• Transactions of Materials Processing
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• v.24 no.6
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• pp.395-399
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• 2015

A microstructure-based finite element simulation was conducted to predict the plastic strain ratio (R-value) of a dual-phase (DP) steel. The representative volume elements (RVEs) concept was adopted for the image-based FE modeling and a 3D model was constructed using sequential 2D images. Each phase was considered with the von-Mises yield criterion and the Swift model. The Swift parameters were defined by the empirical equations based on the chemical composition. The developed model was applied to analyze the effect of residual stress on the R-value and stress distribution. In order to consider the residual stress development after cold rolling, 10 % compression was applied in the thickness direction and unloaded before the tensile stress was applied in the rolling direction. The results showed a reasonable prediction for the R-value evolution: a sharp increase at small strains was well described and a transition followed in the downward direction. The R-value evolution was analyzed using the stress distribution change on the π-plane

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2823-2834
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• 2023

Austenitic stainless steel welds (ASSWs) of nuclear components undergo aging-related degradations caused by high temperature and neutron radiation. Since irradiation leads to the change of material characteristics, relevant quantification is important for long-term operation, but limitations exist. Although ion irradiation is utilized to emulate neutron irradiation, its penetration depth is too shallow to measure bulk properties. In this study, a systematic approach was suggested to estimate mechanical properties of ion irradiated 308 ASSW. First of all, weld specimens were irradiated by 2 MeV proton to 1 and 10 dpa. Microstructure evolutions due to irradiation in δ-ferrite and austenite phases were characterized and micropillar compression tests were performed. In succession, dislocation density based stress-strain (S-S) relationships and quantification models of irradiation defects were adopted to define phases in finite element analyses. Resultant microscopic S-S curves were compared to verify material parameters. Finally, macroscopic behaviors were calculated by multiscale simulations using real microstructure based representative volume element (RVE). Validity of the approach was verified for the unirradiated specimens such that the estimated S-S curves and 0.2% offset yield strengths (YSs) which was 363.14 MPa were in 10% agreement with test. For irradiated specimens, the estimated YS were 917.41 MPa in 9% agreement.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.627-638
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• 2019

Estimation of representative elementary volume (REV) of jointed rock masses is critical to predict the mechanical behavior of field-scale rock masses. The REV of jointed rock masses at site is strongly influenced by stress state. The paper proposed a method to systematically studied the influence of confining stress on the REV of jointed rock masses with various strengths (weak, medium and strong), which were sourced from the water inlet slope of Xiaowan Hydropower Station, China. A finite element method considering material heterogeneity was employed, a series of two-dimensional (2D) models was established based on the Monte-Carlo method and a lot of biaxial compressive tests were conducted. Numerical results showed that the REV of jointed rock masses presented a step-like reduction as the normalized confining stress increased. Confining stress weakened the size effect of jointed rock masses, indicating that the REV determined under uniaxial compression test can be reasonably taken as the REV of jointed rock masses under complexed in-situ stress environment.

• Multiscale and Multiphysics Mechanics
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• v.1 no.1
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• pp.65-76
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• 2016

In this study, an influence of local variation of nanoparticulate volume fraction on the homogenized elastic properties is investigated. It is well known that interface effect is dependent on the radius and volume fraction of reinforced nanofillers. However, there is no study on the multiscale modeling and analysis of polymer nanocomposites including polydispersed nanoparticles with consideration of interphase zone, which is dependent on the volume fraction of corresponding nanoparticles. As results of numerical examples, it is confirmed that an influence of local variation of nanoparticulate volume fraction should be considered for non-dilute system such as cluster of nanoparticles. Therefore representative volume element analysis is conducted by considering local variation of nanoparticle volume fraction in order to analyze the practical size of cell including hundreds of nanoparticles. It is expected that this study could be extended to the multiparticulate nanocomposite systems including polydispersed nanoparticles.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.153.2-153.2
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• 2005

• Transactions of Materials Processing
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• v.32 no.1
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• pp.28-34
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• 2023

In this research, a representative volume element (RVE)-based FE Model is presented to estimate the mechanical properties of additively manufactured continuous fiber-reinforced composites with different fiber orientations. To construct the model, an ABAQUS Python script has been implemented to produce matrix and fiber in the desired orientations at the RVE. A script has also been developed to apply the periodic boundary conditions to the RVE. Experimental tests were conducted to validate the numerical models. Tensile specimens with the fiber directions aligned in the 0, 45, and 90 degrees to the loading direction were manufactured using a continuous fiber 3D printer and tensile tests were performed in the three directions. Tensile tests were also simulated using the RVE models. The predicted Young's moduli compared well with the measurements: the Young's modulus prediction accuracy values were 83.73, 97.70, and 92.92 percent for the specimens in the 0, 45, and 90 degrees, respectively. The proposed method with periodic boundary conditions precisely evaluated the elastic properties of additively manufactured continuous fiber-reinforced composites with complex microstructures.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.76-85
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• 2014

In this paper, the equivalent coefficient of thermal expansion (CTE) of fiber reinforced plastic composite material is investigated with various CTE prediction schemes. Although there are several methods for predicting the equivalent CTEs, most of them have some limitations of are not much accurate when comparing prediction results with test results. In the framework of computational homogenization, a representative volume element is taken from the predefined fiber-volume ratio, and modelled with finite element mesh. Finally, the equivalent CTEs are obtained by applying periodic boundary condition. To verify the performance of the proposed method, the results obtained are compared with those by the existing methods and test results. Additionally, the thermal pointing error analysis for star tracker support structure is conducted and its accuracy is estimated according to CTE prediction schemes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.78-81
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• 2002

Printed Circuit Boards for satellite are composed of multi-layered copper plate and glass epoxy. Each copper layer have the complicated and different pattern to operate correctly for its mission. Especially. copper layer give effect on the PCB stiffness seriously. But It can make more complicate to predict the exact stiffness of PCB. In KOMPSAT-2 program, too many type of PCB are used for each electronic unit, and they have different type of pattern of copper layer. Solar array regulator has two type of PCB and it will be considered for this study. In this study. we calculate the PCB board stiffness of KOMPSAT-2 SAR unit considering the concept of simplified representative volume element. It will be correlated with the test results under KOMPSAT-2 vibration environmental condition to increase the reliability of this study.

• Journal of Ocean Engineering and Technology
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• v.6 no.2
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• pp.94-102
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• 1992

This paper presents the method of numerical analysis concerned with the hydropdynamic forces and moments of the floating bodies exerted by waves. The analytic methods of hydrodynamic wave forces and moments for large volume structures are generally classified into four categories ; the strip method, the boundary element method, the finite element method, and the potential matching method. In the case of the comparatively large structures, diffraction theory can be applied. However, there are no application limits of diffraction theory which have been known concerning with the analytic method of the rectangular structures. In this paper, the two-dimensional B.E.M. is treated for a moored small rectangular structure in order to evaluate applicability of diffraction theory. Numerical calculation is carried out for the structure. The results are compared with some other ones for verification. The result shows that diffraction theory is applicable to structures smaller than 0.15 in the ratio of the representative structure length d to wave length L for rectangular ones.

• Tunnel and Underground Space
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• v.8 no.4
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• pp.275-286
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• 1998

The effective permeability and the representative element volume(REV) of fracture network model were evaluated based on the parameters such as permeability tensor, principal permeability and the direction of principal permeability. The effective permeability ranges between the harmonic mean and the arithmetic mean of the local permeabilities of subdivided blocks. From the numerical experiments, which were for investigating the influence of model volume on the variation of flux for the cubic models, it was found that the variation of flux became reduced as the model volume approached REV. The variation of groundwater flux into the tunnel in the fracture network model was mainly dependent on the ratio of the tunnel length to model size rather than REV. And it was found that groundwater flux into the tunnel was not completely consistent between the fracture network model and the equivalent porous media model, especially when the ratio of the tunnel length to model size is small.