• Journal of Welding and Joining
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• v.34 no.3
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• pp.47-51
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• 2016

Recently, the market of liquefied natural gas is growing in accordance with shale gas development and environmentally friendly policies. Also, LNG is in the spotlight as an alternative fuel to previously used fossil fuel and the fuel for the ship to meet emission standards which takes effected by IMO (International Maritime Organization). According to growth of LNG, LNG carriers needs are also expected to increase significantly. This study investigates low cycle fatigue (LCF) performance of 304L stainless steel weldments to investigate fatigue performance in plastic strain region. 304L stainless steel is known to have improved fatigue performance at cryogenic conditions. LCF behavior are investigated by a strain-controlled condition up to 1% strain range and conducted with three different thickness (3mm, 5mm, 10mm). Also, test were performed with three different strain ratio R such as R = -1, -0, 0.5, Finally, the fatigue design curve for 304L stainless steel weldments at room tem- perature are proposed. Considering all test conditions, it is shown that LCF performance have similar tendency regardless of thickness and strain ratio. LCF design curve of 304L stainless steel weldments are lower than 304L stainless steel base metal.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.2
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• pp.307-315
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• 1989

In recent years, the fatigue design method by analysis for the mechanical components and the welded structures has much increased, instead of the fatigue design method by rule that has been widely used from the past days. When a fatigue design is conducted by that method, the basic informations, fatigue life curves are mainly obtained from the results of the strain controlled low cycle fatigue test. From these point of views, the low cycle fatigue test is coming to be given a much importance lately. In this paper, the strain controlled low cycle fatigue properties at room temperature in air environment were investigated for the low carbon forged steel, SF45A, and the rolled steel for the welded structure, SM 41B. Throughout the test, strain ratio, R, was maintained constant with the fully reversed condition, -1. As the experimental results, the cyclic stress-strain behaviours of the test materials were different each other, but the low cycle fatigue life-time of them appeared to show little difference in the region of this test conditions.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.221-232
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• 1998

This study presents a fatigue line with a plastic rotational angle to a great extent of plastic strain of Low-Cycle-Fatigue period, such as earthquake, etc. This fatigue line with a plastic rotational angle is measured and analysed more simply in practice rather than Woehler's fatigue line which is developed in stress variation of the structure. It shows that the slope of fatigue line with a plastic rotational angle is equal to that with plastic strain through the experiments by proving the correlation that the plastic strain ratio is directly proportional to the plastic rotational angle in plastic hinge. The theory is induced by Manson and Coffin strain fatigue line, and the experiments are tested by ECCS. The location of the plastic hinge is achieved and accurate plastic strain ratio is calculated through FEM.

• Geotechnical Engineering
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• v.10 no.2
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• pp.85-96
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• 1994

Resonant column test huts been widely used as a primary laboratory testing technique in investigating dynamic soil properties expressed in therms of shear and Young's moduli and material damping. In thin Paper, dynamic Properties of typical Korean subgrade boils are investigated at shearing strains between 10-4% and 10-1% using Stokoe-type resonant column teat. The elastic threshold strains(yte) above which shear modulus and damping ratio are affected by strain amplitude, are defined at strain amplitude of about 10-3%. Below yte", small-strain shear modulus (Gmn) increases with confining pressure (Qc) as proportional to (Qe)0.61, and small-strain damping ratio(Dmin) ranges between 1% and 5.7%. Above yte, normalized shear modulus reduction curve(G/Gma. versus log strain) can be quite well expressed with Ramberg Osgood stress -strain equation and match well the curve suggested for sand by Seed and Idriss.riss.

• Korean Journal of Materials Research
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• v.28 no.12
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• pp.702-708
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• 2018

This study deals with the effect of microstructure factors on the strain aging properties of API X70 pipeline steels with different microstructure fractions and grain sizes. The grain size and microstructure fraction of the API pipeline steels are analyzed by optical and scanning electron microscopy and electron backscatter diffraction analysis. Tensile tests before and after 1 % pre-strain and thermal aging treatment are conducted to simulate pipe forming and coating processes. All the steels are composed mostly of polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite. After 1 % pre-strain and thermal aging treatment, the tensile test results reveal that yield strength, tensile strength and yield ratio increase, while uniform elongation decreases with an increasing thermal aging temperature. The increment of yield and tensile strengths are affected by the fraction of bainitic ferrite with high dislocation density because the mobility of dislocations is inhibited by interaction between interstitial atoms and dislocations in bainitic ferrite. On the other hand, the variation of yield ratio and uniform elongation is the smallest in the steel with the largest grain size because of the decrease in the grain boundary area for dislocation pile-ups and the presence of many dislocations inside large grains after 1 % pre-strain.

• Korean Journal of Agricultural Science
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• v.45 no.4
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• pp.687-694
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• 2018

This study was conducted to investigate the laying performance of six strains of Korean domestic chickens (KDC 1A, 2A, 3A, 1B, 2B and 3B). A total of 288 20-week-old KDC hens were allocated in a completely randomized design to give 12 replicates per each strain (4 chickens per pen). The chickens were fed commercial diets (i.e., week 20 - 32, crude protein [CP] 18.0% and metabolizable energy [ME] 2,850 kcal/kg; week 32 - 40, CP 17.0% and ME 2,800 kcal/kg) ad libitum together with fresh water during the 20-week experiment. Body weight, age of sexual maturity, egg weight, hen-day egg production (HDP) and feed conversion ratio (FCR) were measured during the experiment period (week 20 - 40). Our results show that strain 3B had an improved (p < 0.05) HDP and FCR compared with the other strains on week 24 - 28. However, strain 3A had an improved (p < 0.05) HDP and FCR compared to the other strains on week 28 - 40. Similarly, strain 3A had a higher egg weight (p < 0.05) compared to the other strains on week 28, 32 and 40. In conclusion, the higher laying performance of strain 3A indicates its potential in the development of a KDC strain with improved commercial laying performance.

• Journal of Korean Society on Water Environment
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• v.35 no.3
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• pp.201-208
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• 2019

In this study, we analyzed composition of the bioflocculant, which strain YG-02 produces. First, supernatant and suspension from centrifugation of culture fluid of the strain, were used in the flocculation experiment. As a result, the SVI(sludge volume index) added with the suspension, was 182 mL/g, same as the control group with no additive, and the SVI added with supernatant, was 164 mL/g. So, the result above showed that flocculation capacity of the bioflocculant, was dependent on the substance which strain YG-02 produces, not on factors such as the body of germs. As a result of the thermostability test on substances that cause flocculation, the flocculation effect was significantly reduced, compared to the result of the flocculation test, before applying heat to the culture fluid, and it was able to assume that the substance that causes flocculation, was damaged by heat. Additionally, to understand the component of the bioflocculant, analyzation of sugar composition and fatty acid, was conducted. As a result, sugar composition was the polysaccharide consisting of glucose: lactose with molar ratio of 90.75:9.25. Fatty acid content was detected, as 0.0012 g/100g, showing that it contained glycolipid in the bioflocculant. Such results show that the bioflocculant which strain YG-02 produces, is the new bioflocculant, different from bioflocculantstudiedto date.

• 한국연소학회:학술대회논문집
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• 2006.10a
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• pp.65-72
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• 2006

Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified.

• Computers and Concrete
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• v.11 no.2
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• pp.149-167
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• 2013

The complete stress-strain behavior of steel fiber reinforced concrete in compression is needed for the analysis and design of structures. An experimental investigation was carried out to generate the complete stress-strain curve of high-performance steel fiber reinforced concrete (HPSFRC) with a strength range of 52-80 MPa. The variation in concrete strength was achieved by varying the water-to-cementitious materials ratio of 0.40-0.25 and steel fiber content (Vf = 0.5, 1.0 and 1.5% with l/d = 80 and 55) in terms of fiber reinforcing parameter, at 10% silica fume replacement. The effects of these parameters on the shape of stress-strain curves are presented. Based on the test data, a simple model is proposed to generate the complete stress-strain relationship for HPSFRC. The proposed model has been found to give good correlation with the stress-strain curves generated experimentally. Inclusion of fibers into HPC improved the ductility considerably. Equations to quantify the effect of fibers on compressive strength, strain at peak stress and toughness of concrete in terms of fiber reinforcing index are also proposed, which predicted the test data quite accurately. Compressive strength prediction model was validated with the strength data of earlier researchers with an absolute variation of 2.1%.

• Structural Engineering and Mechanics
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• v.63 no.3
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• pp.371-384
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• 2017

Ultra high performance concrete (UHPC) has recently been applied as an alternative to conventional concrete in construction due to its extremely high compressive and tensile strength, and enhanced durability. However, up to date, there has been insufficient information regarding the confinement behavior of UHPC columns. Therefore, this study aims to perform an assessment of axial stress-strain model for UHPC confined by circular steel tube stub columns. The equations for calculating the confined peak stress and its corresponding strain of confined concrete in existing models suggested by Johansson (2002), Sakino et al. (2004), Han et al. (2005), Hatzigeorgiou (2008) were modified based on the regression analysis of test results in Schneider (2006) in order to increase the prediction accuracy for the case of confined UHPC. Furthermore, a new axial stress-strain model for confined UHPC was developed. To examine the suitability of the modified models and the proposed model for confined UHPC, axial stress-strain curves derived from the proposed models were compared with those obtained from previous test results. After validating the proposed model, an extensive parametric study was undertaken to investigate the effects of diameter-to-thickness ratio, steel yield strength and concrete compressive strength on the complete axial stress-strain curves, the strength and strain enhancement of UHPC confined by circular steel tube stub columns.