• Proceedings of the KSME Conference
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• 2004.04a
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• pp.13-18
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• 2004

The objective of this study is to investigate fracture toughness and fatigue crack propagation behavior in the Reduced Activation Ferritic Steel (RAFs) JLF-I. The fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The fatigue crack propagation behavior of the JLF-I steel was investigated by the constant-amplitude loading test for the stress ratios R=O.I, 0.3 and 0.5 respectively. The effects of stress ratios and specimen size on the fatigue crack growth behaviors for JLF-I steel were discussed within the Paris law. The test results showed the standard CT specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen. The fatigue crack propagation rate of a half size specimen was similar to that of a full size specimen at the stress ratios of 0.1, 0.3 and 0.5 respectively. The fatigue crack propagation behavior of this material were evaluated by using a half size specimen.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.11
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• pp.69-76
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• 1997

The rotating bending fatigue tests were performed using the specimens taken from Cr-Mo-V steel, widely sued in thermal power plant turbines, at various temperatures such as room temperature, 300 .deg. C, 425 .deg. C and 550 .deg. C. The characteristics of fatigue crack propagation were examined and analyzed by using fracture mechanics parameter. The plastic replica method was also applied in order to measure the crack length on the basis of serial observation of fatigue crack propagation behavior on the defected specimen surface. The fatigue crack propagation behavior of Cr-Mo-V steel was investigated within the frame work of elastic-plastic fracture mechanics. The propagation law of fatigue crack is obtained uniquely by using the term .sigma. $^{n}$ sub a/where .sigma. $_{a}$ is the service stress, a is the crack length and n is a constant. The values of constant n are nearly equal to 2.48, 2.60 and 8.61 at room temperature, 300 .deg. C and 425 .deg. C.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1373-1380
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• 1992

The local cyclic strain distribution near the crack tip has been investigated by the fine Dot Grid Strain Measurement Method, which had been suggested strain measurement method to resolve experimental difficulties by authors. It has been found that the magnitude of the local cyclic strain distribution(.DELTA..epsilon.$_{eq}$ )near a crack tip has been varied by the applied cyclic load level and material, but the shape of the local cyclic strain distribution near the crack tip has been experimentally scrarcely altered : that is .DELTA..epsilon.$_{eq}$ = .DELTA.A.f(.theta.). $r^{-1}$ . Consequently, the local cyclic strain field near the crack tip could be favorably characterized by a single parameter fatigue strain intensity factor .DELTA.A. In addition, with the viewpoint that .DELTA.A depends on material and load level, .DELTA.A has been applied to evaluate the fatigue crack propagation rate and usefulness of the result has been considered. As a result, it has been ascertained that .DELTA.A has been a useful parameter to evaluate the fatigue crack propagation rate.

• Corrosion Science and Technology
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• v.9 no.2
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• pp.57-66
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• 2010

Since nuclear power plants are being operated under high temperature and high pressure, on-line monitoring technique to detect corrosion could be more effective than off-line method in shut-off period. In this operating condition, electrochemical noise method may be suitable to monitor the corrosion. This paper aims the analysis on the relation between the cracking and electrochemical noise signal of Alloy 600 under U-bending. When electrochemical noise monitoring technique was used during SCC test, it was judge to be obvious that if cracks generate, its generation can be detected by electrochemical current noise. Cracking-related noise was defined as the noise showing 5~10 times greater than the average value of background noise bands. On the base of crack noise, crack initiation time was determined. From SCC test and electrochemical noise monitoring in $25^{\circ}C$, 0.1 M $Na_2S_4O_6$ solution (Reverse U-Bended Alloy 600 SE+), average crack initiation time was obtained as 9,046 seconds and from its initiation time, it could be defined that net crack propagation rate is the crack length divided by ${\Delta}T$(= total test period - crack initiation time). Therefore, average net crack propagation rate was obtained to be $1.18{\times}10^{-9}\;m/s$.

• Fire Science and Engineering
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• v.27 no.4
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• pp.41-46
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• 2013

The present study has been conducted to investigate the reaction kinetics and pyrolysis parameters for flame propagation analysis of furniture material components. TGA measurement for component materials such as MDF (medium density fiberboad) panel including coating material, synthetic leather and foam cushion are performed under maximum temperature of $600^{\circ}C$ and heating rate of $10^{\circ}C/min$. The results of TGA have shown that the peak temperature of MDF panel was $324^{\circ}C$ and the initial peak temperature of coating material decreased by $270{\sim}280^{\circ}C$. In the case of synthetic leather and foam materials, the reference temperature and reference rate depend on the type of polymer consisting the sample, the initial kinetic characteristics was classified into 2 categories of about $270^{\circ}C$ and $420^{\circ}C$ of reference temperature for the tested synthetic materials. The present study showed the pyrolysis parameters of reference temperature and reference rate proposed by Lyon to evaluate the pre-exponential factor and activation energy. The present study can contribute to improve the reliability of computational fire analysis and enhance the understanding of fire propagation phenomena based on the thermal properties study of material.

• Korean Journal of Medicinal Crop Science
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• v.18 no.2
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• pp.93-97
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• 2010

Cultural practices of Asparagus cochinchinensis in highland area were performed for a potential medicinal crop. These studies were examined to propagation methods, planting densities, nitrogen treatments, and cropping years. The results are summarized as follows. The adequate number of buds per tuberous root was 4 for vegetative propagation because the number of tuberous root harvested was 16.8 and the yield was also the highest, exhibiting 1,060 kg/10a. The suitable planting time for vegetative propagation was later than early April. If the earlier tuberous roots were planted, the less they emerged. The highest emergence rate was obtained from the planting density of $30{\times}20cm$ as 97.2% while the yield was highest in the $30{\times}15cm$ density, exhibiting 1,883 kg/10a with emergence rate at 94.9. It seemed that the higher planting density promoted plant height growth and yield in Asparagus cochinchinensis. The highest fresh weight was recorded at 6 kg/10a of nitrogen fertilizer into the sandy loam soil compared to the level of 0, 3, 9 kg/10a. The yield was increased with cropping years. However, the proper harvesting time was the second year of cultivation because the rate of weight increase was maximized in the 2-year-old tuberous root. The yield in the third year was decreased as compared to that of the second year.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.140-145
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• 1997

In case of spot-welded joints, the fatigue cracks generally originate from the weld interfaces of the neighborhood nugget tips, and propagate toward the outer surfaces of the sheets. Generally, because fatigue crack was observed in nugget around, strain gage was attached at nugget zone. Accordingly, it was very difficult to detect the generation time of fatigue crack in spot-welded joints and to measure the propagation speed of fatigue crack. We developed the non-destructive method, according to which th fatigue crack propagation rate can be quantitatively estimated by utilizing information obtained from strain gages bonded on the electrode indentations of spot welds. The results measured by real crack were compared with the data which was measured by strain gauge method in fatigue testing. And so fatigue strength was evaluated by stress intensity factor. In this study behavior of fatigue crack propagation under repeated load were considered.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.3
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• pp.181-189
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• 2001

For the Tailor Welded Blank sheet used fur automobile body panel, the characteristics of fatigue crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9+0.9mm) and different (0.9+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The crack propagation rate was noticeably decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness. Elasto-Plastic analysis was performed by finite element analysis fur explaining the test results.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.119-124
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• 2003

In this study, retardation behavior of fatigue crack under single overloading of the mixed mode I+II state was experimentally investigated. To produce single overload in the mixed mode I+II state, the compact tension shear (CTS) specimen and loading device were used. The propagation tests for fatigue crack were performed under mode I loading overloading afterwards. We examined the observed deformation aspects, variation of fatigue life and crack propagation rate, and the aspects of retardation behavior from tests. The retardation effect of mixed-mode single overload on fatigue crack propagation behavior was smaller than that of mode I single overload. It has been confirmed that the retardation behavior did not immediately appear and the retardation length was short when the component of mixed-mode overload was changed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1508-1512
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• 2003

In this study, retardation behavior of fatigue crack under single overloading of the mixed mode state was experimentally investigated. To produce single overload in the mixed mode I+II state, the compact tension shear (CTS) specimen and loading device were used. The propagation tests for fatigue crack were performed under mode I and mixed-mode loading overloading afterwards. We examined the observed deformation aspects, the variation of fatigue life and crack propagation rate, and the aspects of retardation behavior from tests. The retardation effect of mixed-mode single overload on fatigue crack propagation behavior was smaller than that of mode I single overload. Also the loading modes of variable and constant amplitude loads have influence on the retardation behavior of fatigue cracks.