• Bulletin of the Society of Naval Architects of Korea
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• v.12 no.2
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• pp.43-58
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• 1975

There are many reports on fatigue crack of metallic materials but most of them relate crack propagation rate to stress intensity factor. The problem of crack propagation is not yet clarified, especially the bridge between micro and macro phenomena In this experiment rotating bending fatigue tests have been carried out with smoothed specimen of rolled steel plates including 0.2% carbon under application of three stress conditions to investigate the slip band and the crack propagation behaviour. The results obtained are as follows; 1) The length of cracks which have grown at initial crack tips can be expressed as follows; $l=Ae^{BNr}$(A,B: constant, $N_r$: cycle ratio) $\frac{dl}{dN}=\frac{AB}{N_f}{\cdot}e^{BNr}$($N_f$:fatigue life) 2) The ratio of slipped grain number to total grain number is $S_f=7{\sigma}-5.6$-5.6{\sigma}_c$($\sigma$: stress amplitude) (${\sigma}_c$: fatigue limit) 3) When the fatigue process transfers from Stage I to Stage II, the crack which propagates into specimen changes its direction from that of the maximum shear stress to the direction of perpendicular to principal stress and this is same in the circumferential direction of specimen. the crack propagation behaviors of both sides of a crack are different each other when they approach to the grain boundary.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.4
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• pp.27-33
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• 1997

Spot welding has been used in the sheet metal jointing processes because of its high productivity and convenience. In this study, effects of welding conditions on the fatigue life and prediction methods of fatigue life of spot welded joint have been studded . Fatigue life was estimated by stress index parameter considering multiaxial stresses. Fatigue tests were conducted with the tensile-shear specimens using SPCC. Fatigue life of spot welded joint was influenced by welding currents and was predicted exactly with taking into account StageIII.

• Journal of Industrial Technology
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• v.21 no.B
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• pp.213-222
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• 2001

In the study, the fatigue strength improvement and mechanism have been estimated by the Spot-Heating treatment on welded bead toes. For this, web-gusset specimens were made without residual stresses and the others with residual stresses imposed by Spot-Heating. The 4-point bending tests were performed in order to estimate the effect of spot-heating on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue test, fatigue strength of As-Welded specimen for non load-carrying fillet welded joints subjected to pure bending has satisfied the grade of fatigue prescribed in specifications of korea, AASHTO and JSSC. As compare with As-Welded specimen and Spot-Heating specimen have increased about 20% for the fatigue strength at $7.7{\times}10^6$ cycles. The Spot-Heating by reformation of the residual stress on welded bead toes has greatly affected the fatigue crack propagation life, but has slightly affected the fatigue crack initiation life.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.2
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• pp.186-192
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• 2002

The fatigue crack propagation characteristics were investigated on dissimilar friction weld of two kind of heat-resisting steels (STR3 and STR35) commonly used in valve materials for vehicles. A small circular artificial defect was machined to induce fatigue crack at bonded line, heat affected zone and base metal of the weld on the surface of the specimens. From the results of the experiment, the fatigue limits of the materials STR3 and STR35 were obtained to be 429.0MPa and 409.4MPa respectably. The STR35 base metal and 1.0mm HAZ specimens showed 190% and 82% higher fatigue life than STR3 base metal. And the fatigue life of 1.0mm HAZ specimen was shown 99% on STR3 and 29% on STR35 higher than that of their base metal. But the fatigue life of weld interface specimen was shown 18% on STR3 and 72% on STR35 lower than that of their base metal because of the weld interface separation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.75-84
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• 2021

In this study, to evaluate deterioration propagation life and deterioration curve of the shop painted and field re-painted steel bridges, accelerated corrosion tests were carried out on 4 types of heavy-duty painting systems with different surface treatments. The surface treatments prior to painting were examined by hand tool(SSPC SP-2), power tool(SP-3,) or blast cleaning(SP-10) considering shop painting and field re-painting. The paint deterioration curves for each painting system and surface treatment were evaluated based on corrosion propagation from the initial paint defects. From the test results, the paint deterioration life of shop painted and field re-painted system was evaluated and compared by using corrosivity categories and durability performance evaluation of structural steel. The deterioration propagation life of shop and field paint was estimated in 18 to 21 years and 5.3 to 8.0 years with atmospheric corrosion category C4.

• Journal of agriculture & life science
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• v.44 no.6
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• pp.39-44
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• 2010

An efficient method for the rapid propagation of Smilax china from axillary buds was established. Plants with thick leafage were selected from Korea native S. china population. Axillary buds of S. china collected from selected plant and were cultured in various culture media (2MS, MS, 1/2MS, WPM, B5 and SH medium). Shoot was induced from axillary bud on MS basal medium after 4 weeks of culture. 1/2MS medium showed a higher growth rate than those of the others, while the lowest shoot growth was obtained in 2MS medium. Among the sucrose concentrations, 5% sucrose was the optimum level for shoots growth from axillay buds. Among cytokinins, $0.5mgL^{-1}$ 6-benzylaminopurine (BAP) treatment showed the best performance on shoot multiplication, yielding average shoot multiplication forming about 2.4. Rooting was induced directly near the base of the shoot on 1/2MS medium containing with three-auxins ${\alpha}-napthalene$ acetic acid (NAA), indole acetic acid (IAA) and ${\beta}-indolebutyric$ acid (IBA) (0.5 and $1.0mgL^{-1}$). The $1.0mgL^{-1}$ IBA treatments induced earliest rooting with maximum of root number and root growth. These rooted plantlets were successfully transferred to pots for 4 weeks hardening process, and were transferred to soil with above 90% survival rate.

• Korean Journal of Medicinal Crop Science
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• v.12 no.2
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• pp.129-134
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• 2004

Optimal culture conditions for efficient in vitro propagation and polysaccharide production of Orostachys japonicus were established. The highest growth yield was achieved in 1/2 MS medium, while the lowest growth yield was obtained in 4 MS medium. The patterns of polysaccharide formation were a little similar in all cases, but on MB5 medium, the po]ysaccharide contents of plant were higher than others. Among the modified nitrate levels, effective growth level were obtained in 1/4 N and 1/2 N. High contents of polysaccharide were obtained in 4 N. Different concentration of potassium and calcium did not improve the growth and polysaccharide production. The micropropagated shoots were successfully acclimatized artificial soils.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.557-562
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• 2003

The responses of the floor system of a railway bridge are investigated for fatigue life prediction of damaged members using fracture mechanics approach. Numerical analysis of the structure is performed in order to see the influence of track-structure interaction and continuity of the truss connection on the response of the bridge members. Fatigue crack growth analysis is carried through equivalent stress obtained from time-history analysis. The results of time-history analysis agree with measured responses. The fatigue propagation life increases as the curvature in the coped stringer increases.

• Journal of the East Asian Society of Dietary Life
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• v.16 no.3
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• pp.349-356
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• 2006

This study was carried out to survey the effect of Jujube extract on the growth of 3 strains of lactic acid bacteria(LBA) starter cultures in the MRS broth by the addition of 0, 0.1, 0.5, 1 and 2% extract The pH, titratable acidity and OD of LAB were investigated in order to get fundamental knowledge for the development a new product. The effects of Jujube extract on the growth of LAB were variable depending upon the LAB species and concentrations of Jujube extract significantly (p<0.05). In the results, Jujube extract enhanced the acid production and propagation by the 3 LAB strains with increasing concentration of Jujube extracts until 2.0% added was to the MRS broth medium (p<0.05). Addition of Jujube extract markedly stimulated the acid production and propagation of Lactobacillus acidophilus, Streptococcus thermophilus and Bifidobacterium longum.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.306-312
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• 1992

The prevention of roll breakage in hot rolling process is improtant to reduce maintenance cost and production loss. Rolling conditions such as the roll force and torque have been intensively studied to overcome the roll breakage. in the present work, a model for life prediction of work rolls under working condition was developed and discussed. The model consists of stress analysis, crack propagation, wear and fatigue calculation model. Roll life can be predicted by stress, crack depth and fatigue damage calculated from this model. The reliability of stress analysis is backed up by the FEM analysis. From the result of simulation using by pressent model, although the fatigue damage of back up roll reachs 80% of practical limit, that of workroll was less than 40%. In edge section of workroll stress amplification is found by wear and bender effect. We can judge that workroll failures are not due to fatigue damage, crack propagation by bending stress but stress amplification by wear and bender in present working condition.