• Proceedings of the KSME Conference
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• 2007.05a
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• pp.108-113
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• 2007

In this report, stress corrosion cracking generation due to pipe material degradation in the primary stage of the nuclear power plant was investigated. Firstly, after artificially degrading the CF8A steel during 2, 4, and 6 months in actual temperature, $400^{\circ}C,$ assessed corrosion susceptibility of the degraded material following ASTM G5 standard. And next, the S.C.C. tests for the degraded material were conducted under the condition of $60^{\circ}C,$ 2wt.% H2BO3+Li70H solution, 0.8 oy. From the results, Corrosion rates linearly increased with degradation period and solution temperature increase. And both the raw material and the degraded materials were not failed in the S.C.C. test condition. In spite of long time test (about 3,900 hrs) under S.C.C. condition, surface pits or surface corrosion by the electro chemical reaction were not observed. And also, even though the nondestructive DCPD and ACPD methods were applied to on-line monitor the S.C.C. failure processes it was impossible because the surface pits and cracks were not generated.

• Journal of the Korea Safety Management & Science
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• v.2 no.4
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• pp.33-43
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• 2000

The consequence analysis for the unconfined vapor cloud explosion(UVCE) accident by the continuous release of butane vapor was performed and effects of process parameters on consequences were analyzed in standard conditions. For the case of continuous release(87.8 kg/s) of butane vapor at 8 m elevated height in the debutanizing process of tile naphtha cracking plant operating at 877 kPa ＆ 346.75 K, we found that combustion ranges of dispersed vapor estimated by HMP model were 11.2~120.2 m and overpressures estimated by TNT equivalency model at 200 m were about 37.35~55.1 kPa. Also, overpressures estimated by Model UVCE I based on advective travel time to $X_{LFL}$ were smaller than those estimated by Model UVCE IIbased on real travel time between $X_{UFL}$ and $X_{LFL}$. At the same time, damage intensities at 200 m and effect ranges by overpressure could be predicted. Furthermore, simulation results showed that effects of operating pressures on consequences were larger than those of operating temperatures and results of accidents were increased with increasing operating pressures. At this time, sensitivities of overpressures for UVCE accident by the continuous release were about 5 kPa/atm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6D
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• pp.819-829
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• 2008

Fatigue cracking occurs over long time period because dynamic strength of slab continuously decreases by vehicle loading repetitively applied to the concrete pavement. To more accurately predict the fatigue life of the concrete pavement, the stress due to environmental loading should be considered prior to calculating the stress due to the vehicle loading because the stress due to temperature and moisture distribution always exists within the slab. Accordingly, a new fatigue model considering the environmental loading was developed in this research by evaluating factors of existing fatigue models most widely used and by making data points from the models. The applicability of the new model was evaluated by performing a fatigue analysis on the general concrete pavement structure using local climatic and traffic conditions in Korea. It was concluded that the top-down cracking due to the tensile stress at top of the slab is dominant cause of the fatigue failure than the bottom-up cracking occurred at bottom of the slab. More advanced fatigue analysis considering vehicle speed is expected by developing this study.

• Structural Engineering and Mechanics
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• v.51 no.3
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• pp.487-502
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• 2014

In buildings structures, the flexural stiffness reduction of beams and columns due to concrete cracking plays an important role in the nonlinear load-deformation response of reinforced concrete structures under service loads. Most Seismic Design Codes do not precise effective stiffness to be used in seismic analysis for structures of reinforced concrete elements, therefore uncracked section properties are usually considered in computing structural stiffness. But, uncracked stiffness will never be fully recovered during or after seismic response. In the present study, the effect of concrete cracking on the lateral response of structure has been taken into account. Totally 120 cases of 3 Dimensional Dynamic Analysis which considers the real and accidental torsional effects are performed using ETABS to determine the effective structural system across the height, which ensures the performance and the economic dimensions that achieve the saving in concrete and steel amounts thus achieve lower cost. The result findings exhibits that the dual system was the most efficient lateral load resisting system based on deflection criterion, as they yielded the least values of lateral displacements and inter-storey drifts. The shear wall system was the most economical lateral load resisting compared to moment resisting frame and dual system but they yielded the large values of lateral displacements in top storeys. Wall systems executes tremendous stiffness at the lower levels of the building, while moment frames typically restrain considerable deformations and provide significant energy dissipation under inelastic deformations at the upper levels. Cracking found to be more impact over moment resisting frames compared to the Shear wall systems. The behavior of various lateral load resisting systems with respect to time period, mode shapes, storey drift etc. are discussed in detail.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.33-36
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• 2014

Gasification of biomass produces syngas containing CO, $H_2$ and/or $CH_4$, which can then be converted into energy or value-added fuels. One of key issues for efficient gasification is to minimize tar concentration in the syngas for use in a final conversion device such as gas engine. This study investigated the decomposition of primary tar by catalytic cracking using char as catalyst, of which the feature can be integrated into a fixed bed gasifier design. The pyrolysis vapor containing tar from pyrolysis of wood at $500^{\circ}C$ was passed through a reactor filled with or without char at $800^{\circ}C$ for a residence time of 1, 3 or 5 sec. Then, the condensable vapor (water and tar) and gases were analyzed for the yields and elemental composition. Four types of char particles with different microscopic surface area and pore size distribution: wood, paddy straw, palm kernel shell and activated carbon. The results were analyzed for the mass and carbon yields of tar and the composition of product gases to conclude the effects of char types and residence time.

• Explosives and Blasting
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• v.32 no.3
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• pp.10-17
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• 2014

In this study, the effect of the hole spacing and the detonation delay time in the long hole blasting of two free surface rock mass on the variation of the principal strains in the vicinity of blasting holes is investigated by use of the finite element program, Visual FEA. The cross section perpendicular to blasting holes is modelled and the maximum principal strains at some major points in the cracking zone are examined. As a result, it was found that the maximum principal strain in the cracking zone becomes larger in the long hole blasting with the narrower hole spacing and the longer detonation delay time. The maximum principal strain was affected by the detonation position in charge hole.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.86-94
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7N01 spot-welded by pulse Nd : YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed : center line crack({TEX}$C_{C}${/TEX}), diagonal crack({TEX}$C_{D}${/TEX}), and U shape crack({TEX}$C_{U}${/TEX}). Also, HAZ crack({TEX}$C_{H}${/TEX}) was observed in the HAZ region, furthermore, mixing crack({TEX}$C_{M}${/TEX}) consisting of diagonal crack and HAZ crack was observed. White film was formed at th hot crack region in the fractured surface after it was immersed to 10% NaOH water. In the case of A5083 alloy, white films in {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack region were composed of low melting phases, {TEX}$Fe_{2}SiAl_{8}${/TEX} and eutectic phases, $Mg_2$Al$_3$ and $Mg_2$Si. Such films observed $CuAl_2$, {TEX}$Mg_{32}(Al,Zn)_{3}${/TEX}, MgZn$_2$, $Al_2$CuMg and $Mg_2$Si were observed in the whitely etched films near {TEX}$C_{C}${/TEX} crack and {TEX}$C_{D}${/TEX} crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Sim in the case of A7N01 alloy, respectively. The {TEX}$C_{C}${/TEX} and {TEX}$C_{D}${/TEX} cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of {TEX}$C_{M}${/TEX} crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The {TEX}$C_{U}${/TEX} crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification.

• Structural Engineering and Mechanics
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• v.54 no.2
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• pp.319-336
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• 2015

Life cycle performance of corrosion affected RC structures is an important and challenging issue for effective infrastructure management. The accurate condition assessment of corroded RC structures mainly depends on the effective evaluation of deterioration occurring in the structures. Structural performance deterioration caused by reinforcement corrosion is a complex phenomenon which is generally uncertain and non-decreasing. Therefore, a stochastic modelling such as the gamma process can be an effective tool to consider the temporal uncertainty associated with performance deterioration. This paper presents a time-dependent reliability analysis of corrosion affected RC structures associated bond strength degradation. Initially, an analytical model to evaluate cracking in the concrete cover and the associated loss of bond between the corroded steel and the surrounding cracked concrete is developed. The analytical results of cover surface cracking and bond strength deterioration are examined by experimental data available. Then the verified analytical results are used for the stochastic deterioration modelling, presented here as gamma process. The application of the proposed approach is illustrated with a numerical example. The results from the illustrative example show that the proposed approach is capable of assessing performance of the bond strength of concrete structures affected by reinforcement corrosion during their lifecycle.

• Journal of the Korean Applied Science and Technology
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• v.28 no.3
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• pp.345-350
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• 2011

Antioxidant agent, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane were prepared and investigated the antioxidant activity on recycled rubber mat manufactured with waste tire powder. Mechanical properties of rubber mat are influenced by many factor such as compounding ingredients and state of cure, process of rubber, and fillers. Our study aim is to investigate influence of antioxidant activities on ozone cracking and the thermal aging time. In this work, the degradation of recycled rubber mat was studied and suggested mechanism to involve two-type of degradation, thermal aging and cracking both of which can be contained antioxidant or non-antioxidant agent.

• Journal of Industrial Technology
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• v.7
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• pp.49-58
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• 1987

To investigate the effect of the Retrogression and Reaging (RRA) treatment on the strength and the stress corrosion cracking in AA 7039 the measurement of hardness, tensile properties and the time to failure in a constant rate method were measured. Transmission electron microscope was used to examine the microstructural changes within graln and grain boundary. The results show that the RRA treatment of the T6 condition results in a significant increase in the time to failure without sacrifying the original T6 strength. It is believed that high density and even distribution of precipitates in RRA condition were observed within grain so that the RRA condition could have similar strength to the T6 condition. The presence of fine dispersion of semicohernt ${\eta}^{\prime}$ transition phase is also believed to contribute to that effect. Examination of the grain boundary microstructure shows that the RRA treatments increases significantly the average size of the grain boundary preciptates. It is suggested that the benificial effect of the RRA treatment on the susceptibility to SCC be due to the increase in the size of grain boundary precipitates obtained during the retrogression treatment.