• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.41-45
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• 2000

The effective elastic constants of a single-crystal superlattice film have been determined by two methods based on the velocities of surface acoustic waves (SAW). One method uses formulas to calculate the effective elastic constants of a superlattice from the known elastic constants of the constituent layers. The calculated effective elastic constants are tested by comparing the corresponding SAW velocities calculated for thin-film/substrate systems with the corresponding SAW velocities measured by line-focus acoustic microscopy (LFAM). The other method determines the effective elastic constants of the superlattices by inverting the SAW velocity dispersion data measured by LFAM. The results of both methods applied to a TiN/NbN superlattice film are in good agreement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.81-92
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• 2010

In design of steel frames, it is generally believed that elastic system buckling analysis cannot predict real behaviors of structures, while inelastic system buckling analysis can give informative buckling behaviors of individual members considering inelastic material behavior. However, the use of Euler buckling equation with these system buckling analyses have the inherent problem that the methods evaluate unexpectedly large effective lengths of members having relatively small axial forces. This paper proposes a new method of obtaining elastic and inelastic effective lengths of all members in steel frames. Considering a fictitious axial force factor for each story of frames, the proposed method determines the effective lengths using the inelastic stiffness reduction factor and the iterative eigenvalue analysis. In order to verify the validity of the proposed method, the effective lengths of example frames by the proposed method were compared to those of previously established methods. As a result, the proposed method gives reasonable effective lengths of all members in steel frames. The effect of inelastic material behavior on the effective lengths of members was also discussed.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.47-55
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• 2000

Non-linear behavior of rock under compression can be predicted by a crack model. Crack growth in rock renders rock anisotropic. The degree of anisotropy is explained in terms of elastic moduli as a function of load level. In this study, we calculate the changes of elastic moduli due to crack growth numerically by using a crack model and compare these values with experimental results obtained from the measurement of ultrasonic wave velocities. Image processing technique is used to obtain the initial crack information needed for the numerical calculation of elastic moduli.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.06a
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• pp.96-99
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• 1992

섬유강화 복합재료의 동탄성계수와 감쇠특성을 규명하기 위하여 랜덤하게 분포된 무한 실린더 형상의 산란체를 가진 매질내에서, 조화운동을 하는 압축 및 SV탄성파의 전파에 관하여 연구하였다. 단일 실린더에 대한 산란계수로부터 La의 준결정근사법을 이용하여 다중산란에 관한 이론을 유도하였고, 매질내에서의 파동전파 특성을 내포하는 분산관계식을 얻었다. 수치적으로 분산관계식의 해를 구함으로써 2 차원 유효체적강성, 횡방향 유효전단강성 및 각 파동의 전파에 따른 감쇠계수를 주파수와 체적비의 함수로서 제시하였다.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.301-308
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• 2000

Non-linear behavior of rock under compression can be predicted by a crack model. Crack growth in rock renders rock anisotropic. The degree of anisotropy is explained in terms of elastic moduli as a function of load level. In this study, we calculate the changes of elastic moduli due to crack growth numerically by using a crack model and compare these values with experimental results obtained from the measurement of ultrasonic wave velocities. Image processing technique is used to obtain the initial crack information needed for the numerical calculation of elastic moduli.

• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.369-377
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• 2013

The age-adjusted effective modulus method has been known to provide more precise assessment than the traditional Yassumi method for long-term behavior estimation of prestressed composite girders. The age-adjusted effective modulus method, however, involves complicated calculation, thereby making the Yassumi method more prevalent in actual design. This study presents rational approaches to revise creep coefficients for the Yassumi method by using parametric study results obtained from the age-adjusted effective modulus method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.2
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• pp.169-179
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• 2005

An improved method for evaluating effective buckling lengths of beam-column members in plane frames is newly proposed based on system inelastic buckling analysis. To this end, the tangent stiffness matrix of be am-column elements is first calculated using stability functions and then the inelastic buckling analysis method is presented. The scheme for determining effective length of individual members is also addressed. Design examples and numerical results ?uc presented to show the validity of the proposed method.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.372-377
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• 2001

A theory developed in Part I has been applied to calculate effective elastic and thermoelastic moduli of particle-strengthened, unidirectionally fiber-reinforced, and layered composites. For the unidirectional fiber composites the effect of fiber aspect ratio is taken into account. The analytical solutions obtained to the effective elastic moduli are compared with some of existing expressions and the following results are found. The effective bulk and shear moduli of the particle strengthened composites coincide with Korner's expressions, which correspond with the lower bounds of Hanshin and Shtrikman. The same expressions as the lower bounds of Hill and Hanshin are obtained for five independent moduli of the aligned continuous fiber composites, four of which coincide with Hanshin and Rosen's exact solutions for 'composite cylinder assemblage'.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2C
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• pp.71-79
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• 2009

This study is to develope the resilient modulus prediction model, which is the function of mean effective principal stress and axial strain, for three types of railroad trackbed materials such as crushed stone, weathered granite soil, and crushed-rock soil mixture. The model consists of the maximum Young's modulus and nonlinear values for higher strain, analogous to dynamic shear modulus. The maximum value is modeled by model parameters, $A_E$ and the power of mean effective principal stress, $n_E$. The nonlinear portion is represented by modified hyperbolic model, with the model parameters of reference strain, ${\varepsilon}_r$ and curvature coefficient, a. To assess the performance of the prediction models proposed herein, the elastic response of a test trackbed near PyeongTaek, Korea, was evaluated using a 3-D elastic multilayer computer program (GEOTRACK). The results were compared with measured elastic vertical displacement during the passages of freight and passenger trains at two locations, whose sub-ballasts were crushed stone and weathered granite soil, respectively. The calculated vertical displacements of the sub-ballasts are within the order of 0.6mm, and agree well with measured values. The prediction models are thus concluded to work properly in the preliminary investigation.

• Composites Research
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• v.29 no.2
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• pp.66-72
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• 2016

Porosity in polymer matrix composites increases rapidly during thermochemical decomposition at high temperatures. The generation of pores reduces elastic moduli and failure strengths of composite materials, and gas pressures in internal pores influence thermomechanical behaviors. In this paper, micromechanical finite element analysis is carried out by using two-dimensional representative volume elements for unidirectionally fiber-reinforced composites with porous matrix. According to the state of the pores, effective elastic moduli, poroelastic parameters and failure strengths of the overall composites are investigated in detail. In particular, it is confirmed that the failure strengths in the transvers and through-thickness directions are predicted much more weakly than the strength of nonpored matrix, and decrease consistently as the porosity of matrix increases.