• 소성∙가공
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• 제8권4호
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• pp.331-339
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• 1999

In this study, to analyze the shaped drawing process from round bar, the practical conical die with considering die radius and bearing was defined by a mathematical expression, and also a simple technique for initial mesh generation to the shaped drawing process was proposed. The drawing of rectangular section from round bar, one of the shaped drawing process, has been simulated by using non-steady state 3D rigid plastic finite element method in order to evaluate the influence of semi-die angle and reduction in area to corner filling. Other process variables such as friction constant, rectangular ratio, die radius and bearing length were fixed during the simulation. An artificial neural network has been introduced to obtain the optimal process conditions which gave rise to a fast simulation.

• 소성∙가공
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• 제8권6호
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• pp.541-553
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• 1999

Cold forging is a special type of forging process in which metal is forced to flow plastically under compressive force into a variety of shapes in room temperature. Gear blank, which is produced by cold forging, is concerned with the production method of transmission gear. Based on the results of simulation of the current four-stage process, the gear blank forging process for improving the conventional process sequence is designed. The rigid plastic finite element analysis for improving the conventional process. The new process consists of three stage operations with one annealing treatment after first operation. Based on the results of simulation of the proposed process, a required equipment could be selected. The new designed process appears to be more economical in producing the gear blank.

• 소성∙가공
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• 제5권4호
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• pp.281-287
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• 1996

Two kinds of blank shapes optimum and square are adopted to investigate formability. Optimum blank shape is determined to construct an L-shape cup with uniform height and without flange part. For this purpose rigid-plastic FEM analysis is applied with backward tracing technique. Maximum cup depth and strain distribution are measured experimentally for the products of the two kinds of blank shapes which are optimum and square. it is confirmed that deeper cup without severe thickness reduction can be obtained from the optimum shape.

• 소성∙가공
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• 제5권2호
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• pp.138-144
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• 1996

The differences of formability with maximum cup depth of drawn product and thickness strain distribution are compared for two kinds of blank shapes which are suggested optimum shape and conventional square shape. The suggested blank is determined by backward tracing technique of rigid-plastic FEM. The deeper cup without wrinkle and flange part could be obtained from the suggested blank shape however the cross sevtion sup from the square blank could not be kept smooth thickness strain distribution and defended those phenomena..

• 한국CDE학회논문집
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• 제12권4호
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• pp.255-262
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• 2007

In the finite element analysis of forming process, objects are described with a finite number of elements and nodes and the approximated solutions can be obtained by the variational principle. One of the shortcomings of a finite element analysis is that the structure of mesh has become inefficient and unusable because discretization error increases as deformation proceeds due to severe distortion of elements. If the state of current mesh satisfies a certain remeshing criterion, analysis is stopped instantly and resumed with a reconstructed mesh. In the study, a new remeshing algorithm using tetrahedral elements has been developed, which is adapted to the desired mesh density. In order to reduce the discretization error, desired mesh sizes in each lesion of the workpiece are calculated using the Zinkiewicz and Zhu's a-posteriori error estimation scheme. The pre-constructed mesh is constructed based on the modified point insertion technique which is adapted to the density function. The object domain is divided into uniformly-sized sub-domains and the numbers of nodes in each sub-domain are redistributed, respectively. After finishing the redistribution process of nodes, a tetrahedral mesh is reconstructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• Steel and Composite Structures
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• 제31권1호
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• pp.99-112
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• 2019

Semi-rigid joints have been widely studied in literature in recent decades because they affect greatly the structural response of frames. In literature, the behavior of semi-rigid joints is commonly assumed to be identical under positive and negative moments which are obviously incorrect in many cases where joint details such as bolt arrangement or placement of haunch are vertically asymmetrical. This paper evaluates two common types of steel frames with asymmetrical beam-to-column joints by Direct Analysis allowing for plasticity. A refined design method of steel frames using a proposed simple forth order curved-quartic element with an integrated joint model allowing for asymmetrical geometric joint properties is presented. Furthermore, the ultimate behavior of six types of asymmetrical end-plate connections under positive and negative moment is examined by the Finite Element Method (FEM). The FEM results are further applied to the proposed design method with the curved-quartic element for Direct Analysis of two types of steel frames under dominant gravity or wind load. The ultimate frame behavior under the two different scenarios are examined with respect to their failure modes and considerably different structural performances of the frames were observed when compared with the identical frames designed with the traditional method where symmetrical joints characteristics were assumed. The finding of this research contributes to the design of steel frames as their asymmetrical beam-to-column joints lead to different frame behavior when under positive and negative moment and this aspect should be incorporated in the design and analysis of steel frames. This consideration of asymmetrical joint behavior is recommended to be highlighted in future design codes.

• Tribology and Lubricants
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• 제36권6호
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• pp.378-384
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• 2020

The friction surfaces of mechanical parts are heat-treated or coated with hard materials to minimize wear. Increasing the hardness is a very useful way to reduce abrasive wear. The general Brinell hardness test, which is widely used for metallic materials, is not suitable because it hardly shows any change in hardness when coated with thin films. In this study, we propose a basis for the application of the new Brinell hardness test method to the coated friction surface. An indentation analysis of the rigid sphere and elastic-perfectly plastic materials is performed using a commercial finite element analysis software. The results indicate that their loadto-diameter ratio is the same; the Brinell hardness test method can be applied even when the indenter diameter is on the micrometer scale. In the case of hard coating, it is difficult to calculate Brinell hardness using the diameter of the indentation, but the study revealed, for the first time, that it can be calculated using the depth of the indentation regardless of coating. The change in hardness owing to thin film coating over a wide load range implies that the hardness evaluation method is appropriate. Additional studies on various properties related to the substrate and coating material are required to apply the proposed method.

• 대한조선학회지
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• 제24권3호
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• pp.43-51
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• 1987

In this paper, dynamic elastic, plastic response of beam-columns is analysed using discrete models. composed of rigid bars and springs. The equation of motion is formulated including the shear deformation effect, and the stress change of yielding points is calculated with various yielding criteria. The effect of initial axial force is considered by two ways: (1) including the effect in interaction curve only. (2) including the effect directly in the equation of motion in terms of initial stiffness method is also used in nonlinear interaction procedure. It is found that this model is very effective in analysing not only the plastic response but the elastic response, and present method is more efficient than Finite Element Method from the viewpoint of calculation time and accuracy.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.124-127
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• 2009

In this paper, a longitudinal die insert fracture which occurred during cold forging of a high strength ball-stud with a sound die design nearly optimized empirically for relatively low strength material of SCM435 is introduced and the reason is revealed. A comparative study between SCM435 and ESW105 is quantitatively made using a thermoelastic finite element method for die structural analysis coupled with a forging simulator theoretically based on a rigid-plastic finite element method. It has been shown that the longitudinal die insert fracture caused from non-optimized value of shrink fit, emphasizing that the die optimal design is inevitable for cold forging of high strength materials.

• 유변학
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• 제1권1호
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• pp.36-45
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• 1989

아이어닝 공정은 제품의 치수정밀도가 정확하게 조절괴는 정밀 금속 성형공정이다. 아이어닝 공정은 대개 냉간상태에서 행하여지며 그리고 때로는 단공정 대신에 다단식이 적 용된다. 본연구의 목적은 강소성 유한 요소법으로 단공정과 다단식 아이어닝 공정을 해석하 여 아이어닝 공정에 대한 적절한 설계변수와 최적 설계조건을 찾는데 있다. 본 연구에서는 공정설계게 있어서 공정변수를 다이의 원추각과 단의 개수로 주었다. 본 해석에서는 단공정 아이어닝과 다단식 아이어닝 공정의 성형하중, 응력과 변형도 분포 그리고 격자 변형을 계 산하였다 그리고 이 값들에 대한 공정 변수의 영향을 검토한 결과 성형하중과 격자 변형에 있어서 계산 결과와 잘 일치하였다.