• Title/Summary/Keyword: Dynamic Modulus of Elasticity

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Vibration analysis of boron nitride nanotubes by considering electric field and surface effect

  • Zeighampour, Hamid;Beni, YaghoubTadi
    • Advances in nano research
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    • v.11 no.6
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    • pp.607-620
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    • 2021
  • In this paper, the vibrations of boron nitride nanotubes (BNNTs) are investigated by considering the electric field. To consider the size effect at nanoscale dimensions, the surface elasticity theory is exploited. The equations of motion of the BNNTs are obtained by applying Hamilton's principle, and the clamped-guided boundary conditions are also considered. The governing equations and boundary conditions are discretized using the differential quadrature method (DQM), and the natural frequency is obtained by using the eigenvalue problem solution. The results are compared with the molecular dynamic simulation in order to validate the accurate values of the surface effects. In the molecular dynamics (MD) simulation, the potential between boron and nitride atoms is considered as the Tersoff type. The Timoshenko beam model is adopted to model BNNT. The vibrations of two types of zigzag and armchair BNNTs are considered. In the result section, the effects of chirality, surface elasticity modulus, surface residual tension, surface density, electric field, length, and thickness of BNNT on natural frequency are investigated. According to the results, it should be noted that, as an efficient non-classical continuum mechanic approach, the surface elasticity theory can be used in scrutinizing the dynamic behavior of BNNTs.

Mechanical Properties of Soil under Repeated Load (반복하중(反復荷重)을 받는 흙의 역학적(力學的) 특성(特性))

  • Chun, Byung Sik;Park, Heung Gyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.10 no.4
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    • pp.113-122
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    • 1990
  • In case of repeated wheel-loads are acted on subbase course material, field test is generally executed to get the design standard, but the study shows dynamic properties of soils especially under repeated loads, which have not been well known to us. We try not only to obtain yield stress and elastic modulus of soil in terms of rheological model interpretation but also to investigate the influence of the repeated loads. Yield stress of soil induces hardening until approaching critical value along with the increase in number of cycle, whereas the change in modulus of elasticity with respect to the number of cycle greatly depends on the strength of repeated stress, if weak in strength of repeated stress, the modulus of elasticity increases along with the number of cycle, while if strong, it tends to decrease.

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Comparison of Longitudinal Wave Velocity in Concrete by Ultrasonic Pulse Velocity Method and Impact-Echo Method (초음파 속도법과 충격반향기법에 의한 콘크리트의 종파 속도 비교)

  • Lee, Hoi-Keun;Lee, Kwang-Myong;Kim, Young-H.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.23 no.2
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    • pp.98-106
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    • 2003
  • Nondestructive test (NDT) provides much information on concrete without damage of structural functions. Of NDT methods, elastic wave propagation methods, such as ultrasonic pulse velocity (UPV) method and impact-echo (IE) method, have been successfully used to estimate the strength, elastic modulus, and Poisson's ratio of concrete as well as to detect the internal microstructural change and defects. In this study, the concretes with water-binder ratio ranging from 0.27 to 0.50 and fly ash content of 20% were made and then their longitudinal wave velocities were measured by UPV and IE method, respectively. Test results showed that the UPV is greater than the longitudinal wave velocity measured by the If method, i.e., rod-wave velocity obtained from the same concrete cylinder. It was found that the difference between the two types of velocities decreased with increasing the ages of concrete and strength level. Moreover, for the empirical formula, the dynamic Poisson's ratio, static and dynamic moduli of elasticity, and velocity-strength relationship were determined. It was observed that the Poisson's ratio and the modulus of elasticity determined by the dynamic method are greater than those determined by the static test. Consequently, for the more accurate estimation of concrete properties using the elastic wave velocities, the characteristics of these velocities should be understood.

The Stress-Strain Properties of No-Fines Lightweight Concrete Using Synthetic Lightweight Coarse Aggregate (인공경량조골재(人工輕量粗骨材)를 사용(使用)한 무세골재(無細骨材) 경량(輕量)콘크리트의 응력(應力)-변형특성(變形特性))

  • Min, Jeong Ki;Kim, Seong Wan;Sung, Chan Yong;Kim, Kyung Tae
    • Korean Journal of Agricultural Science
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    • v.23 no.1
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    • pp.120-130
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    • 1996
  • Concrete is the most commonly used structural materials, but in concrete construction, its self-weight represents a very large proportion of the total load on the structure, and there are clearly considerable advantages in reducing the density of concrete. This study was carried out to investigate the stress-strain properties of no-fines synthetic lightweight concrete with synthetic lightweight coarse aggregates. The used synthetic lightweight coarse aggregate were two types, one was expanded clay with grading 3~8mm, the other is pumice stone with grading 4.75~10mm. The results of this study were summarized as follows ; The static modulus of elasticity of the synthetic lightweight concrete was $1.8{\times}10^5kg/cm^2$ at type CE using the expanded clay and $1.6{\times}10^5kg/cm^2$ at type CL using the pumice stone. The dynamic modulus of elasticity was $1.9{\times}10^5kg/cm^2$(CE) and $2.0{\times}10^5kg/cm^2$(CL). The dynamic modulus of elasticity was 10~30% larger than that of the static modulus of elasticity. The load-time curves of synthetic lightweight concrete were shown approximately similar to each other type except for added foaming agent. The stress-strain curves in uniaxial compressive of synthetic lightweight concrete were similar to each other.

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Bending Strength of Board Manufactured from Sawdust, Rice Husk and Charcoal (톱밥과 왕겨 및 숯을 이용하여 제조한 보드의 휨성능)

  • HWANG, Jung-Woo;OH, Seung-Won
    • Journal of the Korean Wood Science and Technology
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    • v.49 no.4
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    • pp.315-327
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    • 2021
  • Purpose of this study is reviewing the use method for the sawdust (sawmilling by-product) and rice husk (Agriculture by-product) by adding charcoal, an eco-friendly material. Mixed composite boards were manufactured with those materials with each density and mixing ratio, and bending performance was investigated. When the addition ratio of sawdust, rice husk and charcoal is 50:20:20 and the resin addition ratio is 10%, as the density of the prepared mixed board ranges from 0.5 g/cm3 to 0.7 g/cm3, the bending strength was 0.42~3.24 N/mm2, dynamic modulus of elasticity was 94.5~888.4 N/mm2, and the static modulus of elasticity was in the range of 31.4~220.7 N/mm2. As the density increased, the bending performance increased, indicating that the density had a significant effect on the bending performance. In a board prepared by setting the density of 0.6 g/cm3, the addition ratio of sawdust to 50%, and the addition ratio of rice husk and charcoal at different ratios, the bending performance showed a tendency to decrease as the addition ratio of charcoal increased. The relationship between the addition ratio of rice husk and charcoal, bending strength, resonance frequency, and dynamic and static bending modulus showed a rather low correlation with the values of the coefficient of determination (R2) of 0.4562, 0.4310, 0.4589, and 0.5847, respectively. Thus, we found that the effect of the addition ratio on the bending performance was small.

A Study on the Physical Properties of Recycled Asphalt Mixtures Using Glass Fiber Reinforcement (유리섬유 보강재를 이용한 재활용 아스팔트 혼합물의 물리적 특성에 관한 연구)

  • Park, Ki Soo;Yoo, Pyeong Jun
    • International Journal of Highway Engineering
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    • v.20 no.4
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    • pp.27-34
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    • 2018
  • PURPOSES : The objective of this study is to evaluate the physical properties of recycled asphalt mixtures reinforced with glass fiber. METHODS : Firstly, mixing design was conducted on recycled asphalt mixture for use of 50% recycled aggregate. Various laboratory tests were performed on four types of recycled asphalt mixtures with different glass fiber content to evaluate the physical properties. The laboratory tests include indirect tensile strength test, dynamic modulus test, Hamburg wheel tracking test and tensile-strength ratio to evaluate cracks, rutting and moisture resistance of mixtures. RESULTS : The indirect tensile strength of fiber reinforced glass increased about 139.4%. As a result of comparing the master curves obtained by the dynamic modulus test, the elasticity was low in the low temperature region and high in the high temperature region when the glass fiber was reinforced. The glass fiber contents of PEGS 0.3%, Micro PPGF 0.1% and Macro PPGF 0.3% showed the highest moisture resistance and rutting resistance. CONCLUSIONS : The test results show that use of glass fiber reinforcement can increase the resistance to cracking, rutting, and moisture damage of asphalt mixtures. It is also necessary to validate the long-term performance of recycled asphalt mixtures with glass fiber using full scale pavement testing and field trial construction.

Relative Dynamic Modulus of Elasticity Comparison of the Eco-friendly Lightweight Concreate According to the Experimental Method (시험방법에 따른 친환경 경량콘크리트의 상대동탄성 계수 비교)

  • Lee, Soo-Hyung;Lee, Han-Baek
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2016.05a
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    • pp.181-182
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    • 2016
  • We developed eco-friendly lightweight concrete in order to apply eco-friendly lightweight concrete into structural wall or slab of shallow depth urban railway system. However, since lightweight aggregate has different structural feature of porous and it has been overvalued at current KS standard when applied, we did compare the characteristics of freezing and thawing of normal weight aggregate concrete by comparative test method(KS, ASTM). According to test method, there was a big difference of dynamic elastic modulus in lightweight concrete rather than in normal weight aggregate concrete. The big absorption factor in lightweight aggregate is main reason for that. For more detail, in KS law in which only 14 days water curing is carried out, the big amount of moisture in lightweight aggregate is frozen and high heaving pressure occurs and finally that lead to destruction of lightweight concrete. Therefore, it is considered that in case of lightweight concrete, resistibility against freezing and thawing has been undervalued in domestic KS law compared to ASTM law, which is overseas standard. So, a variety of examination about testing criteria and rule would be necessary for exact assessment of lightweight concrete.

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Dynamic Deformation Behavior of Metal Matrix Composites Under Impact Loading (충격하중을 받는 금속복합재료의 동적변형거동에 관한 연구)

  • Kim, Moon-Saeng;Lee, Hyeon-Chul
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.7 s.94
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    • pp.1772-1782
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    • 1993
  • The characteristics of metal matrix composite under dynamic tension at high strain rates up to the order of $10^3/sec$ is studied by using newly developed apparatus. The composite material processed in this research is aluminum-alumina metal matrix composites, arid fabricated by compocasting with the fiber volume fraction from 5 to 20%. The whisker and matrix material used in this paper were ${\delta}-Al_2O_3$ and Al-6061, respectively. The mechanical tests performed in this research are low and high strain rate tensile test. At low strain-rate tensile test, the modulus of elasticity and the ultimate tensile strength of the composites were improved about 77 pct. and 55 pct., respectively comparing with the unreinforced materials. At strain-rate from $10^{-3}\;to\;10^3/s$, the effect of strain-rate on the modulus, ultimate strength, flow stress is determined. Also the effect of strain rate on the modulus, ultimate tensile strength, flow stress and elongation to failures were investigated.

Measurement of Mechanical and Physical Properties of Pepper for Particle Behavior Analysis

  • Nam, Ju-Seok;Byun, Jun-Hee;Kim, Tae-Hyeong;Kim, Myoung-Ho;Kim, Dae-Cheol
    • Journal of Biosystems Engineering
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    • v.43 no.3
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    • pp.173-184
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    • 2018
  • Purpose: This study was conducted to investigate the mechanical and physical properties of a Korean red pepper variety for particle behavior analysis. Methods: Poisson's ratio, modulus of elasticity, shear modulus, density, coefficient of restitution, and coefficient of friction were derived for "AR Legend," which is a domestic pepper variety. The modulus of elasticity and Poisson's ratio were measured through a compression test using a texture analyzer. The shear modulus was calculated from the modulus of elasticity and Poisson's ratio. The density was measured using a water pycnometer method. The coefficient of restitution was measured using a collision test, and the static and dynamic friction coefficients were measured using a inclined plane test. Each test was repeated 3-5 times except for density measurement, and the results were analyzed using mean values. Results: Poisson's ratios for the pepper fruit and pepper stem were 0.295 and 0.291, respectively. Elastic moduli of the pepper fruit and pepper stem were $1.152{\times}10^7Pa$ and $3.295{\times}10^7Pa$, respectively, and the shear moduli of the pepper fruit and pepper stem were $4.624{\times}10^6Pa$ and $1.276{\times}10^7Pa$, respectively. The density of the pepper fruit and the pepper stem were $601.8kg/m^3$ and $980.4kg/m^3$, respectively. The restitution coefficients between pepper fruits, pepper stems, a pepper fruit and a pepper stem, a pepper fruit and plastic, and a pepper stem and plastic were 0.383, 0.218, 0.277, 0.399, and 0.148, respectively. The coefficients of static friction between pepper fruits, pepper stems, a pepper fruit and a pepper stem, a pepper fruit and plastic, and a pepper stem and plastic were 0.455, 0.332, 0.306, 0.364, and 0.404, respectively. The coefficients of dynamic friction between a pepper fruit and plastic and a pepper stem and plastic were 0.043 and 0.034, respectively.

Physical and Mechanical Properties of Concrete Using Waste Activated Carbon (폐활성탄을 혼입한 콘크리트의 물리.역학적 성질)

  • Kang, Hyun-Soo;Sung, Chan-Yong
    • Journal of The Korean Society of Agricultural Engineers
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    • v.51 no.1
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    • pp.21-26
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    • 2009
  • This study was performed to evaluate the physical and mechanical properties of concrete using waste activated carbon. Materials used were ordinary portlant cement, crushed coarse aggregate, natural fine aggregate, waste activated carbon, and superplasticizer. The substitution ratios of waste activated carbon were 0,1,2,3,4,5,6,7,8,9 and 10%. The unit weight was decreased and water absorption ratio was increased with increasing the waste activated carbon content, respectively. When the substitution ratio of waste activated carbon was 3%, compressive strength, flexural strength and dynamic modulus of elastisity were more higher than that of the ordinary portland cement (OPC), and it was decreased with increasing the waste activated carbon content, respectively. The most effective contents of waste activated carbon was 2% in performance and 4% in practical use Accordingly, waste activated carbon can be used for concrete material.