• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.4
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• pp.253-257
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• 2016

The effects of re-peening on the compressive residual stress and fatigue life of Al7075-T6 were investigated. The compressive residual stress induced on the surface of components by shot peening is known to increase the fatigue life. However, the fatigue load relaxes the compressive residual stress of components. Re-peening is a technique to again induce the relaxed compressive residual stress and increase the total fatigue life of components. In this study, the re-peening process was applied to fatigue-loaded specimens. The compressive residual stress and fatigue life were examined for re-peened specimens with fatigue ratios of 30%, 50%, and 70%. The results showed that the compressive residual stress of the specimens was relaxed under the fatigue load. The re-peening process significantly increases the compressive residual stress and total fatigue life.

• Journal of Power System Engineering
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• v.6 no.1
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• pp.61-67
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• 2002

15Cr-5Ni 석출강화 스테인리스강 3종류의 피로균열 발생과 성장 특성 및 파괴인성에 대하여 노치함수로서 연구하였다. 3종류강의 열처리 조건은 $482\;^{\circ}C,\;579\;^{\circ}C$ 및 $621\;^{\circ}C$이다. $621\;^{\circ}C$에서 4시간동안 열처리한 시험편 C는 약 $280\;MPa\;\sqrt{m}$의 가장 높은 파괴인성을 보였으며, 3종류에서 피로균열 성장이 가장 늦었다. $482\;^{\circ}C$에서 1시간 열처리한 시험편 A에서, 피로균열발생한계, ${\Delta}k{\rho}$, 는 노치반경0.3 mm에서 약 $280\;MPa\;\sqrt{m}$의 가장 높은 값을 보였다. 시험편 A는 시험편 B와 C보다 피로균열 성장이 빨랐지만, 피로균열 발생이 늦었다. 예 하중에 의한 노치선단의 압축잔류응력은 노치 시험편의 피로강도 향상에 유용한 방법이었다.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.583-590
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• 2008

Blasting has been applied in newly-built steel structures for cleaning forged surfaces and increasing the adhesive property of applied painting systems. However, the effect of the blast cleaning on fatigue behavior of welded joints is not clear. In this paper, fatigue tests were carried out on out-of-plane gusset welded joints and the effect of the blast cleaning on the fatigue behavior was studied. The curvature radius at the weld toe of the surface-treated specimens by using the blast method is larger than that of as-welded specimens. By the blast cleaning compressive residual stresses were induced into weld toes. The experimental results showed that the fatigue life of surface-treated specimens is longer than that of as-welded specimens, even though the fatigue life of surface-treated specimens and that of as-welded specimens are not clearly different in the high stress range. About a 160% increase in fatigue limit could be realized by using blast cleaning.

• Journal of Ocean Engineering and Technology
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• v.17 no.2
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• pp.47-53
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• 2003

The development of new materials with light weight and high strength has become vital to the machinery, aircraft and auto industries. However, there are a lot of problems with developing such materials that require such expensive tools, as well as a great deal of time and effort. Therefore, the improvement of fatigue life through, the adoption of residual stress, is the main focus. The compressive residual stress was imposed on the surface according to each shot velocity(1800, 2200, 2600, 3000rpm) based on Shot-peening, which is the method of improving fatigue life and strength. By using the methose mentioned above, we arrived at the following conclusions; 1. The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. In stage I, $\Delta$K$_{th}$, the threshold stress intensity factor, of the shot-peen processed material is high in critical parts, unlike the Un-peened material. Also m, fatigue crack growth exponent and number of cycle of the Shot-peened material was higher than of the Un-peened material. That is concluded from effect of da/dN. 2. Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. Compressive residual stress of the surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.73-80
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• 2017

In this study, cyclic loading analysis was conducted in order to understand the behavior of self-centering connections based on the number of PT(posttensioning) strands and initial posttensioning force. The initial posttensioning force needs to be above the yield moment of an angle for obtaining noticeable self-centering effect and it is proper that decompression moment ratio needs to be below 0.35 to minimize the residual displacement of major elements. As the number of PT strands increased, self-centering capacity also improved since initial posttensiong force in each PT strand has been decreased. It is also appropriate that initial posttensiong force needs to be less than or equal to 75% of yield strength of PT strands.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.519-525
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• 2008

For this study, SM45C steel rods using generally for power transmission shafts and machine components was selected and welded by butt-GMAW method. And then it was studied about estimation of fatigue strength and the region of infinite life by Haigh diagram using Goodman's equation. Fatigue strength in weld zone presents highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. This result agrees with distribution of hardness in weld zone. Fatigue strength in base metal zone presents highly compared with weld zone in low cycles between $10^4$ cycles and $10^6$cycles, but it presents the lowest fatigue strength on the order of heat affected zone in the vicinity of $10^6$cycles. It is the result that the first high compressive residual stress distributed by drawing process of the steel rods is released and the base metal is softened by alternating stresses. The region of infinite life by Haigh diagram presents highly in order of the boundary between deposited metal zone and heat affected zone, deposited metal zone, heat affected zone. From this results, it is demanded that the stress for safety design of machine components using SM45C butt-welded steel rods must be selected in the region of the lowest infinite life of heat affected zone.

• Geotechnical Engineering
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• v.9 no.2
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• pp.5-14
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• 1993

Weathered granite soil is the most representative as a surface soil in Korea. In this paper, the dynamic properties and settlement characteristics of Korea granite soil are studied through the dynamic triaxial compression tests. The dynamic characteristics are very important on the analysis of the foundations under dynamic loading such as machine vibration and earthquake. Soil samples having different grain sixtes were prepared at the relative densities between 80oA and 90oA and tested to measure shear moduli and damping ratios at each level of shear strain. The measured shear moduli of weathered granite soils showed large variations according to the grain sizes, confining pressures, relative densities and shear strains. Sandy weathered granite had a little larger dynamic properties than the average values of the sand studied by Seed and Idriss. Pot the well compacted granite soils, little residual settlements occured due to dynamic loading.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.313-318
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• 2003

The development of new materials with light weight and high strength has become vital to the machinery, aircraft and auto industries. However, there are a lot of problems with developing such materials that require expensive tools, and a great deal of time and effort. Therefore, the improvement of fatigue strength and fatigue life are mainly focused on by adopting residual stress(in this thesis). The compressive residual stress was imposed on the surface according to each shot velocity(57, 70, 83, 96 m/sec) based on Shot-peening, which is the method of improving fatigue lift: and strength. By using the methods mentioned above, I arrived at the following conclusions 1. The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. And in stage I, ${\Delta}K_{th}$, the threshold stress intensity factor, of the shot-peen processed material is high in critical parts unlike the Un-peened material. Also m, fatigue crack growth exponent and number of cycle of the Shot-peened material was higher than that of the Un-peened material. That is concluded from effect of da/dN. 2. Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• Journal of the Korean Geotechnical Society
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• v.26 no.4
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• pp.27-36
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• 2010

In this study, a series of flat dilatometer tests are performed for Busan sand reconstituted in a large calibration chamber to evaluate the state parameter ($\Psi$). Experimental result shows that the horizontal amplification factor ($K_D/K_0$) is linearly related with state parameter in semi-logarithmic space, but the $K_D/K_0$ of OC specimen is smaller than that of NC specimen because of the horizontal residual stress by stress history of OC specimen. The relation between the normalized dilatometer modulus ($E_D/\sigma_m'$) and the state parameter is also linearly expressed in semi-logarithmic space, and the effect of stress history is relatively insignificant in this relation. However, the variation in $E_D/\sigma_m'-\Psi$ relation of NC state is slightly higher than that of OC state due to the effect of the stress level, and the correlation curve is descending with increase of confining stress. The comparison of test result with previous results of Ticino and Toyoura sands shows that the $E_D/\sigma_m'-\Psi$ relation of Toyoura sand is located on upper side than that of Busan and Tieino sands due to the effect of the higher compressibility, whereas the $K_D/K_0-\Psi$ relation of each sand is irregularly distributed.

• Journal of the Korean Geotechnical Society
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• v.32 no.8
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• pp.15-25
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• 2016

In order to analyze undrained shear strength for clayey silt with low plasticity from Hwaseong site, a series of laboratory and in-situ tests were performed. The Unconfined Compressive (UC) test and Simple Consolidated-Undrained Triaxial (SCU) test were examined in order to assess their applicability to the measurement of the undrained strength of this soil. In the case of clayey silt with low plasticity, although the samples were properly taken by undisturbed sampling method, the residual effective stress and the unconfined compressive strength were reduced considerably. Therefore, an effective confining pressure that corresponds to the typical marine clay should be applied to the soil specimen before shearing in order to compensate for the loss of residual effective stress. By evaluating the shear strengths of clayey silt with low plasticity as 75% of $s_{u(scu)}$, the in-situ shear strength of this kind of soil can be duplicated.