• Journal of the Korean Society of Safety
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• v.7 no.2
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• pp.47-56
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• 1992

The retardation effect of fatigue crack propagation after cyclic overloading seems to be affected by strain hardening exponent. Namely, for the material with high values of n, the delay effect is found to be severe. We proposed a modified crack retardation equation which may apply the retardation of fatigue crack growth after a cyclic overloading, as (da/dN)'$_{cyc}$=($\mu$n＋λ)B $\Delta$ $K^{q}$ /[(1－ $R_{eff}$) $K_{cf}$ －$\Delta$K]. where, $R_{eff}$ is effective stress ratio [＝( $K_{min}$－K, os)/( $K_{max}$－ $K_{res}$)] The constants $\mu$＝－0.5 and λ＝0.6, and the values are found to be identical for materials such as aluminum (A 1060), steel (SS 34), brass ( $B_{s}$ SIB) and stainless steel (SUS 304) used in this investigation. (SUS 304) used in this investigation.ation.n.n.

• Steel and Composite Structures
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• v.32 no.6
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• pp.717-729
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• 2019

A horizontal cyclic test was carried out to study the seismic performance of lightweight aggregate concrete filled steel tube (LACFST). The constitutive and hysteretic model of core lightweight aggregate concrete (LAC) was proposed for finite element simulation. The stress and strain changes of the steel tube and concrete filled inside were measured in the experiment, and the failure mode, hysteresis curve, skeleton curve, and strain curve of the test specimens were obtained. The influence of axial compression ratio, diameter-thickness ratio and material strength were analysed based on finite element model. The results show that the hysteresis curve of LACFST indicated favourable ductility, energy dissipation, and seismic performance. The LACFST failed when the concrete in the bottom first crushed and the steel tube then bulged, thus axial force imposed by prestressing was proved to be feasible. The proposed constitutive model and hysteretic model of LAC under the constraint of its steel tube was reliable. The bearing capacity and ductility of the specimen increase significantly with increasing thickness of the steel tube. The bearing capacity of the member improves while the ductility and energy dissipation performance slightly decreased with the increasing strength of the steel and concrete.

• Journal of Welding and Joining
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• v.5 no.3
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• pp.53-61
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• 1987

Post weld heat treatment(PWHT) is usually carried out to remove the residual stress and to improve the microstructure and mechanical properties of welded joints. By the way, welding structure transformed owing to PWHT and reheating for repair loads the random cycles fatigue as offshore welding structure of constant low cycle fatigue as pressure vessel, and then, pre-existing flaws or cracks exist in a structural component and those cracks grow under cyclic loading. Therefore, the effects of PWHT and stress ratio on fatigue crack growth behaviors were studied on the three regions such as HAZ, sub-critical HAZ and deposit metal of welded joints in SM53 steel. Fatigue crack growth behavior of as-weld depended on microstructure and fatigue crack growth rate of HAZ was the lowest at eac region, but after PWHT it was somewhat higher than that of as-wel. In case of applying the stress($10kg/mm^2$) during PWHT, fatigue crack growth resistance tended to increase in the overall range of .DELTA.K.

• Journal of the Korean Geotechnical Society
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• v.28 no.7
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• pp.31-40
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• 2012

In most design codes, soils are classified as either sandy or clayey soils, and appropriate design equations for each soil type are used to estimate their soil behaviour. However, sand-fine mixtures, which are typically referred to as intermediate soils, are somewhere at the middle of sandy or clayey soils, and therefore a unified interpretation of soil behaviour is necessary. In this paper, a series of cyclic shear tests were carried out for three different combinations of sand-fine mixtures with various fines content. Silica-sand mixture and fines (Iwakuni natural clay, Tottori silt, kaolinite) were mixed together with various mass ratios, while paying attention to the changes of void ratios expressed in terms of sand structure. The cyclic shear strengths of the mixtures below the threshold fines content were examined with the increasing fines contents. As a result, as the fines contents increased, their cyclic deviator stress ratios decreased for dense samples while it increased for loose samples. Additionally, cyclic deviator stress ratio of the mixtures was estimated using the concept of equivalent granular void ratio.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.109-120
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• 2013

This paper presents the results of a laboratory investigation into a study on undrained characteristics of a geogrid-encased stone column (GESC) installed in soft clay under cyclic load. In order to analyze behavior of settlement, pore water pressure, stress concentration ratio and strain of the GESC compared to a stone column, a series of reduced-scale laboratory tests were performed. The model tests show that GESC provides a simple and effective method of deformation resistance and settlement restraint when a short-term cyclic load is applied. The maximum strain of geogrid occurred at 1.2D and 1.5D from the top of the column. This paper highlights the importance of considering overlay effect and replacement ratio on cyclic load supporting GESC.

• Journal of the Korean GEO-environmental Society
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• v.23 no.5
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• pp.5-13
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• 2022

In this study, dynamic characteristics and liquefaction resistance characteristics of silica sand which is used to simulate sandy layer were conducted using the cyclic triaxial test according to the relative density difference. The difference in liquefaction resistance with the relative density was confirmed through the test results, which the relative density conditions were changed to 40%, 60%, and 80%, and the cyclic resistance ratio (CRR) curve of the silica sand was obtained. In addition, in order to examine the validity of the liquefaction resistance ratio (CRR) curve, artificial silica sand ground was created, and liquefaction potential was evaluated through the simple assessment method and the detailed assessment method, and the safety factors of each were compared.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.591-596
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• 2001

The purpose of this study is to examine the change of half value breadth and residual stress during fatigue process in S45C Steel by X-ray diffraction. For S45C Steel, the relationship between the change in fatigue damage of the specimen and the half value breadth, and residual stress of X-ray diffraction profiles during the fatigue processes has been investigated. The half value breadth(HVB) decreases in he early period of fatigue cycle. The change of HVB is relation to cyclic work hardening. In $10{\sim}20%$ of ratio of fatigue life, the change in the half value breadth is not marked. During fatigue process, the residual stress is changed with fatigue cycle increasing.

• The Journal of Engineering Geology
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• v.31 no.2
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• pp.149-163
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• 2021

Damage characteristics of granite, marble and sandstone whose properties were different were investigated by uniaxial compression test and cyclic loading-unloading test. Strength, elastic constants and damage threshold stresses were measured by uniaxial compression test and were compared with those measured by cyclic loading-unloading test. Average rock strengths measured by cyclic loading-unloading test were either lower than or similar with those measured by uniaxial compression test. Rocks with high strength and low porosity were more sensitive to fatigue than that with low strength and high porosity. Although permanent strains caused by cyclic loading-unloading were different according to rock types, they could be good indicators representing damage characteristics of rock. Damage threshold stress of granite and marble might be measured from stress-permanent strain curves. Acoustic emissions were measured during both tests and felicity ratios which represented damage characteristics of rocks were calculated. Felicity ratio of sandstone which was weak in strength and highly porous could not be calculated because of very few measurements of acoustic emissions. On the other hand, damage threshold could be predicted from felicity ratios of granite and marble which were brittle and low in porosity. The deformation behaviors and damage characteristics of rock mass could be investigated if additional tests for various rock types were performed.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.5 no.2
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• pp.53-62
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• 2002

The objectives of this study were to understand the tolerance mechanism of woody plants to water stress and tolerance changes in relation to mycorrhizal formation. Lespedeza cyrtobotrya Miq. commonly used for erosion control in slopes were raised from seeds and transplanted to 120 plastic pots. Sixty pots received the top soil of a Fraxinus americana forest, while remaining 60 pots received the autoclaved top soil. The forest soil contained 1,200 spores per 100g of arbuscular endomycorrhizal fungus, mostly Glomus sp. The plants were raised outside with regular supply of water and mineral nutrients. Two kinds of water deficit treatment and a control were started at the middle of July : cyclic water deficit treatment with 3 cycles of sequential water stress at the point of xylem water potential of about -0.6, -0.6, and -1.7 MPa and recovery, and non-cyclic water deficit treatment with single water stress at about -1.5 MPa. The non-stressed plants received plenty of water throughout the period. In late August the plants were harvested for measurements of dry weight, N, P, carbohydrate contents, net photosynthesis and superoxide dismutase(SOD) activities. Both cyclic and non-cyclic water deficit treatments reduced dry weight by 60% and 40%, respectively, and reduced nitrogen absorption, while increased SOD activities. Water-stressed plants also showed increased carbohydrate contents in the leaves and lowered stomatal conductance. Mycorrhizal inoculation resulted in an average of 40% infection of roots and 2-3 times increase in P absorption in water-stressed as well as non-stressed plants. Mycorrhizal formation also increased shoot-root ratio. The results that SOD activities of water-stressed plants with mycorrhizal infection were significantly lower than those of non-mycorrhizal plants suggest the possibility of improvement of water-stressed condition by mycorrhizal formation. It was concluded that endomycorrhizal formation increased tolerance of Lespedeza cyrtobotrya seedlings to water stress.

• Geomechanics and Engineering
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• v.31 no.2
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• pp.167-181
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• 2022

Soil liquefaction has been one of the most important concerns in geotechnical earthquake engineering in recent years, due to its damages to structures and its destructive effects. The cyclic liquefaction of silty sands, in particular, remains of great interest for both research and application. Although many factors are known that affect the liquefaction resistance of sands, the effect of fine grain content is perhaps one of the most studied and still controversial. In this study, 48 deformation-controlled cyclic simple shear tests were performed on BS and CS silt samples mixed with 5%, 15% and 30% by weight of Krk085, Krk042 and Krk025 sands in constant-volume conditions to determine the liquefaction potential of silty sands. The tests were carried out at 30% and 50% relative density and under 100 kPa effective stress. The results revealed that the liquefaction potential of silty sand increases with increasing average particle size ratio (D_50sand / d_50silt) of the mixture for a fixed silt content. Furthermore, for identical base sand, the liquefaction potentials of coarse grained sands increase with increasing silt content, while the respective potentials of fine grained sands generally decrease. However, this situation may vary depending on the silt grain structure and is affected by the nature of the fine grains. In addition, the variation of the void ratio interval was shown to provide a good intuition in determining the liquefaction potentials of silty sands, while the intergranular void ratio alone does not constitute a criterion for determining the liquefaction potentials of silty sands.