• 한국정밀공학회지
• /
• 제13권8호
• /
• pp.96-101
• /
• 1996

Glass fiber reinforced polymeric composites hold considerable promise for increased use in low cost high volume applications because of the potential for processing by solid phase forming. Unfortunately, because of the wide variety of such materials, inherent bariability in properties, and complex temperature and strain rate dependence, large strain behavior of these materials has not been well characterized. Of particular importance is failure during processing due to localized necking instability, and it is this phenomenon that is primary focus of this study. The strain rate and temperature dependence is used to predict limiting tensile strains, based on Mackinack imperfection theory. Excellent correlation was obtained between theory and experiment, and the results are summarized in the limit strains as a function of temperature and stain rate.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 1998년도 제2회 박판성형심포지엄 논문집 박판성형기술의 현재와 미래
• /
• pp.156-163
• /
• 1998

During an actual forming operation, a material may undergo considrably large changes in strain path, and these changes can significantly alter the forming limits. So, in this study, modified forming limit curves(FLCs) in complex strain path are determined with specially designed jig to give test specimens with desired prestrains in uniaxial or biaxial deformation mode. In another part of present study, theoretical prediction of FLCs is attempted with MK's theory and Hosford's yield criterion to give forming limit curves in positive minor strain region and with Hill's local necking theory in negative minor strain region. Comparison of these theoretical results with experimental ones will be mentioned for both linear and complex strain path.

• 대한기계학회논문집
• /
• 제15권1호
• /
• pp.145-153
• /
• 1991

본 연구에서는 Toh가 개발하여 stretchforming에 응용한 강소성 대변형 이론 을 압연문제에 적용하여 강소성 대변형 유한요소 프로그램을 개발하는데 있다.

• Journal of Ship and Ocean Technology
• /
• 제8권3호
• /
• pp.40-49
• /
• 2004

Welding deformations injure the beauty of appearance of a structure, decrease its buckling strength and prevent increase of productivity. Welding deformations of real structures are complicated and the accurate prediction of welding deformations has been a difficult problem. This study proposes a method to predict the welding deformations of large structures accurately and practically based on the simplified thermal elasto-plastic analysis method. The proposed method combines the inherent strain theory with the numerical or theoretical analysis method and the experimental results. The weld joint is assumed to be divided into 3 regions such as inherent strain region, material softening region and base metal region. Characteristic material properties are used in structural modeling and analysis for reasonable simplification. Calculated results by this method show good agreement with the experimental results. It was proven that this method gives an accurate and efficient solution for the problem of welding deformation calculation of large structures.

• Journal of Hydrospace Technology
• /
• 제1권1호
• /
• pp.111-124
• /
• 1995

An improved analysis model for material nonlinearity induced by elasto-plastic deformation and damage including a large strain response was proposed. The elasto-plastic-damage constitutive model based on the continuum damage mechanics approach was adopted to overcome limitations of the conventional plastic analysis theory. It can manage the anisotropic tonsorial damage evolved during the time-independent plastic deformation process of materials. Updated Lagrangian finite element formulation for elasto-plastic damage coupling problems including large deformation, large rotation and large strain problems was completed to develop a numerical model which can predict all kinds of structural nonlinearities and damage rationally. Finally a finite element analysis code for two-dimensional plane problems was developed and the applicability and validity of the numerical model was investigated through some numerical examples. Calculations showed reasonable results in both geometrical nonlinear problems due to large deformation and material nonlinearity including the damage effect.

• 한국지반공학회지:지반
• /
• 제13권3호
• /
• pp.5-20
• /
• 1997

본 연구에서는 유한변형률 이론에 근거하여 3차원 압밀 지배 방정식을 유도하였다. 이 방정식은 비교적 압밀층의 두께가 두꺼운 경우, 비선형 물성치, 공극비에 따른 비선형 투수계수를 갖는 지반에 적합하다. 기존의 유한차분 수치해석 기법(FTCS)은 지배 방정식이 비선형 이며 복잡한 경우 안정된 해를 얻을 수 없기 때문에 본 연구에서는 특수 유한 차분 기법을 도입하였다. 이 수치해석 기법을 지배 방정식에 적용하면 시간에 따른 압밀량을 예측할 수 있다. 본 해석기법에 의해 구해진 값들을 윅드레인을 설치한 여러 가지 고압축성 토질에서의 실험 결과와 비교한 결과, 최종 압밀량과 시간에 따른 압말량이 잘 일치하고 있다.

• 한국지반공학회논문집
• /
• 제16권4호
• /
• pp.183-190
• /
• 2000

본 연구에서는 피에조콘 시험의 유한요소해석을 점탄소성 bounding surface 구성모델과 large displacement large deformation 개념을 이용하여 수행하였다. 이에 따라 구성모델, 가상일의 방정식 및 관련 유한요소 식 등을 Updated Lagrangian reference frame에서 formulation 하였으며 지반의 거동은 theory of mixtures를 통하여 설명하였다. Theory of mixtures 역시 Updated Lagrangian reference frame에서 formulation하였다. 구성모델 중 점성 부분이 전체 formulation 과정에 중요한 영향을 미친다는 사실이 고찰되었다. 유한요소 해석의 결과는 실내에서 실시한 대형 모델시험의 결과와 비교, 분석하였다. Formulation 과정은 'I' 결과는 'II'에서 설명된다.

• 한국농공학회지
• /
• 제34권1호
• /
• pp.41-48
• /
• 1992

Various soil behaviors usually occurring in the geotechnical problems, such as, cutting and embankments, stability of slope, seepage, consolidations, shearing failures and liquefaction, should be predicted and analyzed in any way. An approach of these predictions may be followed by the development of the constitutive equations as first and subsequently solved by numerical methods. The purpose of this paper is develop the constitutive equation of sands uder monotonic or cyclic loadings. The constitutive equation which is based on elasto-plastic theory, modified anisotropic consolidated stress parameter by Sekiguchi et al and Pender's theory is derived. And the equation is included a new stress parameter, hardening function, Bauschinger's effects and Pender's theory. The model is later evaluated and confirmed the validity by the test data of Ottawa sand, Banwol sand Hongseong sand. The following conclustions may be drawn: 1. The consititutive equation which is based on elasto-plastic theory, modified anisotropic consolidated stress parpameter by Sekiguchi et al and Pender's theory is derived. The equation in included a new stress parameter, hardening function, Bauschinger's effect and Pender's theory. 2. For Ottawa sand, the result of the constitutive equation shows a better agreement than that of Oka et al. The result of axial strain agrees well with the tested data. However, the result of horizontal strain is little bit off for the cyclic loadings or large stress. It is thought that the deviation may be improved by considering Poisson's ratio and precise measurement of shear modulus. 3. Banwol sand is used for the strain and stress tests with different relative densitites and confining pressures. The predeicted result shows a good agreement with the tested data because the required material parameters were directly measurd and determined form this laboratory. 4. For Hongseong sand, the tests under same amplitude of cyclic deviatoric stress shows a similar result with the tested data in absolute strain. It shows the acute shape of turning point because the sine wave of input is used in the test but the serrated wave in prediction.

• 전산구조공학
• /
• 제7권4호
• /
• pp.69-83
• /
• 1994

평면 뼈대구조물의 매우 큰 변형에 대하여 정확한 비선형 유한요소의 정식화 과정을 나타내었다. 유한요소의 구성은 변화되는 재료의 기준 물성치에 근거를 두고 형성하였으며 매우 큰 변형을 받는 재료의 성질을 명확하게 특정지어 진응력-변형율 관계식을 직접 적용할 수 있도록 하였다. 큰회전과 작은 변형율을 받는 문제들을 형성하기 위하여 Co-rotation 접근 방법을 사용하였다. 큰 변형을 일으키는 요소의 문제를 해결하기 위하여 직선보 형태의 유한요소를 사용하였으며 개개의 유한요소의 정식화는 축방향력의 영향을 고려하여 미소 처짐보이론을 바탕으로 형성하였다. 본 연구에서 형성된 큰 변형에 대한 비선형 유한요소의 타당성을 확인하기 위해 몇몇 수치해들을 해석하고 검토하였다.

• 한국재료학회지
• /
• 제11권5호
• /
• pp.354-360
• /
• 2001

본 연구에서는 탄성문제에 관한 Eshelby의 이론을 응용하여 다수의 개재물이 모상 중에 균일하게 분산하고 탄성적으로 불균질한 복합재료의 거시적 응력-변형관계를 정식화하였다. 정식화의 과정에서, 주위의 구속을 받지 않는 어떤 영역에 응력의 발생을 동반하지 않는 변형률 (transformation strain $\varepsilon_{kl}$), 즉 열팽창 제수를 갖는 물체가 온도변화 ${\Delta}T$ 를 갖는 경우의 열팽창 변형 $\alpha$${\Delta}T$나, 물체가 일정한 소성 변형을 받았을 때의 소성 변형 등을 예로들 수 있는 역학 장을 정의하였다. 본 연구에서 전개한 방법은 선형 탄성론에 기초를 두고 있으며 복합체의 탄성거동만이 아니라 탄성-소성 거동의 해석 또한 가능하게 하였다