• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.125-132
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• 2010

In the recent construction industry, an external strengthening method using fiber reinforced polymers has been widely used. Since reinforced concrete structures strengthened with fiber reinforced polymers are always under sustained loads, influence of creep and shrinkage on the structures is inevitable. Due to the creep and shrinkage, behaviors of the structures, such as deflection, deformation, recovery capability, strength and so on are also under the influence of creep and shrinkage. Thus, in order to estimate efficacy, creep recovery and residual strength of FRP strengthened RC beams, long-term flexural experiments and static flexural experiments were carried out. As the result of the experiments, FRP strengthened RC beams were very effective in terms of deflection control. Furthermore, the strengthened beams had higher immediate deformation recovery than immediate deformation. Through the static flexural experiments, it was shown that the CFRP strengthened beam had high residual strength. It seems that the sustained loads did not affect bond and residual strength of the beams.

• Journal of dental hygiene science
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• v.6 no.4
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• pp.231-235
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• 2006

This study evaluated the properties of polyvinylsiloxane impression materials: Strain-in-compression, Elastic recovery, Consistency, and Wettability. Four polyvinylsiloxane impression materials(Examixfine, GC, Japan; Aquasilultra, Dentsply, USA; Extrude, Kerr, USA; Perfect-F, Handae, Korea) were used in this study. The measured data were analyzed with SPSSWIN 12.0 program. The results were as follows : 1. The strain-in-compression values showed that Extrude had the lowest value, 4.86% and Examixfine had the highest value, 6.78%. Significant difference between Examixfine and Perfect-F was not found but the other groups had significant differences(p = 0.000). 2. In the elastic recovery test, Extrude had the highest, 99.83% and Perfect-F had the lowest, 96.54%. There is no significant difference between Examixfine and Aquasilultra. The other impression material groups showed significant differences(p = 0.000). 3. The measurement of consistency results that the diameter of Examixfine was the largest, 45.12mm and one of Perfect-F was the smallest, 40.28 mm. No differences were shown between Examixfine and Aquasilultra and between Extrude and Perfect-F(p = 0.001). 4. Aquasilultra had a better hydrophilicity($47.85^{\circ}$) than other materials. Perfect-F had a larger contact angle($94.89^{\circ}$) and was hydrophobic. There were significant differences between groups(p = 0.000). 5. As for correlation among the test types, contact angle correlated with strain-in-compression, elstic recovery and consistency. The strain-in-compression had correlation to contact angle and elastic recovery. The elastic recovery correlated with contact angle and strain-in-compression. And the consistency had correlation to contact angle.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.15-24
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• 2007

This paper will present a simple approach (or predicting layer deformation of unbound pavement materials with stress-dependent material properties. The approach is based on an uncoupled formulation in which the resilient and deformation response of unbound materials are considered separately. As a result, an uncoupled approach incorporating a resilient stiffness and Poisson's ratio model is able to simulate field measured deformation in pavement foundations. In addition, a sensitivity analysis is conducted to identify the significant factors in the stress-dependent modulus and Poison's ratio model. The predicted trends of deformation from this analysis are presented and discussed.

• Elastomers and Composites
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• v.44 no.4
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• pp.442-446
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• 2009

Recovery behaviors of unfilled NR, BR, and SBR vulcanizates after aging with a circular deformation were compared to prevent the influence of reinforcing agent. Samples were aged at room temperature, 50, 70, and $90^{\circ}C$ for 10 days. Recovery increased by increasing the measurement time. Instantaneous recoveries less than 1.0 sec were obtained using the recovery variations with the measurement time. For aging at room temperature, difference in the recoveries of the rubber samples was not significant because the aging time was too short. However, for accelerated thermal aging at 50, 70, and $90^{\circ}C$, difference in the recoveries of the rubber samples was significant. Degree of recovery of BR specimen was higher than those of the others, while that of SBR was lowest. However, for accelerated thermal aging at $90^{\circ}C$, recovery of the NR sample was higher than that of the BR one. The initial recovery decreased by increasing the aging temperature and the decrement of SBR was larger than the others. The experimental results were explained with the resilience properties of rubbers and the crosslink density changes by thermal aging.

• Elastomers and Composites
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• v.48 no.3
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• pp.181-189
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• 2013

Unfilled, carbon black-filled, and silica-filled natural rubber (NR) composites were aged with a circular deformation at $60-90^{\circ}C$ and the recovery behaviors were investigated. The samples were aged under the altering aging medium systems of air and distilled water every day for 10 days. The order of the recoveries according to the filler systems was unfilled > silica > carbon black. The recoveries of the samples aged in the air to water altering system were greater than those of the samples aged in the water to air altering system. The initial aging medium dominantly influenced the deformation level.

• Journal of Chest Surgery
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• v.33 no.11
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• pp.876-880
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• 2000

배경: Maze수술은 승모판 질환에 동반되는 심방세동의 효과적인 치료방법으로 알려져있다. 이 연구는 승모판 수술과 심방세동 수술을 동시에 시행한 환자에서 심방세동 수술 후 중기적인 결과와 그 재발 여부를 조사하였다. 대상 및 방법: 심방세동 수술과 승모판 수술을 받은 11예의 환자(10예는 류마티스성 승모판 질환)를 대상으로 하였다. Maze II 수술 및 그 변형수술을 6예에서 시행했고, Maze III 수술 및 그 변형수술을 5예에서 시행하였다. 심방세동 수술 후 좌심방의 수축정도를 심방세동 수술 없이 승모판 수술만으로 동율동을 얻은 경우와 비교하였다. 결과: Maze II 수술을 받은 환자 6예 중 5예(83.3%)에서, maze III 수술을 받은 환자 5예 모두에서 동율동을 회복하였다(전체적으로 90.9%). 전자의 1예(20%)와 후자의 2예(40%)에서 수술 후 각각 23, 2, 13개월만에 심방세동이 재발하였다. 그 후 다시 2예는 동율동으로 전환되었으나, 1예는 재발된 심방세동을 그대로 유지하고 있다. 변형술을 받은 3예에서는 심방세동의 재발이 없었다. Maze 수술 후 4예(40%)에서만 좌심방의 수축기능을 보였으며, maze 수술 후 좌심방 수축 정도(승모판의 A파의 속도)도 maze 수술 없이 승모판 수술과 항부정맥제 투여로 동율동을 회복한 경우보다 낮았다. 결론: 심방세동을 동반한 승모판 수술 환자에서 maze 수술로써 심방세동으로부터 동율동을 회복할 수 있으나 중기적으로 재발할 수 있으며, maze 수술 후 좌심방 수축정도는 상당히 떨어질 수 있다고 생각된다.

• Elastomers and Composites
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• v.40 no.4
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• pp.258-265
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• 2005

To study the compressive stress, recovery force and permanent strain of foams for footwear midsole, polyurethane(PU), phylon(PH) and injection phylon(IP) foams were repetitively compressed with constant compressive stress. Maximum compressive stress of PU did not decrease with repetitive compression on the constant compressive stress, but that of IP largely decreased. Engineering strain of foams were formed by repetitively compressing the three types of foam. The engineering strain of PU was smaller than that of IP and PH. Compressive stress and recovery force of IP and PH at certain strain were decreased with repetitive compression, but that of PU was not noticeably changed.

• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.623-630
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• 2012

Formation used as trackbed foundation for providing vertical bearing capacity onto rail foundation are composed of crushed stones usually with certain type of grain size distribution. Permanent deformation in trackbed foundation can be generated by increasing number of load repetition due to train traffic increases, causing track irregularity. In this study, a specially prepared trackbed foundation materials (M-40) used in Korea has been tested using a large repetitive triaxial compression apparatus in order to understand resilient and permanent deformation characteristics of the material. From these test results, resilient and permanent deformation characteristic are analyzed so that a permanent deformation model is developed which can consider number of load repetition N, confining stress (${\sigma}_3$), shear stress ratio(${\tau}/{\tau}_f$) and stiffness of the material.

• Journal of Chest Surgery
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• v.33 no.11
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• pp.863-868
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• 2000

배경: Cox-Maze III (CM-III) 술식은 복잡한 심방 절개로 인한 긴 수술시간 때문에 다른 개심 수술과 병행하여 시행하기 어려운 단점이 있다. 대상 및 방법: 저자들은 CM-III 술직을 다음과 같이 변형하여 시행하고 그 임상성적을 분석하였다. \circled1 좌심방이를 절제하는 대신 좌심방이를 외부에서 결찰하고, \circled2 폐정맥 분리 절개선과 좌심방이 사이에 냉동절제술을 시행하며, \circled3 우심방이를 절제하는 대신에 우심방 외측 절개선을 우심방이까지 연장하고, \circled4 후종 우심방 절개 하부에서 우심방 외측을 지나 삼첨판막륜으로 향하는 T-자 절개선을 생략하였다. 저자들이 시행한 변형 술식의 용이성과 효율성을 평가하기 위하여, 우리나라에서도 빈도가 높은 류마치스성 승모판막 질환에서, 전통적인 Cox-III 술식(그룹 I)의 임상결과와, 변형된 CM-III 술식(그룹 II)의 임상결과를 비교하였다. 결과: 그룹 I(n=18)에서 동반된 수술은 승모판막 치환술 10례, 승모판막 성형술3례, 승모판막 치환술과 삼첨판막륜 성형술3례, 승모판막 재치환술 2례 등이었다. 그룹II(n=23)에서 동반된 수술은 승모판막 치환술 7례, 승모판막 성형술 5례, 승모판막 치환술과 삼첨판막륜 성형술 1례, 승모판막 재치환술 10례 등이었다. 그룹 I과 그룹 II에서 평균 대동맥 차단 시간(ACC)은 각각 135$\pm$29분과 104$\pm$18 분, 심패바이패스(CPB) 시간은 각각 240$\pm$33분과 185$\pm$42분이었다. 그룹 I과 그룹 II의 평균 추적 관찰 기간은 각각 47$\pm$14 개월과 29$\pm$4 개월이었다. 그룹 I에서는 16례(88.9%)에서 정상 동율동으로 회복되었고 1례에서 심방세동이 남아 있었으며, 다른 1례는 서맥증후군(sick sinus syndrome)으로 인공 심박조율기를 삽입하였다. 그룹 II에서는 21례(91.3%)에서 정상 동율동으로 회복되었고 2례는 심방세동이 지속되었다. 그룹 I에서 정상동율동으로 회복된 16례는 100%(16/16)에서 우심방의 수축을 심장 초음파검사에서 확인할 수 있었으며, 좌심방의 수축은 75%(12/16)에서 확인할 수 있었다. 그룹 II에서는 정상 동율동으로 회복된 21례 중 100%(21/21)에서 우심방의 수축을 확인할 수 있었으며, 좌심방의 수축은 76.2%(16/21)에서 확인할 수 있었다. 결론: 변형 CM-III 술식은 전통 CM-III 술식에 비하여 ACC time(p<0.005)과 CPB time(p<0.001)을 의미있게 줄이면서도 필적할 만 한 정상 동율동 전환율과 심방 수축력의 회복을 보여주었다.

• Elastomers and Composites
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• v.47 no.2
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• pp.156-161
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• 2012

Difference in recovery behaviors from the circular deformation of natural rubber (NR) composites aged in air and distilled water, respectively were investigated. Recoveries of the samples aged in air were larger than those of the samples aged in distilled water. Recovery rates of the samples reinforced with filler were faster than those of the unreinforced ones. Recovery rates of the carbon black-filled samples were faster than those of the silica-filled ones. Difference in the recovery behaviors according to the aging media can be explained by the crosslinking density changes and the annealing effect.