• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.913-916
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• 2008

Direct tensile response of strain hardening cement composites(SHCC) depends primarily on the material's tensile response, which is a water cement ratio, direct function of fiber and matrix characteristics, the bond between them, and the fiber volume fraction. This paper discusses effect of aspect ratio of the direct tensile response of SHCC with PET and PVA fibers. The main variables considered include the aspect ratio of PET fibers(Aspect ratio, ${\ell}/d_f$ : 150, 300, 600). For the same mixture proportion, PET1.5+PVA0.5-300 and PET1.5+PVA 0.5-600(Aspect ratio 300, 600) showed better overall behavior(Pseudo strain-hardening, Multiple cracking) than specimens with PET1.5+PVA0.5-150(Aspect ratio 150). Tensile strain of PET1.5+PVA0.5-300 and PET1.5+PVA 0.5-600 at ultimate tensile stress were 0.5, 2.0% respectively.

• The Journal of the Korean bone and joint tumor society
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• 제8권1호
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• pp.27-31
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• 2002

Clinical symptoms of fibrous dysplasia in proximal femur include pain, limping, and leglength discrepancy. Occasionally varus deformity, which may range from mild coxa vara to a marked shepherd's crook deformity was developed. Surgical intervention generally is considered advisable in the presence of persistent pain unresponsive to conservative treatment or significant or progressive deformity. Depending on the lesion size, lesion site, and deformity, several treatment methods have been used. This is a report on one case of bilateral shepherd's crook deformity in fibrous dysplasia, which was treated with corrective osteotomy by Huckstep nail.

• Proceedings of the Korean Fiber Society Conference
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• 한국섬유공학회 2003년도 가을 학술발표회 논문집
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• pp.195-196
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• 2003

Polyurethane(PU)은 물리적 화학적 성질이 매우 다른 두 segment(hard/soft)로 이루어진 block copolymer로서 상온에서 미세상분리된 구조를 가진다. 이런 미세 상분리 구조는 PU의 물리적 성질을 결정하는 가장 중요한 요소이며, hard segment(H/S)의 화학적 구조에 따른 PU사슬의 강직성은 H/S의 packing및 상분리도에 큰 영향을 미친다. 본 연구에서는 H/S의 화학적 구조를 변화시켜 사슬의 강직성이 서로 다른 다양한 PU을 합성하였으며 Synchrotron SAXS와 FTIR-dichioism을 이용하여 PU 사슬의 강직성에 따른 거시적인 domain의 변형거동과 미시적인 사슬의 변형거동을 관찰 하였다. (중략)

• The Korean Journal of Rheology
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• 제4권2호
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• pp.138-147
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• 1992

사출성형충전공정에서 금형구조가 단섬유배향에 미치는 영향을 예측하기 위하여 수 치모사 프로그램을 개발하였다. 유한요소 /관찰 부피 방법에 복잡한 금형에서의 유동을 해 석하고 섬유와 섬유간의 상호작용을 고려한 섬유배향텐서 변화식을 이용하여 입자 추적법으 로 섬유배향분포를 구하였다. 수치모사 결과 금형 옆벽면과 내부 방해체의 주위에 있는 섬 유들이 전단변형의 영향으로 그들주위를 따라서 정렬되려는 경향을 보였다, 두 유동이 내부 방해체를 지나 접하면서 생성된 웰드라인을 따라서 단섬유들이 정렬되려는 경향을 나타내엇 다. 그리고 수축유동에서는 흐름방향으로 정렬되나 확장유동에서는 흐름방향에 수직으로 배 열되려는 경향을 확인하였다. 위아래 벽에 의한 전단변형의 영향으로 서로 다른두 배향구조 를 보여주는 skin-core 구조를 두께방향의 속도구배를 고려한 수치모사를 통하여 예측할 수 있었다. skin구조에서는 섬유들이 흐름방향으로 정렬되고 core 구조에서는 흐름방향에 수직 으로 배향되는 것을 확인하였으며 섬유상호계수값이 커질수록 임의 배향화하는 경향을 보였다.

• The Korean Journal of Rheology
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• 제5권1호
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• pp.49-64
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• 1993

사출성형충전공정에서 금형구조가 단섬유배향에 미치는 영향을 예측하기 위하여 수 치모사 프로그램을 개발하였다. 유한요소 /관찰 부피 방법에 복잡한 금형에서의 유동을 해 석하고 섬유와 섬유간의 상호작용을 고려한 섬유배향텐서 변화식을 이용하여 입자 추적법으 로 섬유배향분포를 구하였다. 수치모사 결과 금형 옆벽면과 내부 방해체의 주위에 있는 섬 유들이 전단변형의 영향으로 그들주위를 따라서 정렬되려는 경향을 보였다, 두 유동이 내부 방해체를 지나 접하면서 생성된 웰드라인을 따라서 단섬유들이 정렬되려는 경향을 나타내엇 다. 그리고 수축유동에서는 흐름방향으로 정렬되나 확장유동에서는 흐름방향에 수직으로 배 열되려는 경향을 확인하였다. 위아래 벽에 의한 전단변형의 영향으로 서로 다른두 배향구조 를 보여주는 skin-core 구조를 두께방향의 속도구배를 고려한 수치모사를 통하여 예측할 수 있었다. skin구조에서는 섬유들이 흐름방향으로 정렬되고 core 구조에서는 흐름방향에 수직 으로 배향되는 것을 확인하였으며 섬유상호계수값이 커질수록 임의 배향화하는 경향을 보였다.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Journal of the Korean Geosynthetics Society
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• 제2권3호
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• pp.39-46
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• 2003

The major pavement distress types found in the domestic roadways include rutting, fatigue cracking, and reflection cracking which are results of the environment and repeated traffic loads. These distresses usually occur before pavements approach their design life, and therefore, a significant amount of national budget is spent for maintenance of roadway pavements. The purpose of this study is to establish a geosynthetics-asphalt pavement system. For the study, wheel tracking tests are conducted to analyze the controlling effect of geosynthetics on rutting of asphalt pavement. On the basis of these works, the reinforcement effect of geosynthetics on the rutting of the asphalt pavement is clarified and deformation characteristics of geosynthetics-asphalt mixture is examined.

• Journal of the Korea Concrete Institute
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• 제17권6호
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• pp.911-922
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• 2005

A theoretical study was performed to investigate the behavioral chracteristics and shear strength of fiber reinforced concrete slender beams. In the fiber reinforced concrete beam, the shear force applied to a cross section of the beam was resisted by both compressive zone and tensile zone. The shear capacity of the compressive zone was defined addressing the interaction with the normal stresses developed by the flexural moment in the cross section. The shear capacity of the tensile zone was defined addressing the post-cracking tensile strength of fiber reinforced concrete. Since the magnitude and distribution of the normal stresses vary according to the flexural deformation of the beam, the shear capacity of the beam was defined as a function of the flexural deformation of the beam. The shear strength of the beam and the location of the critical section were determined at the intersection between the shear capacity and shear demand curves. The proposed method was developed as a unified shear design method which is applicable to conventional reinforced concrete as well as fiber reinforced concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• 제16권1호
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• pp.55-63
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• 2012

This paper presents materials and processing technique to manufacture low viscous strain-hardening cementitious composite which is suitable for structures requiring low viscosity of materials. The micromechanics and fracture mechanics tools coupled with processing techniques were adopted to achieve low viscosity of composites as well as high tensile strain capacity. Optimal volume and length of fibers and interfacial properties between fibers and matrix for composites with tensile strength of 2~3MPa were determined on the basis of the micromechanical analysis and the steady-state cracking theory. Then six mixtures were determined and the experiment was carried out to evaluate the viscosity and uniaxial tensile performance of those. From the test results, it is verified that the strain-hardening cementitious composite with low viscosity suitable for grouting applications in fresh state as well as high ductility over 1.5% in hardened state can be feasible.

• International Journal of Highway Engineering
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• 제10권4호
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• pp.281-292
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• 2008

In Korea-LTPP(Long Tenn Pavement Performance) project, the full depth asphalt pavement test sections are constructed on the national highway to evaluate the structural capacity of asphalt pavement reinforced with glass fiber. Truck loading test and FWD test were performed to measure the structural capacity of test sections. Test results showed that the reinforcement of glass fiber installed at between surface and intermediate asphalt layer decreased the strain at the bottom of surface layer and moved up the stress neutral axis in asphalt layer. As a result, the tensile stress was developed at the bottom of intermediate asphalt layer of reinforced asphalt pavement, while the compressive stress was developed at the bottom of intermediate asphalt layer of unreinforced asphalt pavement. On the other hand, the tensile strain at the bottom of asphalt base layer didn't show a difference between glass fiber reinforced and unreinforced pavements. From the FWD test, it was shown that the surface deflection of asphalt pavement reinforced with glass fiber decreased 24 percents comparing to that of unreinforced asphalt pavement. This shows that the reinforcement with glass fiber appears to improve the rutting resistance of asphalt pavement.