• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.803-808
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• 1998

As carbon fiber is a light-weight materials, high tensile strength and durability compared with rebar, the retrofitting method for RC structures using carbon fiber sheet (CFS) must be use widely. In this paper, the tensile strength test for carbon fiber sheet variable of CF's weight and elastic modulus to evaluate the design tensile strength of carbon fiber sheet which is needed for the strengthening design of CFS and the calculation of strengthening effect. As a result, the design tensile strength of CFS can be calculate using the effect coefficient of strengthening(α) of CFS, the average tensile strength of CFS and the standard deviation of CFS(equation 5)

• Journal of the Korean Wood Science and Technology
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• 제50권6호
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• pp.392-403
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• 2022

Currently, composite board manufacturing using natural fibers has the potential to expand owing to environmental awareness. To produce a composite board, treatment is required to improve the mechanical and physical properties of the natural fibers. In this study, sodium chloride (NaCl) was used for the chemical treatment. However, studies on chemical treatments using NaCl are limited. This study aimed to investigate the characteristics of kenaf fibers after NaCl treatment. The NaCl treatment concentrations were 1, 3, and 5 wt.% at room temperature, with soaking durations of 1, 2, and 3 h. The tensile strength, strain, and Young's modulus were measured to evaluate the mechanical properties of the fibers. The fiber bundle diameter, weight change owing to treatment, and contact angle were determined to analyze the effect of NaCl treatment. The kenaf fiber bundle treated with 5 wt.% NaCl for 3 h exhibited the highest tensile strength, Young's modulus, reduction in fiber bundle diameter, weight change, and decrease in contact angle compared to those of untreated fiber bundles. The tensile properties of the fiber bundle exhibited a tendency to decrease with increasing fiber bundle diameter. Increasing the soaking duration from 1 to 2 h did not result in a significant decrease in the fiber bundle diameter or an increase in tensile strength. However, a further increase in the soaking duration from 2 to 3 h resulted in a considerable decrease in the fiber bundle diameter and an increase in the tensile strength.

• 한국안광학회지
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• 제19권4호
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• pp.429-434
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• 2014

목적: 국내 유통되고 있는 고분자 소재 안경테의 열에 의한 기계적 물성을 분석하고자 하였다 방법: 본 연구에서는 cellulose acetate, polyamide, epoxy 그리고 polyetherimide 소재를 고온과 저온의 열에 노출시킨 후 만능 재료 시험기(Universal Test Machine TO-100-IC)를 이용하여 인장강도 시험(Tensile Strength Test)을 실시하였다. 다양한 온도에 따른($-25^{\circ}C$, $25^{\circ}C$, $60^{\circ}C$) 탄성 변화와 영률, 최대 변위, 그리고 피로거동을 관찰하였다. 결과: 그 결과, 상온($25^{\circ}C$)에서 충격 하중이 증가함에 따라 소재마다 변위가 다르게 나타났다. 낮은 온도($-25^{\circ}C$)에서 최대 변위는 모든 재료에서 감소하였으나 영률은 증가하였다. 그러나 높은 온도($60^{\circ}C$)에서는 최대 변위가 증가하고 영률이 감소하였다. 결론: 피로누적으로 인한 변형의 정도는 PEI, epoxy, polyamide, acetate 순으로 증가하여 나타났다. 안경테에 사용되는 고분자는 노출되는 온도에 따라서 소재마다 기계적 물성이 다르게 변화되어 나타났다.

• 한국세라믹학회지
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• 제54권6호
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• pp.506-510
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• 2017

One of the characteristics of polycrystalline graphene that determines its material properties is grain size. Mechanical properties such as Young's modulus, yield strain and tensile strength depend on the grain size and show a reverse Hall-Petch effect at small grain size limit for some properties under certain conditions. While there is agreement on the grain size effect for Young's modulus and yield strain, certain MD simulations have led to disagreement for tensile strength. Song et al. showed a decreasing behavior for tensile strength, that is, a pseudo Hall-Petch effect for the small grain size domain up to 5 nm. On the other hand, Sha et al. showed an increasing behavior, a reverse Hall-Petch effect, for grain size domain up to 10 nm. Mortazavi et al. also showed results similar to those of Sha et al. We suspect that the main difference of these two inconsistent results is due to the different modeling. The modeling of polycrystalline graphene with regular size and (hexagonal) shape shows the pseudo Hall-Petch effect, while the modeling with random size and shape shows the reverse Hall-Petch effect. Therefore, this study is conducted to confirm that different modeling is the main reason for the different behavior of tensile strength of the polycrystalline structures. We conducted MD simulations with models derived from the Voronoi tessellation for two types of grain size distributions. One type is grains of relatively similar sizes; the other is grains of random sizes. We found that the pseudo Hall-Petch effect and the reverse Hall-Petch effect of tensile strength were consistently shown for the two different models. We suspect that this result comes from the different crack paths, which are related to the grain patterns in the models.

• Steel and Composite Structures
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• 제17권6호
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• pp.825-834
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• 2014

This manuscript presents an experimental investigation on the effect of Multi-walled carbon nanotubes (MWCNTs) addition on the tensile, flexural and impact properties of woven Kevlar fabric reinforced epoxy composites. MWCNTs were dispersed in the epoxy resin by sonication technique and the samples were fabricated by hand layup laminating procedure. Scanning electron microscopy (SEM) was used to characterize the microstructure of produced samples. The effects of adding small amounts (${\leq}1%$) of MWCNT on the tensile, flexural and impact (Izod) behaviors of laminated composites were analyzed. Results revealed that MWCNTs enhanced the Young's modulus up to 20%, bending modulus up to 40%, and impact strength up to 45% in comparison with woven Kevlar fabric/epoxy composites. It was found that the maximum improvements in mechanical properties were happened for 0.5 wt.% MWCNT.

• 대한기계학회논문집A
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• 제36권9호
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• pp.1053-1057
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• 2012

본 연구에서는 풍력 발전 블레이드용 재료인 GFRP(Glass fiber-Reinforced Plastic) 복합재의 인장특성의 온도에 따른 의존성을 고찰하였다. 섬유 방향이 $0^{\circ}$와 $0/{\pm}45^{\circ}$로 적층된 두 종류의 복합재로 제작된 인장 시험편으로부터 인장 강도와 탄성계수 그리고 푸아송비에 대한 특성을 상온, $-30^{\circ}C$, $-50^{\circ}C$ 그리고 $60^{\circ}C$에서 측정하였다. 인장 시험으로부터 섬유방향이 축방향으로 적층된 복합재의 인장강도와 탄성 계수는 섬유 적층 방향의 의존성을 보였고 단축으로 적층된 복합재의 강도 및 탄성 계수가 상대적으로 우수함을 보았다. 그리고 시험온도의 의존성도 확인할 수 있었으며, 푸아송비는 온도의 영향이 크지 않음을 확인할 수 있었다.

• International Journal of Concrete Structures and Materials
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• 제11권1호
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• pp.17-28
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• 2017

Although concrete is a noncombustible material, high temperatures such as those experienced during a fire have a negative effect on the mechanical properties. This paper studies the effect of elevated temperatures on the mechanical properties of limestone, quartzite and granite concrete. Samples from three different concrete mixes with limestone, quartzite and granite coarse aggregates were prepared. The test samples were subjected to temperatures ranging from 25 to $650^{\circ}C$ for a duration of 2 h. Mechanical properties of concrete including the compressive and tensile strength, modulus of elasticity, and ultimate strain in compression were obtained. Effects of temperature on resistance to degradation, thermal expansion and phase compositions of the aggregates were investigated. The results indicated that the mechanical properties of concrete are largely affected from elevated temperatures and the type of coarse aggregate used. The compressive and split tensile strength, and modulus of elasticity decreased with increasing temperature, while the ultimate strain in compression increased. Concrete made of granite coarse aggregate showed higher mechanical properties at all temperatures, followed by quartzite and limestone concretes. In addition to decomposition of cement paste, the imparity in thermal expansion behavior between cement paste and aggregates, and degradation and phase decomposition (and/or transition) of aggregates under high temperature were considered as main factors impacting the mechanical properties of concrete. The novelty of this research stems from the fact that three different aggregate types are comparatively evaluated, mechanisms are systemically analyzed, and empirical relationships are established to predict the residual compressive and tensile strength, elastic modulus, and ultimate compressive strain for concretes subjected to high temperatures.

• Composites Research
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• 제26권4호
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• pp.218-222
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• 2013

본 연구에서는 제강 과정의 부산물로 발생하는 슬래그의 구조용 충전제로써의 사용 가능성을 검토하였다. 고분자 기지 슬래그 복합재료를 제작하여 슬래그 입자의 크기(8~12 ${\mu}m$ and 12~16 ${\mu}m$), 체적 비(0-30 vol.%)에 따른 슬래그 복합재료의 기계적 특성에 대한 실험적 연구를 수행하였다. 복합재료 물성에 영향을 주는 요인인 입자 분산 도와 계면상태를 고찰하기 위해 각각 시편에 대하여 조직사진을 촬영하였다. 인장 시험 결과 슬래그 복합재료의 재료강성은 슬래그 체적비가 증가할수록 증가하였고 인장 강도는 체적비가 증가할수록 감소하였다. 슬래그 복합재료의 재료강성은 슬래그 입자의 크기의 변화에 따른 뚜렷한 경향성을 띄지 않았고 인장강도는 입자의 크기가 작을수록 높은 값을 가졌다. 조직 사진 촬영 결과 슬래그 복합재료가 양호한 계면상태를 보였고, 낮은 체적 비에서는 좋은 분산 도를 나타냈지만 체적비가 높아지면 입자들의 뭉침 현상이 발생하는 것을 알 수 있었다.

• 한국소음진동공학회논문집
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• 제16권11호
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• pp.1158-1164
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• 2006

For the description of the elastic properties of linear objects a convenient parameter is the ratio of the stress to the strain, a parameter called the Young's modulus of the material. Young's modulus can be used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material. Conventional method for estimating Young's modulus measured the ratio of stress to corresponding strain below the proportional limit of a material using a tensile testing machine. But the method needs precision specimens and expensive equipment. In this paper, we proposed method for estimating Young's modulus using accelerometer. The basic idea comes from that the wave velocity is different as the Young's modulus. To obtain Young's modulus, a group velocity is obtained. It is difficult to measure group velocity. This is because plate medium has a dispersive characteristics which has different wave speed as frequency. In this paper, we used Wigner-Ville distribution to measure group velocity. To verify the proposed method, steel and acryl plate experiments have been performed. Experimental results show that the proposed method is powerful for estimating Young's modulus.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.1027-1032
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• 2007

For the description of the elastic properties of linear objects a convenient parameter is the ratio of the stress to the strain, a parameter called the Young's modulus of the material. Young's modulus can be used to predict the elongation or compression of an object as long as the stress is less than the yield strength of the material. Conventional method for estimating Young's modulus measured the ratio of stress to corresponding strain below the proportional limit of a material using a tensile testing machine. But the method needs precision specimens and expensive equipment. In this paper, we proposed method for estimating Young's modulus using accelerometer. The basic idea comes from that the wave velocity is different as the Young's modulus. To obtain Young's modulus, a group velocity is obtained. It is difficult to measure group velocity. This is because plate medium has a dispersive characteristics which has different wave speed as frequency. In this paper, we used Wigner-Ville distribution to measure group velocity. To verify the proposed method, steel and acryl plate experiments have been performed. Experimental results show that the proposed method is powerful for estimating Young's modulus.