• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.23 no.2
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• pp.15-15
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• 1987

In this study, the characteristics of TRC (tensile restraint crack) critical stress in the gravity type underwater wet welding process and in the in-air welding have been investigated for Y, y and 45°r grooves using the KR Grade A-3 steel plates and the E4303 covered electrodes. The following results were obtained: (1) In the TRC tests, the initial critical stress of Y groove is higher than those of the 45°r single bebel grooves in both in-air and underwater weldings, and the cold fracture sensitivity is higher in the underwater welding than in the in-air welding. (2) The hardness of underwater weld metal is the highest in heat affected zone is about Hk 365 in the in-air weld but Hk 670 in the underwater weld which is higher for cooling speed is more rapid, resulting in the lower critical stress by increase of fracture sensitivity. (3) The diffusible hydrogen quantity for 48 hours is about 18cc/100g-weld-metal in the in-air welding but 48cc/100g-weld-metal in the underwater welding. So that, in the case of underwater welding the diffusible hydrogen penetrates about 3 times more than that in the in-air welding.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.63-73
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• 1987

This study is a part of the research on the coupled vibration of train wheel with the stepped thickness and rail. The research was conducted for the purpose of examining the dynamic characteristics of train wheel at the running state and preventing the vibrations of the high speed railway. The stress at the boundary surface of web and rim, .sigma.$_{c}$, was analyzed in consideration of the uniform In-plane compressive stress depending on the conditions of rolling and the In-plane compressive stress depending on the rotation of train wheel. Then the equation of transverse vibration of the annular plate with the stepped thickness was analyzed by Rayleigh-Ritz's method. As a result of study, it was known that the rotational speed increase the natural frequency slightly and the acceleration level highly while the reaction force between train wheel and rail decrease the natural frequency linearly and the critical buckling is generated at n=1.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.78-83
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• 1998

Alloy 600과 Alloy 690의 응력부식파괴(Stress corrosion cracking, SCC)에 미치는 TiO$_2$의 영향을 315$^{\circ}C$의 10%NaOH 수용액에서 RUB(reverse U-bend) 시편, C-Ring 시편과 CT(compact tension)시편을 사용하여 평가하였다. 시편은 alloy 600 MA(mill anneal), alloy 600 TT(thermal treatment) 그리고 alloy 690 TT로 제작하였다. SCC 시험은 탈산된 10%NaOH 수용액에 2 g/1 TiO$_2$를 첨가한 용액과 첨가하지 않은 용액에서 수행하였으며, 이 조건에서 분극곡선도 얻었다. SCC 시험시 시편을 부식전위로부터 +150 ㎷ 양극분극을 가하였다. 기준전극으로 external Ag/AgCl electrode를 사용하였다. Alloy 600 MA로 제작한 RUB 시편은 TiO$_2$가 없는 용액에서 5일 안에 벽 관통 균열을 보였으나 TiO$_2$가 첨가된 용액에서는 균열을 관찰할 수 없었다. TiO$_2$가 첨가됨에 따라 alloy 600과 alloy 690의 임계전류밀도는 크게 감소하였고 또한 부동태 전류밀도도 감소하였다. 부동테 영역에서 TiO$_2$가 있는 용액의 경우 여러 peak가 있는 반면에 TiO$_2$가 없는 용액은 peak가 뚜렷하지 않았다. 이런 결과는 TiO$_2$가 첨가점에 따라 active region에서도 안정한 부동태 피막이 존재한다는 것을 시사한다. 또한 TiO$_2$가 없는 경우 SCC가 잘 일어나는 영역에 존재하는 부동태 피막이 TiO$_2$ 첨가에 따라 repassivation kinetics 등의 성질이 변화한 것으로 판단된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.713-721
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• 2012

The finite element simulations of fatigue crack growth are carried out. Using only the mechanical properties usually obtained from the tensile test as input data, we attempted to predict the fatigue crack growth behavior. The critical crack opening displacement is determined by monitoring the change in displacements at the node close to the crack tip. Crack growth is simulated by debonding the crack tip node. The exponent in the Paris law was determined and compared to the published exponent. Plotting with respect to the effective stress intensity factor range yielded more consistent results.

• Journal of Ocean Engineering and Technology
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• v.25 no.5
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• pp.47-51
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• 2011

This paper analyzes the fatigue-life of welded joints using the notch stress approach. In the notch stress approach, the notch effects are usually approximated by introducing weld-bead parameters for the local detailed weld joints. The actual bead shape is complex and 3-dimensional. It may also greatly influence the fatigue strength. In this study, the welded shape was modeled using a 3D-scanner. The critical distance method was adopted in the evaluation of the fatigue effective notch stress for the weldments. Fatigue life tests were performed to verify the present method of fatigue life estimation for two types of welded plates with longitudinal attachments. The estimated results of the present methods were applied to the results of the experiment. The results of the analysis showed that the scatter of fatigue-life for the experimental data expressed in the nominal stress was significantly reduced by applying the effective fatigue stress of the present study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.161-168
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• 2018

This study is the analytical review on the inelastic region of CRC column strength curve. The inelastic region of CRC column strength curve is based on the Bleich theory and the maximum residual stress of $0.5{\sigma}_y$. This is somewhat conservative by considering the fact that the maximum residual stress of $0.3{\sigma}_y$ is well known. This study proposes column strength curve for nonlinear behavior of hot rolled structural steel members under axial force and tangent modulus Et, with the maximum residual stress of $0.3{\sigma}_y$ and compares them with those of CRC. The stress of the inelastic column under axial compression exceeds proportional limits and reaches yielding point before applied load render the column bent. The column strength curve that depends on gradually yielding state of section needs to be reviewed. In this study, it is derived that the critical load formular according to material yielding with the maximum residual stress of $0.5{\sigma}_y$ and compared with CRC column design curve.

• The Journal of Engineering Geology
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• v.32 no.4
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• pp.643-659
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• 2022

Geologic sequestration technologies such as CCS (carbon capture and storage), EGS (enhanced geothermal systems), and EOR (enhanced oil recovery) have been widely implemented in recent years, prompting evaluation of the mechanical stability of storage sites. As fluid injection can stimulate mechanical instability in storage layers by perturbing the stress state and pore pressure, poroelastic models considering various injection scenarios are required. In this study, we calculate the pore pressure, stress distribution, and vertical displacement along a surface using commercial finite element software (COMSOL); fault slips are subsequently simulated using PyLith, an open-source finite element software. The displacement fields, are obtained from PyLith is transferred back to COMSOL to determine changes in coseismic stresses and surface displacements. Our sequential use of COMSOL-PyLith-COMSOL for poroelastic modeling of fluid-injection and induced-earthquakes reveals large variations of pore pressure, vertical displacement, and Coulomb failure stress change during injection periods. On the other hand, the residual stress diffuses into the remote field after injection stops. This flow pattern suggests the necessity of numerical modeling and long-term monitoring, even after injection has stopped. We found that the time at which the Coulomb failure stress reaches the critical point greatly varies with the hydraulic and poroelastic properties (e.g., permeability and Biot-Willis coefficient) of the fault and injection layer. We suggest that an understanding of the detailed physical properties of the surrounding layer is important in selecting the injection site. Our numerical results showing the surface displacement and deviatoric stress distribution with different amounts of fault slip highlight the need to test more variable fault slip scenarios.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.795-805
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• 1994

This paper presents the analytical results for the prediction of elastical local buckling stress of fiber reinforced plastic (orthotropic) structural shapes manufactured from pultrusion process. In the derivation, existing Bleich's approach which was originally derived for the isotropic structural shapes was extended and non-dimensionalized parameters which can simplify the numerical calculations were adopted. Analytical results were compared with reported closed-form solutions and experimental results. It is graphically shown that the results can be used effectively to predict the local buckling stress of pultruded fiber reinforced plastic structural shapes. Numerical results were presented graphically to estimate the local buckling stress of various cross-sectional dimensions and lengths of columns. In addition, limits of width to thickness ratio of flange and web of pultruded structural shapes were suggested in which material failure or overall buckling occurs prior to local buckling.

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.131-139
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• 1992

The understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading is very important for life prediction of the air travel structures. Particularly, the retardation and arrest behavior of fatigue crack propagation by single tension overloading is essential to the understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading. Numerous studies of the retardation behavior have been performed, however investigations of the arrest behavior have not been enough yet. As for the arrest behavior, Willenborg had reported that the overload shut-off ratio $[R_{so}=(K_{OL})/K_{max})_{crack arrest}]$ had been the material constant, but recently several investigators have reported that the overload shut-off ratio depends upon the stress ratio. In this study, authors have investigated the effect of stress ratio on the threshold overload shut-off ratio to generate arrest of fatigue crack growth in high tensile aluminum alloy 7075-T735 which have used in material for air travel structures, It has been $-0.4\leqqR\leqq0.4$ till now, the region of stress ratio investigated. The threshold overload shut-off ratio has decreased as stress ratio has increased in overall region of -$-0.4\leqqR\leqq0.4$ and the linearity has been seen in this material. Moreover, the experimental equation between $R_{so}$ and R has been made; The relation has been $R_{so}=-R+2.6$.

• Journal of the Korean Geotechnical Society
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• v.29 no.10
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• pp.57-66
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• 2013

Societal interest on a faster transportation demands an increase of the train speed exceeding current operation speed of 350 km/h. To trace the pattern of variations in displacements and subsoil stresses in the concrete slab track system, finite element simulations were conducted. For a simple track-vehicle modeling, a mass-point system representing the moving train load was developed. Dynamic responses with various train speeds from 100 to 700 km/h were investigated. As train speeds increase the displacement at rail and subsoil increases nonlinearly, whereas significant dynamic amplification at the critical velocity has not been found. At low train speed, the velocity of elastic wave carrying elastic energy is faster than the train speed. At high train speed exceeding 400 km/h, however, the train speed is approximately identical to the elastic wave velocity. Nonlinearity in the stress history in subsoil is amplified with increasing train speeds, which may cause significant plastic strains in path-dependent subsoil materials.