• Journal of Industrial Technology
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• v.18
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• pp.87-95
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• 1998

Cracking is considered to be one of the important factors in determining the durability of reinforced concrete structures. When the bending stress exceeds the modulus of rupture of the concrete, cracking form along the length of members. The total load is transferred across these cracks by the reinforcement, but the concrete between cracks is still capable of carrying stresses due to the bond between steel and concrete. This phenomenon is called the tension stiffening effect. The tension stiffening effect is affected by many variables, such as the bond stress, strength of concrete, interrocking of aggregate, type of steel, and dowel action of steel. Also, this tension stiffening effect is usually quite significant in beams under service loading, and must be taken into account in the calculation of deflection and crack widths. In this study, the experiment was carried out on types of specimen, strength of concrete, and steel ratio and finite element analysis were compared in terms of load-deflection relationship, crack pattern.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.13-19
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• 2013

This study examines thermal safety on three-way catalyst that dominates 70% among whole exhaust gas purification device in 2003. Three-way catalyst maintains high temperature in interior domain but maintains low temperature on outside surface. Therefore this device shows tensile stress on outside surface. Temperature distribution of three-way catalyst was acquired by thermal flow analysis for predicted thermal flow parameter. Thermal stress analysis for three-way catalysis was performed based on this temperature distribution. Thermal safety of three-way catalyst was estimated by strength reduction factor and failure probability.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.515-521
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• 2011

Small punch creep testing has received attention due to the convenience of using smaller specimens than those of conventional uniaxial creep tests, which enables creep testing on developing or currently operational components. However, precedent studies have shown that it is necessary to consider friction between the punch and specimen when computing uniaxial equivalent stress from a finite element model. In this study, small punch creep behaviors of AISI 316L stainless steel, which is widely used in high temperature-high pressure machineries, have been compared for the two different ceramic balls such as $Si_3N_4$ and $Al_2O_3$. The optimal range of the friction coefficient is 0.4~0.5 at $650^{\circ}C$ for the best fit between experimental and simulation data of AISI 316 L stainless steel. The higher the friction coefficient, the longer the creep rupture time is. Therefore, the type of ceramic ball used must be specified for standardization of small punch creep testing.

• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1570-1578
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• 2022

During a severe accident, steam generator (SG) tubes undergo rapid changes in the pressure and temperature. Therefore, an appropriate creep model to predict a short term creep damage is essential. In this paper, a novel creep model for Alloy 690 SG tube material was proposed. It is based on the theta (θ) projection method that can represent all three stages of the creep process. The original θ projection method poses a limitation owing to its inability to represent experimental creep curves for SG tube materials for a large strain rate in the tertiary creep region. Therefore, a new modified θ projection method is proposed; subsequently, a master curve for Alloy 690 SG material is also proposed to optimize the creep model parameters, θ_i (i = 1-5). To adapt the implicit creep scheme to the finite element code, a partial derivative of incremental creep with respect to the stress is necessary. Accordingly, creep model parameters with a strictly linear relationship with the stress and temperature were proposed. The effectiveness of the model was validated using a commercial finite element analysis software. The creep model can be applied to evaluate the creep rupture behavior of SG tubes in nuclear power plants.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.207-216
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• 2005

External confinement by CFS (Carbon Fiber Sheet) is a very effective retrofit method for the reinforced concrete columns subject to either static or seismic loads. For the reliable and cost-effective design of CFS, an accurate stress-strain model is required for CFS-confined concrete. In this paper, uniaxial compression test on short RC column with square section was performed. To evaluate the effect of confinement on the stress-strain relationship of CFS-confined concrete, CFS area ratio and tie area ratio are considered. Based on the experimental results, a stress-strain model is proposed for concrete confined by CFS wraps. In the development of the model, the method to compute the actual hoop strains in CFS jackets at the rupture was examined and resolved. Overall, the results of the model agree well with test data.

• Journal of radiological science and technology
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• v.33 no.2
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• pp.93-96
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• 2010

This study evaluates usefulness of the developed assistant device by taking projection of patellofemoral joint in emergency patients who were doubt posterior cruciate ligament injury in knee joint. The subjects of experiment were patients who visited Eul-Ji University Hospital due to knee injury from January 2006 to December 2006. Seventeen patients, who took the Knee post stress view, Knee merchant view, Knee Seo's view to use assistant device and Knee MRI. To make assistant device of $170{\times}50{\times}70\;cm$, we evaluated its usefulness by measuring posterior dislocation of tibia. Seo's view is more accurate to make judgment of posterior cruciate ligament injury than original knee post stress view. Interval difference of posterior dislocation of original knee post stress view is $6.17{\pm}3.04$ and Seo's view is $8.74{\pm}4.47$. The results show injury of patellofemoral joint, vertical fracture of patella and posterior cruciate ligament injury by taking a projection using Seo's view. Therefore, it is useful to take projection earlier than talometer and MRI in emergency patients who were doubt posterior cruciate ligament injury in knee joint.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.596-603
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• 2011

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

• Korean journal of food and cookery science
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• v.19 no.4
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• pp.511-520
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• 2003

This study was carried out to determine the effects of various contents of kiwifruit contents on the quality characteristics of mixed polysaccharide gels made from $\kappa$-carrageenan and locust bean gum. The color value, gelling temperature, melting temperature, break down rate, syneresis, rupture properties, TPA properties and sensory properties of mixed polysaccharide gels with various contents of kiwifruit contents were measured. As the kiwifruit contents was increased, the lightness (L), yellowness (b) and greenness (-a) of the mixed polysaccharide gels increased. There were no differences in the color values of gels during storage. As the kiwifruit content was increased, the gelling and melting temperatures of the mixed polysaccharide gels also increased. The mixed polysaccharide gels with high kiwifruit contents were difficult to melt, and it seemed that the addition of kiwifruit to the mixed polysaccharide gels could improve the thennal stability of the gels. The syneresis of the gel increased with increasing storage time, whereas the addition of kiwifruit to the gel resulted in suppression of syneresis. With regard to the rupture properties, stress, energy and strain, they were all decreased with increasing kiwifruit contents. The TPA properties, adhesiveness, hardness and chewiness increased and cohesiveness decreased with increasing kiwifruit contents. The results showed that the gel became tough and adhesive, and could be easily broken under small deformation, with increasing kiwifruit contents. The sensory evaluation showed that the green color, aroma, sweetness and sourness increased with increasing kiwifruit contents. The texture, adhesiveness, springiness and cohesiveness decreased, and brittleness and hardness increased, with increasing kiwifruit contents. The overall acceptability of the gel with 30% kiwifruit content was the highest. Thus, mixed polysaccharide gels made from kiwifruits could be useful, as the addition of kiwifruit to a mixed polysaccharide gel results in a good aroma, taste and stability, despite a lowering of the textural properties.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.76-84
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• 1998

In this 1st report, the relationship between pure creep properties and initial strain was studied and also its acoustic emission test was performed during creep test at 500, 600 and $700^{\circ}C$. And the applicability of the acoustic emission technique was investigated to analyze the quantitive relationship between all the pure properties (creep strength, creep repture time or creep life, steady state creep rate, total creep rate, creep strain, total creep strain, etc.) and the initial strains as well as to analyze AE properties during the pure creep loading condition.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.659-664
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• 2001

This paper was studied to effects of fatigue by low flexural load on micro structures and carbonation of mortar. Mortar specimens cured at various conditions were first subjected to bending repeated loads, and it was made clear that insufficient cure reduced fatigue resistance of them. Next, fatigue tests that the stress levels are lower than the ones of fatigue rupture were carried out, The effect of curing conditions in early age on carbonation was furthermore studied using the scale, and it was made clear that insufficient cure is also susceptible to carbonation of them. Finally, the reason for rapid carbonation of fatigued mortars insufficiently outed was discussed from the view point of changes in pore structure of them.