• Coupled systems mechanics
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• 제3권1호
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• pp.89-110
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• 2014

In this work we provide the theoretical formulation, discrete approximation and solution algorithm for instability problems combing geometric instability at large displacements and material instability due to softening under combined thermo-mechanical extreme loads. While the proposed approach and its implementation are sufficiently general to apply to vast majority of structural mechanics models, more detailed developments are provided for truss-bar model. Several numerical simulations are presented in order to illustrate a very satisfying performance of the proposed methodology.

• Journal of Mechanical Science and Technology
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• 제17권2호
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• pp.171-180
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• 2003

One of the most significant problems in the processing of composite materials is residual stress. The high residual stress may cause cracking in the matrix without external loads and degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in an aluminum liner-inserted polymer composite cylinder are investigated. This type of the structure is used for rocket fuselage due to the convenience to attach payloads and equipment to the metal liner by machining. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite cylinder and also in the interface between the liner and the composite during cure.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1653-1665
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• 2002

One of the most significant problems in the processing of composite materials is residual stresses. The residual stresses may be high enough to cause cracking in the matrix even before external loads are applied and can degrade the integrity of composite structures. In this study, thermo-viscoelastic residual stresses occurred in the polymeric composite cylinder are investigated. This type of structure is used for the launch vehicle fuselage. The time and degree of cure dependent thermo-viscoelastic constitutive equations are developed and coupled with a thermo-chemical process model. These equations are solved with the finite element method to predict the residual stresses in the composite structures during cure. A launch vehicle experiences high thermal loads during flight and re-entry due to aerodynamic heating or propulsion heat, and the thermal loads may cause thermal buckling on the structure. In this study the thermal buckling analysis of composite cylinders are performed. Two boundary conditions such as all clamped and all simply supported are used for the analysis. The effects of laminates stacking sequences, shapes and residual stresses on the critical buckling temperatures of composite cylinders are investigated. The thermal buckling analysis is performed using ABAQUS.

• 한국전산구조공학회논문집
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• 제23권5호
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• pp.535-541
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• 2010

본 연구에서는 정상상태의 비선형 열탄성 문제에 대하여 탄성 계수 및 열전도 계수에 대해서 보조변수법을 이용한 연속체 기반의 설계민감도 방정식을 유도하였고, 온도와 변위장이 연성된 보조방정식을 정의하여 효율적으로 설계민감도 해석을 수행하여 위상 최적설계에 적용하였다. 수치 예제를 통하여 열탄성 문제에서 위상 최적설계가 갖는 요소망 의존성을 살펴보았다. 또한 열 하중이 지배적인 경우와 기계적 하중이 지배적인 경우를 비교하여 다중 물리 연성문제에서 위상 최적설계가 갖는 하중에 대한 의존성을 고찰하였다.

• 한국레이저가공학회지
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• 제4권1호
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• pp.21-28
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• 2001

Simulation on the electron beam welding of Al 2219 alloy was carried out by using commercial FEM code MARC, which encounters moving heat sources. Due to axisymmetry of geometry, a half of the cylinder was simulated. A coupled thermo-mechanical analysis was carried out and subroutine for heat flux was substituted in the program. The material properties such as specific heat, heat transfer coefficient and thermal expansion coefficient were given as a function of temperature and the latent heat associated with a given temperature range is considered. As a result, the proper beam power is 60㎸${\times}$60㎃ and welding speed is 1∼1.5 m/min. The residual stress in the heat-affected zone as well as the fusion zone does not increase. It is necessary to use jigs for preventing distortion of cylinder and improving weld quality.

• Structural Engineering and Mechanics
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• 제22권5호
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• pp.517-539
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• 2006

Friction problems involving rubber components are frequently encountered in industrial applications. Their treatment within the framework of numerical simulations by means of the Finite Element Method (FEM) is the main issue of this paper. Special emphasis is placed on the choice of a suitable material model and the formulation of a contact model specially designed for the particular characteristics of rubber friction. A coupled thermomechanical approach allows for consideration of the influence of temperature on the frictional behavior. The developed tools are implemented in the commercial FE code ABAQUS. They are validated taking the sliding motion of a rubber tread block as example. Such simulations are frequently encountered in tire design and development. The simulations are carried out with different formulations for the material and the frictional behavior. Comparison of the obtained results with experimental observations enables to judge the suitability of the applied formulations on a structural scale.

• 한국지반공학회논문집
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• 제27권11호
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• pp.55-69
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• 2011

다양한 지반공학적 문제들에서 불포화 상태의 중요성이 강조되면서, 불포화 지반의 열-수리-역학적 현상들에 대한 거동특성을 모사하기 위한 역학적 구성모델 개발이 진행되고 있다. 본 연구에서는 Bishop의 유효응력 정의에 근거한 불포화 지반의 역학적 탄소성 구성모델을 제시하였다. 유효응력에 근거한 구성관계는 유효응력과 온도를 주 변수로 증분 형식으로 표현되었으며, 이를 이용하여 응력 갱신과 강성 텐서를 산정하였다. 개발된 구성모델을 이용하여 THM 현상을 포함하는 불포화토의 1차원 거동, 불포화토의 삼축 압축시험, 그리고 고준위 방사성폐기물 시설의 완충재의 거동 특성에 관한 예제 해석을 수행하여 해의 안정성과 구성모델의 적용성에 대하여 논의하였다. 수치해석결과는 개발된 역학적 구성모델이 THM 현상의 매우 복잡한 거동을 효과적으로 모사할 수 있었으며, 일반적인 불포화토의 거동 해석뿐만 아니라 다양한 환경 조건하에서의 THM 거동 해석에 적용이 가능할 것으로 판단된다.