• 오토저널
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• 제14권6호
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• pp.1-8
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• 1992

본 고에서는 균질화법의 정식화를 이용하여 복합재료의 거시적 균질화된 재료상수를 구하고, 이 재료상수를 이용하여 거시구조물의 변형과 응력을 구하고, 이로부터 다시 미시구조의 응력분포와 변형도를 구하는 방법을 기술하였다. 주기성을 가정한 균질화법은 복합재료 구조물의 물성평가와 거동예측에 대한 매우 적절한 수치해석 방법이다. 균질화법은 이러한 선형변형의 문제뿐만 아니라, 내압을 존재하는 빈공간 소재의 물성, 기지재료와 강화재료 계면의 미끄러짐 등으로 인한 미세 파손현상 등의 예측이 가능하다. 그외에도 탄소성 대변형 거동 이론과 균질화법을 함께 적용하여, squeeze casting에서 발생하기 쉬운 계면분리나 파단 등의 미소결함과 같은 2차 성형성의 예측도 가능하다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.120-126
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• 2003

Finite element analysis model is suggested for analysis of milli-forming process, which forms milli-size products. Since the size of workpiece in a milli-forming process ranges from a few hundred micrometers to a few millimeters, microstructural changes such as the growth of micro-voids and the development of preferred orientation in a grain become crucial factors for the success of milli-forming. This analysis model incorporates anisotropy from deformation torture and deterioration of mechanical properties due to the growth of micro-voids. Applications of the proposed modeling to milli-forming are given and the results are carefully examined to understand the deformation characteristics such as texture development and damage evolution during extrusion/drawing of a milli-bar.

• 대한기계학회논문집A
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• 제25권8호
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• pp.1213-1219
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• 2001

In this paper, modeling of the multi-pass roll forming process with the finite element method and defect prediction in roll forming process are presented. In the roll forming process, there occurs the defect of scratch. It appears on tubes because of the friction between the strip and the roll, the unexpected sliding velocity and the contact pressure when fabricating the tubes. The surface of the product will be not uniform due to the defect. The scratch can be predicted with the simulation modeling of the finite element method, and can be avoided by modifying the design.

• 대한기계학회논문집A
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• 제26권7호
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• pp.1366-1375
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• 2002

In cold forging of piston-pin for automobile parts, the flow defect appears by the dead metal zone. This appearance evidently happens in products with a thin piercing thickness for the dimension accuracy and the decrease of material loss. The best method that can prevent flow defect is removing dead metal zone. The purpose of this study is to investigate the material flow behavior of forward-backward extruded piston-pin through the relative velocity ratio and the stroke control of upper moving punch & container using the flow control forming technique. The finite element simulations are applied to analyse the flow defect, then the results are compared with the plasticine model material experiments. The model experiment results are in good agreement with the FE simulation ones.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.952-956
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• 1997

This paper describes the method that can expand the forming limit of T type forging products used in aircraft and automotive forged products. The forming limitis determined by the ratio of web thickness to rib width in T type and the reduction in height of workpiece and especially depends on the ratio of web thickness to rib width. For this method, the geometric condition that consists of triangle type was introduced and FEM simulations and model exoeriments were carried out and compared with each other. The objective of this paper is to give the method not only that sink mark and folding phenomenon are eliminated but also that the forming limit and the structural strength of rib and web is increased.

• 소성∙가공
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• 제18권8호
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• pp.596-600
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• 2009

Finite element simulation is an alternative method to practically find the forming limit diagram(FLD). In this paper, the novel fracture criterion is utilized to predict the FLD in conjunction with finite element analysis for sheet forming. The principal scheme of the fracture criterion in this paper is that growth of the micro voids leads up to fracture in the viewpoint of micro-mechanics. The numerical FLD is verified by results of the out-of plane stretching test using hemispherical punch. The verification is also conducted about two types of material. These results are in good accord with the experimental results. Especially, the proposed scheme is appropriate to predict FLDs for a restricted material with low ductility after the instability point or ultimate tensile strength.

• 한국주조공학회지
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• 제20권6호
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• pp.368-376
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• 2000

Rheology forming technology has been accepted as a new method for fabricating near net shaped products with lightweight aluminum alloys. The rheology forming process consists of reheating process of billet, billet handling, filling into the die cavity and solidification of rheology formed part. The rheology forming experiments are performed with two different die temperatures ($T_d$ = $200^{\circ}C$, $300^{\circ}C$) and orifice gate type. The filling behavior and various defects of Al-Si materials with wear resistance (A357, A390 and ALTHIX 86S) fabricated in rheology forming process are evaluated in terms of alloying elements and surface non-uniformity. Finally, the methods to obtain the rheology formed products with high quality are described by solutions for avoiding the surface and internal defects.

• 소성∙가공
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• 제18권5호
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• pp.422-427
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• 2009

Computed tomography(CT) has been applied to measure micro-defects in the aluminum knuckle parts manufactured by the thixoforming process. 6061 aluminum alloys were used to form knuckle samples in the semi-solid temperature after the SIMA processing of billets. Tensile specimens were cut from the different locations in a thixoformed knuckle. The size and the distribution of forming defects in tensile specimens were analyzed using CT scanning and image analysis technology before tensile tests. It has been qualitatively shown that the stress-strain curves were significantly affected by the size and the distribution of forming defects although the defect sizes lie in the range of micro-meters.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.29-33
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• 2000

The purpose of this paper is to determine the effect of the autoclave inner pressure rate, heat-up rate, tool round angle, Thickness of core, height of joggle on defects, and to minimize the defects of aircraft sandwich structure reinforced with honeycomb core occurred in autoclave processing. The results showed that the geometry of aircraft sandwich structure and tool such as tool round angle, Thickness of core, height of joggle, and the autoclave cure conditions such as inner pressure rate, heat up rate strongly affected the core movement, core wrinkle, bridge phenomenon of prepreg and depression of core that occurred in autoclave processing.

• 한국광학회지
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• 제33권5호
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• pp.218-229
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• 2022

실리콘 카바이드(SiC) 소재를 이용해서 위성용 대구경 망원경의 경량 반사경을 제작하는 과정에서 발생할 수 있는 결함과 SiC 소재의 기계 및 열적 특성을 조사했다. SiC 반사경 제작에는 advanced ceramic material (ACM) 공법이라고 불리는 탄소성형체를 이용한 액상 실리콘 침투 소결법 및 화학기상 증착법이 사용되었으며, 크기와 형상이 다른 네 가지 SiC 반사경을 개발했다. 반사경의 크기 및 형상에 따라 구분하여 광학 소재의 결함을 검사하는 기준과 방법을 체계적으로 제시했고, 경면 표면검사 및 소재 내부 결함 탐지를 위한 비파괴 검사법과 결과에 대해 분석했다. 또한, 반사경을 설계하고, 최종 완성품의 기계적 열적 안정성을 계산하고 예측하기 위해 필요한 밀도, 탄성계수, 비열, 열전달 계수 등을 포함한 14종의 물성 계수 측정값을 공인시험을 통해 추출했으며, 특히 측정 신뢰도 향상을 위해 주요 물성인 탄성계수, 열팽창 계수, 굽힘 강도 측정 방법과 결과에 대해 자세히 연구했다.