• Advances in concrete construction
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• 제5권3호
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• pp.221-240
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• 2017

The modeling of the mechanical behavior of quasi-brittle materials is still a challenge task, mainly in failure processes when fracture and plasticity phenomena become important actors in dissipative processes which occur in materials like concrete, as instance. Many homogenization-based approaches have been proposed to deal with heterogeneous materials in the last years. In this context, a computational homogenization modeling for concrete is presented in this work using the concept of Representative Volume Element (RVE). The material is considered as a three-phase material consisting of interface zone (ITZ), matrix and inclusions-each constituent modeled by an independent constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes symmetrically and nonsymmetrically placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements. The inclusion is modeled as linear elastic and matrix region is considered as elastoplastic material. A set of examples is presented in order to show the potentialities and limitations of the proposed modeling. The consideration of the fracture processes in the ITZ is fundamental to capture complex macroscopic characteristics of the material using simple constitutive models at mesoscopic level.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3048-3057
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• 1996

Analysis model containing two inclined surface cracks on semi-infinite elastic body is established and analyzed on the basis of linear fracture mechanics to examine mutual interference of two surface cracks. Muskhelishvili's complex stress functions are introduced and a set of singular integral equations is obtained for a dislocation density function. The stress intensity factors at crack tip are obtained by using the Gerasoulis'method. When two surface cracks are parallel and have the same length, the values of $K_1$and $\Delta K_11$(variation of $K_11$) for crack 1 and crack 2 decrease by the mutual interference of two surface cracks as the distance between the two surface cracks shortens. The effect of mutual interference is remarkable in high friction coefficient. In case that two surface cracks are parallel, the values of $K_1$and $\Delta K_11$for crack 2 decrease as the length ratio ot crack 2 to crack 1 becomes small. As the crack inclination angle rises, the value of $K_1$ and the mutual interference of $K_1$for crack 2 increase and the value of$\Delta K_11$ for crack 1 becomes smaller than that for crack 2.

• KCI Concrete Journal
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• 제12권1호
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• pp.57-68
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• 2000

The effect of structure size on the nominal strength of unidirectional fiber-polymer composites, failing by propagation of a kink band with fiber microbuckling, is analyzed experimentally and theoretically. Tests of novel geometrically similar carbon-PEEK specimens, with notches slanted so as to lead to a pure kink band (without shear or splitting cracks), are conducted. The specimens are rectangular strips of widths 15.875, 31.75. and 63.5 mm (0.625, 1.25 and 2.5 in and gage lengths 39.7, 79.375 and 158.75 mm (1.563, 3.125 and 6.25 in.). They reveal the existence of a strong (deterministic. non-statistical) size effect. The doubly logarithmic plot of the nominal strength (load divided by size and thickness) versus the characteristic size agrees with the approximate size effect law proposed for quasibrittle failures in 1983 by Bazant This law represents a gradual transition from a horizontal asymptote, representing the case of no size effect (characteristic of plasticity or strength criteria), to an asymptote of slope -1/2 (characteristic of linear elastic fracture mechanics. LEFM) . The size effect law for notched specimens permits easy identification of the fracture energy of the kink bandand the length of the fracture process zone at the front of the band solely from the measurements of maximum loads. Optimum fits of the test results by the size effect law are obtained, and the size effect law parameters are then used to identify the material fracture characteristics, Particularly the fracture energy and the effective length of the fracture process zone. The results suggest that composite size effect must be considered in strengthening existing concrete structural members such as bridge columns and beams using a composite retrofitting technique.

• 한국가스학회지
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• 제25권6호
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• pp.14-21
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• 2021

-162℃ 초저온 상태의 LNG를 저장하는 저장탱크의 내조는 균열과 같은 결함에 대한 구조 건전성 평가가 필요하다. 전통적인 파괴역학 관점에서는 응력확대계수 K, J-적분 그리고 CTOD를 이용한 단일 매개변수 평가가 주로 수행되어왔다. 그러나 실제 구조에서 발생되는 균열선단은 구조물의 크기, 시편형상 그리고 인장과 굽힘과 같은 하중의 형태에 따라 구속효과의 차이로 인한 영향이 발생하게 된다. 단일 매개변수 파괴역학을 보완하기 위해 다양한 시도가 있었고, 대표적으로 Q-응력법이 있다. 본 논문에서는 비선형 탄성영역의 균열선단 응력장 평가에 적합한 J적분에 Q응력을 유도하여 2 매개변수 접근법을 사용하고자 한다. SENB 시편의 균열비 0.1~0.7 그리고 광폭시편 균열비 0.2~0.6에 시편 균열선단의 응력을 J-Q 평가법을 이용하여 구속효과를 정량적으로 평가 하였다.

• 한국전산구조공학회논문집
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• 제12권3호
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• pp.485-494
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• 1999

본 연구에서는 요소를 사용하지 않고 절점들만을 이용하여 해석이 가능한 새로운 수치해석기법인 EFG(Element-Free Galerkin)법을 사용하여 임의의 균열의 성장과정을 해석할 수 있는 효율적인 알고리즘을 개발하고, 이를 바탕으로 균열의 성장방향과 경로를 정확히 추정하여 일련의 균열진전해석을 수행할 수 있는 프로그램을 개발하였다. 균열해석에 있어서는 균열선단의 특이성과 균열면의 분연속성을 수치적으로 반영할 수 있는 기법을 도입하여 균열을 모형화하였으며, 선형탄성파괴역학이론에 근거하여 균열해석과정을 정식화하였다. 또한, EFG 형상함수가 kronecker delta 조건을 만족시키지 못함으로써 발생하는 필수경계조건의 처리문제를 penalty법을 이용하여 해결하였다. 개발된 균열진전해석 알고리즘을 정지상태와 성장하는 상태에 있는 모드 Ⅰ, 모드 Ⅱ 및 혼합모드상태의 대표적인 균열문제들에 적용하여 응력확대계수와 균열성장방향 및 균열의 성장경로를 추정하고 이를 이론적·실험적 결과들과 비교함으로써 그 정확성과 효율성을 검증하였다.

• 대한기계학회논문집
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• 제15권2호
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• pp.596-603
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• 1991

Fatigue life prediction of pressure vessel is studied analytically using cumulative damage models and linear elastic fracture mechanics method. The stresses are analyzed by finite element method. During operation, the maximum stress occurs at the outside of neck region while fatigue analysis indicates that the bottom of nozzle part has the shortest fatigue life. Previously proposed fatigue life prediction equation and cumulative damage model are modified successfully by introducing reference fatigue modulus. It is found that the modified life prediction equation and damage model are useful for lower stress level application.

• 대한기계학회논문집A
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• 제30권5호
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• pp.505-511
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• 2006

In the present paper, approximate plastic limit load solutions fur pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The present FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the present FE results. The proposed limit load solutions would be a basis of defective pipe bends and be useful to estimate non-linear fracture mechanics parameters based on the reference stress approach.

• 대한기계학회논문집
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• 제6권3호
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• pp.197-203
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• 1982

The fatigue crack propagation behavior or non-heat-treatment and thermally aged type 304 stainless steel was investigated on the basis of linear elastic fracture mechanics. This Study was concentrated on the relations between the crack propagation rate and the stress intensity factor range. The following results are obtained : The precision measurement and observation of fatigue crack propagation behavior is studied with moire grating. The effect of thermally aged type 304 stainless steel is investigated under small load. In the equation da/dN=c(.DELTA. k)/SUP m/, factor m of thermally aged steel is a little higher than non-heat-treatmented steel and its limit is m=1.35-4.2.

• 한국공간구조학회:학술대회논문집
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• 한국공간구조학회 2005년도 춘계학술발표회 및 정기총회 2권1호(통권2호)
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• pp.89-98
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• 2005

Membrane structures, a kind of lightweight soft structural system, are used for spatial structures. The material property of the membrane has strong axial stiffness, but little bending stiffness. Therefore membrane structures arc unstable structures initially. These soft structures need to be introduced initial stresses first because of its initial unstable state, and it happens large deformation phenomenon. To find the structural shape after large deformation caused by initial stiffness introduced, we need the shape analysis considering geometric nonlinearity in structural design procedure. In this study, we investigate into the stress concentration at crack of membrane structures. Therefore, using the nonlinear analysis program that NASS (Nonlinear Analysis for Spatial Structures) perform nonlinear analysis, and stress distribution for creak length investigate for using linear elastic fracture mechanics.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.401-402
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• 2006

In the present paper, approximate plastic limit load solutions for pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The present FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the present FE results. The proposed limit load solutions would be a basis of defective pipe bends and be useful to estimate non-linear fracture mechanics parameters based on the reference stress approach.