• Computers and Concrete
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• 제19권6호
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• pp.631-639
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• 2017

This study experimentally investigated the flexural capacity of a concrete beam reinforced with a newly developed GFRP bar that overcomes the lower modulus of elasticity and bond strength compared to a steel bar. The GFRP bar was fabricated by thermosetting a braided pultrusion process to form the outer fiber ribs. The mechanical properties of the modulus of elasticity and bond strength were enhanced compared with those of commercial GFRP bars. In the four-point bending test results, all specimens failed according to the intended failure mode due to flexural design in compliance with ACI 440.1R-15. The effects of the reinforcement ratio and concrete compressive strength were investigated. Equations from the code were used to predict the deflection, and they overestimated the deflection compared with the experimental results. A modified model using two coefficients was developed to provide much better predictive ability, even when the effective moment of inertia was less than the theoretical $I_{cr}$. The deformability of the test beams satisfied the specified value of 4.0 in compliance with CSA S6-10. A modified effective moment of inertia with two correction factors was proposed and it could provide much better predictability in prediction even at the effective moment of inertia less than that of theoretical cracked moment of inertia.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.125-128
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• 2005

The dispersion of carbon nanofiber (CNF) was carried out by solution blending, mechanical mixing, and sonication. CNFs at levels of 5-50% fiber weight content were mixed with polypropylene (PP) powder, and then were melt-mixed using a twin-screw extruder. For the further alignment of fibers, extruded rods were stacked uni-directionally in the mold cavity for the compression molding. For the evaluation of mechanical properties of nanocomposites, tension, in-plane shear, and flexural tests were conducted. CNF/PP composites clearly showed reinforcing effect in the longitudinal direction. The tensile modulus and strength have improved by 100% and 40%, respectively for 50 % fiber weight content, and the flexural modulus and strength have increased by 120% and 25%, respectively for the same fiber weight content. The shear modulus showed 65% increase, but the strength dropped sharply by 40%. However, the property enhancement was not significant due to the poor adhesion between fiber and matrix. In the transverse direction, the tensile, flexural, and shear strength decreased as more fibers were added.

• Computers and Concrete
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• 제26권5호
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• pp.451-465
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• 2020

This paper presents experimental and numerical investigations on mechanical properties of ultra-high-performance fiber-reinforced concrete (UHPFRC) with four types of steel fibers; micro steel (MS), crimped (C), round crimped (RC) and hooked-end (H), in two fiber contents of 1% and 2% (by volume) and two lengths of 13 and 30 mm. Compression, direct tension, and four-point bending tests were carried out on four types of specimens (prism, cube, dog-bone and cylinder), to study tensile and flexural strength, fracture energy and modulus of elasticity. Results were compared with UHPC specimens without fibers, as well as with available equations for the modulus of elasticity. Specimens with MS fibers had the best performance for all mechanical properties. Among macro fibers, RC had better overall performance than H and C fibers. Increased fibers improved all mechanical properties of UHPFRC, except for modulus of elasticity, which saw a negligible effect (mostly less than 10%). Moreover, nonlinear finite element simulations successfully captured flexural response of UHPFRC prisms. Finally, nonlinear regression models provided reasonably well predictions of flexural load-deflection behavior of tested specimens (coefficient of correlation, R² over 0.90).

• 대한기계학회논문집A
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• 제24권7호
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• pp.1697-1702
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• 2000

This study has been performed to investigate the effects of glass fiber characteristics on the mechanical properties of thermoplastic composite. The surface of glass fiber was coated with the silan e to enhance the bonding strength between fiber and matrix. A micro-droplet pull-off test was performed to investigate the influence of the silane concentration on the bonding strength. The maximum bonding strength was observed around 10.8% silane concentration. In order to examine the influence of the fiber length and fiber content on the properties of the composite, the composite materials involving tile fiber lengths of 5mm, 10mm, 15mm 20mm, and 25mm were tested. The composites used contain 20%, 30%, and 40% by weight of glass fibers. Tension and flexural tests were performed to investigate their mechanical properties of the composites. The tensile strength and tensile modulus of the composite increase with increasing the glass fiber content. The tensile modulus increases slightly with increasing the fiber length. The maximum tensile strength is observed around the fiber length of 15-20mm. The flexural modulus and strength also increase slightly with increasing the fiber length.

• 대한치과기공학회지
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• 제31권4호
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• pp.37-43
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• 2009

This study evaluated the effect of concentration of glass fiber reinforcement on the flexural properties of auto and heat polymerized denture base resin. The test specimens($64{\times}10{\times}3.3mm$) were made of auto and heat polymerized resin(Vertex, Dentimax, Netherlands). Glass fiber(ER 270FW, Hankuk Fiber Glass, Korea) were used to reinforce the denture base resin. The 2.6%, 5.3% and 7.9% volume pre-impregnated fiber were located at the bottom of specimen. The test specimens(n=7) of each group were stored in distilled water at $37^{\circ}C$ for 50 hours before test. The flexural strength and modulus were measured by an universal testing machine(Z020, Zwick, Germany) at a crosshead speed of 5 mm/min in a three-point bending mode. The data was analyzed by one-way ANOVA and the Duncan's multiple range test(${\alpha}$=0.05). The difference of auto polymerized resin groups and heat polymerized resin groups were statistically analyzed by t-test(${\alpha}$=0.05). Glass fiber showed significant reinforcing effects on auto and heat polymerized resin. For flexural strength and modulus, auto polymerized resin was the highest in 7.9% volume, while heat polymerized resin was the highest in 5.3% volume. In this study, glass fiber at 7.9% volume ratio showed most effective reinforcing effect on auto polymerized resin and glass fiber at 5.3% volume ratio showed most effective reinforcing effect on heat polymerized resin in terms of flexural strength and flexural modulus.

• 대한치과기공학회지
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• 제42권2호
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• pp.91-98
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• 2020

Purpose: This study is to compare the flexural strength and modulus by inserting a mesh and stick type fiberglass reinforcement into resin specimens. Methods: Wax specimens (length 64 mm, width 39 mm, thickness 5 mm) are prepared according to ISO 20795-1:2013. Mesh type and stick type glass fiber reinforcements were prepared. The prepared wax specimens were used plaster and flask for investment. The flask was separated and the wax was removed. The heat curing resin was injected into the flask, and then a mesh type and stick type fiberglass reinforcement were inserted. The prepared resin specimen was cut into three equal parts (length 64 mm, width 10 mm, thickness 3.3 mm). The mesh type glass fiber reinforcement (MT group) and the stick type glass fiber reinforcement (ST group) were classified into two groups. The prepared specimen was measured using a universal testing machine (UTM). The data were analyzed by Mann-Whitney U test, and the significance level was set to 0.05. Results: In the flexural strength, the ST group was higher than the MT group, and there was a significant difference between the two groups (p<0.05). In the flexural modulus, the ST group was higher than the MT group, and there was a significant difference between the two groups (p<0.05). Conclusion: The stick-type glass fiber inreased the flexural strength than the mesh-type glass fiber reinforcement.

• 구강회복응용과학지
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• 제27권2호
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• pp.197-207
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• 2011

의치상의 첨상에 사용하는 레진의 종류가 의치상의 굴곡강도와 굴곡계수에 미치는 영향을 비교하는데 있다. 국제표준규격 제 1567 호(ISO 1567:1999)를 참고로 2 가지의 의치상용 열중합레진(Lucitone199(Dentsply Int., NewYork, USA), SR-Ivocap(Ivoclar AG, Schaan, Liechtenstein))을 이용하여 길이 64 mm ${\times}$ 폭 50 mm ${\times}$ 두께 3.3 mm 의 시편을 제작하였다. 각각의 제작된 시편을 다시 두께 2.0 mm 로 규격화한 뒤 3 종류의 레진(Lucitone199 (Dentsply), SR-Ivocap(Ivoclar), Rebase II(Tokuyama Co., Ltd, Tokyo, Japan))으로 각각 1.3 mm 의 두께로 첨상을 하였다. 제작된 시편(n=10)을 증류수가 담긴 밀폐된 용기 내에 $37^{\circ}C$에서 50 시간 동안 보관하였다. 그 후 만능시험기를 이용하여 시편의 3 점 굴곡강도와 굴곡계수를 측정하였다. 지지대간의 거리는 50 mm, crosshead speed 는 5 mm/min 였다. 측정값은 One-way ANOVA 로 비교 분석하였고, Tukey test 를 이용하여 사후 검정하였다. 열중합형 레진과 자가중합형 레진으로 첨상한 군들은 모두 첨상을 시행하지 않은 대조군보다 통계적으로 유의하게 낮은 굴곡강도와 굴곡계수를 나타났다. 본래의 의치상용 레진의 종류와 무관하게 Lucitone199 을 이용해 첨상한 군이 SR-Ivocap 을 이용한 군보다 통계적으로 유의하게 높은 굴곡강도와 굴곡계수를 보였다. 자가중합형 레진을 이용한 군은 열중합형 레진을 이용한 군 보다 통계적으로 유의하게 낮은 굴곡강도와 굴곡계수를 보였다. 의치상의 첨상 시 자가중합형 레진 보다 열중합형 레진을 이용하는 것이 우수한 기계적 성질을 보였다. 열중합형 레진을 이용한 첨상 시 본래의 의치상과 같은 종류의 레진을 사용하는 것은 의치상의 기계적 성질에 영향을 미치지 않았으며 Lucitone199 를 이용한 가압주형법에서 가장 우수한 물성을 나타냈다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.463-468
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• 2003

A finite element formulation to predict the flexural behavior of composite girder is presented in which the early-age properties of concrete are specified including maturing of elastic modulus, creep and shrinkage. The time dependent constitutive relation accounting for the early-age concrete properties is derived in an incremental format by expanding the total form of stress-strain relation by the first order Taylor series with respect to the reference time. The total potential energy of the flexural composite member is minimized to derive the time dependent finite element equilibrium equation. Numerical applications are made for the 3-span double composite steel box girders which is a composite bridge girder filled with concrete at the bottom of the steel box in the negative moment region. The numerical analysis with considering the variation of concrete elastic modulus are performed to investigate the effect of it on the early-age behavior of composite structures. The one dimensional finite element analysis results are compared with the analytical method based on the sectional analysis. Close agreement is observed among the two methods.

• Computers and Concrete
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• 제21권6호
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• pp.705-715
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• 2018

This paper presents an experimentally investigation pertinent to the mechanical properties of rubberized mortar (RM) with styrene-butadiene rubber (SBR). The SBR were used with constant water-to-cement ratio of 0.485 and two different volume proportion of SBR particles were utilized as aggregates. One types of SBR particles with fineness modulus of 4.951 were utilized 0%, 10%, and 20% of aggregate volume. Effectiveness of SBR replacement ratio, curing and aging effect on the compressive strength, flexural strengths as well as load-displacement. Compressive and flexural strength of concrete were investigated at the end of 28-days and 56-days age. Obtained results demonstrated that utilization of SBR reduced the flexural strength of SBR mortar at the earlier curing age while SBR increased. Moreover, mechanical properties of mortar mentioned above were significantly affected by the water cure timing with an increasing proportion of the replacement level of SBR.

• The Journal of Advanced Prosthodontics
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• 제11권1호
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• pp.32-40
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• 2019

PURPOSE. The purpose of this study was to compare mechanical and physical properties of injection-molded thermoplastic denture base resins. MATERIALS AND METHODS. In this study, six commercially available products (VA; Valplast, LC; Lucitone, ST; Smiltone, ES; Estheshot-Bright, AC; Acrytone, WE; Weldenz) were selected from four types of thermoplastic denture base materials (Polyamide, Polyester, Acrylic resin and Polypropylene). The flexural properties and shore D hardness have been investigated and water sorption and solubility, and color stability have evaluated. RESULTS. For the flexural modulus value, ES showed the highest value and WE showed significantly lower value than all other groups (P<.05). Most of experimental groups showed weak color stability beyond the clinically acceptable range. CONCLUSION. Within the limits of this study, thermoplastic denture base resin did not show sufficient modulus to function as a denture base. In addition, all resins showed discoloration with clinical significance, and especially polyamides showed the lowest color stability.