• Journal of Ocean Engineering and Technology
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• v.16 no.5
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• pp.73-79
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• 2002

In this paper, the effect of the compressive residual stresses was obtained at the test conditions of the higher temperature than the ambient temperature. The examination was performed with the CT specimen result of the material(JISG SUP9) which is being commonly used for the marine engine parts and the ocean structures. As a result, the test conditions at the higher temperature were acquired considering the peak values of the compressive residual stresses of the specimens and the effect on the fatigue crack propagation speed da／dN in stage II and the threshold stress intensity factor range Δth in stage I. Also the material constant C and the fatigue crack propagation index m in the formula of Paris Law da／dN＝C (ΔK)$^{m}$ were suggested to estimate the dependence on the test temperature.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.314-319
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• 2004

High temperature fracture toughness characteristics of shot peened spring steel(SUP-9), which is used for automobile suspension system and railroad, was investigated in this paper. Fracture tougness test for room temperature, $100^{\circ}C$ , and $200^{\circ}C$ were evaluated by material test system(MTS). The experimental results show that the fracture toughness was improved by peened and unpeened. The fracture toughness for high temperature were also improved by peened and unpeened.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.4
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• pp.117-124
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• 2003

The lightness of components required in automobile and machinery industry is requiring high strength of components. In particular, manufacturing process and new materials development for solving the fatigue fracture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in high temperatures($100^{\circ}C$, $150^{\circ}C$, $180^{\circ}C$) was investigated with considering fracture mechanics. So, we can obtain followings. (1)Compressive residual stress decreases in high temperature, that is, with increasing temperature. (2)The effect of compressive residual stress on fatigue crack growth behavior in high temperature increases below $\Delta$K=17~19MPa (3)It was investigated by SEM that the constraint of compressive residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.5
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• pp.149-157
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• 2004

Residual stresses can have a significant influence on the fatigue lives of structural engineering components. For the accurate assessment of fatigue lifetimes a detailed knowledge of the residual stress profile is required. Significant advances have been made in recent years fur obtaining accurate and reliable determinations of residual stress distributions. These include both experimental and numerical methods. The purpose of this study is to simulate peening process with the help of the finite element method in order to predict the magnitude and distribution of the residual stresses in accordance with the parameters, which are, e.g. shot velocity, shot diameter, shot impact angle, shot shape, distance between two impinging shots, and material parameters.

• Journal of the Korean institute of surface engineering
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• v.37 no.5
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• pp.273-278
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• 2004

The requirements of getting spring steel with higher fatigue strength have been increased to achieve the weight reduction of a vehicle. As the possible increment in fatigue strength by using the conventional shot peening treatment is found to be limited, it is necessary to modify the shot peening treatment. In this study, to investigate the effects of warm shot peening on increasing fatigue strength, tests are conducted on spring steel SAE9524. By the results of rotating bending fatigue tests, the fatigue strength increases up to 23.8% in warm shot peening specimens at $200^{\circ}C$ compared with conventional shot peening. The major reason why the warm shot peening is effective to the improvement of fatigue strength is the increment of the compressive residual stress, which can be effectively formed by shot peening under the condition of warm temperature than room temperature.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.33-42
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• 2004

Making use of SN steel in the building structure should be a prerequisite to adopt the design strength of said steel. As a preceding study, the material properties of STKN400B/490B tubes and SPAP235/325 and SPAR295 square pipes manufactured using SN400B/490B plates were evaluated. Compared with the yield and ultimate strengths of SN400B/490B plates, those of STKN400B/490B tubes increase. Nonetheless, the yield and ultimate strengths of STKN400B/490B tubes satisfied the design codes of STKN400B/490B tubes even though the tubes were fabricated via roll bending or press forming. On the other hand, the yield and ultimate strengths at the edges of SPAP235/325 square pipes did not satisfy the design codes based on the values at the sides. The maximum tensile and compressive residual stresses at the SN490B tube were equal to and 40% of the yield strength of the SN490B plate, respectively, In the case of the SPAP325 square pipe, both the maximum tensile and compressive residual stresses were 80% of the yield strength of the SN490B plate. The axial compressive loaded column test results snowed that the buckling strengths were not very different regardless of the mode of fabrication of STKN490B tunes. i.e., through roll bending or press forming. On the other hand, the buckling strength of the SPAP325 square pipe was higher than that of the built-up square pipe.

• Journal of the Korean Electrochemical Society
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• v.14 no.3
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• pp.163-170
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• 2011

Nanocrystalline Ni thin films were electodeposited from chloride baths to investigate the influences of additive concentration, current density and solution pH on residual (or internal) stress, surface morphology, and microstructure of the films. It was observed that residual stress in Ni thin film was changed from tensile stress mode (about 150 MPa) to compressive stress mode (about -100 MPa) with increasing saccharin concentration as an additive. Microstructure of Ni thin films was changed with/without saccharin in baths. Ni thin films electrodeposited from saccharinfree bath mainly consisted of both FCC(111) and FCC(200) phases. However, Ni thin film electrodeposited from the baths containing saccharin exhibited FCC(111), FCC(200) and FCC (311) phases [sometimes, FCC (220)]. Current density influenced residual stress of Ni thin films. It was measured to be the lowest compressive stress value (about-100 MPa) in range of current density of $2.5\sim10mA{\cdot}cm^{-2}$. Solution pH also influenced residual stress of Ni thin film. Addition of saccharin in baths affected grain size of Ni thin films. Grain sizes of Ni thin films were measured to be about 60 nm without saccharin and 24~38 nm with more than 0.0005M saccharin concentration. Surface of Ni thin films was changed from nodular to smooth surface morphology with addition of saccharin.

• Proceedings of the Korean Fiber Society Conference
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• 1997.04a
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• pp.207-212
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• 1997

• Proceedings of the Korean Vacuum Society Conference
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• 2004.08a
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• pp.156-156
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• 2004

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.128-128
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• 2000

박막의 탄성 특성을 평가하는 방법으로 nano-indentation, Brillouin light scattering measurement, ultrasonic surface wave measurement, bulge test, vibration membrane method 등 여러 가지가 제시되어 왔다. 이러한 방법들은 필름의 두께가 일정 두께 이상이 되어야 정확한 측정이 가능한 방법으로 매우 얇은 박막에서도 탄성특성을 평가할 수 있는 freehang, bridge 방법이 제시되었으며, 이 방법은 간단한 식각 공정을 통해 매우 얇은 박막에도 적용시킬 수 있다는 장점을 가지고 있다. 본 연구에서는 아주 얇은 박막에서도 탄성특성을 평가할 수 있는 freehang 방법을 이용하여 순수한 Diamond-like carbon (DLC) 필름과 Sidl 첨가된 DLC 필름의 탄성 특성을 평가하고자 한다. 실험에서 사용한 필름은 rf-PACVD 장비를 이용하여 증착하였다. 이때 전극과 플라즈마 사이의 바이어스 음전압은 -400 Vb로 합성압력은 10mTorr로 고정하였다. 사용한 반응 가스는 벤젠(C6H6), 그리고 벤젠과 희석된 실렌(SiH4 : H2 = 10 : 90)이며, 희석된 실렌의 첨가량을 조절하여 필름 내에 일정량의 Si을 함유시켰다. 각각의 조건에서 증착시간을 조절하여 필름의 두께를 변화시켰으며, KOH(5.6mol) 용액을 이용하여 습식 식각을 함으로써 freehang을 제작하였다. 이때 식각액에 의한 DLC 필름의 손상은 관찰되지 않았다. 필름의 잔류 응력을 측정하기 위해 200$\pm$10 혹은 100$\pm$5$\mu\textrm{m}$ 두께의 얇은 (100) Si wafer를 5$\times$50 mm2의 strip 형태로 절단하여 사용하였다. 필름의 압축 잔류 응력에 의해 발생한 필름/기판 복합체의 곡률은 laser 반사법과 $\alpha$-step profiler를 이용하여 측정하였으며, 이 결과를 Brenner 등에 유도된 식을 이용하여 잔류 응력을 계산하였다. 또한 제작된 frddhang은 광학 현미경과 전자주사현미경에 의해 관찰되었다. 이렇게 제작된 freehang을 이용하여 필름이 기판에 부착되기 위해 필요한 변형률을 측정하고, 독립적으로 측정된 필름의 잔류 응력을 박막의 응력-변형률 관계식에 적용하여 biaxial elastic modulus, E/(1-v)를 구할 수 있었다. 측정 결과 필름의 잔류 응력과 biaxial elastic modulus는 필름의 두께가 감소함에 따라 감소하는 경향을 나타냈으며, 같은 두께의 필름인 경우, 식각 깊이에 따른 biaxial elastic modulus 의 변화를 통해 최적의 식각 깊이를 알 수 있었다.