• Structural Engineering and Mechanics
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• v.91 no.2
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• pp.135-147
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• 2024

The objective of this study is to analyze, using the finite element method, the durability of damaged and repaired structures under the effect of mechanical loading coupled with environmental conditions (water absorption and/or temperature). The study is based on the hybrid patch repair technique, considering several parameters based on the J integral to observe the behavior of the adhesive in transferring load from a damaged plate to the repair patch. The results clearly show that water absorption and increased temperature cause degradation of the mechanical properties of the adhesive, leading to an increase in its plasticization, which is beneficial for the assembly's strength. However, the degradation of the adhesive's properties due to aging in the repair results in poor load transfer from the damaged area to the patch. The findings of this study allowed the authors to conclude that the [0°]8 sequence consistently offers the best performance, with the lowest J integral values and superior crack resistance. The lowest the J integral for the [0°]8 stacking sequence is typically 3-7% lower than that of the [0/-45/45/90]S and [0/-45/90/45]S sequences at elevated temperatures. At 60℃, the J integral increases by approximately 3-6% compared to 40℃ and 20, depending on the aging duration and stacking sequences.

• Korean Journal of Materials Research
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• v.27 no.10
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• pp.524-529
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• 2017

The effect of strain aging on the tensile properties of API X70 linepipe steel was investigated in this study. The API X70 linepipe steel was fabricated by controlled rolling and accelerated cooling processes, and the microstructure was analyzed using optical and scanning electron microscopes and electron backscatter diffraction. Strain aging tests consisting of 1 % pre-strain and thermal aging at $200^{\circ}C$ and $250^{\circ}C$ were conducted to simulate U-forming, O-forming, Expansion(UOE) pipe forming and anti-corrosion coating processes. The API X70 linepipe steel was composed of polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite whose volume fraction was dependent on the chemical composition and process conditions. As the thermal aging temperature increased, the steel specimens showed more clearly discontinuous type yielding behavior in the tensile stress-strain curve due to the formation of a Cottrell atmosphere. After pre-strain and thermal aging, the yield and tensile strengths increased and the yield-to-tensile strength ratio decreased because yielding and aging behaviors significantly affected work hardening. On the other hand, uniform and total elongations decreased after pre-strain and thermal aging since dislocation gliding was restricted by increased dislocation density after a 1 % pre-strain.

• Korean Institute of Interior Design Journal
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• v.22 no.5
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• pp.188-198
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• 2013

Advancement toward aging society has presented the importance of house planning in consideration of the elderly, increasing the necessity of such planning. Therefore the importance of indoor design guideline for elderly houses has been stressed and the understanding of the aging in regard to this trend will create more mature spaces. In line with this trend the purpose of this study is to study the medical factors related with bathroom interior design guidelines of the existing elderly houses from the viewpoint of deteriorating physical functions due to aging process. In order to research the deterioration of physical functions due to aging literatures of medical and exercise physiology were used and concerning the existing bathroom design guidelines for the aged people, the guideline items of behavior facilitation, physiological maintenance and perceptual maintenance aspects out of Murtha & Lee's user benefit criteria(1976) related with physical functions were selected to research in relation with the knowledge about the deterioration phenomena of physical functions. Physical aging and deterioration aspects were classified from the viewpoint of musculoskeletal disorder, cardiovascular disorder, respiratory disorder, gastronomy disorder, urology disorder, somatosensory disorder, endocrine disorder, immune disorder, nervous disorder and skin diseases and these were utilized in interpreting total 100 items of bathroom design guideline. Because bathroom is the space where many physical movements are done, it had the closest relationship with the deterioration of musculoskeletal health in general and as bathroom is the space where people use water and feel the difference in temperature and moisture more than other spaces, deterioration of skin and somatosensory health had the next closest relationship. The result of this study revealed that regarding the deterioration of physical functions of the elderly people in aspect of their perceptibility as designers will design creatively and sincerely based on its relationship with nervous system in future, the result of this study will be used to develop better spatial designs efficiently to meet for the aging society.

• Korean Journal of Materials Research
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• v.18 no.5
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• pp.266-271
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• 2008

Magnesium alloys are alloyed with rare earth elements (Re, Ca, Sr) due to the limited use of magnesium in high-temperature conditions. In this study, the influences of Zr and Zn on the aging behavior of a Mg-Nd-Y alloy were investigated. magnesium alloys containing R.E elements require aging treatments Specifically, Nd, Y and Zr are commonly used for high-temperature magnesium alloys. Various aging treatments were conducted at temperatures of 200, 250 and $300^{\circ}C$ for 0.5, 1, 3, 6, and 10 hours in order to examine the microstructural changes and mechanical properties at a high temperature ($150^{\circ}C$). Hardness and high-temperature ($150^{\circ}C$) tensile tests were carried out under various aging conditions in order to investigate the effects of an aging treatment on the mechanical properties of a Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy. The maximum hardness was 67Hv; this was achieved after aging at $250^{\circ}C$ for 3 hours. The maximum tensile, yield strength and elongation at $150^{\circ}C$ were 237MPa, 145MPa and 13.6%, respectively, at $250^{\circ}C$ for 3 hours. The strengths of the Mg-3.05Nd-2.06Y-1.13Zr-0.34Zn alloy increased as the aging time increased to 3 hours at $250^{\circ}C$ This is attributed to the precipitation of a Nd-rich phase, a Zr-rich phase and $Mg_3Y_2Zn_3$.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.133-137
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• 2003

The effect of Bi additions to the eutectic Sn-3.5Ag solder alloy on the growth kinetics of the intermetallic compound (IMC) layers during solid-state aging of Sn-Ag-Bi/Cu solder joints has been Investigated. The Bi additions enhanced the growth rate of the total IMC layer comprising of $Cu_6Sn_5$ and $Cu_3Sn$ sublayers. This enhanced IMC growth rate was primarily due to the rapid increase In the growth rate of $Cu_6Sn_5$ sublayer. The growth rate of $Cu_3Sn$ sublayers was little influenced and appeared to be retarded by the Bi additions. The observed growth behavior of $Cu_6Sn_5$ and $Cu_3Sn$ sublayers could be understood if the interfacial reaction barrier at the $Cu_6Sn_5/solder$ interface were reduced by the segregation of Bi at the interface.

• Journal of Biomedical Engineering Research
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• v.15 no.4
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• pp.389-394
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• 1994

The age-hardening behavior and the structural changes in a commercial dental Au-Ag-Cu-Pd alloy were investigated by means of hardness test, optical and scanning electron microscopic observation, energy dispersive spectroscopy and X-ray diffraction study. The drastic reduction in hardness by prolonged aging occurred after a rapid increase in hardness at the initial stage by the isothermal aging at $350^{\circ}C$. This softening was due to the broad precipitates formation of the lamellar structure which was composed of the f.c.t. AuCu I ordered f.c.t. phase containing Pd and the f.c.c. Ag-rich $\alpha$1 solid solution f.c.c.phase containing Au.

• Sleep Medicine and Psychophysiology
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• v.8 no.1
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• pp.18-21
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• 2001

The change of sleep pattern is one of the most often altered normal physiological functions in elderly people. Besides normal change of sleep, insomnia and sleep apnea syndrome (SAS) are (one of) the main complaints. In addition, parasomnia is also frequent in this age group. Several parasomnias frequently found in the elderly are reviewed. Periodic limb movements in sleep (PLMS), restless legs syndrome (RLS), and REM sleep behavior disorder are the most frequent parasomnias in old age. Most parasomnias could be diagnosed by polysomnography, and be treated easily. Therefore, early and precise diagnosis and management for parasomnia in aging people are needed.

• Proceedings of the KIEE Conference
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• 2005.07e
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• pp.82-84
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• 2005

In a transformer, thermal stress is the most influential parameter affecting the aging behavior of insulation system. The aging behavior of insulation system in transformer is determined mainly by the thermal conditions inside the transformer. The thermal stress on the insulation system may occur from operation in a high temperature caused by overloading or local overheating. Thus, this paper investigated the condition monitoring of insulation condition in thermally accelerated aged transformer oils by in-situ sensor. The condition of aged samples was investigated by measurements of relative permittivity i.e. capacitance change by capacitive sensor. Results from the experiments are presented in this paper.

• Computers and Concrete
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• v.17 no.6
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• pp.703-721
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• 2016

A novel approach to modeling concrete behavior at the stage of its maturing is presented in this paper. This approach assumes that at any point in the structure, concrete is composed of a set of layers that are activated in time layer by layer, based on amount of released heat that is produced during process of the concrete's maturing. This allows one to assume that each newly created layer has nominal stiffness moduli and tensile/compressive strengths. Hence introduction of explicit stiffness moduli and tensile/compressive strength dependencies on time, or equivalent time state parameter, is not needed. Analysis of plain concrete (PC) and reinforced concrete (RC) structures, especially massive ones, subjected to any kind of straining in their early stage of existence, mostly due to external loads but especially by thermal loading and shrinkage, is the goal of the approach. In this article a simple elasto-plastic softening model with creep is used for each layer and a general layered model behavior is illustrated on one-dimensional (1D) examples.

• Korean Journal of Materials Research
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• v.24 no.11
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• pp.610-616
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• 2014

In this study, we investigated the precipitation behavior of the R-phase precipitated at the initial stage of aging and its effect on the pitting corrosion of 25%Cr-7%Ni-4%Mo super duplex stainless steel. The R-phase in super duplex stainless steel was mainly precipitated at the interface of ferrite/austenite phases and inside of the ferrite phase during the initial stage of aging, and it was transformed into the ${\sigma}$-phase with an increase in aging time. The ferrite phase was decomposed into a new austenite phase and ${\sigma}$-phase. The R phase was an intermetallic compound, which represented a lower Ni and higher Mo than the matrix, and also had a higher Mo and Cr concentration than the ${\sigma}$ phase. With an increasing aging time, the pitting potential $E_p$ was increased slowly by the precipitation of the R-phase, and it was then steeply decreased by the precipitation of the ${\sigma}$-phase. The R-phase was decreased the pitting potential, but its effect was smaller than effect of ${\sigma}$-phase.