• Title/Summary/Keyword: Residual elements

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A model of fatigue crack growth based on plastic stretch at the crack tip (균열선단의 소성스트레치를 이용한 피로균열성장모델)

  • Ju, Yeong Sik;Kim, Jae Hun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.3
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    • pp.15-22
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    • 2003
  • The fatigue crack growth model is derived and the retardation model is proposed. The fatigue crack growth model considers the residual plastic stretch on the crack surface which results from the plastic deformation at the tip of fatigue crack. The fatigue crack growth rate is calculated by using the cumulative fatigue damage and plastic strain energy in the material elements at the crack tip. This model gives the crack growth rate in reasonable agreement with test data for aluminum alloy AL6061-T651 and 17-4PH casting steel. The fatigue crack growth retardation model is based on the residual plastic stretch produced from a tensile overload which reduced the plastic strain range of the following load cycles. A strip-yield model of a crack tip plasticity is used for the calculation of a plastic zone size. The proposed retardation model characterized the observed features and delayed retardation of the fatigue crack growth under tensile overload.

An adaptive frequency-selective weighted prediction of residual signal for efficient RGB video compression coding (능률적 RGB 비디오 압축 부호화를 위한 잔여신호의 적응적 주파수-선택 가중 예측 기법)

  • Jeong, Jin-Woo;Choe, Yoon-Sik;Kim, Yong-Goo
    • Journal of Broadcast Engineering
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    • v.15 no.4
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    • pp.527-539
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    • 2010
  • Most video coding systems use YCbCr color space for their inputs, but RGB space is more preferred in the field of high fidelity video because the compression gain from YCbCr becomes disappeared in the high quality operation region. In order to improve the coding performance of RGB video signal, this paper presents an adaptive frequency-selective weighted prediction algorithm. Based on the sign agreement and the strength of frequency-domain correlation of residual color planes, the proposed scheme adaptively selects the frequency elements as well as the corresponding prediction weights for better utilization of inter-plane correlation of RGB signal. Experimental results showed that the proposed algorithm improves the coding gain of around 13% bitrate reduction, on average, compared to the common mode of 4:4:4 video coding in the state-of-the-art video compression standard, H.264/AVC.

Parametric Study on Reinforced Concrete Columns under Blast Load (주철근의 개수 및 단면비에 따른 폭발하중을 받는 철근콘크리트 기둥의 해석적 연구)

  • Choi, Hosoon;Kim, Min-Sook;Lee, Young-Hak
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.25 no.3
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    • pp.219-226
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    • 2012
  • Columns are the key elements supporting load in structure. Column failure causes the structure to collapse. It is important to evaluate residual strength for damaged columns under blast load for preventing progressive collapse. In this paper, columns were investigated to compare the blast resistance on the change of the number of steel bars within the range of reinforcement ratio. And this study was carried out 4 different analytical models to evaluate effects of aspect ratio. The results indicate that the vertical strain was unaffected by the number of steel bars and aspect ratio. As the number of steel bars facing blast load increase, the blast resisting capacity of the columns was improved in the lateral strain. Also, the analysis results showed that a large moment of inertia of area, as compared to a small one would be superior in residual strength as well as force of restitution.

Evaluation of A Removal Process for the Residual Uranium from the Simulated Radwaste Solution by Solvent Extraction with TBP (TBP 용매추출에 의한 잔존 우라늄 제거공정 평가)

  • Lee, Eil-Hee;Kim, Kwang-Wook;Lim, Jae-Gwan;Kwon, Seon-Gil;Yoo, Jae-Hyung
    • Applied Chemistry for Engineering
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    • v.9 no.2
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    • pp.232-237
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    • 1998
  • This study was carried out to find the optimal operating conditions for separation of residual uranium from the simulated radwaste solution containing 19 elements, and to evaluate the validity of the process. The selected process was based on the solvent extraction with TBP(tributyl phosphate). As an extractor, two miniature mixer-settlers with a total of 18 stages were used. Extraction yield of U, Np and Tc was about 99.2%. 32.1%, and 99.9%, respectively. The other elements were coextracted in the range of 1~4%. Extraction yield of U exceeded those of the previous work performed with batch system, which resulted in the low extractability of U (about 80%) according to the coexisting element such as Nd and Fe. It was due to the characteristics of multi-stage extractor. On the other hand, low extractability of Np was caused by various oxidation states in the nitric acid medium. In the case of Tc, its high extractability may be attributed to the complex formation with Zr and U, which is not well proved yet. All elements extracted with TBP were stripped into aqueous phase more than 99% by 0.01M $HNO_3$. From the results, this process has no problem with respect to in the same step was required, because Np was distributed in the raffinate and U product, respectively.

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Dynamic Analysis of a Rotating System Due to the Effect of Ball Bearing Waviness (I) -Vibration Analysis- (Waviness가 있는 볼베어링으로 지지된 회전계의 동특성 해석 (II)-안정성 해석 -)

  • Jeong, Seong-Weon;Jang, Gun-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.12
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    • pp.2647-2655
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    • 2002
  • This research presents an analytical model to investigate the stability due to the ball bearing waviness i n a rotating system supported by two ball bearings. The stiffness of a ball bearing changes periodically due to the waviness in the rolling elements as the rotor rotates, and it can be calculated by differentiating the nonlinear contact forces. The linearized equations of motion can be represented as a parametrically excited system in the form of Mathieu's equation, because the stiffness coefficients have time -varying components due to the waviness. Their solution can be assumed as a Fourier series expansion so that the equations of motion can be rewritten as the simultaneous algebraic equations with respect to the Fourier coefficients. Then, stability can be determined by solving the Hill's infinite determinant of these algebraic equations. The validity of this research is proved by comparing the stability chart with the time responses of the vibration model suggested by prior researches. This research shows that the waviness in the rolling elements of a ball bearing generates the time-varying component of the stiffness coefficient, whose frequency is called the frequency of the parametric excitation. It also shows that the instability takes place from the positions in which the ratio of the natural frequency to the frequency of the parametric excitation corresponds to i/2 (i=1,2,3..).

An Elastic-Plastic Stress Analysis in Silicon Carbide Fiber Reinforced Magnesium Metal Matrix Composite Beam Having Rectangular Cross Section Under Transverse Loading

  • Okumus, Fuat
    • Journal of Mechanical Science and Technology
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    • v.18 no.2
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    • pp.221-229
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    • 2004
  • In this work, an elastic-plastic stress analysis has been conducted for silicon carbide fiber reinforced magnesium metal matrix composite beam. The composite beam has a rectangular cross section. The beam is cantilevered and is loaded by a single force at its free end. In solution, the composite beam is assumed perfectly plastic to simplify the investigation. An analytical solution is presented for the elastic-plastic regions. In order to verify the analytic solution results were compared with the finite element method. An rectangular element with nine nodes has been choosen. Composite plate is meshed into 48 elements and 228 nodes with simply supported and in-plane loading condations. Predictions of the stress distributions of the beam using finite elements were overall in good agreement with analytic values. Stress distributions of the composite beam are calculated with respect to its fiber orientation. Orientation angles of the fiber are chosen as $0^{circ},\;30^{circ},\;45^{circ},\;60^{circ}\;and\;90^{circ}$. The plastic zone expands more at the upper side of the composite beam than at the lower side for $30^{circ},\;45^{circ}\;and\;60^{circ}$ orientation angles. Residual stress components of ${\sigma}_{x}\;and \;{\tau}_{xy}$ are also found in the section of the composite beam.

Seismic multi-level optimization of dissipative re-centering systems

  • Panzera, Ivan;Morelli, Francesco;Salvatore, Walter
    • Earthquakes and Structures
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    • v.18 no.1
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    • pp.129-145
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    • 2020
  • Seismic resilience is a key feature for buildings that play a strategic role within the community. In this framework, not only the structural and non-structural elements damage but also the protracted structural dysfunction can contribute significantly to overall seismic damage and post-seismic crisis situations. Reduction of the residual and peak displacements and energy dissipation by replaceable elements are some effective aspects to pursue in order to enhance the resilience. Control systems able to adapt their response based on the nature of events, such as active or semi-active, can achieve the best results, but also require higher costs and their complexity jeopardizes their reliability; on the other hand, a passive control system is not able to adapt but its functioning is more reliable and characterized by lower costs. In this study it is proposed a strategy for the optimization of the dissipative capacity of a seismic resistant system obtained placing in parallel two different groups dissipative Re-Centering Devices, specifically designed to enhance the energy dissipation, one for the low and the other for the high intensity earthquakes. In this way the efficiency of the system in dissipating the seismic energy is kept less sensitive to the seismic intensity compared to the case of only one group of dissipative devices.

Evaluation of the Stress Occurring Phenomenon for Cold-Rolled Carbon Steel During a Laser Welding Process (냉연 압연 강판의 레이저 용접 공정 시 발생하는 응력 평가)

  • Lee, Chulku;Lee, Wooram
    • Journal of Welding and Joining
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    • v.31 no.1
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    • pp.51-57
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    • 2013
  • Residual stress caused in the weldments with high restraint force are often observed during welding in the weldments of Inner and outdoor materials or radial tanks. The reason is that quantitative analysis about thermal stresses during laser welding is lacking for this weldments. To verify Finite Elements Method (FEM) theory, the temperature was measured with thermocouple in a real time in this paper. Also analysis of the thermal stress for welding condition is performed by Comsol program package on various welding condition in SCP1-S butt welding. The principal stress in laser welding process is seen through the width direction. Also, it was confirmed that a change in base metal by thermal expansion made the stress in width direction stronger. Base metal close to the weld bead as the process progresses to the tensile stress in the compressive stress was varied. It was shown that the change of stress was quantitative from the bead at a certain distance.

An Analysis of Electromagnetic Field Scattering for the Dielectric Cylinders (유전체주의 전자장 산란 해석)

  • 박동희;김정기
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.17 no.2
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    • pp.181-186
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    • 1992
  • The scattering property of TMz illuminated perfectly conducting and dielectric cylinders of arbitrary cross section are analyzed by the boundary element techniques. The boundary element equations are formulated via Maxwell’s equations, weighted residual or Green’s theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by the boundary element integral equations. Once the surface fields are found, the scattered fields in from a perfectly conducting circular and elliptic cylinders, a dielectric circular and elliptic cylinders are numerically analyzed. A general computer program has been developed using the quadratic elements(higher order boundary elements) and the Gaussian quadrature.

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Characteristics of Machined Surface Roughness and Surface Layers of WC-Co Tools with Plasma Source Ion Implantation (WC-Co 공구의 이온 주입에 따른 표면층 및 가공된 표면거칠기 특성)

  • Kang, Seong-Ki;Kim, Yung-Kyu;Wang, Duck-Hyun;Chun, Young-Rok;Kim, Won-Il
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.9 no.1
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    • pp.106-113
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    • 2010
  • The most suitable condition for plasma source ion implantation(PSII) was found based on the study of the characteristics of PSIIed tool and machined surfaces. The depth analysis according to the chemical bonding state of elements and surface component elements through the XPS and SIMS, was conducted to find the improved property of the PSIIed surface. Due to the diffusion of PSII, the nitrogen was found up to a depth of about 150nm according to the supplied voltage and ion implanted time. The deep diffusion by nitrogen caused the surface modification, but the formation of oxide component was found due to the residual gas contamination on the surface. Statistical method of ANOVA was conducted to find the effects of spindle speed and feed rate in interaction for machined surface roughness with PSIIed tools. The surface modification was found largely occurred by the nitrogen implanted surface with 2 hours for 27kV, 35kV and 43kV.