• Corrosion Science and Technology
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• 제7권4호
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• pp.224-232
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• 2008

During the hot rolling process, steels develop an oxide scale on their surface. This scale can affect the mechanical properties of the rolled steel and its surface aspect. The main problem comes from the mechanical integrity of the oxide scales which could delaminate or crack, leading eventually to later oxide incrustation within the steel. The objective of the present work is to qualify the mechanical integrity of the iron oxide scales during the hot rolling process. The laboratory experiments use a four point bending test to simulate the mechanical solicitation which takes place during the rolling sequence of the steel slabs. The oxide scales grow on a mild steel at $900^{\circ}C$ under wet or dry atmosphere and the oxidized steel is then mecahnically tested at $900^{\circ}C$ or $700^{\circ}C$. The high temperature four point bending tests are completed with microstructural observations and with the record of acoustic emission to follow in-situ the mechanical damages of the oxide scales. The results show the role of water vapor which promotes the scale adherence, and the role of the temperature as the oxide are more damaged at $700^{\circ}C$ than at $900^{\circ}C$.

• 대한기계학회논문집A
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• 제20권3호
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• pp.968-977
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• 1996

The linear/nonlinear vibration response of the rotating hybrid cylindrical shell with simply supported boundary condition is studied. The Ritz-Galerkin method is applied to obtain the nonlinear frequency equation, which excludes in-plane and rotatory inertia but includes bending stretching coupling terms. The bifurcation phenomena for the linear frequency and the frequency ratio(nonlinear/linear frequency ratio) are presented. The hybrid cylindrical shells are composed of composite(GFRP, CFRP) metal(aluminium, steel) with symmetric and antisymmetric stacking sequence. The effects of the Coriolis and centrifugal force are considered The results also present the effects of length-to- radies ratio, radius-to-thickness ratio, the circumferential wave number, the stacking sequence, the material property, the initial excitation amplitude and the rotating speed. The present linear frequency results are compared with those of the available literature.

• Journal of Welding and Joining
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• 제27권2호
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• pp.76-81
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• 2009

Tandem GMAW is one of the high performance welding process and used in many industries to increase the productivity. An evaluation is presented of the mechanical properties and microstructural characteristics of the Tandem GMAW and conventional Single GMAW welds in 30mm thickness 490MPa grade steel by comparison method. Welding sequence and bead with and hight was kept, avoiding the effect of the bead shape and welding sequence. Tension, bending, hardness and Charpy impact test results of Tandem GMAW met the requirement of specification and showed similar distribution with conventional Single GMAW. Volume fraction of ferrite phase in weld metal showed little difference between Tandem GMAW and Single GMAW

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.17-30
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• 2022

The use of composite patches for the reduction of stresses at the level of the damaged zone in aeronautical structures has experienced rapid expansion given its advantages over conventional mechanical processes (riveting, bolting, etc.). Initially, The research axes in this field were aimed at choosing suitable mechanical properties for the composite and the adhesive, then to optimize the shape of the composite patch in order to ensure good load transfer and avoid having a debonding at the level of the edges essentially for the case of a repair by single side where the bending moment is present due to the non-symmetry of the structure. Our work falls within this context; the objective is to analyze by the finite element method the fracture behavior of a damaged plate repaired by composite patch. Stress reduction at the edge is accomplished by creating a variable angle chamfer on the composite patch. The effects of the crack length, the laminate sequence and the nature of the patch as well as the use of a hybrid patch were investigated. The results show clearly that a beveled patch reduces the stress concentrations in the damaged area and even at its edges. The hybrid patch also ensures good durability of the repair by optimizing its stacking sequence and the location of the different layers according to the fibers orientations.

• 대한치과교정학회지
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• 제30권4호
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• pp.467-473
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• 2000

각형 호선이 edgewise 브라켓에 삽입되면 first, second order는 bending에 의해, third order는 torsion(비틀림)에 의해 3차원적인 force system이 발생한다. Bending에 관하여는 분석적 그리고 실험적인 많은 연구가 보고 되어 있는 반면 비틀림에 관해서는 상대적으로 많은 연구가 이루어 지지 않았다. 본 연구의 목적은 각형 와이어의 재료와 단면의 형태가 와이어의 비틀림 모멘트에 어떻게 영향을 주는지를 이론적, 실험적으로 밝혀서 임상적으로 적절한 모멘트를 가할 때 호선의 재료와 굵기를 합리적으로 선택할 수 있도록 하는데 있다. 실험재료로는 third order조절을 위해 가장 많이 사용하는 호선을 사용하였다. 크기별로 0.016x0.022, 0.017x0.025, 0.019x0.025인치 그리고 재료로는 stainless steel (Ormco), TMA(Ormco), NiTi(Ormco), 그리고 braided stainless steel(DentaFlex, Dentauum) 네 가지를 사용하여 총 12개의 조합을 사용하였다. Torsion formula를 이용하여 비틀림 강성 (torque/twist rate)을 계산하였고 torque gauge를 이용하여 비틀림 강성, 항복 비틀림 모멘트 (yield torsional moment), 그리고 최대 비틀림 모멘트 (ultimate torsional moment)를 측정하였다. Torsion formula에 의하면 비틀림 강성 (T/$\theta$)은 재료적인 특성(G)과 호선의 단면의 특성(J)에 비례하고 호선의 길이(L)에 반비례한다. 대부분의 실험치는 이론적인 값과 비슷하게 나타났다.

• 소성∙가공
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• 제23권2호
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• pp.75-81
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• 2014

Progressive dies are used for metal stamping during which multiple operations are performed in a sequence. Material is fed automatically from a coil into the press and advances from one die station to the next with each press stroke. Transfer dies are used in high-volume manufacturing for round, deep-drawn, and medium-to-large parts. Several different operations may be incorporated within a transfer die such as blanking, bending, piercing, trimming, and deep drawing. The main challenge in the current study is how to deform a seat cushion panel meeting the design specifications without any defects. A complex automation die manufacturing technology for the automotive seat cushion panel, mixing both semi-progressive die and transfer die for continuous production, was developed.

• 한국지반공학회지:지반
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• 제14권3호
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• pp.5-24
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• 1998

사질토 지반에서 앵커로 지지된 토류벽의 거동을 연구하기 위하여 텍사스 에이엔엠 대학에 소재한 미국 국립 토질 시험장에 계측기가 장착된 실물 크기의 앵커 토류벽을 시공하였다. 기간 중의 단계별 계측과 시공후의 계측을 실시하여 사질토 지반에서의 앵커 토류벽의 현장 거동을 분석하였다. 시공 단계별 토류벽의 수평 변천, 토류벽의 휨 모멘트, 토류벽의 연직 하중, 배면토의 침하와 앵커 하중을 계측하여 앵커 토류벽의 현장 거동을 분석하여 제시하였다. 사질토 지반에서의 토류벽의 거동 특성을 실측결과와 비교하여 분석하였다.

• 소성∙가공
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• 제10권3호
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• pp.246-246
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• 2001

The conventional and new forming processes of a steel shell body are analyzed by the rigid-plastic finite element method. The conventional process contains five forming stages such as bending, drawing, ironing, heading and sizing, which was designed by a forming equipment expert. The results of simulation of the conventional forming process are summarized in terms of deformation patterns and load-stroke relationships for each forming operation. Based on the simulation results of the current five-stage, the shell body forming Process including backward extrusion is designed for improving the conventional process sequence. Forming loads of the proposed process are within the limit value, which is proposed by experts and the proposed process is found to be proper for manufacturing steel shell body.

• 소성∙가공
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• 제10권3호
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• pp.245-252
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• 2001

The conventional and new forming processes of a steel shell body are analyzed by the rigid-plastic finite element method. The conventional process contains five forming stages such as bending, drawing, ironing, heading and sizing, which was designed by a forming equipment expert. The results of simulation of the conventional forming process are summarized in terms of deformation patterns and load-stroke relationships for each forming operation. Based on the simulation results of the current five-stage, the shell body forming Process including backward extrusion is designed for improving the conventional process sequence. Forming loads of the proposed process are within the limit value, which is proposed by experts and the proposed process is found to be proper for manufacturing steel shell body.

• Structural Engineering and Mechanics
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• 제21권5호
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• pp.591-620
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• 2005

A general analytical model for thin-walled composite beams with an arbitrary open/(or/and) closed cross section and arbitrary laminate stacking sequence i.e., symmetric, anti-symmetric as well as un-symmetric with respect to the mid plane of the laminate, is developed in the first paper. All the mechanical properties, mechanical centre of gravity and mechanical shear centre of the cross section are defined in the function of the geometry and the material properties of the section. A program "fungen" and "clprop" are developed in Fortran to compute all the mechanical properties and tested for various isotropic sections first and compared with the available results. The locations of mechanical centre of gravity and mechanical shear centre are given with respect to the fibre angle variation in composite beams. Variations of bending and torsional stiffness are shown to vary with respect to the fibre angle orientations.