• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.12
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• pp.1547-1557
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• 2013

A forced vibration model of a rail system was established using the Timoshenko beam theory to determine the dynamic response of a rail under time-varying load considering the damping effect and stiffness of the elastic foundation. By using a Fourier series and a numerical method, the critical velocity and dynamic response of the rail were obtained. The forced vibration model was verified by using FEM and Euler beam theory. The permanent deformation of the rail was predicted based on the forced vibration model. The permanent deformation and wear were observed through the experiment. Parametric studies were then conducted to investigate the effect of five design factors, i.e., rail cross-section shape, rail material density, rail material stiffness, containment stiffness, and damping coefficient between rail and containment, on four performance indices of the rail, i.e., critical velocity, maximum deflection, maximum longitudinal stress, and maximum shear stress.

• Proceedings of the KAIS Fall Conference
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• 2009.12a
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• pp.885-888
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• 2009

자동차용 Alloy Wheel은 차량의 수직하중이나 가로 방향 하중, 구동, 제동토크 등 주행 시에 발생하는 여러 형태의 응력을 받으면서 사용되므로 이러한 응력을 견딜 수 있는 강성은 물론 차량 부품으로서의 요구 수명도 만족하여야 한다. 알루미늄 휠은 개발 후 규격에 준하는 내구성 평가를 위하여 반경 방향 부하 내구시험과 굽힘모멘트 내구시험과 주행 중 요철이나 벽돌 등에 의한 노면으로부터 갑작스런 하중에 대한 내충격성 평가를 위한 충격시험이 실행되고 있다. 이러한 시험은 많은 시간이 소요되고 있으며, 또한 시험 중 불합격 판정이 날 경우 또다시 처음의 공정을 모두 거쳐 다시 시험을 하게 된다. 3 Piece와 같은 알루미늄 휠은 여러 공정에 의한 생산되어지기 때문에 많은 시간적, 물질적 손실이 일어나고 있다. 따라서 자동차용 알루미늄 휠의 요구조건을 충분히 만족시키며 소비자의 요구에 맞는 품질과 시간을 충족시켜 기업경쟁력 확보는 물론 원가절감에 의한 기업 경쟁력 향상을 위하여 설계 단계서부터 시험조건을 고려한 내구성 해석에 의한 알루미늄 휠의 시험횟수를 단축하고자 한다. 본 논문에서는 3 Piece 알루미늄 휠의 축(shaft)하중에 의한 내구성 평가에 대하여 CAE시스템을 이용하여 보다 빠르고 정확한 결과를 산출함으로서 설계시간의 단축은 물론 다양한 형상의 제품들을 설계단계에서부터 생산에 이르기까지의 해석활용법을 수립하고자 하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.161-161
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• 2000

Ferromagnetic 3d 전이금속과 paramagnetic 5d 금속으로 이루어지진 Pt-Co 계는 자기이방적 (magnetic anisotropy) 성질로 인하여 많은 관심을 모으고 있는 계로서는 다층박막 및 합금박막에 대한 지기적 성질에 대한 많은 연구가 있어 왔다. 최근 sputtering method 에 의해 제작된 Pt-Co 합금박막에 대해 Ar 기체분압에 따라 보자력 (coercivity)이 변화되고 PMA (perpendicular magnetic anisotropy)를 갖는 것을 관측하였다. PMA의 근원은 주로 계면에서의 anisotropy 에너지와 관련이 있는 것으로 이해되기 때문에 합금박막의 경우는 PMA가 불가능한 것으로 여겨져 왔다. 그럼으로서 PMA에 대한 근원에 대한 명확한 해석이 필요하게 되었다. 또한 보자력(coercivity)은 불순물의 함량이 감소할수록, 그리고 내부적 변형이 제거될수록 감소하기 때문에, 계면 및 결정구조와 관련이 있는 것으로 알려져 있다. 이러한 자기적 특성을 관찰하고자 [Pt(51 )/Co(112 )]4, [Pt(90 )/Co(66 )]4, 그리고 [Pt(121 )/Co(30 )]4, 다층박막과 이들 박막을 80kV Ar+ 이온선 혼합후 박막의 결정성 변화를 관찰하기 위하여 GXRD (glancing x-ray diffraction) 스펙트럼을 얻어보았다. 그 결과 세 system 모두 disordered fcc 합금박막임을 확인하였다. fcc(111) 방향에 대한 평균 격자공간(lattice spacing)의 크기변화는 한층 당의 Co 두께가 두꺼울수록 거의 선형적으로 감소함을 볼수 있었다. MOKE 실험에 의하면, 이들 다층박막이나 합금박막의 경우 모두, in-plane 방향에 대해 자화 용이축(easy magnetization axis)을 가지고 있었다. 그리고 보자력의 크기에 있어서, 다층 박막의 경우에 있어서 Co 층에 두께 두꺼울수록 보자력의 크기가 감소하였지만 그림1에서와 같이 합금박막의 경우는 정반대로 Co층의 두께가 얇을수록 보자력의 크기가 감소함을 관찰하였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.2
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• pp.129-138
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• 2012

This paper deals with geometrical non-linear analyses of the tapered variable-arc-length beam, subjected to the combined load with an end moment and a point load. The beam is supported by a hinged end and a frictionless sliding support so that the axial length of the deformed beam can be increased by its load. Cross sections of the beam whose flexural rigidities are functionally varied with the axial coordinate. The simultaneous differential equations governing the elastica of such beam are derived on the basis of the Bernoulli-Euler beam theory. These differential equations are numerically solved by the iteration technique for obtaining the elastica of the deformed beam. For validating theories developed herein, laboratory scaled experiments are conducted.

• Journal of the Korean Society of Radiology
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• v.12 no.4
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• pp.525-532
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• 2018

This study is filmed by applying the axial angle variation of the X-ray tube instead of the patient's position change during the perimetric examination of the ribs. A Reference image with the rib oblique examination using a chest phantom and experimental images applied with a six-phase variation in the axial angle by increasing $5^{\circ}$ tube angle each from $5^{\circ}{\sim}30^{\circ}$ from the vertical incident direction of the chest phantom to the right horizontal axis were obtained. For the quantitative comparative evaluation of the images, SNR and CNR were calculated for regions of interest in the experimental images based on the reference image. Also, the left-right rib ratio in the reference image and the left-right rib ratio in the experimental images are measured and compared. As a result of the study, the experimental images with a tube angle of $25^{\circ}$ were best shown in the measurements of the SNR, CNR and left-right rib ratio compared to the reference image with a standard examination method. The modified rib examinations will consider useful, if it is difficult to maintain the patient's examination position.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.543-552
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• 1994

A series of drained plane strain compression tests was performed on dried samples of dense Toyoura sand and Silver Leighton Buzzard sand prepared by air-pluviation method to find out the deformation and strength characteristics on the value of confining pressure ${\sigma}{_3}^{\prime}({\sigma}{_3}^{\prime}=0.05{\sim}4.0kgf/cm^2)$. The axial and lateral strains measured in this apparatus ranged from $10^{-6}$ up to the failure of the specimen. So the stress-strain characteristics would be investigated from very small to very large strain levels. It was found that the change of the angle of internal friction ${\phi}^{\prime}{_{max}}=arcsin\{({\sigma}{_1}^{\prime}-{\sigma}{_3}^{\prime})/({\sigma}{_1}^{\prime}+{\sigma}{_3}^{\prime})\}_{max}$ with the change of ${\sigma}{_3}^{\prime}$ is very small when ${\sigma}{_3}^{\prime}$ is lower than higher. Furthermore, the effect of confining pressure on stiffness of sands was evaluated. It was also found that for the range of shear strain ${\gamma}$ from $10^{-6}$ to those at peak, the Rowe's stress-dilatancy relation seems to be a good approximation for air-dried Toyoura sand and Silver Leighton Buzzard sand, irrespective of the change of ${\sigma}{_3}^{\prime}$.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.10-19
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• 2014

Corrugated steel plates are made by fabricating thin steel plates to have trapezoidal or sinusoidal corrugation, and the corrugated plates are able to maintain high out-of-plane rigidity even when they are used instead of thick flat plates. Also, corrugated steel plates have almost no axial rigidity due to the accordion effect. Thus, if they are applied to the webs of plate girders, designing can be easily conducted so that the webs bear only shear stresses. However, unlike flat plates, the shear buckling of corrugated steel plates has very complex characteristics where buckling occurs due to the interaction of local and global buckling, besides local buckling and global buckling. For the investigation of the cause and characteristics of this interactive buckling, studies on sinusoidal corrugated steel plates are fewer than studies on trapezoidal corrugated steel plates. Therefore, in this study, the shear buckling characteristics of sinusoidal corrugated steel plates and the occurrence pattern of interactive buckling were investigated. For the calculation of shear buckling strength, a finite element program was used, and the analysis results were compared with the exact solution. In addition, the characteristics of buckling stress change and the change of buckling mode shape depending on corrugation thickness and shape parameter were analyzed, and by comparing these results with the results of a theoretical equation, the timing of buckling mode change was analyzed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.519-529
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• 2009

Fiber reinforced composite materials have various advantages in mechanical and chemical aspects. Not only high fatigue and chemical resistance, but also high specific strength and stiffness are attained, and therefore, damping characteristics are beneficial to marine piles. Since piles used for marine structures are subjected to compression and bending as well, detailed research is necessary. Current study examine the mechanical behavior under flexural and/or compressive loads using concrete filled fiber reinforced plastic composite piles, which include large size diameter. 25 pile specimens which have various size of diameters and lengths were fabricated using hand lay-up or filament winding method to see the effect of fabrication method. The inner diameters of test specimens ranged from 165 mm to 600 mm, and the lengths of test specimens ranged from 1,350 mm to 8,000 mm. The strengths of the fill-in concrete were 27 and 40 MPa. Fiber volumes used in circumferential and axial directions are varied in order to see the difference. For some tubes, spiral inner grooves were fabricated to reduce shear deformation between concrete and tube. It was observed that the piles made using filament winding method showed higher flexural stiffness than those made using hand lay-up. The flexural stiffness of piles decreases from the early loading stage, and this phenomenon does not disappear even when the inner spiral grooves were introduced. It means that the relative shear deformation between the concrete and tube wasn't able to be removed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.614-621
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• 2019

A generalized laminated composite beam element is presented for the flexural and buckling analysis of laminated composite beams with double and single symmetric cross-sections. Based on shear-deformable beam theory, the present beam model accounts for transverse shear and warping deformations, as well as all coupling terms caused by material anisotropy. The plane stress and plane strain assumptions were used along with the cross-sectional stiffness coefficients obtained from the analytical technique for different cross-sections. Two types of one-dimensional beam elements with seven degrees-of-freedom per node, including warping deformation, i.e., three-node and four-node elements, are proposed to predict the flexural behavior of symmetric or anti-symmetric laminated beams. To alleviate the shear-locking problem, a reduced integration scheme was employed in this study. The buckling load of laminated composite beams under axial compression was then calculated using the derived geometric block stiffness. To demonstrate the accuracy and efficiency of the proposed beam elements, the results based on three-node beam element were compared with those of other researchers and ABAQUS finite elements. The effects of coupling and shear deformation, support conditions, load forms, span-to-height ratio, lamination architecture on the flexural response, and buckling load of composite beams were investigated. The convergence of two different beam elements was also performed.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.3
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• pp.1-8
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• 2001

Seismic design forces for bridge components may be determined by modifying elastic member forces of design earthquakes using appropriate response modification factors according to the national design code of bridges Modeling technique of pile foundation system is one of the important parameters which greatly affects the results in the process of the elastic seismic analysis of a bridge system with pile foundation. In this paper, a approximate and simplified modeling technique of a pile foundation system for the practical purposes is presented. The modeling technique is based on the stiffnesses of pile foundation during earthquake. The horizontal stiffnesses are determined from the resistance-deflection curves derived from the results of dynamic field tests using cyclic loads and the vertical stiffness includes the effects of the end bearing capacities and side friction of piles as well as the pile compliances under the expected vertical load level. The applicability of the proposed technique has been validated through the some example bridge analyses.