• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.227-230
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• 2009

In order to predict failure behavior of advanced high-strength steel sheets (AHSS) in hole expansion tests, damage model was developed considering surface condition sensitivity (with specimens prepared by milling and punching: 340R, TRIP590, TWIP940). To account for the micro-damage initiation and evolution as well as macro-crack formation, the stress triaxiality dependent fracture criterion and rate-dependent hardening and ultimate softening behavior were characterized by performing numerical simulations and experiments for the simple tension and V-notch tests. The developed damage model and the characterized mechanical property were incorporated into the FE program ABAQUS/Explicit to perform hole expansion simulations, which showed good agreement with experiments.

• 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.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.277-280
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• 2006

This paper deals with the shear deformation charateristics of concrete beams strengthened with steel/FRP Bar. Applying the shear behavioral model based on shear deformation compatibility to RC beams tested by Ahmed K. El-Sayed et al.(2006), their transverse deformation in the web are calculated at ultimated loads after decoupling the shear carried by arch action in each beams. The calculated transverse deformation at ultimated loads are nearly same for the different reinforcement ratio. From these results, the temporary transverse deformation limit criterion is deduced. Using the proposed temporary limit criterion, the shear strength of concrete beams strengthen with FRP Bar tested by Ahmed K. El-Sayed et al.(2006) is predicted. These predicted values are compared with the measured values and the results are also compared with the current ACI and JSCE equation. The proposed method predicts the ultimate shear capacities more accurately than the equation of ACI and JSCE code. The predictions by the ACI and JSCE code are founded to be very conservative.

• Steel and Composite Structures
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• 제15권2호
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• pp.203-220
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• 2013

The study of the tensile strength of composite materials is far more complex than analysis of the properties of elasticity and plasticity. Indeed, during mechanical loading, micro-cracks in the matrix, the fibers break, debonding of the interfaces are created. The failure process of composites is of great diversity and cannot be described if even we know: the strength criterion of each individual component, the state of stress and strain in the material, the propagation phenomena cracks in the structure and nature of the interface between the matrix and the reinforcement. This information is only partially known and the obtained by the analysis of a stress limit beyond which there is destruction of the material is almost impossible. To partially process the issue, a solution lies in a mesoscopic approach of seeking a law to locate the ultimate strength of the material for a plane stress state. Tests on rectangular plates in bending PEEK/APC2 and T300/914 three were made and this in order to validate our approach, the calculation has been implemented in a nonlinear finite element code (Castem 2000), in order to make comparison with the numerical results. The results show good agreement between numerical simulation and the two materials; however, it would be interesting to consider other phenomena in the criterion.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1393-1400
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• 2009

The objective of this study is to validate local failure criteria, which were proposed based on the notched-bar specimen tests combining with finite element (FE) simulations, using the results of real-scale pipe failure tests. This study conducted burst test using wall-thinned pipe specimens, which were made of 4 inch Sch.80 ASTM A106 Gr.B carbon steel pipe, under simple internal pressure at ambient temperature and performed associated FE simulations. Failure pressures were estimated by applying the failure criteria to the results of FE simulations and were compared with experimental failure pressures. It showed that the local stress based criterion, given as true ultimate tensile stress of material, accurately estimated the failure pressure of wall-thinned pipe specimens. However, the local strain based criterion, which is fracture strain of material as a function of stress tri-axiality, could not predict the failure pressure. It was confirmed that the local stress based criterion is reliably applicable to estimation of failure pressure of local wall-thinned piping components.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.275-282
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• 2001

In this paper, nonlinear analyses of RC (Reinforced Concrete) columns are conducted, and an improved criterion to estimate the design load carrying capacity of slender RC columns is proposed. To simulate the material nonlinearty including the cracking of concrete, the layer model is adopted, and the initial stress matrix is considered for the simulation of P- effect. After correlation studies with previous numerical results to verify the efficiency of the developed numerical model, many parameter studies are followed, and a regression formula which can give more exact resisting capacity of slender RC columns is introduced on the basis of the obtained numerical results.

• 한국산림과학회지
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• 제101권4호
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• pp.606-612
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• 2012

기후변화협약 제16차 당사국총회에서 결정된 칸쿤 합의문의 REDD+ 결정문과 노르웨이의 인도네시아 REDD+ 국가 전략을 평가하기 위한 중요 요소를 바탕으로 인도네시아의 REDD+ 전략을 사전에 평가하기 위한 4가지 정성적인 기준을 개발하였다. '산림전용 및 산림황폐화의 원인 규명'(평가기준 1)과 '국가 MRV 체계 수립'(평가기준 2)은 REDD+가 성공할 수 있는 토대이다. '실질적인 온실가스 감축'(평가기준 3)은 REDD+의 궁극적인 목적이고 지역주민 및 원주민의 권리를 보장하고 생물다양성을 보장하는 '안전장치의 보장'(평가기준 4)은 REDD+의 보완적인 목적이자 REDD+ 성공의 토대라 할 수 있다. 본 연구에서 개발한 REDD+ 평가를 위한 기준 및 지표는 인도네시아뿐만 아니라 개도국의 REDD+ 국가 전략을 이해하기 위한 기본 틀을 제공한다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1991년도 가을 학술발표회 논문집
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• pp.133-138
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• 1991

The aim of the present paper is to develop a computer program predicting ultimate fracture strength of initially cracked structure under monotonically increasing external loads. For this purpose, two kinds of 3-D isoparametric solid elements, one 6-node wedge element and another 8-node brick element are formulated along the small deformation theory. Plasticity in the element is checked using von Mises' yield criterion. Elasto-plastic stiffness matrix of the element is calculated taking account of strain hardening effect. If the principal strain at crack tip which is one nodal point exceeds the critical strain dependin on the material property, crack tip is supposed to be opened and the crack tip node which was previously constrained in the direction perpendicular to the crack line is released. After that, the crack lay be propagated to the adjacent node. Once a crack tip node is fractured, the energy of the newly fractured node should be released which is to be absorbed by the remaining part. The accumulated reaction force which was carried by the newly fractured node so far is then applied in the opposite direction. During the action of crack tip relief force, since unloading may be occured in the plastic element, unloading check should be made. If a plastic element unloads, elastic stress-strain equation is used in the calculation of the stiffness matrix of the element, while for a loading element, elasto-plastic stress-strain equation is continuously used. Verification of the computer program is made comparing with the experimental results for center cracked panel subjected to uniform tensile load. Also some factors affecting ultimate fracture strength of initially cracked plate are investigated. It is concluded that the computer program developed here gives an accurate solution and becomes useful tool for predicting ultimate fracture load of initially cracked structural system under monotonically increasing external loads.

• Computational Structural Engineering : An International Journal
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• 제1권2호
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• pp.117-130
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• 2001

Investigations of low-rice unbounded reinforced concrete shear walls with or without openings are performed with comparison of analytical and experimental results. Theoretical analysis is based on nonlinear finite element algorithm, which incorporates concrete failure criterion and nonlinear constitutive relationships. Studios focus on the effects of height-to-length ratio of shear walls, opening ratio, horizontal and vertical reinforcement radios, and diagonal reinforcement. Analytical solutions conform well with experimental results. Equations for cracking, yielding and ultimate loads with corresponding lateral displacements are derived by regression using analytical results and experimental data. Also, failure modes of low-rise unbounded shear walls are theoretically investigated. An explanation of change in failure mode is ascertained by comparing analytical results and ACI code equations. Shear-flexural failure can be obtained with additional flexural reinforcement to increase a wall's capacity. This concept leads to a design method of reducing flexural reinforcement in low-rise bounded solid shear wall's. Avoidance of shear failure as well as less reinforcement congestion leer these walls is expected.

• 한국농공학회논문집
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• 제47권4호
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• pp.15-24
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• 2005

This study is focused on modeling to predict the behavior of two-way RC slabs. A new finite element model will be presented to analyze the nonlinear behavior of RC slabs. The numerical approach is based on the p-version degenerate shell element including theory of anisotropic laminated composites, theory of materially and geometrically nonlinear plates. In the nonlinear formulation of this model, the total Lagrangian formulation is adopted with large deflections and moderate rotations being accounted for in the sense of von Karman hypothesis. The material model is based on the Kuper's yield criterion, hardening rule, and crushing condition. The validity of the proposed p-version nonlinear RC finite element model is demonstrated through the load-deflection curves and the ultimate loads. It is shown that the proposed model is able to adequately predict the deflection and ultimate load of two-way slabs with respect to steel arrangements and steel ratios.