• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.423-430
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• 2013

In this research, a paramteric study to account for the effect of interfacial strength and nanotube agglomeration on the elastoplastic behavior of carbon nanotube reinforced polypropylene composites is performed. At first, the elastoplastic behavior of nanocomposites is predicted from molecular dynamics(MD) simulations. By combining the MD simulation results with the nonlinear micromechanics model based on the Mori-Tanaka model, a two-step domain decomposition method is applied to inversely identify the elastoplastic behavior of adsorption interphase zone inside nanocomposites. In nonlinear micromechanics model, the secant moduli method combined with field fluctuation method is used to predict the elastoplastic behavior of nanocomposites. To account for the imperfect material interface between nanotube and matrix polymer, displacement discontinuity condition is applied to the micromechanics model. Using the elastoplastic behavior of the adsorption interphase zone obtained from the present study, stress-strain relation of nanocomposites at various interfacial bonding condition and local nanotube agglomeration is predicted from nonlinear micromechanics model with and without the adsorption interphase zone. As a result, it has been found that local nanotube agglomeration is the most important design factor to maximize reinforcing effect of nanotube in elastic and plastic behavior.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.734-739
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• 2008

In this study, the nonlinear mechanical behavior of flexible textile composites was predicted by two-step analyses: micromechanics and mesomechanics. The effective material properties for fiber tows of flexible textile composite lamina were calculated in micromechanics, which were then used to calculate the effective tensile stress-strain curve of flexible textile composites in mesomechanics. A user defined material algorithm was developed and inserted in ABAQUS to account for the geometric non-linearity due to the large rotation and shear deformation of fiber tows in mesomechanics. It was found that the stress-strain behavior of flexible textile composites exhibited significant non-linearity. The effective tensile modulus agreed well with the test result.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.5-5
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• 1997

고체추진제에 대한 비선형 점탄성 구성모델이 제시되었다 추진제 손상의 원인으로서 바인더와 AP 충전제사이의 접착분리를 고려하였으며, 점탄성 드웨팅판별식이 개발되었다. 손상에 의한 추진제의 연화는 모듈러스 저하로서 취급되었으며, 모듈러스저하 계산시에 드웨팅에 의하여 야기된 미소진공구의 모듈러스는 유한 상수로서 간주되었다. 바인더와 AP 충전제사이의 접착에너지는 180$^{\circ}$ 접착박리시험으로 측정하였다. 반복하중시의 비선형성은 전단변형률 불변량의 함수로서 고려되었다. 이 구성모델은 여러 하중조건에 대한 시편실험과 비교되어 잘 일치하였으며, 복잡한 미시구조학적 역학기구 없이 간단하게 고체 추진제의 거동을 예측할 수 있게 한다.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.89-100
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• 2007

In the companion paper, we provided the novel elastic-plastic constitutive model based on the micromechanics theory. Herein, the elastic and elastic-plastic deformation of granular soils is meticulously analyzed. To guarantee high accuracy of the microscopic parameter, the systematic procedure to evaluate the parameters is provided. The analysis of the elastic response during the isotropic and triaxial compression shows that the stress-level dependency of cross-anisotropic elastic moduli is induced by the power relationship of the contact force in the normal contact stiffness, while the evolution of fabric anisotropy is more pronounced during triaxial compression. The micromechanical analysis indicates that the plastic strains are likely to occur at very small strains. The plastic deformation of tangential contacts has an important role in the reduction of soil stiffness during axial loading.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.399-404
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• 2000

Functionally graded materials(FGMs) involve dual-phase graded layers in which two different constituents are mixed continuously and functionally according to a given volume fraction. For the analysis of their thermo-mechanical response, conventional homogenized methods have been widely employed in order to estimate equivalent material properties of the graded layer. However, such overall estimations are insufficient to accurately predict the local behavior. In this paper, we compare the thermo-elastic behaviors predicted by several overall material-property estimation techniques with those obtained by discrete analysis models utilizing the finite element method, for various volume fractions and loading conditions.