• 소성∙가공
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• 제10권1호
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• pp.59-66
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• 2001

Recently, the technology of incremental forming for sheet metal components has drawn attention for small-batch productions. In the present investigation, a forming tool containing a freely-rotating ball was developed and applied to forming of various shapes with full annealed Al 1050 sheet. Deformation characteristics occurring during forming with this tool was examined through FEM analysis and grid measurement. It was found that deformation modes developed along a straight path and around a corner are close to those of plane-strain and equi-biaxial stretching, respectively, and that cracks occur mostly at corners for the same depth of tool. FEM analysis was successfully applied to this special type of forming process and provided comparable results to the measurements from experiment.

• 대한기계학회논문집A
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• 제39권7호
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• pp.645-652
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• 2015

본 논문은 이전 연구에서 제시한 여러 가지 Ramberg-Osgood 상수 결정법을 비교하여 파단전 누설평가에 사용되기 가장 적합한 상수 결정법을 선정하였다. 비교에 사용한 재료는 운전온도인 $316^{\circ}C$에서 실험한 SA312 TP316 과 SA508 Gr.1a 이다. 상수 결정법을 선정하기 위해 실제 응력-변형률 데이터를 모두 이용하는 증분 소성 이론과 Ramberg-Osgood 상수를 이용하는 변형 소성이론을 유한요소 해석에 적용하여 계산한 J 적분과 균열 열림 변위를 비교하였다. 비교 결과에서 증분 소성 이론 결과와 가장 잘 일치하는 상수 결정법을 최종적으로 파단전 누설 평가에 적합한 방법으로 선정하였다.

• 대한기계학회논문집A
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• 제24권8호
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• pp.2108-2114
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• 2000

The buckling of two elastic layers bonded to a semi-infinite substrate under a transverse compressive plane strain is investigated. Incremental deformation theory, which considers the effect of the initial stress on the incremental stress field, is employed to describe the buckling behavior of both two isotropic layers and the semi-infinite substrate. The problem is converted to an eigenvalue-eigenvector case, from which the critical buckling strain and the buckling wavelength are obtained. The results are presented on the effects of the layer geometries and material properties on the buckling behavior.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.185-192
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• 2000

A novel indentation theory is proposed by examining the data from the incremental plasticity theory based finite element analyses. First the optimal data acquisition location is selected, where the strain gradient is the least and the effect of friction is negligible. This data acquisition point increases the strain range by a factor of five. Numerical regressions of obtained data exhibit that strain hardening exponent and yield strain are the two main parameters which govern the subindenter deformation characteristics. The new indentation theory successfully provides the stress-strain curve with an average error less than 3%.

• 소성∙가공
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• 제7권3호
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• pp.233-245
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• 1998

A new approach has been proposed for the incremental analysis of the nonsteady state large deformation of planar anisotropic elastic-plastic sheet forming. A mathematical brief review of a constitutive law for the incremental deformation theory has been presented from flow theory using the minimum plastic work path for elastic-plastic material. Since the material embedded coordinate system(Lagrangian quantity) is used in the proposed theory the stress integration procedure is completely objective. A new return mapping algorithm has been also developed from the general midpoint rule so as to achieve numerically large strain increment by successive control of yield function residuals. Some numerical tests for the return mapping algorithm were performed using Barlat's six component anisotropic stress potential. Performance of the proposed algorithm was shown to be good and stable for a large strain increment, For planar anisotropic sheet forming updating algorithm of planar anisotropic axes has been newly proposed. In order to show the effectiveness and validity of the present formulation earing simulation for a cylindrical cup drawing and front fender stamping analysis are performed. From the results it has been shown that the present formulation can provide a good basis for analysis for analysis of elastic-plastic sheet metal forming processes.

• 한국강구조학회 논문집
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• 제15권1호
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• pp.59-68
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• 2003

최근, 강합성 구조의 외부 프리스트레스 도입 기법에 대한 응용연구가 왕성하게 수행되고 있다. 이는 역학적 효율성, 시공성 및 경제적 합리성면에서 우수한 강합성 구조에 외부 프리스트레스를 도입하므로써, 여러 가지 구조적 장점을 획득할 수 있기 때문이다. 이 논문에서는 외부 프리스트레스를 강합성 교량의 강주형에 도입할 때, 재료 비선형을 고려한 프리스트레스 합성형의 탄소성영역 휨 거동특성을 해석적으로 검토하기 위한 변형증분법(Incremental Deformation Method, IDM)을 제안하였다. 그리고 이를 실험을 통해 검증하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 춘계 학술발표회 논문집
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• pp.268-275
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• 2006

Excavation works of cylindrical shafts and tunnels for the construction of a variety of infrastructures have been frequently going on in the urban areas. When ground excavations of cylindrical shafts and shallow tunnels proceed in the ground condition of high water level and silt particle component, ground water drawdown involving soil particle migration causes loosening of ground around tunnels and shafts, causes settlement and deformation of ground. Damages due to ground sinking and differential settlement can occur in the adjacent ground and structures. The extent and possibility of damage relevant to ground water drawdown and soil particle migration can't be so precisely expected in advance that we will face terrible damages in case of minor carefulness. This paper introduces two examples of construction management where using incremental deformation graph of inclinometer, we noticed the possibility of soil migration due to ground water drawdown in the excavation process of vertical shaft and shallow tunnel, analysed a series of measurement data in coupled connection, properly prepared countermeasures, so came into safe and successful completion of excavation work without terrible damages. The effort of this article aims to improve and develop the technique of design and construction in the coming projects having similar ground condition and supporting method.

• 소성∙가공
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• 제32권4호
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• pp.208-214
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• 2023

This paper discusses the deformation characteristics of a scaled-down automotive outer door panel with vacuum-assisted incremental sheet forming. The vacuum condition between the die and Al6052-H32 sheet with a thickness of 1.0 mm is reviewed with the goal of improving the geometrical accuracy of the target product. The material flow according to the forming tool path, including the multi-tool path and conventional contour tool path, is investigated considering the degradation of the pillow effect. To reduce friction between the tool and the sheet during incremental forming, automotive engine oil (5W-30) is used as a lubricant, and the strain field on the surface of the formed product is analyzed using ARGUS. By comparing the geometry and material flow characteristics of products under different test conditions, it is confirmed that the product surface quality can be significantly improved when the vacuum condition is employed in conjunction with a multi-tool path strategy.

• 소성∙가공
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• 제32권6호
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• pp.360-366
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• 2023

This study is concerned with the surface quality of products according to the material and coating condition of the forming tool in incremental sheet forming. Three forming tools, SKD11 with and without diamond-like-coating (DLC) and polymer tool tip, were used to form conical and pyramidal geometries to take into account the influence of friction between the forming tool and the sheet on the surface quality including geometric accuracy of deformed samples. Each test was performed using SUS304 with a thickness of 0.4 mm according to different incremental depths per lap of 0.5 mm, 1.0 mm, and 1.5 mm for the contour tool path, considering the increase in normal force which is associated with the frictional behavior during local deformation. The surface quality was then investigated through surface roughness measured with KEYENCE VR-6000 and relative strain distribution including deformed shape analyzed with ARGUS which is a non-contact optical strain measurement system. Differences between 3D CAD surfaces and captured geometry from experiments were evaluated to compare the effect of friction on geometric accuracy. From comparisons of experimental results, it was revealed that the polymer-based tool tip can improve surface quality and geometric accuracy by reducing the undesired material flow due to local friction in the increment sheet forming process.

• 한국자동차공학회논문집
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• 제6권3호
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• pp.54-62
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• 1998

In this study, collapse behavior of frame composed of thin-walled rectangular tube is investigated. Considering the collapse of frame, the bending and compression members undergo large deformation. The stiffness of the compound element is obtained from analytical moment-rotation relationship and approximated load-deflection relationsh- ip of thin-walled rectangular tube. A computer program is developed for the large deformation analysis of frame. An incremental displacement method is used in the program and at each incremental stage, the stiffness matrix of the total structure is checked with the state of each element for bending and compression.