• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.100-100
• /
• 2009

This paper is concerned with numerical analyses of residual stresses in welds and material's susceptibility to stress corrosion cracking (SCC) for the primary piping system in nuclear power plants: Both the dissimilar metal weld (DMW) for stainless steel to low alloy steel joints and the similar metal weld (SMW) for forged stainless steel to cast stainless steel joints are considered. Thermal elasto-plastic analyses using the finite element method (FEM) are performed to predict residual stresses generated in fabrication welding and its related processes for both the DMW and SMW, including effects of quenching for cast stainless steel piping, machining of the DMW root, and grinding of the SMW root. As a result, the effect of quenching should be included in the evaluation of residual stresses in the SMW for the cast stainless steel piping. It is deemed that residual stresses in both the DMW and SMW would not affect the SCC susceptibility of the welds providing that the welding processes are completed without any weld repair on the inside wall of the joint. However, the grinding process if performed on the safe-end to piping weld, would produce a high level of residual stresses in the inner surface region and thus a stress improvement process (e.g. buffing) should be considered to reduce susceptibilities to SCC.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.5
• /
• pp.561-565
• /
• 2010

Stainless steel sheets are widely used as structural materials for the manufacture of railroad cars and commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. For the fatigue design of gas welded joints such as fillet joints and plug joints, it is necessary to obtain information on the stress distribution at the weldment and the fatigue strength of the gas welded joints. Moreover the influence of the geometrical parameters corresponding to the gas welded joints on the stress distribution and fatigue strength must be evaluated. ${\Delta}P-N_f$ curves were obtained from the data recorded in fatigue tests. Using these results, the ${\Delta}P-N_f$ curves were rearranged according the relation between $\Delta\sigma-N_f$ and the maximum stress at the edge of the fillet welded joint.

• Journal of the Korean GEO-environmental Society
• /
• v.8 no.6
• /
• pp.77-83
• /
• 2007

In this study, deformation behavior of existing concrete face rockfill dam, which is raised to a certain height to enhance storage capacity or to improve hydraulic and hydrologic stability, is examined using numerical analysis method. The results obtained from FEM analysis show a possibility that additional fill at downstram slope of existing CFRD dam body may lead undesirable deformations and stresses in existing dam body, especially in face concrete, such as settlements in upper part and bulging in lower part, excessive bending moments, and eventualy tensile cracks. Therefore, in designing multi-staged raising construction of CFRD, it is essential to consider deformations and stresses to be developed within and between exisiting dam body and added parts due to additional fill, and to prepare a proper measure to prevent abnormal deformations and stresses in the dam body including added parts.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.12
• /
• pp.1153-1157
• /
• 2013

A steam turbine blade is one of the core parts in a power plant. It transforms steam energy into mechanical energy. It is installed on the rim of a rotor disk. Many failure cases have been reported at the final stage blades of a low-pressure (LP) turbine that is cyclically loaded by centrifugal force because of the repeated startups of the turbine. Therefore, to ensure the safety of an LP steam turbine blade, it is necessary to investigate the fatigue strength and life. In this study, the low cycle fatigue life of an LP steam turbine blade is evaluated based on actual damage analysis. To determine the crack initiation life of the final stage of a steam turbine, Neuber's rule is applied to elastic stresses by the finite element method to calculate the true strain amplitude. It is observed that the expected life and actual number of starts/stops of the blade were well matched.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.8 no.2
• /
• pp.87-100
• /
• 2006

A kinematically constrained microplane constitutive model is developed for intact granite. The model is verified by fitting the experimented data of Westerly granite and Bonnet granite. Using the model with the standard finite element method, the behavior of the intact granite subjected blasting impact is studied. What is studied includes the attenuation of the blasting waves, the size of the fractured zone and the effect of the charge condition to avoid overbreak of the rock mass. The model developed captures the energy loss due to the inelastic behavior and the microcracking of granite during blasting very well. The attenuation of the blasting waves calculated based on the model is much more than that based on the linear-elastic constitutive law. The size of damaged (or fractured) zone is calculated directly from the principal strain as blasting impact is spreading, not like in the case with the linear elasticity model.

• Journal of Navigation and Port Research
• /
• v.26 no.4
• /
• pp.435-440
• /
• 2002

The quantitative assessment of the effect of the residual stress on fracture behavior was executed by some experiment and numerical analysis. First of all, artificial residual stresses were imposed on CT(Compact Tension) specimens by local heating using gas torch, and an appropriate distribution of residual stresses was obtained by thermal elastic-plastic FE analysis. To certify the result of the FE analysis, an experimental measurement was performed in accordance with ASTM standard. Fracture toughness test was executed on the several types of specimens. The first type was the specimen without residual stresses, and the others had different peak value of compressive residual stress at crack front via controlling the heat flux. All the test results were presented on th J resistance(JR) curves and discussed to verify the effect of compressive residual stresses on fracture behavior.

• Journal of Korean Society of Steel Construction
• /
• v.10 no.3 s.36
• /
• pp.423-435
• /
• 1998

In this paper fatigue strength reduction of butt weld with penetration defect, which can be seen frequently in the steel bridge, was assessed quantitatively. S-N curves were derived and investigated through the constant amplitude fatigue test of fully or partially penetrated welded specimen made of SWS490 steel. The fracture mechanical method was applied in order to calculate the remaining fatigue life of the partially penetrated butt welds. The fatigue limit of the fully penetrated butt welds was higher than that of category A in AASHTO's fatigue design curves, and the slope of S-N curves with 5.57 was stiffer than that of other result for welded part generally accepted as 3. The fatigue strength of the partially Penetrated butt weld was strongly influenced by the size of lack of penetration, D. It decreased drastically with increasing D from 3.9 to 14.7mm. Fracture behaviour of the partially penetrated butt weld is able to be explained obviously from the beach mark test that a semi-elliptical surface crack with small a/c ratio initiates at a internal weld root and propagates through the weld metal. To estimate the fatigue life of the partially penetrated butt weld with fracture mechanics, stress intensity factors K of 3-dimensional semi-elliptical crack were calculated by appling finite elements method and fracture mechanics parameters such as C and m were derived through the fatigue test of CT-specimen. As a result, the fatigue lives obtained by using the fracture mechanical method agreed well with the experimental results. The results were applied to Sung-Su bridge collapsed due to penetration defects in butt weld of vertical member.

• Tunnel and Underground Space
• /
• v.18 no.1
• /
• pp.44-57
• /
• 2008

In this study, a 2D finite-element analysis, using the SEEP/W program, was carried out to estimate the amount of groundwater flawing into a tunnel, as well as the groundwater tables around wetland areas during and after a tunnel excavation through rock mass. Four sites along the Wonhyo-tunnel in Cheonseong Mountain (Gyeongnam, Korea) were analysed, where the model damain of the tunnel included both wetland and fault zone. The anisotropy of the hydraulic conductivities of the rock mass was calculated using the DFN model, and then used as an input parameter for the cantinuum model. Parametric study on the influencing factors was perofrmed to minimize uncertainties in the hydraulic properties. Moreover, the volumetric water content and hydraulic conductivity functions were applied ta the model to reflect the ability of a medium ta store and transport water under both saturated and unsaturated conditions. The conductivity of fault zone was assumed ta be $10^{-5}m/sec\;or\;10^{-6}m/sec$ and the conductivity of grouting zone was assumed as 1/10, 1/50 or 1/100 of the conductivity of rock mass. Totally $6{\sim}8$ cases of transient flow simulation were peformed at each site. The hydraulic conductivities of fault zone showed a significant influence on groundwater inflow when the fault zone crossed the tunnel. Also, groundwater table around wetland maintained in case that the hydraulic conductivity of grouting zone was reduced ta be less than 1/50 of the hydraulic conductivity of rock mass.

• Korean Journal of Agricultural Science
• /
• v.23 no.1
• /
• pp.25-38
• /
• 1996

To investigate the stability problem of irrigation-drainage channel excavation slope on soft ground, analyzed the behavior of the soft ground with excavation slope by the limit equilibrium method and the finite element method, and compared with field tests. The results of this study were summarized as follows; 1. When rapid drawdown the water level, the crack was occurred by the effect of the excess pore water pressure, and the pore water pressure was decreased slowly. 2. As the width of excavation was larger, the crack width was larger. And, excavated depth was deeper, the progressive failure was appeared. 3. When the soft ground excavation was small-scale, the minimum safety factor was more effected by cohesion(1.0, 1.5, 2.0, 2.5, 3.0) than excavated slope inclination(1:l, 1:1.5, 1:2). 4. As excavation was progressed, the settlement occurred on the top-slope due to plastic domain, and heaving was occurred at the bottom of excavation. 5. The maximum shear stress was appeared greatly as the base part of slope went down. Because of the increase of the maximum shear stress, tension area occurred and local failure possibility was increased. 6. As the excavation depth was increased, the maximum shear strain was appeared greatly at the base of slope and distribution pattern was concentrated beneath the middle of slope.

• Journal of Korean Society of Steel Construction
• /
• v.9 no.4 s.33
• /
• pp.697-705
• /
• 1997

The conventional preflex beams are designed by the method of paritial prestressing and allow the tensile stresses at the lower concrete of beams. As a consequence, most of preflex beams experience the tensile cracks under the service loads. This study was conducted to develop the most effective preflex beams, which do not allow tensile stress under the service load, by introducing additional prestressing called 'represtressing' at the lower concrete of beams. The objective of the study was accomplished by developing a computer analysis and design program and conducting experiments. Using the developed computer program, standard sections of the represtressed preflex beams were determined by computer modeling. In the experiment, two actual size of represtressed beams were tested under the imitated service loads. The results of test have shown that the performance of the represtressed preflex beams is generally excellent. A remarkable improvement was made in the design of preflex composite beams. Since the represtressed preflex beams(RPF) do not experience the tensile cracks under the service loads, the use of this beam for the bridge structures will lead to easy bridge maintenance and management. Furthermore, due to the low beam depth, high clearance and economical design can be realized in the bridge design using RPF.