• 한국정밀공학회지
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• 제13권6호
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• pp.34-44
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• 1996

In order to examine the accuracy of the intensity method, the fiber orientation-angle distribution of fiber-reinforced polymeric composites is measured using image processing. The fiber orientation function is calculated from the fiber orientation measured by the soft X-ray photograph. Theoretical and experimental results of fiber orientation function are compared for the composites with different fiber contents and fiber orientations. The intensity method is used for the experimental investigation and the measured fiber orientation function is compared to the calculated one. The relations between the measured and the simulated fiber orientation functions $J{\small{M}}$ and $J{\small{S}}$ respectively are identified. For the fiber length of 1.000mm and 2.000mm, it shows that $J{\small{M}}=0.83J{\small{M}}$. However. in general. the value of $J{\small{M}}$ decreases as the fiber length increases. For GFRP composites the relations between $J{\small{M}}$ and theoretical value J show that $J{\small{M}}$=0.73J for short fiber and $J{\small{M}}$=0.81J for long fiber.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.365-368
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• 2006

In this paper, the post cracking stress-crack width relationship of the composite is studied from a micromechanics points of view. Cook-Gordon debonding effect is studied by more refined method with considering of chemical friction of fiber interface. As a result, fiber with pre-debonding length retards stress development and shows more wide crack width for the same force level. longer pre-debonding length and lower pre-debonding bond strength results in lower full-debonding force, but same crack width.

• 대한치과교정학회지
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• 제48권2호
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• pp.107-112
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• 2018

Objective: The aim of this study was to examine the properties of fiber-reinforced composite and stainless steel twisted retainers for orthodontic retention. Methods: Three different span lengths (5.0, 8.0, and 14.0 mm) of fiber-reinforced composite were investigated. The three fiber-reinforced composite retainer groups were subdivided according to the storage condition (dry and wet), resulting in a total of six groups. Each stainless steel and fiber-reinforced composite group was comprised of six specimens. The three-point bending flexural test was conducted using a universal testing machine. ANOVA was used to assess differences in the maximum load and maximum stress according to the span length, material, and storage condition. Post-hoc comparisons were performed if necessary. Results: The maximum stress and maximum load were significantly (p < 0.001) associated with the span length, material, and storage condition. The significant interaction between the material and span length (p < 0.001) indicated the differential effects of the material for each span length on the maximum stress and maximum load, with the difference between materials being the highest for the maximum span length. Conclusions: Our findings suggest that fiber-reinforced composite retainers may be an effective alternative for orthodontic retention in patients with esthetic concerns or allergy to conventional stainless steel wires.

• 한국안전학회지
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• 제28권1호
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• 펄프종이기술
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• 제30권2호
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• pp.47-54
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• 1998

Refining is one of the most important processes of fiber treatment that provides optical and physical properties of final paper products. The evaluation method of refining progress is usually freeness (CSF) or wetness (SR) test because of its rapidity and convenience. However, there are some deficiencies in using freeness or wetness test to evaluate pulp fibers accurately because its results are more influenced by fines contents than extent of fibers treatment. The objective of this study is to show the deficiency of wetness in evaluating the refining process. For this, beating is done by varying the beating load. Handsheets are made after beating until 25 and $32^{\circ}C$ SR, and then paper properties are measured. Refined fibers are analyzed by fiber length, fines contents, curl, kink, WRV, and zero-span tensile strength. The results show that longer beating time is required to reach the same wetness at lower beating load. There are differences in the average fiber length, distribution curve of fiber length, fines contents, curl, kink, WRV of long fiber fraction, drainage time, and zero-span tensile strength of rewetted sample at different beating load. At the low beating load in the same wetness, apparent density, breaking length, burst strength, and tear strength are higher, while opacity and air permeability are lower than those of the high beating load. Using Page s equation, which shows the relationship among tensile strength, intrinsic fiber strength, and interfiber bonding strength, interfiber bonding strength is calculated and analyzed to explain final paper properties. At $25^{\circ}C$ SR, interfiber bonding strength is only slightly higher at 2.5kgf beating load, while the intrinsic fiber strength is substantially higher. At $32^{\circ}C$ SR, intrinsic fiber strength is a little bit higher at 2.5kgf beating load, and interfiber bonding strength is remarkably higher than those of 5.6kgf beating load. These results can be used to explain the different properties of the final paper at selected beating loads.

• Journal of the Korean Wood Science and Technology
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• 제25권2호
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• pp.75-80
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• 1997

This research has been examined to measure the degree of the fiber damage of ozonenation high yield pulp in the beating process. Ozone treated the TMP(Thermomechanical Pulp) and CTMP(Chemithermomechanical Pulp) of spruce and the CTMP of birch has been beaten to be reached 200ml(freeness) of its content. It had been studied the forming of fiber distribution by treatment for long fiber, short fiber, fine with the above method. As ozone treatment time gets longer, the pulp has showed the tendency of increasing the fiber content of 28, 48mesh. Ozone treated fiber has been increased long fiber content by being added softness. By given longer ozone treatment time, the TMP and CTMP of spruce has showed the decreasing of fiber content. On the contrary, CTMP of birch has showed the increasing its fiber content. It had proved that the results of difference are rather closer to the species of tree than closer to the kinds of pulp. The fiber content of over 200mesh which has created in beating process demonstrates the decreasing of its fiber content by getting longer ozone treatment time. The softness of fiber can be extracted by the lignin of fiber surface that had been formed by ozone treatment. Thus we assume that the fiber in the process of beating obtains less physical damage.

• 한국정밀공학회지
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• 제33권6호
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• pp.447-452
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• 2016

The simulation of Carbon fiber reinforced polymer (CFRP) machining facilitates the selection of optimal cutting parameter for high machining efficiency and better surface quality. In this study, This paper proposes a dual-dexel model to represent the fiber laminate with computational geometry method to calculate the fiber length removed per revolution and fiber cutting angles. A flat end milling simulation software is developed in C# to simulate and display the CFRP milling process. During simulation, fiber lengths, fiber cutting angle and engaged cutting angle can be displayed in real-time. A CFRP plate with different angles in different layer is used to compare the simulation results.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.258-263
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• 1999

In this study, the numerical and experimental investigations were conducted to understand ultrasonic wave propagation and to evaluate the degree of fiber waviness in thick composites nondestructively. The path, energy and traveling time of insonified wave were predicted by adopting the ray and plane wave theories. In the analysis, the composites were assumed to have continuous fiber with sinusoidal waviness in a matrix and were modeled as stacks of infinitesimally short length off-axis elements with varying fiber orientation along the length direction. From the experiments on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness, the energy distributions of received wave were obtain for the various positions of transmitter. It was observed that the energy of wave was converged to the adjacent peaks of fiber waviness. The location where maximum energy of wave was detected from the experiments showed good agreement with the location obtained from theoretical predictions. Finally, the test procedure was Proposed to evaluate fiber waviness in thick composites by considering the energy of wave and relative distance between transmitter and receiver.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.341-348
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• 1997

Fibers have been used to improve the tensile strength or toughness of concrete. Therefore many different kinds of fibers have been developed and tested to reinforcing concrete. Basalt fiber is one of the recently developed materials for this purpose. Basalt fibers have the advantage which is the fiber itself is a same kind of material as concrete. In this study, fiber length change, orientation of fiber, the strength properties of fiber reinforced concrete have been tested. The test result show that as the amount of fiber increases, 1) workability of concrete has been reduced significantly, 2) the length of fiber reduced down to less than 4mm, 3) orientation factors are between 0.248 and 0.350, 4) compressive strength and elastic modulus have been increased significantly, however, the other strength have not increased significantly.

• 한국구조물진단유지관리공학회 논문집
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• 제2권1호
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• pp.136-141
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• 1998

It is demanded to obtain the design data for bond length of the strengthening carbon fiber sheets. An objectives of this study is to provide preliminary data of rational strengthening design method which is adequate to current domestic status. The present experimental study was performed to evaluate flexural strengthening effects of steel reinforced concrete beams strengthened with carbon fiber sheets. Following conclusions can be extracted. It is revealed that the maximum load carrying capacity is increased up to 9% when the reinforced concrete beams were strengthened with 1-ply of carbon fiber sheet which is half-width of beam. The performance of reinforced concrete sections were improved due to the strengthening carbon fiber sheets on the tensile side of beams. It is believed that the strengthening length of carbon fiber sheets must be provided as (0.5l+3d) to secure the ductile capacity of above three for the flexural strengthening of reinforced concrete beams.