• Imaging Science in Dentistry
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• 제37권1호
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• pp.53-59
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• 2007

Purpose : Bone mineral density (BMD) and bone microarchitecture are important determinants for bone strength. Recently micro-CT have provided possibilities for measuring a variety of structural indices to characterize bone microarchitecture. The objective of this study was to compare the BMD and micro-CT parameters with Young's modulus calculated by finite element analysis (FEA) for the evaluation of bone strength. Materials and Methods Bone specimens were obtained from the 18 female rabbits aged 16 weeks. Of those, 36 samples (right and left femur) were selected for 3D micro-CT analysis $(ANT^{TM},\;SKYSCAN,\;Belgium)$ and BMD by PIXlmus 2 (GE Lunar Co. USA). Five microstructural parameters of micro-CT, such as trabecular thickness (Tb.Th), bone specific surface (BS/BV), percent bone volume (BV/TV), structure model index (SMI) and degree of anisotropy (DOA) were studied. Young's modulus was obtained by software program (ANSYS 9.0, ANSYS Inc, Canonsburg, PA) based on micro-CT three dimensional images. Results : Young's modulus assessed by FEA correlated significantly with Tb.Th, BV/TV, BS/BV and SMI respectively. Young's modulus showed higher correlation with these rnicrostructural parameters of micro-CT than BMD. Microstructural parameters except DOA showed significant correlations within the examined group. Conclusion The microarchitectural parameters o( micro-CT and BMD represented some informations in the evaluation of bone strength assessed by FEA.

• 비파괴검사학회지
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• 제30권2호
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• pp.146-154
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• 2010

알루미늄 5052 합금의 탄성특성에 대한 ECAP 강소성변형과 어닐링효과를 연구하였다. 알루미늄 5052 합금은 용체화 처리 후 ECAP 가공하고 어닐링처리를 수행하였다. 탄성계수는 기존의 인장시험과 나노압입시험을 통해 측정하고 음향현미경의 음향재료신호를 이용하여 시료의 표변에서 탄성계수를 측정하였다. 기존의 시험법으로는 불가능한 소성변형과 열처리에 따른 탄성계수의 변화를 음향재료신호를 이용하여 성공적으로 측정하였고 개개의 결정립에서도 결정방위에 의존하는 탄성계수를 얻었다.

• 한국환경과학회지
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• 제26권1호
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• pp.1-10
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• 2017

In this study, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/graphene oxide (GO) nanocomposite films containing various content of GO were prepared using solution casting method. The effect of GO content on Young's modulus and dispersion of GO in PHBV matrix was investigated. Also, the thermomechanical properties, oxygen transmission rates and hydrolytic degradation of PHBV/GO nanocomposite films were studied. The addition of GO into PHBV improves the Young's modulus and decreases thermal expansion coefficient. The improvement can be mainly attributed to good dispersion of GO and interfacial interactions between PHBV and GO. Furthermore, PHBV/GO nanocomposite films show good oxygen barrier properties. PHBV/GO nanocomposites show lower hydrolytic degradation rates with increasing content of GO.

• The Journal of the Acoustical Society of Korea
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• 제21권1E호
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• pp.12-17
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• 2002

Two improvements are discussed in measurement of the complex Young's modulus of the acoustic materials by using the transfer function method. It is found that the accelerometer misalignment might result in the severe measurement error, particularly in high frequency range. The supporting structure is modified to attach the upper and lower accelerometers along the vertical axis. Secondly, the method fur solving the equation associated with wave model is described. The solution of the lumped mass-spring model is chosen as the starting value for low frequency range, while in the mid and high frequency, the solution to the previous frequency step is used as the initial values. Measurements are done for hard and soft rubber specimens. It is shown that the erroneous peaks in the transfer function, due to the measurement error, cause highly incorrect Young's modulus and loss factors.

• Geomechanics and Engineering
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• 제12권5호
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• pp.863-870
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• 2017

With the increasing interest in using bacterial biofilms in geo-engineering practices, such as soil improvement, sealing leakage in earth structures, and hydraulic barrier installation, understanding of the contribution of bacterial biofilm formation to mechanical and hydraulic behavior of soils is important. While mechanical properties of soft gel-like biofilms need to be identified for appropriate modeling and prediction of behaviors of biofilm-associated soils, elastic properties of biofilms remain poorly understood. Therefore, this study investigated the microscale Young's modulus of biofilms produced by Shewanella oneidensis MR-1 in a liquid phase. The indentation test was performed on a biofilm sample using the atomic force microscopy (AFM) with a spherical indentor, and the force-indentation responses were obtained during approach and retraction traces. Young's modulus of biofilms was estimated to be ~33-38 kPa from these force-indentation curves and Hertzian contact theory. It appears that the AFM indentation result captures the microscale local characteristics of biofilms and its stiffness is relatively large compared to the other methods, including rheometer and hydrodynamic shear tests, which reflect the average macro-scale behaviors. While modeling of mechanical behaviors of biofilm-associated soils requires the properties of each component, the obtained results provide information on the mechanical properties of biofilms that can be considered as cementing, gluing, or filling materials in soils.

• 한국생산제조학회지
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• 제24권4호
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• pp.421-427
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• 2015

In this paper, a description is given of finite element method (FEM) simulations of the elastic bending modulus of multi-layered graphene sheets that were carried out to investigate the mechanical behavior of graphene sheets with different gap thicknesses through molecular mechanics theory. The interaction forces between layers with various gap thicknesses were considered based on the van der Waals interaction. A finite element (FE) model of a multi-layered rectangular graphene sheet was proposed with beam elements representing bonded interactions and spring elements representing non-bonded interactions between layers and between diagonally adjacent atoms. As a result, the average elastic bending modulus was predicted to be 1.13 TPa in the armchair direction and 1.18 TPa in the zigzag direction. The simulation results from this work are comparable to both experimental tests and numerical studies from the literature.

• 터널과지하공간
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• 제21권6호
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• pp.480-493
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• 2011

암석의 동적물성은 내진설계의 동적해석에 필요한 물성이다. 본 연구에서는 충남 연기군 지역의 화강암 시험편을 대상으로 양단자유 공진주시험을 실시하여 동적물성인 동탄성계수, 동전단계수, 감쇠비 등의 특성을 분석하고, 역학적 물성과의 상관관계를 분석하였다. 탄성파속도를 기준으로 동적물성을 분석한 결과, 탄성파속도가 빠를수록 동탄성계수와 동전단계수는 선형적으로 증가하는 경향을 보였으며, 감쇠비는 비선형적으로 감소되는 것으로 조사되었다. 논문은 사인형태의 입사파에 대한 장점을 설명하고 또한 동하중에 대한 암석의 크기효과를 설명하고 있다.

• Current Applied Physics
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• 제18권12호
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• pp.1486-1491
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• 2018

In recent years, mica has been successfully used as a substrate for the growth of flexible epitaxial ferroelectric oxide thin films. Here, we systematically investigated the flexibility of mica in terms of its thickness, repeated bending/unbending, extremely hot/cold conditions, and successive thermal cycling. A $20-{\mu}m-thick$ sheet of mica is flexible even up to the bending radius of 5 mm, and it is durable for 20,000 cycles of up- and down-bending. In addition, the mica shows flexibility at 10 and 773 K, and thermal cycling stability for the temperature variation of ca. 400 K. Compared with the widely used flexible polyimide, mica has a significantly higher Young's modulus (ca. 5.4 GPa) and negligible hysteresis in the force-displacement curve. These results show that mica should be a suitable substrate for piezoelectric energy-harvesting applications of ferroelectric oxide thin films at extremely low and high temperatures.

• 한국환경과학회지
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• 제23권11호
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• pp.1909-1918
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• 2014

In this experiment no solvent based polyurethane(PU) adhesives were prepared with the polyol, isocyanate, dioctyl phthalate(DOP), 2-hydroxyethylacrylate(2-HEA) and other acrylate monomers. The softenening point of the PU adhesives measured by Ring & Ball method were examined in the present study. And adhesion strength and mechanical properties such as tensile strength and 100% modulus of the PU adhesives were evaluated by Universal Test Machine. The experimental results showed that increase of both DPE-41, benzoylperoxide(BPO) and toluene diisocyanate(TDI) increased softenening point, adhesion strength, tensile strength and 100% modulus. However as DOP content increased sofenening point, adhesion strength decreased and tensile strength, 100% modulus also decreased.

• 한국안전학회지
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• 제17권2호
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• pp.52-57
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• 2002

In this study. stress-strain relationships were investigated by performing the confined extension tests for seven types of geosynthetics such as geotextiles, composite geosynthetics and geogrids. A comparison was made between unconfined and confined moduli for each geosynthetic material to quantify the soil confinement effect on stress-strain properties. A comparison was also made between the increase of moduli at the same strain level with the types of the geosynthetics to demonstrate the different stress-strain responses. Based on the result of the extension tests, the higher the confining stress, the larger the secant modulus of geosynthetics. The secant modulus at 5% strain is twice as much as that of 10% strain, especially there is a noticeable increasing of secant modulus for the two nonwoven geotextiles.