• Journal of the Korea Concrete Institute
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• v.19 no.2
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• pp.135-144
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• 2007

Recently, fiber-reinforced plastic(FRP) wraps are blown as an effective material for the enhancement and rehabilitation of aged concrete structures. The purpose of this investigation is to experimentally investigate behavior of concrete cylinder wrapped with FRP materials. Experimental parameters include compressive strength of concrete cylinder, FRP material, and confinement ratio. This paper presents the results of experimental studies on the performance of concrete cylinder specimens externally wrapped with aramid, carbon and glass fiber reinforced Polymer sheets. Test specimens were loaded in uniaxial compression. Axial load, axial and lateral strains were investigated to evaluate the stress-strain behavior, ultimate strength ultimate strain etc. Test results showed that the concrete strength and confinement ratio, defined as the ratio of transverse confinement stress and transverse strain were the most influential factors affecting the stress-strain behavior of confined concrete. More FRP layers showed the better confinement by increasing the compressive strength of test cylinders. In case of test cylinders with higher compressive strength, FRP wraps increased the compressive strength but decreased the compressive sham of concrete test cylinders, that resulted in prominent brittle failure mode. The failure of confined concrete was induced by the rupture of FRP material at the stain, being much smaller than the ultimate strain of FRP material.

• Journal of Welding and Joining
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• v.33 no.4
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• pp.30-36
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• 2015

Austenite stainless steel(SA213-TP347H) has widely been used for the superheater & reheater tube in USC(ultra-supercritica) coal boiler because of its high creep rupture strength and anti-oxidation. But recently, the short-term failures have happened frequently in heat affected zone for only 4,000~15,000hours of service. Many investigations have been conducted to understand the failure mechanism. The root cause of failure was comfirmed to "strain induce participation hardening crack" or "reheat cracking". This mechanism often occurred due to weld residual stress and precipitation of the Cr, Nb carbides in the stabilized stainless steel such as TP347H. This paper presents an analysis of failure tube and effect of the sample tubes that conducting stabilizing heat treatment in site after 11,380hours & 16,961hours of service. Visual inspection was performed. In addition, microscopic characteristics was identified by O.M, SEM, and hardness test was carried out to find out the heat treatment effects. Failures seem to happen because of being not conducted stabilizing heat treatment in site. And another cause is inadequate weld parameter such as pass, ampere, voltage, inter-pass temperature. Thus, this paper has the purpose to describe that how to prevent similar failures in those weld-joints.

• Journal of the Korean Wood Science and Technology
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• v.18 no.2
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• pp.67-78
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• 1990

This study was performed to determine the characteristics of physical and mechanical properties of domestic wood based materials; plywood, particleboard, medium density fiberboard. Main items of tested properties were panel size, moisture content, water absorption, linear expansion and thickness swelling, glue bond shear strength, bending properties(stress at proportional limit, modulus of rupture. modulus of elasticity), tensile strength, screw holding strength, and internal bond as neccessary. the results were discussed mainly with Korean Standards. The obtained conclusions are as follows; 1. Length and width of 3mm thin plywood(3-ply) and 12mm thick plywood(7-ply) were satished with KS-standard, but thicknesses of these panels were not- passed tolerance limit except one of eight makers. 2. Length and width of particleboard and medium density fiberboard were greater than the tolerance limit value of KS standard, but the thicknesses of these panels were passed this value. 3. Moisture contents of 12mm thick and 3mm thin plywood were satisfied with KS-standard except one mill made 3mm thin plywood. 4. Moisture absortion of plywood was not passed tolerance limit of KS-standard but particleboard was satisfied with this standard value. 5. Dry and wet shear strengths in glue bond of 3mm thin plywood were not reached to KS-standard, but those of 12mm thick plywood were sufficiently satisfied with KS standrad. 6. Modulus of ruptures, parallel to grain and perpendicular to grain of plywood, and particleboard and medium density fiberboard were satisfied with KS-standard. 7. Tensile strengths, parallel to grain and perpendicular to grain of plywood were satisfied with allowance stress of US product standard PS 1-74. 8. Screw holding strength of particleboard was not reached to KS standard, but internal bond was satisfied with KS standard.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.138-146
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• 2013

The present paper provides the elastic stress intensity factors(SIFs) of thick-walled cylinder with non-idealized circumferential through-wall cracks. For estimating these elastic SIFs, the systematic three-dimensional(3D) elastic finite element(FE) analyses were performed. In order to consider practical shape of thick-walled cylinder and non-idealized circumferential through-wall crack, the values of thickness of cylinder, reference crack length and crack length ratio were systematically varied. As for loading conditions, axial tension, global bending and internal pressure were considered. In particular, in order to calculate the SIFs of thick-walled cylinder with non-idealized circumferential through-wall crack from those of thick-walled cylinder with idealized circumferential through-wall crack, the correction factor representing the effect of non-idealized crack on the SIFs were proposed in this paper. The present results can be applied to accurately evaluate the rupture probabilities of nuclear piping considering actual crack growth behaviors.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.40-45
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• 2008

There exist many types of pipe and component fatigue through vibrations, thermal fatigues or shifting. In some cases of thermal stratification/thermal fatigue, pipes & components are receiving thermal stress by means of material expansion and shrinkage by continuous thermal repetitive variation. Small cracks initially occur on the inside surface by thermal stress. These cracks grow in depth the pipe wall and finally come to a rupture. Pipe parts of susceptibility to thermal stratification and thermal fatigue are now being examined by conventional UT(ultrasonic test) as volumetric examination. It is difficult to fully satisfy the code & standards requirements because 3" weldolet weldments of RCS 16" pipe to 3" branch connection lines have complex structural shape. To solve the problems of conventional UT examination, we made a realistic mock-up and UT calibration block. We performed a simulation of phased array UT utilizing CIVA as NDE(Non-Destructive Examination) simulation software. Also we designed phased array UT transducer and wedge, optimal frequency by using simulation data. We performed phased array UT experiment through mock-up including artificial flaws(notch). The phased array UT technique is finally developed to improve the reliability of ultrasonic test at RCS 16" pipe to 3" branch connection weld.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.90-98
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• 2018

Recently, various reinforced concrete joints have been used in reinforced concrete structures. Therefore, it is important to grasp the tensile properties of the spliced rebar. In this study, uniaxial tensile tests were conducted on Grade 60 D22(#7), D29(#9), and two kinds of couplers manufactured according to ASTM A615 standard for evaluating ductility of coupler joints. The strain was measured using an image processing method more accurate and capable of measuring at various points freely. As the result of uniaxial tensile test, it was possible to calculate the stress-strain relationship and the longitudinal strain distribution according to the stress stages and it was founded that the average strain becomes lower as more occupying the coupler joint portions in the same gauge length. In addition, the empirical equations are proposed to account for the effect of the length of the coupler on the ultimate strain and the rupture strain.

• Journal of the Korean Wood Science and Technology
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• v.13 no.4
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• pp.67-72
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• 1985

To improve the bending strength of sawdustboard, verious resin contents of 10, 13, 16, and 19% were applied to the thin shell (face layer) composed with wire net or not. The shell effect of sawdust and wire net composition formed with core sawdustboard were evaluated. Forcusing on the effects of wire net composition and noncomposition including a comparison with chipboard and veneer complyboard, bending properties (Modulus of rupture (MOR), Modulus of elasticity (MOE), Stress at proportional limit ($S_{pl}$). Work to maximum load ($W_{ml}$))were analyzed and discussed. 1. In modulus of rutpute, veneer comply was the highest (621.5 kg/$cm^2$), and next decreasing order was wire net composition (159.1 kg/$cm^2$), chipboard (81.75 kg/$cm^2$), and wire net noncomposition (76.21 kg/$cm^2$) as in modulus of elasticity, work to maximum load, except for stress at proportional limit. 2. The highly significant effects were shown in both wire net composition and noncomposition, at the same time wire net composition exceeded two times of noncomposition throughout resin contents in bending properties. Chipboard was similar to the mean or 16% resin content in noncomposirion. 3. Every board in wire net composition above 10% resin content was beyond 100 kg/$cm^2$ in MOR, minimum allowable strength for structural use according to KS F 3104. In conclusion, the feasibility for improving the bending strength of weak sawdustboard by wire net composed shell was offered.

• Journal of the Korean Wood Science and Technology
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• v.43 no.1
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• pp.36-42
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• 2015

This study examined true modulus of elasticity (MOE) and modulus of rigidity (G) for domestic woods with different slenderness ratios (L/D) using the static bending and stress wave tests. Bending properties of small clear wood specimen of three domestic wood species were determined at 12% moisture content. The results of this study indicated that both MOR and MOE of domestic woods were affected by the slenderness ratio. As the slenderness ratio increased, MOR and MOE increased. G and true MOE of domestic timber beams were obtained at different slenderness ratios by flexure test and stress wave test. The values reported here can be useful if these species woods are used for structural purposes. However, the reported values are only indicative and do not represent the true average of wood species due to the limited number of specimens tested.

• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.31-36
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• 2009

This paper focuses on techniques of improving refinery reliability, availability, and profitability. Our team developed a corrosion control document(CCD) for processing of the crude distillation unit(CDU). Recent study shows the loss due to corrosion in US is around $276 billion. It's a big concern for both managers and engineers of refinery industry. The CCD consists of numerous parts namely damage mechanism(DM), design data, critical reliability variable(CRV), guidelines, etc. The first step in the development of CCD is to build material selection diagram(MSD). Damage mechanisms affecting equipments and process need to be chosen carefully based on API 571. The selected nine DM from API 571 are (1) creep/stress rupture, (2) fuel ash corrosion, (3) oxidation, (4) high temperature sulfidation, (5) naphthenic acid corrosion, (6) hydrochloric acid(HCL) corrosion, (7) ammonium chloride(salt) corrosion, (8) wet $H_2S$ corrosion, and (9) ammonia stress corrosion cracking. Each DM related to corrosion of CDU process was selected by design data, P&ID, PFD, corrosion loop, flow of process, equipment's history, and experience. Operating variables affecting severity of DM are selected in initial stage of CRV. We propose the guidelines for reliability of equipments based on CRV. The CCD has been developed on the basis of the corrosion control in refinery industry. It also improves the safety of refinery process and reduces the cost of corrosion greatly.

• Journal of Korean Neurosurgical Society
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• v.62 no.2
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• pp.183-192
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• 2019

Objective : The objective of this study was to analyze patient-specific blood flow in ruptured aneurysms using obtained non-Newtonian viscosity and to observe associated hemodynamic features and morphological effects. Methods : Five patients with acute subarachnoid hemorrhage caused by ruptured posterior communicating artery aneurysms were included in the study. Patients' blood samples were measured immediately after enrollment. Computational fluid dynamics (CFD) was conducted to evaluate viscosity distributions and wall shear stress (WSS) distributions using a patient-specific geometric model and shear-thinning viscosity properties. Results : Substantial viscosity change was found at the dome of the aneurysms studied when applying non-Newtonian blood viscosity measured at peak-systole and end-diastole. The maximal WSS of the non-Newtonian model on an aneurysm at peak-systole was approximately 16% lower compared to Newtonian fluid, and most of the hemodynamic features of Newtonian flow at the aneurysms were higher, except for minimal WSS value. However, the differences between the Newtonian and non-Newtonian flow were not statistically significant. Rupture point of an aneurysm showed low WSS regardless of Newtonian or non-Newtonian CFD analyses. Conclusion : By using measured non-Newtonian viscosity and geometry on patient-specific CFD analysis, morphologic differences in hemodynamic features, such as changes in whole blood viscosity and WSS, were observed. Therefore, measured non-Newtonian viscosity might be possibly useful to obtain patient-specific hemodynamic and morphologic result.