• Corrosion Science and Technology
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• v.18 no.2
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• pp.49-54
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• 2019

The purpose of this paper is to present failure analysis, of the heat exchanger tube in a district heating system. SS304 stainless steel is used, as material for the heat exchanger tube. The heat exchanger operates in a soft water environment containing a small amount of chloride ions, and regularly repeats operation and standstill period. This causes concentration of chloride ions on the outer surface of the tube, as well as repeat of thermal expansion, and shrinkage of the tube. As a result of microscopic examination, cracks showed transgranular as well as branched propagation, and many pits were present, at the initiation point of each crack. Energy disperstive spectroscopy analysis showed Fe and O peak, as well as Cl peak, meaning that cracks were affected by Cl ion. Failure of the tube was caused by chloride-induced stress corrosion cracking by thermal stress, high temperature, and localized enrichment of chloride ions.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.3
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• pp.87-96
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• 1993

In this study, the peak stress of a fuillet in elastic structure was optimized to have minimum value by using quadratic isoparametric element. The method of auomatic gridding was also developed along with shape algorithm and design element technique was adopted in selecting design variables. The computer program developed was combined with the Hooke-Jeeves direct algorithm of optimization techniques in order to minimize the peak stress of the fillet. The imployment of design element technique significantly cut down computer time by the reduction in design variables, and the opitmum fillet shape with uniform minimum stress was obtained by varying design variables along x and y directions in improving the shape compared to other results. By using automatic gridding, in which Bezier surfaces and Coons surfaces of cubic interpolation were employed, the irregular boundary was removed resulting in smoother anbd more accurate fillet shape possessing uniform minimum stress.

• Journal of the Korean GEO-environmental Society
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• v.7 no.3
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• pp.31-41
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• 2006

The scale effect of specimens on the shear behavior of joints is studied by performing direct shear tests on six different sizes in Granite. The peak and residual shear stress, shear displacement, shear stiffness, and dilation angle are measured with the different normal stress(0.29~2.65MPa) and roughness parameters. It is also shown that both the joint roughness coefficient(JRC) and the joint compression strength(JCS) reduce with increasing joint length. A series of shear tests show about 56~67% reduction in peak shear stress, and about 18~44% in residual shear stress, respectively as the contact area of joint increases from 12.25 to $361cm^2$. Also the variation of dilation angle is $27^{\circ}$ at normal stress of 0.29 MPa and $6^{\circ}$ at normal stress of 2.65 MPa, respectively. The envelopes considering scale effect for JRC are made for the peak shear strength of rock joint in comparison with the Barton's equation.

• Journal of Technologic Dentistry
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• v.41 no.4
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• pp.295-301
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• 2019

Purpose: This study is for the prosthesis of dogs. Observe the occlusal relation between the dog's canine and carnassial teeth. The strength and the direction of the occlusal by 3D FEM analysis. Methods: The mandibular canine and carnassial of dogs were tested. The dog's skull was contact point confirmed by dental CAD. The skull of the dog was 3D modeled by CT. The 3D model was analyzed by ABAQUS. Opening and closing movement has been a force of 100N, 200N, 300N, 500N, 1000N, 1,500N. The peak von Mises stress distribution was confirmed. Results: As occlusal force increased, stress appeared to 1.34 MPa, 3.32 MPa, 5.00 MPa, 6.19 MPa, 5.58 MPa, 5.47 MPa in left canine. and Stress was seen at 2.10 MPa, 3.08 MPa, 3.89 MPa, 5.50 MPa, 7.04 MPa, 7.18 MPa in the right canine. Stress appeared at 2.41 MPa, 3.53 MPa, 5.15 MPa, 7.28 MPa, 31.26 MPa, 67.22 MPa in the left carnassial. and Stress was seen at 1.57 MPa, 2.96 MPa, 3.76 MPa, 6.01 MPa, 20.94 MPa, 64.38 MPa in the right carnassial. Conclusion: Peak von Mises stress values were found at the peak of the canine, the buccal of the central cusp of the carnassial, and the occlusal surface of the distal cusp.

• Journal of the Korean institute of surface engineering
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• v.42 no.5
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• pp.191-196
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• 2009

Nanocrystalline Cu thin films were electrodeposited from sulfate baths and investigated systematically the influences of $Cu^{2+}$ concentration and additives on current efficiency, residual stress, surface morphology, and XRD patterns of electrodeposited Cu film. Current efficiency was nearly 100% at from 0.2M to 1.0 M $Cu^{2+}$ concentration. but it was linearly increased with $Cu^{2+}$ concentration at less than 0.2M. The residual stress was observed in range of 7.9 to 18.4 MPa and tensile stress mode. Dendritic and powdered form was obtained at below 0.1 M. As increased with $Cu^{2+}$ concentration in solution, the main peak in the XRD pattern shifted (111) and (220) from (200). In the other hand, all about 100% current efficiency observed in all additive concentration systems, and residual stress observed in range of 20.4 to 26.3 MPa tensile stress. The condition 5(Ultra make-up - 10 ml/l, Ulta A - 0.5ml/l, Ultr B - 0.5 ml/l) was good surface morphology, and fcc(111) peak in XRD patterns increased with increasing additive concentration.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.2
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• pp.92-100
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• 2016

Reliability analysis of tripod support structure for offshore wind turbine was performed. Extreme distribution function of peak response due to wind and wave loads was estimated by applying peak over threshold(POT) method. Then, stress based limit state function was defined by using maximum stress of support structure which was obtained by multiplying beam stress and concentration factor. The reliability analysis result was compared when maximum stress was calculated from shell element. Reliability index was evaluated using first order reliability method(FORM).

• Computers and Concrete
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• v.12 no.4
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• pp.499-518
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• 2013

Fiber reinforced polymer (FRP) jackets have been widely used as an effective tool for the strengthening and rehabilitation of concrete structures, especially damaged concrete columns. Therefore, a clear understanding of the compressive behavior of FRP-confined concrete is essential. The objective of this paper is to develop a simple efficient method for predicting the compressive strength, the axial strain at the peak stress, and the stress-strain relationship of FRP-confined concrete. In this method, a compressive strength model is established based on Jefferson's failure surface. With the proposed strength model, the strength of FRP-confined concrete can be estimated more precisely. The axial strain at the peak stress is then evaluated using a damage-based formula. Finally, a modified stress-strain relationship is derived based on Lam and Teng's model. The validity of the proposed compressive strength and strain models and the modified stress-strain relationship is verified with a wide range of experimental results collected from the research literature and obtained from the self-conducted test. It can be concluded that, as a competitive alternative, the proposed method can be used to predict the compressive behavior of FRP-confined concrete with reasonable accuracy.

• Geomechanics and Engineering
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• v.24 no.5
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• pp.479-490
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• 2021

Pre-drainage of groundwater in the roof aquifer by boreholes is the main method for prevention of roof water disaster, and the drop in the water level during the drainage leads to the variation of the local stress in the overlying strata. Based on a multitude of boreholes for groundwater drainage from aquifer above the 1303 mining face of Longyun Coal Mine, theoretical analysis and numerical simulation are used to investigate the local stress variation in the process of borehole drainage. The results show that due to the drop in the water level of the roof aquifer during the drainage, the stress around the borehole gradually evolved. From the center of the borehole to the outside, a stress-relaxed zone, a stress-elevated zone, and a stress-recovered zone are sequentially formed. Along with the expansion of drainage influence, the stress peak in the stress-elevated zone also moves to the outside. When the radius of influence develops to the maximum, the stress peak position no longer moves outward. When the coal mining face advances to the drainage influence range, the abutment pressure in front of the mining face is superimposed with the high local stress around the borehole, which increases the risk of stress concentration. The present study provides a reference for the stress concentration caused by borehole drainage, which can be potentially utilized in the optimal arrangement of drainage boreholes in underground mining.

• Proceedings of the KSPS conference
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• 2004.05a
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• pp.161-163
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• 2004

This study concerns the constraints of English Poetic Fixed Meter. In English poems, the metrical pattern doesn't always match the linguistic stress on the lines. These mismatches are found differently among the poets. For the lexical stress mismatched with the weak metrical position, ${\ast}W{\Rightarrow}$ Strength is established by the concept of the strong syllable. The peaked monosyllabic word mismatched with weak metrical position is divided according to which side of the boundary of a phonological domain it is adjacent to. In most poets, ${\ast}$Peak] is ranked higher than ${\ast}$[Peak. In Shakespeare, Adjacency Constraint is ranked higher than ${\ast}$Peak].

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.164-168
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• 1993

Grinding of 3mol% Y-TZP enhanced the texturing of t-ZrO2, which is represented by the increased I(002)t/I(200)t peak intensity ratio, and an asymetric broadening of (111)t peak. The degree of texturing and asymetric broadening depended on a seversity of grinding. The asymetric (111)t peak broadening was resulted by the formation of r-ZrO2. When aged at 25$0^{\circ}C$ for 120h, r-ZrO2 transformed to t-ZrO2 due to the relief of stressed surface area and the amount of tlongrightarrowm transformation inversely varied with the I(002)t/I(200)t. The inverse dependence was interpreted by that the degree of texturing determines the magnitude of residual surface stress and the lattice relaxation of t-ZrO2, which causes the low temperature degradation, is retarded as the residual stress becomes greater.