• Coupled systems mechanics
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• v.11 no.1
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• pp.55-78
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• 2022

The main aim of this paper is the identification of the model parameters for the constitutive model of concrete and concrete-like materials capable of representing full set of 3D failure mechanisms under various stress states. Identification procedure is performed taking into account multi-scale character of concrete as a structural material. In that sense, macro-scale model is used as a model on which the identification procedure is based, while multi-scale model which assume strong coupling between coarse and fine scale is used for numerical simulation of experimental results. Since concrete possess a few clearly distinguished phases in process of deformation until failure, macro-scale model contains practically all important ingredients to include both bulk dissipation and surface dissipation. On the other side, multi-scale model consisted of an assembly micro-scale elements perfectly fitted into macro-scale elements domain describes localized failure through the implementation of embedded strong discontinuity. This corresponds to surface dissipation in macro-scale model which is described by practically the same approach. Identification procedure is divided into three completely separate stages to utilize the fact that all material parameters of macro-scale model have clear physical interpretation. In this way, computational cost is significantly reduced as solving three simpler identification steps in a batch form is much more efficient than the dealing with the full-scale problem. Since complexity of identification procedure primarily depends on the choice of either experimental or numerical setup, several numerical examples capable of representing both homogeneous and heterogeneous stress state are performed to illustrate performance of the proposed methodology.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.4
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• pp.1-10
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• 2014

A progressive failure analysis procedure for composite laminates is developed in here and in the companion paper. An anisotropic plastic constitutive model for fiber-reinforced composite material, is developed, which is simple and efficient to be implemented into computer program for a predictive analysis procedure of composites. In current development of the constitutive model, an incremental elastic-plastic constitutive model is adopted to represent progressively the nonlinear material behavior of composite materials until a material failure is predicted. An anisotropic initial yield criterion is established that includes the effects of different yield strengths in each material direction, and between tension and compression. Anisotropic work-hardening model and subsequent yield surface are developed to describe material behavior beyond the initial yield under the general loading condition. The current model is implemented into a computer code, which is Predictive Analysis for Composite Structures (PACS), and is presented in the companion paper. The accuracy and efficiency of the anisotropic plastic constitutive model are verified by solving a number of various fiber-reinforced composite laminates with and without geometric discontinuity. The comparisons of the numerical results to the experimental and other numerical results available in the literature indicate the validity and efficiency of the developed model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.4
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• pp.361-366
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• 1982

This paper attempts to predict the stress concentration around the corner of rectangular inserts of different material of mechanical properties from the base material of the finite rectangular plate. The problem is analyzed through the FEM and photo-elastic experiment with the inclination angle of the insert as variable parameters. According to the experiments and the numerical analysis, the maximum stress concentration occurs at the point of tangential discontinuity of a insert. When the lain insert or opening was so inclined that the distance from the free end of the plate to a corner became minimum, the maximum stress concentration factor was found.

• Journal of the Korean Society for Advanced Composite Structures
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• v.5 no.4
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• pp.11-17
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• 2014

A progressive failure analysis procedure for composite laminates is completed in here. An anisotropic plastic constitutive model for fiber-reinforced composite material is implemented into computer program for a predictive analysis procedure of composite laminates. Also, in order to describe material behavior beyond the initial yield, the anisotropic work-hardening model and subsequent yield surface are implemented into a computer code, which is Predictive Analysis for Composite Structures (PACS). The accuracy and efficiency of the anisotropic plastic constitutive model and the computer program PACS are verified by solving a number of various fiber-reinforced composite laminates with and without geometric discontinuity. The comparisons of the numerical results to the experimental and other numerical results available in the literature indicate the validity and efficiency of the developed model.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.349-352
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• 1996

When the ideality factor of collector current of AIGaAs/GaAs Heterojunction Bipolar Transistors (HBTs) is larger than unity, conventional $I_{CO}$ / $T^2$ versus 1000/T plot used in the determination of the barrier height of base-emitter junction of HBT was deviated from the straight line. We introduced the effective temperature $T_{eff}$ as nT in the Thermionic-emission equation. The modified $I_{CO}$ /TB versus 1000/ $T_{eff}$ plot was on the straight line in the temperature range considered. The activation energy obtained from the modified plot is 1.61 eV. The conduction band discontinuity calculated using this value was 0.305 eV and this value is coincident with the generally accepted value of 0.3 eV. eV.

• Structural Engineering and Mechanics
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• v.4 no.5
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• pp.469-484
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• 1996

Green's functions are obtained in exact closed-forms for the elastic fields in bi-material elastic solids with slipping interface and differing transversely isotropic properties induced by concentrated point and ring force vectors. For the concentrated point force vector, the Green functions are expressed in terms of elementary harmonic functions. For the concentrated ring force vector, the Green functions are expressed in terms of the complete elliptic integral. Numerical results are presented to illustrate the effect of anisotropic bi-material properties on the transmission of normal contact stress and the discontinuity of lateral displacements at the slipping interface. The closed-form Green's functions are systematically presented in matrix forms which can be easily implemented in numerical schemes such as boundary element methods to solve elastic problems in computational mechanics.

• Structural Engineering and Mechanics
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• v.80 no.5
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• pp.625-643
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• 2021

In this paper, we present a new method to calculate interface warping functions for the analysis of beams with geometric and material discontinuities in the longitudinal direction. The classical Saint Venant torsion theory is extended to a three-dimensional domain by considering the longitudinal direction. The interface warping is calculated by considering both adjacent cross-sections of a given interface. We also propose a finite element procedure to simultaneously calculate the interface warping function and the corresponding twisting center. The calculated interface warping functions are employed in the continuum-mechanics based beam formulation to analyze arbitrary shape cross-section beams with longitudinal discontinuities. Compared to the previous work by Yoon and Lee (2014a), both geometric and material discontinuities are considered with fewer degrees of freedom and higher accuracy in beam finite element analysis. Through various numerical examples, the effectiveness of the proposed interface warping function is demonstrated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.359-370
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• 1993

Up to now, most studies are on interface crack problems in isotropic-isotropic dissimilar materials, but it seems to be not so much on anisotropic dissimlar materials. In this study, the stress intensity factors for an interface crack in anisotropic dissimilar materials are analysed using author's proposed extrapolation method by BEM and we have done a parametric study about material properties or shapes of crack affecting to the stress intensity factors. However, as there are not other's comparable numerical results on these anisotropic dissimilar materials to the best of author's knowledge, the reliability of the present results was proved by following two methods. The first is considering the asymptotic characteristic about stress intensity factors for an interface crack in anisotropic materials when the ansiotropic material approachs to the isotropic material. The second is considering the discontinuity of stress intensity factors between of a crack in an identical homogeneous anisotropic material and an interface crack in anisotropic dissimilar materials.

• Journal of computational fluids engineering
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• v.11 no.1 s.32
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• pp.29-35
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• 2006

A code is developed to analyze a spherically symmetric underwater explosion. The arbitrary Lagrangian-Eulerian(ALE) Godunov scheme for two-phase flow is used to calculate numerical fluxes through moving control surfaces. For detonation gas of TNT and liquid water, the Jones-Wilkins-Lee(JWL) equation of states and the isentropic Tait relation are used respectively. It is suggested to use the Godunov variable to estimate the velocity of a material interface. The code is validated through comparisons with other results on the gas-water shock tube problem. It is shown that the code can handle generation of discontinuity and recovering of continuity in the normal velocity near the material interface during shock waves interact with the material interface. The developed code is applied to analyze a spherically symmetric underwater explosion. Repeated transmissions of shock waves are clearly captured. The calculated period and maximum radius of detonation gas bubble show good agreements with experimental and other numerical results.

• Journal of Ocean Engineering and Technology
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• v.13 no.1 s.31
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• pp.62-69
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• 1999

67Ni-22Cr-10Al-1Y and $ZrO_2-8Y_2O_3$ were coated on the substrate surface of ST304 and Al2024 by the plasma spraying method. The adgesion of the films varies depending on the substrates and the laminating method. In the case of STS304, the cracks were observed at thermal shock temperature difference ${Delta}T$ of $900^{circ}C$ in the non functionally gradient material(NFGM) and at $1100^{circ}C$ in the functionally gradient material(FGM). The film adhesion of the FGM is better than that of the NFGM in ST304. The cumulative AE count of the FGM of STS304 increased continuously at the bending test. But the NFGM of STS304 showed discontinuity of the AE count. The total AE count for the FGM of STS304 decreased as the number of thermal shock increased, and this tendency was evident as the thermal shock temperature difference increased.