• 한국기계가공학회지
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• 제10권2호
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• pp.124-129
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• 2011

The thick plate produced by rolling process is used as the basic members of a ship structure. In this paper, we present a setup model to control the asymmetric factors causing plate bending in the upper or lower direction during rolling. A series of finite element analysis are conducted to predict the relationship between various asymmetric factors and plate bending. The setup model is developed by regressing the relationship to the linear equations with several non-dimensional parameters. The setup model is verified by a pilot rolling test and applied to actual rolling conditions. Results show that the model is substantial to predict the asymmetric deformation in the plate rolling process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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• pp.11-18
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• 2004

Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and $\{001\}<110>$ orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss $\{110\}<001>\;and\;\{112\}<111>$ orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve mechanical properties. Steel sheets, especially ferritic stainless steel sheets, and aluminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.327-334
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• 2002

This paper develops an optimized torsional design method of asymmetric wall structures considering deformation capacities of walls. Contrary to the current torsional provisions, a deformation based torsional design is based on the assumption that stiffness and strength are dependent. Current torsional provisions specify two design eccentricity of stiffness to calculate the design forces of members. But such a methodology leads to an excessive over-strength of some members and an optimal torsional behavior is not ensured. Deformation-based torsional design uses displacement and rotation angle as design parameters and calculates base shear for inelastic torsional response directly. Because optimal torsional behavior can be defined based on the deformation of members, deformation based torsional design procedure can be applied to the optimal and performance-based torsional design. To consider the effect of accidental eccentricity, an over-strength factor is defined. The over-strength factor is determined from performance level, torsional resistance and arrangement of walls.

• 한국지진공학회논문집
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• 제6권1호
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• pp.43-53
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• 2002

기존의 비틀림 설계법은 구조 벽체의 강성은 강도에 무관하게 결정된다는 기본 가정하에 강성을 설계 변수로 비대칭 벽식 구조의 비틀림 효과를 최소화 하기 위한 각 부재의 강도를 결정한다. 이와는 달리 최근의 연구에 의하면 구조 벽체의 강성과 강도는 상호 연관성을 갖는 것으로 알려졌다. 이 경우 벽체의 실제 강성은 비틀림설계를 모두 마친 후에야 결정되므로 강성에 기초하여 비틀림 설계를 수행한다는 것은 모순이다. 이와 같은 문제점을 해결하기 위해 본 논문은 강성이 아닌 변형에 기초한 비대칭 벽식 구조의 비틀림 설계법을 제안한다. 기존의 비틀림 설계법은 탄성 비틀림 응답과 반응수정계수를 이용하여 비탄성 응답에 대한 설계 하중을 간접적으로 계산하지만 변형에 기초한 비틀림 설계법은 변위와 비틀림 회전각을 설계 변수로 비탄성 응답에 대한 설계 하중을 직접적으로 계산한다. 기존의 비틀림 설계법이 비틀림 효과를 최소화하는 것을 목적으로 하는 데 비하여, 변형에 기초한 비틀림 설계법은 내진역량설계법의 기본 개념에 의거하여 설계자가 의도한 비틀림 미케니즘을 발휘하는 데 그 목적을 둔다. 변위와 회전각은 비대칭 구조의 성능수준을 직접적으로 나타내는 성능 지표이므로 본 설계법은 성능기초 내진설계에 효과적으로 사용될 수 있다.

• 대한기계학회논문집A
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• 제35권11호
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• pp.1437-1443
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• 2011

선박 건조를 위한 기본 자재인 후판은 압연공정을 통해 생산된다. 본 논문에서는 후판압연 중에 발생하는 폭방향 휨을 일으키는 비대칭 요인들을 제어할 수 있는 설정모델을 제시한다. 일련의 삼차원 유한요소해석을 통해서 휨과 비대칭 요인 사이의 관계를 예측한다. 그 관계를 무차원 변수로 이루어진 선형 방정식으로 수식화 시킴으로써 설정모델을 도출한다. 소재 폭방향으로 두께 편차와 온도차이가 있는 경우에 대해서 파이롯트 압연 시험으로 통해서 설정모델의 정도를 검증한다. 본 모델에 의해 예측된 휨 곡률이 각각의 비대칭 요인들에 의해 측정된 휨 곡률과 상당히 일치하는 결과를 보여 주었다.

• Journal of Welding and Joining
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• 제17권1호
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• pp.88-96
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• 1999

The effects of root gap on welding residual stress and deformation are dealt with the multi-pass weldment with three kinds(0, 6, 30mm) of root gap by F.E.M common code, and then compared with experiment data. In this analysis, an 100% ramp heat input model was used to avoid numerical convergence problem due to an instantaneous increase in temperature near the fusion zone, and the effect of a moving arc in a two dimensional plane was also included. During the analysis, a small time increment was applied in a period with instantaneous temperature fluctuation while a large time increment was used in the rest period. The residual stress is distributed as symmetric types and maximum value is also equivalent when the weldment with 0mm and 6mm root gap is welded. In the case of 30mm root gap welding, the distribution of the residual stress extends over a wide range as asymmetric types due to the built-up weld, and most of the residual stress is biased in the side of a built-up weld part. In case of 0mm gap welding and 6mm gap welding, a little angular distortion occurs, but the level of deformation is small. When the weldment with 30mm root gap is welded, the angular deformation of the asymmetric types, however, occurs larger than the other specimens. The experimental and the analytic results show good coincidence and indicate that the welding residual stress and deformation distribution of 30 mm root gap specimen may be asymmetric and the amplitude is larger than those of root gap specimen under standard.

• Structural Engineering and Mechanics
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• 제15권4호
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• pp.463-476
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• 2003

This paper deals with nonlinear asymmetric dynamic buckling of clamped laminated angle-ply composite spherical shells under suddenly applied pressure loads. The formulation is based on first-order shear deformation theory and Lagrange's equation of motion. The nonlinearity due to finite deformation of the shell considering von Karman's assumptions is included in the formulation. The buckling loads are obtained through dynamic response history using Newmark's numerical integration scheme coupled with a Newton-Raphson iteration technique. An axisymmetric curved shell element is used to investigate the dynamic characteristics of the spherical caps. The pressure value beyond which the maximum average displacement response shows significant growth rate in the time history of the shell structure is considered as critical dynamic load. Detailed numerical results are presented to highlight the influence of ply-angle, shell geometric parameter and asymmetric mode on the critical load of spherical caps.

• 한국해양공학회지
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• 제16권2호
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• pp.38-43
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• 2002

Die-less forming is a cold forming process which is to bend thick flat plates into compound curved plates using two asymmetric rollers. This forming method has several advantages compared with line heating which is widely used to fabricate compound curved pieces in shipyards. The die-less forming, however, has scarcely been studied. Even the deformation mechanism in this forming process has not been understood clearly. So, in this paper, the deformation characteristics of die-less forming is investigated analytically and numerically. for the analytic investigation, slab method based on equilibrium equation is applied. And the mechanism of curvature generation is derived for the asymmetry in roller applied. And three dimensional numerical analyses are performed with realistic modeling of interactions between the rollers and work-piece using finite element program, ABAQUS. It is shown that curvature generation is mainly due to the difference of normal positive strain distribution between the top and bottom surface of the work-piece. And a convex-type curved plate is formed if the center region of the work-piece is rolled with asymmetric rollers of which the lower is larger than the upper in diameter.

• Geomechanics and Engineering
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• 제22권5호
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• pp.449-460
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• 2020

The double-lane arrangement model is frequently used in underground coal mines because it is beneficial to improve the mining efficiency of the working face. When the double-lane arrangement is used, the service time of the reserved roadway increases by twice, which causes several difficulties for the maintenance of the roadway. Given the severe non-uniform deformation of the reserved roadway in the Buertai Coal Mine, the stress distribution law in the mining area, the failure characteristics of roadway and the control effect of support resistance (SR) were systematically studied through on-site monitoring, FLAC 3D numerical simulation, mechanical model analysis. The research shows that the deformation and failure of the reserved roadway mainly manifested as asymmetrical roof sag and floor heave in the region behind the working face, and the roof dripping phenomenon occurred in the severe roof sag area. After the coal is mined out, the stress adjustment around goaf will happen to some extent. For example, the magnitude, direction, and confining pressure ratio of the principal stress at different positions will change. Under the influence of high-stress rotation, the plastic zone of the weak surrounding rock is expanded asymmetrically, which finally leads to the asymmetric failure of roadway. The existing roadway support has a limited effect on the control of the stress field and plastic zone, i.e., the anchor cable reinforcement cannot fully control the roadway deformation under given conditions. Based on obtained results, using roadway grouting and advanced hydraulic support during the secondary mining of the panel 22205 is proposed to ensure roadway safety. This study provides a reference for the stability control of roadway with similar geological conditions.

• Advances in Computational Design
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• 제4권1호
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• pp.33-41
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• 2019

In this study, 2-mm Al/Cu bimetallic laminates were produced using asymmetric roll bonding (RB) process. The asymmetric RB process was carried out with thickness reduction ratios of 10%, 20% and 30% and mismatch rolling speeds 1:1, 1:1.1 and 1:1.2, separately. For various experimental conditions, finite element simulation was used to model the deformation of bimetallic Al/Cu laminates. Specific attention was focused on the bonding strength and bonding quality of the interface between Al and Cu layers in the simulation and experiment. The optimization of mismatch rolling speed ratios was obtained for the improvement of the bond strength of bimetallic laminates during the asymmetric RB process. During the finite element simulation, the plastic strain of samples was found to reach the maximum value with a high quality bond for the samples produced with mismatch rolling speed 1:1.2. Moreover, the peeling surfaces of samples around the interface of laminates after the peeling test were studied to investigate the bonding quality by scanning electron microscopy.