• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2219-2227
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• 2002

In a nuclear power plant, reactor pressure vessel (RPV) is the primary pressure boundary component that must be protected against failure. The neutron irradiation on RPV in the beltline region, however, tends to cause localized damage accumulation, leading to crack initiation and propagation which raises RPV integrity issues. The objective of this paper is to estimate the integrity of RPV under hot leg leaking accident by applying the finite element analysis. In this paper, a parametric study was performed for various crack configurations based on 3-dimensional finite element models. The crack configuration, the crack orientation, the crack aspect ratio and the clad thickness were considered in the parametric study. The effect of these parameters on the maximum allowable nil-ductility transition reference temperature ($(RT_{NDT})$) was investigated on the basis of finite element analyses.

• Computers and Concrete
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• v.1 no.3
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• pp.261-284
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• 2004

Two enhancements to a recently developed plastic-damage-contact model for concrete are presented. The model itself, which uses planes of degradation that can undergo damage and separation but that can regain contact according to a contact law, is described. The first enhancement is a new damage evolution function which provides a completely smooth transition from the undamaged to the damaged state and from pre-peak to post-peak regions. The second is an improved contact function that governs the potential degree of contact with increasing opening on a crack plane. The use of a damage evolution function with a pre-peak has implications for the consistent tangent matrix/stress recovery algorithm developed for the model implementation, and amendments to this algorithm to accommodate the new function are described. A series of unpublished experimental tests on notched specimens undertaken in Cardiff in the mid 1990s are then described. These include notched beam tests as well as prismatic and cylindrical torsion tests. The tests are then considered in three dimensional finite element analyses using the modified Craft model implemented in the finite element program LUSAS. Comparisons between experimental and numerical data show reasonable agreement except that the numerical simulations do not fully describe the latter stages of the softening responses for the torsion examples. Finally, it is concluded that the torsion tests described provide useful benchmark examples for the validation of three-dimensional numerical models for concrete.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.89-92
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• 2000

In this paper, an effective procedure is presented for the local recovery of displacements and stresses in multilayered composite panels, which incorporate the local refinement using mesh superposition. The mesh superposition method is used to refine the global coarse mesh by superimposing refined mesh to the localized zone of interest without transition zones. The finite element model used is a solid element based on the Hellinger-Reissner variational principle. The a posteriori computation of the through-the-thickness distributions of displacements and stresses is achieved using a predictor-corrector procedure. The procedure utilizes the superconvergent stresses and nodal displacements of the finite element patch. The element patch is generated by locally superimposing a refined local mesh to the coarse global mesh.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.10
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• pp.140-147
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• 1998

The dynamic behavior of elastically restrained beams under the action of distributed tangential forces is investigated in this paper. The beam, which is fixed at one end, is assumed to rest on an intermediate spring support. The governing equations of motion are derived from the energy expressions, and the finite element formulation is employed to calculate the critical distributed tangential force. Jump phenomena for the critical distributed tangential force and instability types are presented for various spring stiffnesses and support positions. Stability maps are generated by performing parametric studies to show how the distributed tangential forces affect the frequencies and the stability of the system considered. Through the numerical simulations, the following conclusioils are obtained: (i) Only flutter type instability exists for the dimensionless spring stiffness K $\leq$ 97, regardless of the position of the spring support. (ii) For the dimensionless spring stiffness K $\leq$ 98, the transition from flutter to divergence occurs at a certain position of the spring support, and the transition position moves from the free end to the free end of the beam as the spring stiffness increases. (iii) For K $\leq$ 10$^{6}$ the support condition can be regarded as a rigid support condition.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.3
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• pp.199-203
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• 2019

The penetration depth of a hypervelocity jet exceeding 4 km/s is described by the density ratio of the jet and the target. In the case of the same density, the difference in strength between the targets does not affect the penetration depth difference. This study focuses on the "strength irrelevance" of such a hypervelocity jet. For this purpose, the change of crater pressure caused by shaped charge jet(SCJ) was calculated by finite element analysis and the possibility of polymorphic phase transition of steel material was investigated. Hypervelocity jets were found to cause polymorphic phase transitions in the steel target craters, and the decrease in the fracture toughness of the target is predicted as the cause of the strength irrelevance.

• Advances in Computational Design
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• v.7 no.4
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• pp.281-295
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• 2022

Tensile property is one of the excellent properties of ultra-high performance concrete (UHPC), and uniaxial tensile test is an important and challenging mechanical performance test of UHPC. Traditional uniaxial tensile tests of concrete materials have inherent defects such as initial eccentricity, which often lead to cracks and failure in non-test zone, and affect the testing accuracy of tensile properties of materials. In this paper, an original integrated design scheme of mould and end fixture is proposed, which achieves seamless matching between the tension end of specimen and the test fixture, and minimizes the cumulative eccentricity caused by the difference in the matching between the tension end of specimen and the local stress concentration at the end. The stress analysis and optimization design are carried out by finite element method. The curve transition in the end of specimen is preferred compared to straight line transition. The rationality of the new integrated design is verified by uniaxial tensile test of strain hardening UHPC, in which the whole stress-strain curve was measured, including the elastic behavior before cracking,strain hardening behavior after cracking and strain softening behavior.

• Transactions of Materials Processing
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• v.29 no.3
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• pp.163-171
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• 2020

We present a multi-step cold drawing for a non-equiatomic Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ high entropy alloy (HEA) with a simple face-centered cubic (FCC) crystal structure. The distribution of strain in the cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wires was analyzed by the finite element method (FEM). The effective strain was expected to be higher as it was closer to the surface of the wire. However, the reverse shear strain acted to cause a transition in the shear strain behavior. The critical effective strain at which the shear strain transition behavior is completely shifted was predicted to be 4.75. Severely cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wires up to 96% of the maximum cross-sectional reduction ratio were successfully manufactured without breakage. With the assistance of electron back-scattering diffraction and transmission electron microscope analyses, the abundant deformation twins were found in the region of high effective strain, which is a major strengthening mechanism for the cold-drawn Co₁₀Cr₁₅Fe₂₅Mn₁₀Ni₃₀V₁₀ HEA wire.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.1
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• pp.160-168
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• 2020

Depending on the water depth and composition of seabed, there exist different alternatives for the wind turbine supporting structures. Among several types of the structures, the monopile foundation is the dominant solution for support structure, accounting for over 80% of the offshore wind turbines in Europe. To develop the monopile foundation suitable for domestic ocean environment, a basic design of a transition piece was carried out. This paper presents the design procedure of a flange connected transition piece and results of the structural safety assessment.

• Steel and Composite Structures
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• v.18 no.1
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• pp.135-148
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• 2015

The cutout hole locating at the place of rib-to-diaphragm welded connection is adopted to minimize the restraint, which is caused by the floor-beam web to rib rotation at the support due to the unsymmetrical loads in orthotropic deck. In practice, an inevitable problem is that there is a large number of welding joint's cracks formed at the edge of cutout hole. In this study, a comparative experiment is carried out with two types of cutout hole, the circular arc transition and the vertical transition. The fatigue life estimation of specimens is investigated with the application of the structural hot spot stress approach by finite element analyses. The results are compared with the ones of the fatigue tests which are carried out on these full-scale specimens. Factors affecting the stress range are also studied.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.63-66
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• 2005

Nanoimprint lithography (NIL) process at room temperature has been newly proposed in recent years to overcome the shape accuracy and sticking problem induced in a conventional NIL process. Success of the room temperature NIL relies on the accurate understand of the mechanical behavior of the polymer. Since a conventional NIL process has to heat a polymer above the glass transition temperature to deform the physical shape of the polymer with a mold pattern, viscoelastic property of polymer have major effect on the NIL process. However, rate dependent behavior of polymer is important in the room temperature NIL process because a mold with engraved patterns is rapidly pressed onto a substrate coated with the polymer by the hydraulic equipment. In this paper, finite element analysis of the room temperature NIL process is performed with considering the strain rate dependent behavior of the polymer. The analyses with the variation of imprinting speed and imprinting pattern are carried out in order to investigate the effect of such process parameters on the room temperature NIL process. The analyses results show that the deformed shape and imprint force is quite different with the variation of punch speed because the dynamic behavior of the polymer is considered with the rate dependent plasticity model. The results provide a guideline for the determination of process conditions in the room temperature NIL process.