• Nuclear Engineering and Technology
• /
• v.30 no.6
• /
• pp.555-567
• /
• 1998

Alloy 600 and 690 steam generator tubes fabricated in Korea were evaluated by flare tests according to ASTM standards. The stress acting in the tube elements during the tests was predicted. All the tubes, including alleys 600 and 690, satisfied the requirement of a 30% or 35% O.D expansion. Flow curves obtained from the flare test were found to be higher in alloy 690 tubes than in alloy 600 ones. The difference between alloy 600 and 690 tubes increased gradually with flaring percentage (F.P,%). An effective stress corresponding to mean yield stress was introduced and calculated. It showed that the prediction values were in good agreement with the measured ones for all the 690 and 600 alloy tubes. It became possible to predict the amount of acting stresses within tubes during expansion process.

• The korean journal of orthodontics
• /
• v.27 no.5 s.64
• /
• pp.711-721
• /
• 1997

The purpose of this study was to investigate the stress distribution and intensity derived from the transpalatal lingual arch in the investing bone composed of photoelastic material(PL-3). The transpalatal lingual arch wire was deflected in the horizontal and vertical direction to give the various conditions. The two-dimensional photoelastic stress analysis was performed, and the stress distrebution was recored by photography The results were as follows: 1. In bilateral expansion, as horizontal deflection was singly applied, the stress was more concentrated on the root apex in square free end than round. In square free end, as vertical deflection was increased gradually, the black line meaning center of rotation moved inferiorly together with the increment of whole fringes. 2. In application of vertical deflection on anchorage side for unilateral expansion, the stress distribution that expansive force leaned to expansion side was observed. As vortical deflection increased, the extruding stress was observed on molar of expansion side. And as horizontal deflection increased, the tipping stress on the molar of anchorage side was observed. 3. In unilateral rotation with the asymmetric toe-in, the fringe appeared on the distal aspect of root apex.

• Journal of Surface Science and Engineering
• /
• v.29 no.2
• /
• pp.100-108
• /
• 1996

The internal stress of acidic electroless nickel deposits on zincated aluminum was determined by spiral contractometer. Several plating conditions such as inhibitor and complexing agent concentrations and pH affecting the internal stress were studied. The resulting intrinsic stress contribution to the total stress was discussed in terms of phosphorous content of the deposit, solution pH, and surface morphology. However, the most important was found to be thermal stress for the total stress of Al substrate, because of high thermal expansion coefficient of the aluminum substrate.

• Journal of Animal Reproduction and Biotechnology
• /
• v.34 no.2
• /
• pp.86-92
• /
• 2019

The aim of this study was to investigate effects of hyaluronidase during IVM on oocyte maturation, oxidative stress status, expression of cumulus expansion-related (PTX, pentraxin; GJA1, gap junction protein alpha 1; PTGS2, prostaglandin-endoperoxide synthase 2) and fatty acid metabolism-related (FADS1, delta-6 desaturase; FADS2, delta-5 desaturase; PPARα, peroxisome proliferator-activated receptor-alpha) mRNA, and embryonic development of porcine oocytes. The cumulus-oocyte complexes (COCs) were incubated with 0.1 mg/mL hyaluronidase for 44 h. Cumulus expansion was measured at 22 h after maturation. At 44 h after maturation, nuclear maturation, intracellular glutathione (GSH) and reactive oxygen species (ROS) levels were measured. Gene expression in cumulus cells was analyzed using real time PCR. The cleavage rate and blastocyst formation were evaluated at Day 2 and 7 after insemination. In results, expansion of cumulus cells was suppressed by treatment of hyaluronidase at 22 h after maturation. Intracellular GSH level was reduced by hyaluronidase treatment (p < 0.05). On the other hand, hyaluronidase increased ROS levels in oocytes (p < 0.05). Only PTGS2 mRNA was enhanced in COCs by hyaluronidase (p < 0.05). Population of oocytes reached at metaphase II stage was higher in control group than hyaluronidase treated group (p < 0.05). Both of cleavage rate and blastocyst formation were higher in control group than hyaluronidase group (p < 0.05). Our present results showed that developmental competence of porcine oocytes could be reduce by hyaluronidase via inducing oxidative stress during maturation process and it might be associated with prostaglandin synthesis. Therefore, we suggest that suppression of cumulus expansion of COCs could induce oxidative stress and decrease nuclear maturation via reduction of GSH synthesis and it caused to decrease developmental competence of mammalian oocytes.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.11
• /
• pp.2253-2261
• /
• 2002

Recently the hydroforming technology has drawn a lot of attention because of its capability to produce high quality and light weight parts. In the present study, the tube expansion - one of the simplest hydroforming processes, has been investigated in order to understand fundamental phenomena such as deformation characteristics and effect of process parameters. As a result, the most important process parameters, which determine the state of stress at the expanded zone, were found to be pressure and die displacement. If the stress becomes equi-axial tension at the zone, necking occurs at some distance from the weld line and develops into a crack along the axial direction. Some aspects of mechanical property measurements as well as distributions of hardness and microstructure are also discussed in this paper.

• Structural Engineering and Mechanics
• /
• v.8 no.4
• /
• pp.343-360
• /
• 1999

This work applies a structural analysis method based on an analytical solution from the Fourier series which transforms a half-range cosine expansion into a static solution involving plated structures. Two sub-matrices of in-plane and plate-bending problems are also formulated and coupled with the prescribed boundary conditions for these variables, thereby providing a convenient basis for a numerical solution. In addition, the plate connection are introduced by describing the connection between common boundary continuity and equilibrium. Moreover, a simple computation scheme is proposed. Numerical results are then compared with finite element results, demonstrating the numerical scheme's versatility and accuracy.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.10a
• /
• pp.809-814
• /
• 2002

Recently, the properties of early-age concrete are increasingly important because these properties directly influence the behavior of early-age concrete structures including stress and cracking behavior. Nevertheless, the studies on early-age concrete are limited to strength and temperature development. The purpose of present study is to propose a simple and rational method which can predict the stress and strain behavior of young age concrete. A series of test have been done to measure the temperature development, strains and stresses in concrete members. The concept of equivalent age was used to define the degree of hydration and this degree of hydration was used to calculate the strength and elastic modulus. The critical degree of hydration and thermal expansion coefficient were calculated using experimental data. It is seen that the critical degree of hydration range from 0.05 to 0.11 based on the measuring method. The thermal expansion coefficient was calculated based on the measured non-mechanical strain and it is found that the coefficient decreases slightly with the increase of age. The consideration of critical degree of hydration in calculating stresses gives more accurate results. The present study provides useful method and data in evaluating early-age behavior of concrete structure.

• Structural Engineering and Mechanics
• /
• v.64 no.6
• /
• pp.793-802
• /
• 2017

The damage of concrete due to the expansion of alkali-aggregate reaction (AAR) and thermal-chemical reactions affecting the strength of concrete is studied. The empirical equations for the variations of expansion of AAR, compressive strength and degradation of the modulus of elasticity with time, and compressive strength with degradation of the modulus of elasticity are proposed by analysing numerous experimental data. It is revealed that the expansion of AAR and compressive strength increase with time. The proposed combination of the time variations of chemical and mechanical parameters provides a satisfactory prediction of the concrete strength. Seismic analysis of the aged Koyna dam is conceded for two different long-term experimental data of concrete incorporating the proposed AAR based properties. The responses of aged Koyna dam reveal that the crest displacement of the Koyna dam significantly increases with time while the contour plots show that major principal stress at neck level reduces with time. As the modulus of elasticity decreases with ages the stress generated in the concrete structure get reduces. On the other hand with lesser value of modulus of elasticity the structure becomes more flexible and the crest displacement becomes very high that cause the seismic safety of the dam reduce.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.17 no.2
• /
• pp.173-178
• /
• 2011

Marine TEMA heat exchanger is the equipment to transfer the heat energy through both fluids that are enclosed separately by applying conduction and convection phenomena for a large vessels, Especially for heat exchanger working under the high temperature and high pressure, the expansion ratio should be taken into account other than under the low temperature and low pressure. This study was tried to find out the ideal expansion ratio through analyzing the elasto-plastic stress behavior of deformation while tubes are expanded with the finite element methods.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2013.11a
• /
• pp.34-35
• /
• 2013

In this study, the ultra high strength concrete which have 80, 130, 180MPa took the heat from 20℃ to 700℃ and the 0, 20% stress in normal condition's to evaluate stress-strain, residual compressive strength and thermal expansion deformation were evaluated. The heating speed of specimen was 0.77℃/min 20~50℃, 50℃ before the target temperature, and the other interval's heating speed was 1℃/min. As a result, the stress-strain curve of non-load specimen showed the liner behavior at high temperature when the specimen's strength increased more. If ultra high strength concrete got loads, its compressive strength tended to decrease different from the normal strength concrete. The thermal expansion deformation was expanded from a vitrification of quartz over 500℃. however, over the 600℃, it was shrinked because of the dehydration of the combined water.