• Journal of Industrial Technology
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• v.19
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• pp.269-278
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• 1999

When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

• Geomechanics and Engineering
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• v.1 no.2
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• pp.143-154
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• 2009

Many factors influence occurrences of rock burst in coal mines, such as mining methods, control methods of the coal roof, lithological characteristics of the roof and floor, tectonic stress, groundwater and so on. Among those factors, lithological characteristics in the roof are the intrinsic controlling factors that affect rock burst during coal mining. Tangshan colliery is one of the coal mines that have suffered seriously from rock bursts in China. In this paper, based on the investigating the lithological characteristics of coal roofs and occurrence of rock bursts in Tangshan colliery, a numerical method is used to study the influence of roof lithological characteristics on rock burst potential. The results show that the lithological characteristics in the roof have an important impact on the distributions of stresses and elastic strain energy in coal seams and their surrounding rocks. Occurrences of rock bursts in this colliery have a close correlation with the thick-bedded, medium- to fine-grained sandstones in the roof. Such strata can easily cause severe stress concentration and accumulate enough energy to trigger rock bursts in the working face during mining operations.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.4
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• pp.565-572
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• 2010

It is difficult to predict the accurate fatigue life of the ship structure because of load uncertainty and load redistribution at the ship structure members. As one of studies for accurate evaluation and prediction of fatigue life, it is a promising way to detect the crack previously by attaching the Fatigue Indicator Sensor (FIS) at the crack prediction region. In order to predict the fatigue life of the ship structure by using FIS, it is required to know previously the crack propagation characteristics according to pre-notch shapes. In this study, we obtained the stress distribution phase, stress concentration factors and stress intensity factor of various pre-notch shapes through FEA. Additionally, we conducted the fatigue test and obtained the characteristics of crack propagation according to the pre-notch shapes through comparison between the fatigue test and the FEA. Consequently, we classified the pre-notch shape into 3 categories: Long, Medium, and Short life type. On the basis of the numerical and experimental results, the FIS can be developed.

• Steel and Composite Structures
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• v.21 no.6
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• pp.1227-1250
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• 2016

Most of the research work has been conducted on K-joints under static loading. Very limited information is available in consideration of fatigue strength of K-joints with concrete-filled chord. This paper aims to describe experimental and numerical investigations on stress concentration factors (SCFs) of concrete-filled circular chord and square braces K-joints under balanced axial loading. Experiment was conducted to study the hot spot stress distribution along the intersection of chord and braces in the two specimens with compacting concrete filled in the chord. The test results of stress distribution curves of two specimens were reported. SCFs of concrete-filled circular chord and square braces K-joints were lower than those of corresponding hollow circular chord and square brace K-joints. The corresponding finite element analysis was also conducted to simulate stress distribution along the brace and chord intersection region of joints. It was achieved that experimental and finite element analysis results had good agreement. Therefore, an extensive parametric study was carried out by using the calibrated finite element model to evaluate the effects of main geometric parameters and concrete strength on the behavior of concrete-filled circular chord and square braces K-joints under balanced axial loading. The SCFs at the hot spot locations obtained from ABAQUS were compared with those calculated by using design formula given in the CIDECT for hollow SHS-SHS K-joints. CIDECT Design Guide was generally quite conservative for predicting SCFs of braces and was dangerous for predicting SCFs of chord in concrete-filled circular chord and square braces K-joints. Finally SCF formulae were proposed for circular chord and square braces K-joints with concrete-filled in the chord under balanced axial loading. It is shown that the SCFs calculated from the proposed design equation are generally in agreement with the values derived from finite element analysis, which were proved to be reliable and accurate.

• Korean Journal of Environmental Agriculture
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• v.40 no.4
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• pp.345-352
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• 2021

BACKGROUND: Salinity is one of the major limiting factors in agriculture that affect the growth and productivity of crops. It is economically difficult to artificially purify the soil affected by salt. Therefore, the use of plant growth-promoting bacteria (PGPB) in an effort to reduce stress caused by salt is emerging as a cost-effective and environment-friendly method. In this study, the purpose was to isolate the salt-tolerant bacteria from the rhizosphere soil and identify their ability to promote plant growth under salt stress condition. METHODS AND RESULTS: The isolates KST-1, KST-2, AST-3, and AST-4 that showed plant growth-promoting activity for barley in salt conditions were close to Bacillus cereus (KST-1, KST-2, and AST-4) and Bacillus thuringiensis (AST-3) and showed high salt tolerance up to 7% of additional NaCl to the media. When inoculated to barley, the strains had only minor effect on the length of the barley. However, the concentrations of chlorophyll in the barley leaves were found to be higher from the bacteria-inoculated pots than those from the uninoculated control. In particular, the chlorophyll concentration in Bacillus cereus AST-4 experiment was 5.45 times higher than that of the uninoculated control under the same experimental condition. CONCLUSION(S): The isolated salt-tolerant bacteria were found to influence on chlorophyll concentration of the barley. As represented by the strain AST-4, microbes may suggest a cost-effective and environmentally benign method to alleviate salt stress of crops cultivated in salt-accumulated soils such as reclaimed lands.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.113-120
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• 2010

The use of Concrete filled circular hollow steel section (CFCHS) members in bridge design is a relatively new concept. The most important part of the design and durability of such structures is the design and the construction of the joints. In the design of recently constructed steel-concrete composite bridges using CFCHS truss girders for the main load carrying structure, the fatigue verification of the tubular spatial truss joints was a main issue. Welded CFCHS joints are very sensitive to fatigue because the geometric discontinuities of the welds lead to a high stress concentration. New research done on the fatigue behaviour of such joints has focused on CFCHS N-joints, directly welded, with finite element analysis method. A commercial software, ABAQUS, is adopted to perform the finite element analysis on the N-joints. This paper is main focused on these topics, including hot spot stress.

• Korean Journal of Community Nutrition
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• v.8 no.3
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• pp.349-355
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• 2003

We developed a dietary supplement using natural herbs and nutrients for the growth and exercise performance improvement. It called 50-22 supplement containing distilled extracts of natural herbs to remove bitterness and the addition of Vitamin B1, B6, Ca and xylitol. We investigated on the effect of 10-22 supplementation on the maximal exercise performance, IGF-1 (insulin like growth factor-1) concentration and antioxidant activity in SD rat model. In result, JR-22 supplement group was better than control group about 10％ in exercise performance test and increased about 63％ of IGF-1 concentration in blood. In addition, the oxidative damage induced by exercise was reduced by JR-22 supplementation. Therefore, we suggested that 50-22 supplementation enhanced effectively exercise performance and IGF-1 concentration and reduced to oxidative stress in muscles. Also, we analysed biochemical factors in blood for the safety of JR-22 supplement. We known that there is no change of blood lactic acid, ammonia, inorganic phosphorous ion and creatine kinase activity. (Korean J Community Nutrition 8(3) : 349∼355, 2003)

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.361-367
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• 2004

The axial compressive strength, relative 3-D stability and osteoconductive shape design of an intervertebral fusion cage are important biomechanical factors for successful intervertebral fusion. Changes in the stress distribution of the vertebral end plate and in cage stability due to changes in the spike shape of a newly contrived box-shaped fusion cage are investigated. In this investigation, the initial contact of the cage's spikes with the end plate and the penetration of the cage's spikes into the end plate are considered. The finite element analysis is conducted to study the effects of the cage's spike height, tip width and angle on the stress distribution of the vertebral end plate, and the micromigration of the cage in the A-P direction. The stress distribution in the end plate is examined when a normal load of 1700N is applied to the vertebra after inserting 2 cages. The micromigration of the cage is examined when a pull out load of l00N is applied in the A-P direction. The analysis results reveal that the spike tip width significantly influences the stress concentration in the end plate, but the spike height and angle do not significantly influence the stress distribution in the end plate touching the cage's spikes. In addition, the analysis results show that the micromigration of the cage can be reduced by adjusting the spike angle and spike arrangement in the A-P direction. This study proposes the optimal shape of an intervertebral fusion cage, which promotes bone fusion, reduces the stress concentration in a vertebral end plate, and increases mechanical stability.

• Korean Journal of Community Nutrition
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• v.23 no.4
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• pp.289-301
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• 2018

Objectives: The aim of this study was to examine the current status of consumption of energy drinks among college students and investigate the effects of general environmental factors, health behavior factors, caffeine knowledge levels, and perceived stress levels on consumption of energy drinks. Methods: A survey was conducted among a total of 479 college students in Gwangju, using self-administered questionnaires. The questionnaire consisted of items about general environmental factors, health behavior, caffeine knowledge, perceived stress, and energy drink consumption behaviors. Results: 69.1% of participants experienced consumption of energy drinks, and specifically 82.8% of male students and 54.1% of female students experienced consumption of energy drinks (p<0.001). The reasons for drinking energy drinks were found to be recovery from fatigue, curiosity, taste, habit, thirst relief, and stress relief. In addition, 40.7% of participants experienced drinking energy drinks mixed with alcohol, and specifically 48.6% of male students and 27.4% of female students reported drinking energy drinks with alcohol (p<0.001). Moreover, 51.5% of participants responded that they experienced the effects of energy drinks, 31.9% reported experiencing adverse effects, and 41.1% were found to perceive the health risks. As a result of the assessment of caffeine knowledge, the participants showed a high level of knowledge of the arousal effect (77.7%) and the concentration increasing effect (70.8%) of caffeine, whereas they exhibited a low level of understanding of the health problems due to caffeine (32.6%) and adequate caffeine intake levels (24.4%). The higher levels of consumption experience of energy drinks was associated with higher body mass indexes (BMI) (p<0.01), higher academic years (p<0.01), lower levels of interest in health (p<0.05), smoking (p<0.001), alcohol consumption (p<0.05), and higher levels of perceived stress (p<0.05). Conclusions: The risk groups related to consumption of energy drinks among college students were identified as male students rather than female students, students in the third or fourth year of study associated with increased stress levels, and students with negative health behaviors. Therefore, support for diverse health and nutrition education for college students is required along with the improvement of internal and external environments of schools in order for college students to manage increased stress levels due to the schoolwork and preparation for employment and maintain positive health behaviors.

• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.935-946
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• 2000

Elastic-plastic stress analysis has been performed to evaluate the fatigue life of an autofrettaged pressure vessel containing cross-bores subjected to pulsating internal pressure of 200 MPa. Finite element analyses were used to calculate the residual and operating stress distributions of the pressure vessel due to the autofrettage process and pulsating internal pressure, respectively. Theoretical stress concentration factors of 3.06, 2.58, and 2.64 were obtained at the cross-bore of the pressure vessel due to internal pressure, 50%, and 100% autofrettage loadings, respectively. Local stresses and local strains determined from the elastic-plastic finite element analysis were employed to calculate the failure location and fatigue life of the pressure vessel with radial cross-bores, incorporating the low-cycle fatigue properties of the pressure vessel steel and fatigue damage parameters. Increase in the amount of overstrain by autofrettage process moved the crack initiation location from the inner radius toward a mid-wall, and extended the crack initiation life. Predicted fatigue life of the fully autofrettaged pressure vessel with cross-bores increased about 50%, compared to the unautofrettaged pressure vessel. At the autofrettage level higher than 50%, the failure location and fatigue life of the pressure vessel were not significantly influenced by the autofrettage level.