• 대한기계학회논문집A
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• 제33권10호
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• pp.1158-1162
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• 2009

Fatigue limit of the copper film coated by Sn was estimated using Goodman diagram and Gerber diagram. To obtain the high cycle fatigue life curve, S-N curve, of the film, the high cycle fatigue test was carried out by applying the constant amplitude load to the film specimen with three different stress ratio of 0.05, 0.3 and 0.5 and the frequency of 40 Hz at room temperature in air. The free-standing film specimen 15.26${\mu}m$ thick was fabricated by etching process. The fatigue limits and S-N curves at the respective stress ratios were determined from the experimental works. It was shown that the S-N curves were dependent on the stress ratio and the fatigue limit was increased with decreasing the stress ratio. The dependency of the fatigue behavior was presented in empirical relationship. Using these relationships, the fatigue limit was predicted.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1108-1117
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• 2005

RAP(rammed aggregate pier) method which is intermediate foundation of deep and shallow foundation is used to improve the ground with high compaction energy. This method is widely spread around the world, but there are few examples and systemic researches for failure mechanism and bearing capacity of this method are not organized yet. In this paper, soil laboratory tests were carried out to evaluate the applicability of RAP method as the foundation of a structure. And the bearing capacity and the failure mechanism of RAP method were studied with respect to various relative densities(35%, 65%, 90%), diameters(45mm, 60mm) and lengths(20cm, 30cm, 40cm). As results, stress concentration ratio decreased as diameter of RAP was increasing or length of RAP was decreased or relative density was decreased. however these results were not always constant. because systematic interaction between relative density and diameter and length of RAP can affect stress concentration ratio, more studies on stress concentration ratio are needed throughout laboratory and field tests.

• 대한기계학회논문집B
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• 제27권7호
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• pp.920-928
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• 2003

The objective of the present study was to investigate the characteristics of flow and wall shear stress under steady and pulsatile flow in the aneurysm. The numerical simulation using the software were carried out for the diameter ratios ranging from 1.5 to 3.0, Reynolds number ranging from 900 to 1800 and Womersley number, 15.47. For steady flow, it was shown that a recirculating vortex occupied the entire bulge with its core located closer to the distal end of the bulge and the strength of vortex increased with increase of the Reynolds number and diameter ratio. The position of a maximum wall shear stress was the distal end of the aneurysm regardless of the Reynolds number and diameter ratios. For the pulsatile flow, a recirculating flow at the bulge was developed and disappeared for one period and the strength of vortex increased with the diameter ratio. The maximum values of the wall shear stress increased in proportion to the diameter ratio. However, the position of a maximum wall shear stress was the distal end of the aneurysm regardless of the diameter ratios.

• 조명전기설비학회논문지
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• 제26권4호
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• pp.57-66
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• 2012

When typical Z-source DC/AC inverter(ZSI) is operated in high voltage gain area, because of its high duty ratio, voltage and current stress in Z-network of typical ZSI are increased. This paper proposes a new switched trans ZSI(STZSI) with two switched trans cells which consist of one trans and two diodes. To confirm the operation performance of the proposed system, the PSIM simulation is performed for typical ZSI, switched inductor ZSI and the proposed STZSI. Voltage / current stress and transient state characteristics of each method are compared under the condition of DC input voltage 100[V] and output phase voltage 66[Vrms]. As a result, we confirmed that transient state of the proposed STZSI is short compared with the conventional ZSI because the high voltage gain is obtained using the same duty ratio, also a low duty ratio is required for the same output voltage. Finally, we could know the proposed system have low voltage and current stress in Z-network compared with the conventional ZSI.

• 한국표면공학회지
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• 제37권6호
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• pp.350-359
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• 2004

Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at $1050^{\circ}C$ for 1hr and $650^{\circ}C$ for 5 hr. The samples for SCC were shot-peened using $\Phi$0.6 mm steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of$ 288^{\circ}C$, 90 kgf pressure, water with 8 ppm dissolved oxygen, and $8.3xl0^{-7}$/s strain rate. After the corrosion and see test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot- peened specimen. Stress corrosion cracking strength decreased with the increase of the Ti/C ratio.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 가을 학술발표회 논문집
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• pp.81-88
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• 1998

• 한국염색가공학회지
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• 제12권2호
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• pp.103-110
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• 2000

To examine the physical properties of POY through the microstructure control, the crystal structure such as the crystallinity, the crystallite size, the orientation, the shrinkage, the tensile properties, and the thermal stress of POY(80/48, SD) were examined at different draw ratios and annealing temperatures. From the examination following conclusions were obtained : 1. The crystallinity was more effected by the heat setting temperature than by the draw ratio. The increasing rate was greatest at the heat setting temperature range of $170~190^\circ{C}$. 2. The crystallite size perpendicular to the fiber axis was more effected by the annealing temperature at lower draw ratios. On the other hand, the crystal and amorphous orientations were more effected by the heat setting at higher draw ratios. 3. The boiling shrinkage did not change significantly, but the total shrinkage showed 13% at the draw ratio 1.9 and the heat setting temperature $170^\circ{C}$. 4. The maximum thermal stress increased with increasing the draw ratio and decreasing the heat setting temperature in the temperature range of $170~210^\circ{C}$. At the draw ratio 1.9 and the heat setting temperature $170^\circ{C}$, the maximum thermal stress found was 1.1gf/d. 5. In the heat setting temperature above $170^\circ{C}$ after the drawing, the crystallinity, the crystallite size, the orientation, and the strength increased with increasing temperature, but the shrinkage and the maximum thermal stress decreased with increasing temperature.

• Geomechanics and Engineering
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• 제20권5호
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• pp.371-384
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• 2020

A settlement prediction method based on shear wave velocity measurements and soil nonlinearity was recently developed and verified by means of centrifuge tests. However, the method was only applicable to heavily overconsolidated soil deposits under enlarged yield surfaces. In this study, the settlement evaluation method was refined to consider the stress history of the sublayer, based on an overconsolidation ratio evaluation technique, and thereby incorporate irrecoverable plastic deformation in the settlement calculation. A relationship between the small-strain shear modulus and overconsolidation ratio, which can be determined from laboratory tests, was adopted to describe the stress history of the subsurface. Based on the overconsolidation ratio determined, the value of an empirical coefficient that reflects the effect of plastic deformation over the elastic region is determined by comparing the overconsolidation ratio with the stress increment transmitted by the surface design load. The refined method that incorporate this empirical coefficient was successfully validated by means of centrifuge tests, even under normally consolidated loading conditions.

• 한국정밀공학회지
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• 제18권12호
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• pp.54-59
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• 2001

The stability of a thin plate structure is very crucial problem which results buckling. Because the buckling strength of thin plates is lower than the yield strength of the material, reinforcement plate must be used to increase the buckling strength. And, in this case, spot welding is commonly used, however, the spot welded joints are practically designed by experimental decisions, so it is Inefficient and has the risks of buckling demolition. In this study, two parameters, such as the area ratio and the distance ratio of spot welding which have influence on the buckling strength, should be chosen. Under compressive and shearing load, the effect of two parameters on the critical stress is discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.651-656
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• 2000

The strain compatibility analysis shows that the influential parameters of loading type, reinforcing ratio, and span-depth ratio affect on the tendon stress in unbonded prestresses concrete member significantly. However, existing test results did not comply exactly with the analytical results. In consequence, the present study was planned to examine the parameters in order to complete Moon/Lim's design equation. The test variables with 12 specimens were loading type, reinforcing ratio, and span-depth ratio. As results, the effect of influential parameters were examined throughly and Moon/Lim's design equation was proven to be accurate.