• 한국재료학회:학술대회논문집
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• 한국재료학회 1992년도 추계학술발표강연 및 논문개요집
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• pp.139-142
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• 1992

• 한국광학회:학술대회논문집
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• 한국광학회 1997년도 Advance Program of 14th optics andquantum Electronics conference, 1997제14 회 광학 및 양자전자 학술 발표회 논문 요약집
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• pp.25-25
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• 1997

• 비파괴검사학회지
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• 제17권2호
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• pp.89-99
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• 1997

단섬유강화금속복합재료는 최근 항공기, 자동차산업에 있어서 관심의 대상이 되고 있는 재료중의 하나이나 재료의 제조 및 성형중에 재료내의 기지재 및 강화재의 열팽창계수의 차이로 인해 재료 내부에 발생되는 열적잔류응력으로 인한 재료 특성의 변화로 실제적인 재료 적용상에 많은 문제점들이 보고되고 있다. 이와 같은 금속복합재료의 잔류응력의 평가에는 몇가지 비파괴적 방법이 적용되고 있으나 그 측정에 많은 어려움이 보고되고 있다. 따라서 금속복합재료의 보다 실제적인 응용을 위하여는 이와 같은 열적잔류응력을 평가하기 위한 이론적모델의 확립이 요구된다. 본 연구에 있어서는 비방향성을 가진 강화재가 2차원 평면 상태로 기지재내에 존재하는 단섬유강화금속복합재료에 있어서 재료에 균일한 온도 변화가 주어질 때 기지재와 강화재의 열팽창계수의 차로 인해 재료 내부에 발생하는 열적잔류응력을 평가, 예측하기 위한 이론적 탄성 모델을 확립하고자 한다. 본 연구에서 해석하고자 하는 이론 모델은 Eshelby의 등가 개재물 방법을 토대로 하고 있으며 과거 제안되고 있는 이론모델을 포함하는 보다 일반성을 가지는 해석 모델로서, 이 해석 모델을 이용하여 열적잔류응력에 미치는 강화재의 체적률, 종횡비, 분포 상태, 분포 cut-off 각도들에 대한 각 인자의 영향을 검토하였다. 그 결과 강화재의 체적률, 종횡비, cut-off 각도들이 강화재의 분포 상태보다도 금속복합재료의 열적잔류응력에 미치는 영향이 현저함을 알 수 있었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 추계학술대회 논문집
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• pp.457-460
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• 2000

Injection molding is the most widely used process for the industrial forming of plastic articles. During an injection molding process of composites, the fiber-matrix separation and fiber orientation are caused by the flow of molten polymer/fiber mixture. As a result, the product tends to be nonhomogeneous and anisotropic. Hence, it is very important to clarify the relations between separation·orientation and infection molding conditions. So far, there is no research on the measurement of fiber orientation using image processing. In this study, the effects of fiber content ratio and molding condition on the fiber orientation-angle distributions are studied experimentally. Using the image processing method, the fiber orientation distribution of welding parts in injection-molded products is assessed. And the effects of fiber content and injection mold shapes on the fiber orientation in case of fiber reinforced polymeric composites are studied. experimentally.

• The Journal of Korean Physical Therapy
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• 제28권5호
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• pp.297-302
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• 2016

Purpose: This study was conducted to evaluate the effects of bridge exercise on the structural characteristics of trunk muscles in patients with lumbar pain by applying the exercise on either a stable or an unstable surface. Methods: Thirty subjects participated in the experiment and were randomly divided into an unstable bridge exercise group (UBEG) and a stable bridge exercise group (SBEG). The exercise program for each group was conducted three times a week over a six-week period. The structural characteristics of trunk muscles were measured by obtaining images using an ultrasound imaging device. Results: The thicknesses of the external oblique (EO), internal oblique (IO), and transverse abdominis (TrA) and the fiber angle of the erector spinae (ES) in the UBEG and the SBEG showed statistically significant increases in all items measured after the experiment. A comparison of groups conducted after the experiment to determine the effects of the exercise on each group showed no significant differences between groups for any of the measured items. Conclusion: A comprehensive review of the study results showed statistically significant increases in the thicknesses of the EO, IO, and TrA and the fiber angle of ES in both the UBEG and the SBEG. While the comparison of the groups with respect to the effects of the exercise revealed no significant differences, there were relatively larger effects in the UBEG than in the SBEG.

• Journal of the Korean Wood Science and Technology
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• 제46권4호
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• pp.323-337
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• 2018

Merkusii pine wood (Pinus merkusii) was extensively planted throughout Indonesia, where it is only indigenous in northern Sumatera, by the Dutch during colonial times. The demand for this wood species, especially in the domestic market, has increased notably, despite its limited durability regarding decay resistance. The purpose of this study was to investigate the occurrence of juvenile and mature wood on merkusii pine and to analyze its radial features from pith to bark based on density, shrinkage, static bending in modulus of rupture and modulus of elasticity, fiber length, microfibril angle, and durability. A segmented modeling approach was used to find the juvenile-mature transition. The graveyard test was performed to characterize the termite resistance from pith to bark of merkusii pine. The maturations were estimated to start at radial increments of 15 cm from the pith by fiber length and of 12 cm from the pith by microfibril angle. The projected figures for the proportion of juvenile wood at breast height were around 65%. The results also indicate that the pine wood was $0.52g/cm^3$ in density, 1.45 in coefficient of anisotropy, which indicates its good stability, 7597 MPa in modulus of elasticity, and 63 MPa in modulus of rupture. Natural durability against subterranean termite of the merkusii pine wood was rated to be grade 4 to 0 from pith to bark. However, after being treated by Entiblu and Enborer preservatives, its rating increased to grade 10 to 9.

• Composites Research
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• 제25권3호
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• pp.76-81
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• 2012

대기압 플라즈마 처리를 통해 탄소나노튜브(CNT) 표면은 개질 되며 개질된 입자의 표면과 탄소섬유 강화 CNT 페놀 복합재료간에 계면접착력에 변화를 확인하였다. CNT 표면에 플라즈마 처리에 따라 표면 변화가 발생되고 표면 개질의 결과를 확인하기 위해 FT-IR을 사용하였다. 또한, 정적 접촉각 실험법을 통해 플라즈마 처리에 따른 CNT의 젖음성을 비교 평가하였다. 순수 CNT 입자의 접촉각은 $118^{\circ}$ 였으나, 플라즈마 처리를 할 경우 $60^{\circ}$도로 표면 개질을 통해 젖음성이 향상됨을 확인하였다. 탄소섬유와 CNT-페놀복합재료 간 계면접착력은 플라즈마 처리에 따라 겉보기 강성도가 증가되는 결과를 확인하였으며, 음향방출 실험법과 전기저항 측정법을 병행한 이중기지평가법을 통해 계면전단강도 (IFSS)를 계산하여 계면접착력 향상을 확인하였다.

• Advances in concrete construction
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• 제14권5호
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• pp.299-307
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• 2022

Cement-based matrixes have low tensile strength and negligible ductility. Adding fibres to these matrixes will improve their mechanical properties and make these composites suitable for structural applications. Post-cracking tensile strength of steel fibers-reinforced cementitious composite materials is directly related to the number of transverse fibers passing through the crack width and the pulling-out behavior of each of the fibers. Therefore, the exact recognition of the pullout behavior of single fibers is necessary to understand the uniaxial tensile and bending behavior of steel fiber-reinforced concrete. In this paper, an experimental study has been carried out on the pullout behavior of 3D (steel fibers with totally two hooks at both ends), 4D (steel fibers with a total of four hooks at both ends), and 5D (steel fibers with totally six hooks at both ends) in which the fibers have been located either perpendicular to the crack width or in an inclined manner. The pullout behavior of the mentioned steel fibers at an inclination angle of 0, 15, 30, 45, and 60 degrees and with embedded lengths of 10, 15, 20, 25, and 30 millimetres is studied in order to explore the simultaneous effect of the inclination angle of the fibers relative to the alongside loading and the embedded length of fibers on the pullout response in each case, including the maximal pullout force, the slip of the maximum point of pullout force, pullout energy, fiber rupture, and concrete matrix spalling. The results showed that the maximum pullout energy in 3D, 4D, and 5D steel fibers with different embedded lengths occurs at 0 to 30° inclination angles. In 5D fibers, maximum pullout energy occurs at a 30° angle with a 25 mm embedded length.

• The Journal of Advanced Prosthodontics
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• 제5권4호
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• pp.434-439
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• 2013

PURPOSE. The aim of the present study was to evaluate the effects of posts with different morphologies on stress distribution in an endodontically treated mandibular premolar by using finite element models (FEMs). MATERIALS AND METHODS. A mandibular premolar was modeled using the ANSYS software program. Two models were created to represent circular and oval fiber posts in this tooth model. An oblique force of 300 N was applied at an angle of $45^{\circ}$ to the occlusal plane and oriented toward the buccal side. von Mises stress was measured in three regions each for oval and circular fiber posts. RESULTS. FEM analysis showed that the von Mises stress of the circular fiber post (426.81 MPa) was greater than that of the oval fiber post (346.34 MPa). The maximum distribution of von Mises stress was in the luting agent in both groups. Additionally, von Mises stresses accumulated in the coronal third of root dentin, close to the post space in both groups. CONCLUSION. Oval fiber posts are preferable to circular fiber posts in oval-shaped canals given the stress distribution at the postdentin interface.

• Advances in concrete construction
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• 제9권4호
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• pp.367-374
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• 2020

Concrete surfaces, industrial floors, sidewalks, roads and parking lots are typically subjected to abrasions. Many studies indicated that the abrasion resistance is directly related to the ultimate strength of the cured concrete. Chemical reactions, freeze-thaw cycles, and damages under abrasion are among many factors negatively affecting the concrete strength and durability. One of the major solutions to address the abrasive resistance of the concrete is to use fibers. Fibers are used in the concrete mix to improve the mechanical properties, strength and limit the crack propagations. In this study, implementation of the steel fibers in concrete to enhance the abrasive resistance of the concrete is investigated in details. The abrasive resistance of the concrete with and without steel fibers is studied with the sandblasting technique. For this purpose, different concrete samples are made with various hooked steel fiber ratios and investigated with the sandblasting method for two different strike angles. In total, 144 ASTM verified cube samples are investigated and it is shown that those samples with the highest steel fiber ratios have the highest abrasive resistance. In addition, the experiments determine that there is a meaningful correlation between the steel fiber percentage in the mix, strike angle and curing time which could be considered for improving structural behavior of the fiber-reinforced concrete.