• 한국산학기술학회논문지
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• 제11권6호
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• pp.2284-2291
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• 2010

본 논문에서는 회전관성과 전단변형이 고려된 8절점 쉘 요소를 이용한 판의 진동해석을 연구하였다. 면내 잠김과 전단 잠김 현상을 극복하기 위하여 가정자연변형률 방법을 이용하였다. 8절점 쉘 요소의 성능 향상을 위해 새로운 보간점의 조합을 이용한 가정변형률 방법을 사용하였다. Reissner-Mindlin 이론에 근거한 개선된 1차 전단변형이론을 적용하여 회전관성을 고려하였으며 전단보정계수를 사용하지 않았다. 본 연구의 결과를 검증하기 위해 참고문헌의 직사각형 판의 동적 해석결과를 제시하였다. 해석결과는 참고문헌의 결과와 잘 일치하였다. 또한 감쇄효과가 고려된 판의 진동해석을 수행하였다.

• Journal of Welding and Joining
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• 제7권1호
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• pp.36-41
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• 1989

Among various calculation methods for residual stresses, inherent strain method can be useful one for its simplicity. In comparison with finite element method, it is more economical and efficient. First, inherent strain is assumed, and then incompatibility can be calculated from this inherent strain. Based on collocation method, incompatibility equation is solved assuming stress functions which satisfies boundary conditions. Assumed inherent strain can be determined through iterations on the condition that longitudinal residual stress in centerline is yield stress and transverse distortion is the same as predicted one from other method. Calculated results according to this analytic method yield good agreement with experimental ones.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.461-469
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• 2002

This paper deals with a fully coupled piezoelectric-mechanical assumed strain solid element that can be used for geometric and material nonlinear modeling of thin piezoelectric actuators. Since the assumed strain solid element can alleviate locking, the element is suitable for performance analysis of very thin actuators without locking. A finite element code is developed based on the finite element formulation and validated by solving typical numerical examples such as bimorph and unimorph beams. Using thecode, we have conducted performance analysis for LIPCA actuator. The estimated actuation displacement of LIPCA agrees well with experimental data under low prescribed voltage.

• 소성∙가공
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• 제3권2호
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• pp.215-228
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• 1994

The purpose of this paper is to pursue a general method to determine both the flow stress of a material and the friction factor by ring compression test. The materials are assumed to obey the expanded n-power hardening rule including the strain-rate effect. Ring compression is simulated by the rigid-plastic finite element method to obtain the database used in determining the flow stress and friction factor. The Simulation is conducted for various strain hardening exponent, strain-rate sensitivity, friction factor, and compressing speed, as variables. It is assumed that the friction factor is constant during the compression process. To evaluate the compatibility of the database, experiments are carried out at room and evaluated temperature using specimens of aluminum 6061-T6 under dry and grease lubrication condition. It is shown that the proposed test method is useful and easy to use in determining the flow stress and the friction factor.

• Geomechanics and Engineering
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• 제18권3호
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• pp.225-234
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• 2019

A numerical stepwise approach for cavity expansion problem in strain-softening rock or soil mass is investigated, which is compatible with Mohr-Coulomb and generalized Hoek-Brown failure criteria. Based on finite difference method, plastic region is divided into a finite number of concentric rings whose thicknesses are determined internally to satisfy the equilibrium and compatibility equations, the material parameters of the rock or soil mass are assumed to be the same in each ring. For the strain-softening behavior, the strength parameters are assumed to be a linear function of deviatoric plastic strain (${\gamma}p^*$) for each ring. Increments of stress and strain for each ring are calculated with the finite difference method. Assumptions of large-strain for soil mass and small-strain for rock mass are adopted, respectively. A new numerical stepwise approach for limited pressure and plastic radius are obtained. Comparisons are conducted to validate the correctness of the proposed approach with Vesic's solution (1972). The results show that the perfectly elasto-plastic model may underestimate the displacement and stresses in cavity expansion than strain-softening coefficient considered. The results of limit expansion pressure based on the generalised H-B failure criterion are less than those obtained based on the M-C failure criterion.

• 복합신소재구조학회 논문집
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• 제2권2호
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• pp.13-19
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• 2011

본 연구에서는 강재가 맞대기 이음으로 연결될 경우 CFRP(Carbon Fiber Reinforced Plastic) 쉬트(sheet)를 맞대기 이음부에 접착할 경우 강재 및 CFRP 쉬트에 발생하는 응력을 해석하였다. CFRP 쉬트로 보강한 경우 접착제의 두께, 강재와의 접착 길이, CFRP 강도 변화를 매개변수로 사용하여 이 매개변수에 변화에 따른 이음부의 응력분포를 분석하였다. 또한 CFRP를 여러 층으로 접착할 경우 각 층의 강도를 다르게 변화시켜 맞대기 이음부에 유리한 응력분포를 나타내는 CFRP의 강도를 제시하였다. 본 연구를 위해 빠른 수렴성을 가지며 왜곡된 요소형상에서도 정확한 응력결과를 보이는 강화변형률장(Enhanced Assumed Strain Field)을 사용한 평면변형률 유한요소에 대한 프로그램을 작성하였다.

• Structural Engineering and Mechanics
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• 제8권6호
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• pp.623-637
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• 1999

This paper presents a four-noded quadrilateral $C^0$ strain plate element for the analysis of thick laminated composite plates. The element formulation is based on: 1) the third-order shear deformation theory; 2) assumed strain element formulation; and 3) interrelated edge displacements and rotations along element boundaries. Unlike the existing displacement-type composite plate elements based on the third-order theory, which rely on the $C^1$-continuity formulation, the present plate element is of $C^0$-continuity, and its element stiffness matrix is evaluated explicitly. Because of the third-order expansion of the in-plane displacements through the thickness, the resulting theory and hence elements do not need shear correction factors. The explicit element stiffness matrix makes the present element more computationally efficient than the composite plate elements using numerical integration for the analysis of thick layered composite plates.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.292-296
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• 2008

A new method of evaluating critical damage values of commercial materials is presented in this paper. The method is based on the previous study of the methodology [1] of acquisition of true stress-strain curves or flow stress curves over large strain from the tensile test in which the flow stress is described by the Hollomon law-like form, that is, by the strain dependent strength coefficient and the strain hardening exponent. The strain hardening exponent is calculated from the true strain at the necking point to meet the Considere condition. The strength coefficient is assumed to be constant before necking and represented by a piecewise linear function of strain after necking. With the predicted flow stress, a tensile test is simulated by a rigid-plastic finite element method with higher accuracy of less than 0.5% error between experiments and predictions. The instant when the fracture begins and thus the critical damage is obtained is determined by observing the stress variation at the necked region. It is assumed that the fracture due to damage begins when the pattern of stress around the necked region changes radically. The method is applied to evaluate the critical damage of a low carbon steel.

• Architectural research
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• 제11권1호
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• pp.15-23
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• 2009

An application of the constrained adaptive topology optimization (CATO) algorithm is described for three-dimensional topology optimization of engineering structures. The enhanced assumed strain lower order solid finite element (FE) is used to evaluate the values of objective and constraint functions required in optimization process. The strain energy (SE) terms such as elastic and modal SEs are employed as the objective function to be minimized and the initial volume of structures is introduced as the constraint function. The SIMP model is adopted to facilitate the material redistribution and also to produce clearer and more distinct structural topologies. The linearly weighted objective function is introduced to consider both static and dynamic characteristics of structures. Several numerical tests are tackled and it is used to investigate the performance of the proposed three-dimensional topology optimization process. From numerical results, it is found to be that the CATO algorithm is easy to implement and extremely applicable to produce the reasonable optimum topologies for three dimensional optimization problems.

• Fibers and Polymers
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• 제2권1호
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• pp.140-143
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• 2001

To better understand the formation of necking in drawing processes of fibers, strain distributions during drawing processes have been analyzed. For simplicity, one-dimensional incompressible steady flow at a constant temperature was assumed and quasi-static model was used. To describe mechanical properties of solid polymers, non-linear visco-plastic material properties were assumed using the power law type hardening and rate-sensitive equation. The effects of various parameters on the neck formation were matematically analyzed. As material property parameters, strain-hardening parameter, visco-elastic coefficient and strain-rate sensitivity were considered and, for process parameters, the drawing ratio and the process length were considered. It was found that rate-insensitive materials do not reach a steady flow state and the rate-sensitivity plays a key role to have a steady flow. Also, the neck formation is mainly affected by material properties, especially for the quasi-static model. If the process length changes, the strain distribution was found to be proportionally re-distributed along the process line by the factor of the total length change.