• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.70-75
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• 2000

In this paper a new constitutive model for ductile materials was proposed. This model can describe the material degradation due to the evolution of isotropic damage during elasto-platic deformation. The plastic flow rule was derived under the framework of thermodynamic approach of continuum damage mechanics(CDM) in which plastic strain hardening parameters and isotropic damage were taken as thermodynamic state variables. And the process to determine material constants for constitutive model using an experimental data was presented.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.3
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• pp.269-273
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• 2015

The study investigated the effect of the distance between two collinear circumferential surface cracks on the primary stress corrosion crack (PWSCC) growth in alloy 600TT steam generator tubes using a finite element damage analysis based on the PWSCC initiation model and macroscopic phenomenological damage mechanics approach. The damage analysis method was verified by comparing the results to the previous study results. The verified method was applied to collinear circumferential surface PWSCCs. As a result, it was found that the collinear cracks showed earlier coalescence and penetration times than the a single crack, and the times increased with the distance. In addition, it is expected that penetration may occur before coalescence of two cracks if they are more than a specific distance apart.

• Tunnel and Underground Space
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• v.17 no.2 s.67
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• pp.109-118
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• 2007

The excavation damaged zone (EDZ) is an area around an excavation where in situ rock mass properties, stress condition. displacement. groundwater flow conditions have been altered due to the excavation. Various studies have been carried out on EDZ, but most studies have been focused on the mechanical bahavior of EDZ by in situ experiment. Even though the EDZ could potentially form a high permeable pathway of groundwater flow, only a few studies were performed on the analysis of groundwater flow in EDZ. In this study, the' hydraulic EDZ' was defined as the rock Lone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation. And hydraulic EDZ (hydraulic aperture changed zone) estimated by two-dimensional DEM program was considered in three-dimensional DFN model. From this approach the groundwater flow characteristics corresponding to hydraulic aperture change were examined. Together. a parametric study was performed to examine the boundary conditions that frequently used in DFN analysis such as constant head or constant flux condition. According to the numerical analysis, hydraulic aperture change induced by the hydraulic-mechanical interaction becomes one of the most important factors Influencing the hydraulic behavior of jointed rock masses. And also from this study, we suggest the proper boundary condition in three-dimensional DFN model.

• Tunnel and Underground Space
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• v.29 no.4
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• pp.262-279
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• 2019

In the engineering barriers of high-level radioactive waste disposal, gases could be generated through a number of processes. If the gas production rate exceeds the gas diffusion rate, the pressure of the gas increases and gases could migrate through the bentonite buffer. Because people and the environment can be exposed to radioactivity, it is very important to clarify gas migration in terms of long-term integrity of the engineered barrier system. In particular, it is necessary to identify the hydro-mechanical mechanism for the dilation flow, which is a very important gas flow phenomenon only in medium containing large amounts of clay materials such as bentonite buffer, and to develop and validate new numerical approach for the quantitative evaluation of the gas migration phenomenon. Therefore, in this study, we developed a two-phase flow model considering the mechanical damage model in order to simulate the gas migration in the engineered barrier system, and validated with 1D gas flow modelling through saturated bentonite under constant volume boundary conditions. As a result of numerical analysis, the rapid increase in pore water pressure, stress, and gas outflow could be simulated when the dilation flow was occurred.

• Tunnel and Underground Space
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• v.30 no.4
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• pp.306-319
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• 2020

Characterizations of Excavation Damage Zone (EDZ), which is hydro-mechanical degrading the host rock, are the important issues on the geological repository for the spent nuclear fuel. In the DECOVALEX 2019 project, Task G aimed to model the fractured rock numerically, describe the hydro-mechanical behavior of EDZ, and predict the change of the hydraulic factor during the lifetime of the geological repository. Task G prepared two-dimensional fractured rock model to compare the characteristics of each simulation tools in Work Package 1, validated the extended three-dimensional model using the TAS04 in-situ interference tests from Äspö Hard Rock Laboratory in Work Package 2, and applied the thermal and glacial loads to monitor the long-term hydro-mechanical response on the fractured rock in Work Package 3. Each modelling team adopted both Finite Element Method (FEM) and Discrete Element Method (DEM) to simulate the hydro-mechanical behavior of the fracture rock, and added the various approaches to describe the EDZ and fracture geometry which are appropriate to each simulation method. Therefore, this research can introduce a variety of numerical approaches and considerations to model the geological repository for the spent nuclear fuel in the crystalline fractured rock.

• Computational Structural Engineering
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• v.10 no.4
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• pp.131-142
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• 1997

In this paper the kinematics of damage for finite elastoplastic deformations is introduced using the fourth-order damage effect tensor through the concept of the effective stress within the framework of continuum damage mechanics. Unlike the approach of strain equivalence or energy equivalence, which is applicable only to small strains, the proposed kinematic description provides a relation between the effective strain and the damage elastoplastic strain in finite deformation. This is accomplished by directly considering the kinematics of the deformation field both real configuration. The proposed approach shows that it is equivalent to the hypothesis of energy equivalence at finite strains. The damage effect tensor in this work is explicitly characterized in terms of a kinematic measure of damage in the elastoplastic domain through a second-order damage tensor.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.76-83
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• 2000

this paper was concentrated on the finite element formulation to solve boundary value problems by using the isotropic elasto-plastic damage constitutive model proposed previously(Noh, 2000) The plastic damage of ductile materials is generally accompanied by large plasticdeformation and strain. So nonlinearity problems induced by large deformation large rotation and large strain behaviors were dealt with using the nonlinear kinematics of elasto-plastic deformations based on the continuum mechanics. The elasto-plastic damage constitutive model was applied to the nonlinear finite element formulation process of Shin et al(1997) and an improved analysis model considering the all nonlinearities of structural behaviors is proposed. Finally to investigate the applicability and validity of the numerical model some numerial examples were considered.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.12
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• pp.30-40
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• 1998

We have calculated ultra-low energy silicon-self ion implantations and silicon damages through classical molecular dynamics simulation using empirical potentials. We tested whether the recently developed Environment-Dependent Interatomic Potential(EDIP) was suitable for ultra low energy ion implantation simulation, and found that point defects formation energies were in good agreement with other theoretical calculations, but the calculated vacancy migration energy was overestimated. Most of the damages that are produced by collision cascades are concentrated into amorphous-like pockets. Also, We upgraded MDRANGE code for silicon ion implantation process simulation. We simulated ultra-low energy boron ion implantation, 200eV, 500eV, and 1000eV respectively, and calculated boron profiles with silicon substrate temperature and tilt angle. We investigated that below 1000eV, channeling effect must be considered.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.239-242
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• 2009

구조물의 표면에 부착된 압전소자(이하 PZT)의 전기역학적 어드미턴스(Electro-mechanical admittance)는 PZT와 구조물의 상호작용에 의해 발생하는 PZT의 압전효과와 유전성(dielectric)이 결합되어 발생되는 신호이다. 고주파수 대역에서 PZT의 전기역학적 어드미턴스는 구조물의 국부손상에 민감하게 반응하는 것으로 알려져 있다. 실험에서 측정된 PZT의 전기역학적 어드미턴스 분석에 널리 쓰이는 Liang 모델은 구조물을 단자유도계로 단순화하여 구조물의 동적특성이 전기역학적 어드미턴스에 미치는 영향을 정확하게 나타내기 어렵다. 유한요소법을 통해 PZT와 구조물의 상호작용을 해석하면 이러한 문제점을 해결할 수 있다. 그러나 고주파 대역에서 정확한 해석을 위해서는 유한요소망을 조밀하게 구성해야 하므로 많은 계산비용이 수반된다. 이 연구에서는 유한요소법과 비교하여 월등히 적은 계산비용으로 고주파 대역의 동적 응답을 매우 정확하게 모사할 수 있는 스펙트럼 요소법(Spectral Element Method ; 이하 SEM)을 통해 판구조물에 부착된 PZT의 전기-역학적 어드미턴스를 해석한다. 수치 예제 및 실험 예제를 통하여 내민보에 부착된 PZT에서 발생하는 전기-역학적 어드미턴스를 취득하고 이를 SEM해석 결과와 비교한다.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.145-156
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• 1993

An improved analysis model for material nonlinearity induced by elasto-plastic deformation and damage including large strain response was proposed. The elasto-plastic-damage constitutive model based on the continuum damage mechanics approach was adopted to overcome limitations of the conventional plastic theory, which can manage the anisotropic tonsorial damages evolved during time-independent plastic deformation process of materials. Updated Lagrangian finite element formulation for elasto-plastic damage coupling problem including large deformation, large rotation and large strain problems was completed to develop a numerical model which can predict all kinds of structural nonlinearities and damage rationally. Finally, a finite element analysis code for the 2-dimensional plane problem was developed and the applicability and validity of the numerical model was investigated through some numerial examples. Calculations showed reasonable results in both geometrical nonlinear problem due to large deformation and material nonlinearity including the damage effect.