• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.96-104
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• 1992

Aircraft structures and engineering structures are always subject to variable amplitude loads. Variable amplitude loads include some kind of loading history; for example, constant amplitude load, single peak overload and block overload etc. Crack growth under variable amplitude loading exhibits retardation effect. In this study, the 4 point bending fatigue test was performed by hydrolic servo fatigue testing machine on 7075-T6 Al-alloy. The retardation effect of overload ratio and numbers of overload cycle was quantitatively studied. 1) Change of retardation effect against increment of overload ratio is more evident when the multiple overload is applied than single overload is done. 2) The number of overload cycle is very important factor about the crack growth retardation effect when the overload ratio is more than 1.75; that is not when the overload ratio is less than 1.75. 3) Overload affected zone size increased gradually by increment of crack growth retardation effect. 4) Crack driving force is more greatly reduced when the crack tip branched off two direction than it sloped to one direction.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.3
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• pp.76-81
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• 2002

In order to study the fatigue crack and retardation mechanism in variable loading, the effects of crack tip branching in crack growth retardation were examined. The characteristics of crack tip branching behavior were considered with respect to microstructure and crack tip branching angle was examined. Crack tip branching was observed along the grain boundary of finite and pearlite structure. It was found that the branching angle ranges from 25 to 53 degrees. Using the finite element method, the variable of crack driving farce to branching angle was examined. The effective crack driving farce (K$\_$eff/) decreased as the branching angle increased. The rate of decrease was 33% for kinked type and 29% for forked one. It was confirmed that the effect of crack tip branching is a very important factor in crack growth retardation. Therefore, crack branching effect should be considered in building the hypothetical model to predict crack growth retardation.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1789-1793
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• 2008

The Oxygen Index was measured for another flame retardant APP, or phosphorus, and other flame retarding assistants ZS, ZHS, AOM, and ZB, which are used as low smoke emitting materials, in order to see the increase in the flame retardation effect in comparison to the volume of additions. The results show that their flame retardation synergy effect was very small compared to the main flame retardants. The mixed use of main flame retardants, low smoking emitting materials, and phosphorus is a very important area of examination for creating synergy effect of flame retardation and lowering smoking and toxicity. For this, the results of flame retardation effect in comparison to the volume of addition of each low smoke emitting material are shown below.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.77-80
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• 2004

The purpose of this study was to examine effects of combustion retardation for paper filter impregnated metal salts by measurement of extinguishing concentration, CO concentration, and limiting oxygen index(LOI, ASTM D 2863). And thermal stability analysis using DSC was carried out. In case of extinguishing concentration, $NH_4H_2PO_4$ showed excellent effect of combustion retardation. The result of LOI measurement showed that metal salts possessed good effect of combustion retardation. And thermal analysis using DSC showed that these metal salts possessed thermal stability. In case of CO concentration, CO concentration was increasing because of imperfect combustion process due to combustion retardation effect of metal salts.

• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.122-129
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• 1988

Recently with the rapid development in marine and shipbuliding industries such as marine structures, ship and chemical plants, there occurs much interest in the study of corrosion fatigue characteristics which was closed up an important role in mechanical design. In this study, the 5086 Al-alloy was tested by use of rotary bending fatigue tester. The retardation effect of overload on the corrosion fatigue crack propagation in sea environment was quantitatively studied. 1) Retardation effect of corrosion fatigue crack propagation is most eminent when overload ratio is 1.52, overload magnitude corresponds to about 77% and 55% of yield strength and tensile strength respectively. 2) After overload ratio 1.52 was used, retardation of corrosion fatigue crack growth rate is largely retarded and quasi-threshold stress intensity factor range($\Delta\textrm{K}_{th}$) appears. 3) According to m of experimental constant, retardation effect of corrosion fatigue crack propagation corresponds to about 25% of constant stress amplitude when overload ratio is 1.52. 4) When overload ratio 1.52 was used, retardation parameter (RP) decreases to about 0.43 and corrosion sensitivity (S)decreses to about 2.1.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.6
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• pp.83-89
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• 1997

In order to study on fatigue crack retardation and retardation mechanism in variable loading, the effects of crack tip branching in fatigue crack growth retardation were examined. The characteristics of crack tip banching behavior was considered to micro structure. It was examined that the variation of crack tip branching angle. Crack tip branching was observed along the grain boundary of ferrite and pearlite structure. It was found that the abanching angle ranges from 25 to 53 degrees. Using the finite element method, the variable of crack driving force to branching angle was examined. The effective crack driving force ( $K_{\eff}$ ) decreased as the braching angle increases. The rate of decrease was 33% for the kinked type and 29% for the forked one. It was confirmed that the effect of crack tip branching is a very important factor in fatigue crack growth retardation. Therefore, crack branching effect should be considered building the hypoth- etical model to predict crack growth retardation.

• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.3
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• pp.26-34
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• 1988

A study of the fatigue fracture accompanied with crack propagation should be investigated systematically by the behavior of the crack propagation. In this study, the effect of crack retardation due to cover plate is investigated by analytical and experimental method. Through the analytical and experimental works, it is confirmed that the retardation of fatigue crack propagation is properly controlled by cove plate and the retardation effects may be estimated exactly by the compliance method.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.4
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• pp.72-77
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• 2002

The load interaction effect can be best illustrated by the phenomenon of overload retardation. Some prediction methods for retardation are reviewed and the problems discussed in the present paper. The so-called under-load effect much of the retardation disappears if a very low level minimum stress follows the overload, is also of importance for a prediction model to work properly under random load spectrum. The concept of Interactive Zone (IZ) fully considering reversed plasticity during unloading was discussed. This IZ concept can be combined with existing models to derive some improved models that can naturally take account of the under-load effect. Some simulations by IZ improved models for test under complex load sequences including multiple overloads and both over/under loads are compared with test results. It is seen that the improvement by IZ concept greatly enhanced the ability of existing models to accommodate complex load interaction effects.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.306-311
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• 2003

A growing fatigue crack is known to be retarded on application of an overload cycle. The retardation may be characterized by the total number of cycles involved during retardation and the retarded crack length. The overload ratio plays an important role to influence the retardation behavior. The objective of the present investigation is to study the effect of different overload ratio on the retardation behavior. For DENT(double edge notched tension) specimens and ESET(eccentrically-loaded single edge crack tension) specimens, fatigue crack growth tests are conducted under cyclic constant-amplitude loading including a single tensile overloading with different overload ratios. The proposed crack retardation model predicts crack growth retardation due to a single tensile overloading. The predictions are put into comparison with the experimental results to confirm the reliability of this model.

• Journal of Nutrition and Health
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• v.30 no.2
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• pp.210-219
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• 1997

Retarding effects of the dietary fibers from tangerine peels on glucose, bile acid and cadmium transport were evaluated by dialysis method, and were compared with those of commercial dietary fibers(citrus pection, CM-cellulose, guar gum, $\alpha$-cellulose). Yields of total (TDF), insoluble(IDF) and soluble dietary fibers(SDF) from tangerine peels on the fresh matter basis were 2.84%, 1.95% and 0.39% respectively. The amount of insoluble fibers was 5.2 times higher than that of soluble fibers. Soluble fibers(guar gum, CM-cellulose, SDF, pectin) had the retarding effect on glucose transport, while IDF, TDF and $\alpha$-cellulose did not have. Guar gum showed the greatest effect, followed by CM-cellulose, SDF and pectin. Among the extracted fibers, only SDF had the effect on glucose transport retardation. Regarding bile acid dialysis, guar gum had the greatest retarding effect, and all dietary fibers from tangerine peels, especially SDF, showed the effect of bile acid retardation. On cadmium transport retardation, CM-cellulose had the greatest effect, followed by SDF, TDF, IDF, guar gum and pectin. Among the extracted fibers, SDF had the greatest effect on Cd trasport transport retardation. The extracted dietary fibers showed higher retarding effect on Cd transport than glucose and bile acid transport, and the effect of SDF was higher than IDF.