loading problem and independently, Schrijver et al. ［to appear in SIAM J. Disc. Math.］ have presented an algorithm which solves the problem with ｛0,1｝ demands in Ο（n$^2$｜K｜ ) time where K denotes the index set of the origin-desㅇtination pairs of nodes having flow demands. In this paper, we develop an algorithm which solves the problem in Ο(n ｜K｜) time.

• Economic and Environmental Geology
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• v.30 no.3
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• pp.231-240
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• 1997

The behavior of rocks and microcrack development due to fatigue stresses are investigated using cyclic loading tests and ultrasonic velocity measurements. Twenty six medium-grained granite samples from the Pochon area are selected for measurements. Ultrasonic velocities are measured for samples before fatigue test to characterize the pre-existing microcracks. Then, thirteen different cycles of loadings with 70% and 80% dynamic strength are applied to the samples. The ultrasonic velocities are measured again to compare velocities after applications of fatigue stress with those before applications of fatigue stress. The results show that most microcracks are developed along the direction parallel to the axis of loading and that the amount of microcracks increases, as loading levels and numbers of cycle increase.

• Proceedings of the Korean Reliability Society Conference
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• 2000.04a
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• pp.213-222
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• 2000

In present study, a stochastic model is developed for the low cycle fatigue life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. In the proposed model, fatigue phenomenon is considered as a Markov process, and damage vector and reliability are defined on every plane. Any low cycle fatigue damage evaluating method can be included in the proposed model. The model enables calculation of statistical reliability and crack initiation direction under variable multiaxial loading, which are generally not available. In present study, a critical plane method proposed by Kandil et al., maximum tensile strain range, and von Mises equivalent strain range are used to calculate fatigue damage. When the critical plane method is chosen, the effect of multiple critical planes is also included in the proposed model. Maximum tensile strain and von Mises strain methods are used for the demonstration of the generality of the proposed model. The material properties and the stochastic model parameters are obtained from uniaxial tests only. The stochastic model made of the parameters obtained from the uniaxial tests is applied to the life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. The predicted results show good accordance with experimental results.

• Smart Structures and Systems
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• v.2 no.4
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• pp.357-363
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• 2006

Equations describing deformation defects, damage accumulation, and fracture condition have been suggested. Analytical and numerical solutions have been obtained for defects produced by a shear in a fixed direction. Under cyclic loading the number of cycles to failure well fits the empirical Koffin-Manson law. The developed model is expanded to the case of the micro-plastic deformation, which accompanies martensite accommodation in shape memory alloys. Damage of a shape memory specimen has been calculated for two regimes of loading: a constant stress and cyclic variation of temperature across the interval of martensitic transformations, and at a constant temperature corresponding to the pseudoelastic state and cyclic variation of stress. The obtained results are in a good qualitative agreement with available experimental data.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.77-80
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• 2006

Longitudinal reinforcements of the plastic hinge region were behaved tensile deformation and compressional deformation by direction of lateral loading. However Confinement steels were behaved only tensile deformation by lateral loading. Transverse steels were laid the state of tension in the lateral loading of time, and they were laid state that stress is zero when it was removed lateral load. Nine specimens were tested under cyclic stresses(tension and zero). The purpose of this research is to investigate the strain behavior and capacity of energy for confinement steel. The selected test variables are $L/d_b(L/d_b=6)$, size of reinforcement and specified yielding strength(300, 400, 500 MPa).

• The KSFM Journal of Fluid Machinery
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• v.13 no.4
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• pp.51-57
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• 2010

This paper describes the structural design and testing for 1.5kW class wind turbine composite blade. In order to calculate the equivalent material properties rule-of-mixture is applied. Lay-up sequence, ply thickness and ply angle are designed to satisfy the requirements for structural integrity. Structural analysis by using commercial software ABAQUS is performed to assess the static, buckling and vibration response. And to verify the structural analysis and design, the full scale structural test in flapwise direction was performed under single point loading according to loading conditions calculated by the aerodynamic analysis and Case H (Parked wind loading) in IEC 61400-2.

• Advances in materials Research
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• v.12 no.1
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• pp.67-81
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• 2023

Basalt and poly-ester fibers along with epoxy resin were used to produce inter-ply, intra-ply and functionally gradient hybrid composites. In all of the composites, the relative content of basalt fiber to poly-ester fiber was equal to 50 percent. The flexural and charpy impact properties of the hybrid composites are presented with particular regard to the effects of the hybrid types, stacking sequence of the plies, loading direction and loading speed. The results show that with properly choosing the composition and the stacking sequence of the plies; the inter-ply hybrid composites can achieve better flexural strength and impact absorption energy compared to the intra-ply and functionally gradient composites. The flexural strength and impact absorption energy of the functionally gradient hybrid composites is comparable to, or higher than the intra-ply sample. Also, by increasing the loading speed, the flexural strength increases while the flexural modulus does not have any special trend.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.461-471
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• 1989

For the mixed-mode crack problems the direction of crack growth, the crack path and the rational representation of fatigue crack growth rates should be studied to predict fatigue life and safety of structures. In this study, a round specimen which produce nearly identical effects in all loading directions is proposed to make an easy measurement of initial direction of crack growth. The mode I and mode II stress intensity factors of the specimen were calculated using finite element method, in which the square root singular stresses at the crack tip are modeled by means of four rectangular quarter-point eight-noded elements surrounding the crack tip. Experimental results for high strength aluminum alloy showed that the direction of mixed-mode crack growth agree well with maximum principal stress criterion as well as minimum strain energy density criterion, but not with maximum shear stress criterion. From data of fatigue crack growth rates using crack geometry projected on the line perpendicular to the loading direction it is easily established that mixed-mode fatigue crack growth in 5083-H115 aluminum alloy goes predominantly with mode I crack growth behaviors.

• The Journal of Engineering Geology
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• v.8 no.3
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• pp.275-284
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• 1998

Deformation behavior and microcrack development due to uniaxial compressive cyclic loading in the Pocheon granite were investigated using the ultrasonic velocity measurements and the differential strain analysis(DSA). Most microcracks were developed along the direction parallel to the loading axis. Microcracks developed at the early stage of cyclic loading were formed by propagation of pre-existing cracks. Ultrasonic velocity measurement, DSA and measurement of permanent deformation are good tools to represent microcrack development in rock. Since results from each method are slightly different, microcrack development should be interpreted from all three methods. The magnitude of microcracks developed at the early stage of cyclic loading under 80% loading level is twice compared with those under 70% loading level. The highest volumetric crack strain is about 3000, indicating that the Pocheon granite will fail with 0.3% occupation of microcrack in volume.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.18 no.1
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• pp.26-35
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• 2022

When piping system in a nuclear power plant is subjected to a beyond design seismic condition, it is important to accurately determine possibility of crack initiation and, if initiation occurs, its location and time. From recent experimental works on elbow pipes, it was found that the crack initiation location and crack propagation direction of the SA403 WP316 stainless steel elbow pipe were affected by the pipe thickness. In this paper, the crack initiation location and crack propagation direction for SA403 WP316 stainless steel elbow pipes with different thickness were analyzed via elastic-plastic finite element analysis. Based on FE results, the effect of the pipe thickness on different crack initiation location and crack propagation direction was analyzed using ovality, stress and strain components. It was also confirmed that the presence of internal pressure had no effect on the crack initiation location and crack propagation direction.