• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.115-123
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• 2008

The performance prediction of fiber-reinforced composites has attracted engineer's attention in many fields, and the various theoretical and numerical methods have been proposed to predict the behavior of the fiber-reinforced composites. An evolutionary damage model for progressive interfacial debonding between circular fibers and the matrix is newly incorporated into the micromechanics-based elastoplastic model proposed by Ju and Zhang (2001) in this framework. Using the proposed model, a series of numerical simulations are conducted to illustrate the elastoplastic behavior and evolutionary damage of the framework. Furthermore, the influence of the evolutionary interfacial debonding on the behavior of the composites is investigated by comparing it with the result of a stationary damage model.

• Magazine of the Korea Concrete Institute
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• v.10 no.1
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• pp.143-151
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• 1998

최근들어 반복하중에 의한 철근콘크리트 구조물의 손상이 자주 발견되고 있으며 교량 등의 구조물 등은 때때로 과적차량에 의한 초과하중을 받아 이러한 피로손상이 심화되고 있다. 본 연구에서는 이러한 반복 하중을 받는 철근 콘크리트보의 누적피로손상에 대한 실험적 연구룰 수행하여 피로하중에 의한 철근콘크리트보의 손상과정을 규명하였다. 실험 변수를 전단철근의 양과 반복되는 하중의 크기 및 반복횟수로 하여 실험부재를 제작하였으며, 하중제어에 의한 휨시험법에 의해 3Hz의 반복하중을 시편에 재하하였다. 사인장 균열하중과 사인장 균열 후 반복하중에서의 보의 손상누적거동 즉 처짐. 전단철근의 변형도, 에너지 손실 등의 변화를 실험적으로 평가하였으며, 이를 통하여 반복하중에 의한 누적손상에 의해 철근 콘크리트보의처짐 및 전단변형도가 초기하중상태에서는 급격히 증가하다가 이후 점진적으로 증가하는 것을 규명하였다. 본 연구의 결과는 사용하중상태에서 점진적으로 발생할 수 있는 피로손상의 누적과정을 기술하여 주고 있다.

• Composites Research
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• v.32 no.5
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• pp.258-264
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• 2019

In this paper, a progressive failure analysis method was developed using the Hashin failure criterion and crack band model. Using the failure criterion, the failure initiation was evaluated. If the failure initiation is occurred, the damage variables at each failure modes (fiber tension & compression, matrix tension & compression) was calculated according to linear softening degradation behavior and the variables are used to derive the damaged stiffness matrix. The damaged stiffness matrix is reflected to damaged material and the progressive failure analysis is continued until the damage variables to be 1 that complete failure of material. A series of processes were performed using FE commercial code ABAQUS with user defined material subroutine (UMAT). To evaluate the proposed progressive failure model, the experimental results of open hole composite laminate tests was compared with numerical result. Using digital image correlation system, the strain behavior also was compared. The proposed numerical results were coincided well with the experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.4
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• pp.256-265
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• 2019

In this paper, the progressive damage of an orthogonal grid shell fabricated with plain weave fabric CFRP under bending load was investigated. The orthogonal grids were cured with the bottom composite shell. Progressive damage analysis of an orthogonal grid shell under bending was performed using nonlinear finite element method with Hashin-Rotem failure criterion and Matzenmiller-Lubliner-Taylor(MLT) model. In addition, the three - point bending test for the structure was carried out and the test results were compared with the analysis results. The comparison results of the strain and displacement agreed well. The damage area estimated by the progressive damage analysis were compared with the visual inspection and ultrasonic non-destructive inspection.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.4
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• pp.233-240
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• 2019

Open-hole tensile tests are usually performed to measure the tensile strengths of composites as they are an essential parameter for designing composite structures. However, correctly modeling the tensile test is extremely challenging as it involves various damages such as fiber and matrix damage, delamination, and debonding damage between the fiber and matrix. Therefore, a progressive damage model was developed in this study to estimate the in-plane failure and delamination between the fiber and matrix. The Hashin damage model and cohesive zone approach were used to model ply and delamination failures. The results of the present model were compared with previously published experimental and numerical findings. It was observed that neglecting delamination during finite element analysis led to overestimation of tensile strength.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2003.11a
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• pp.55-58
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• 2003

3차원 메쉬 영상의 압축 알고리듬들은 예측 부호화 및 엔트로피(entropy) 부호화를 기본 기법으로 이용하므로, 압축된 비트열(bitstream)의 네트워크 전송에서 전송 오류에 매우 민감한 단점을 지닌다. 따라서 본 논문에서는 전송 오류에 강인하고 점진적 부호기를 기본으로 하는 3차원 메쉬 영상의 오류은닉 알고리듬을 제안한다. 전송 오류에 강인한 알고리듬을 개발하기 위해, 3차원 원본 메쉬 영상을 여러 파티션(partition)으로 분할하고, 각각의 파티션을 독립적으로 점진 부호화한다. 복호기에서는 오류가 발생하지 않은 주변 표면 정보를 이용하는 오류 은닉 알고리듬을 오류에 의해 손상 받은 파티션 표면에 적용하여 손상된 파티션의 시각적 손상 정도를 감쇄시킨다. 전산 모의 실험을 통해, 제안하는 알고리듬의 오류에 대한 강인성 및 오류 발생시 손상된 파티션 표면이 제안하는 오류 은닉 알고리듬을 통해 화질이 개선됨을 확인하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.4
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• pp.79-88
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• 1986

A nonlinear cumulative damage theory, which can model the effects of the magnitude and sequence of variable amplitude fatigue loadings, is proposed. The concrete beam specimens are prepared and tested in four-point flexural loading conditions. The variable-amplitude fatigue loadings in two and three stages are considered. The present experimental study indicates that the fatigue failure of concrete is greatly influenced by the magnitude and sequence of applied, variable-amplitude fatigue loadings. It is seen that the linear damage theory proposed by Palmgren and Miner is not directly applicable to the concrete under such loading cases. The sum of the cumulative damage is found to be greater than 1 when the magnitude of fatigue loading is gradually increased and less than 1 when the magnitude of fatigue loading is gradually decreased. The proposed nonlinear damage theory, which includes the effects of the magnitude and sequence of applied fatigue loadings, allows more realistic fatigue analysis of concrete structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1084-1092
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• 2000

Responses of ultrasonic back scattered energy and AE (Acoustic Emission) characteristics related to the progressive damage of $[0/90-{2}]_s$ and $[0/90-{4}]_s$ crossply laminates were studied. It was found that the ultrasonic backscattered energy was sensitive to the matrix cracking but not sensitive to other failure mechanisms. However, AE was proved to be sensitive to matrix cracking as well as other failure mechanisms.AE signals were analyzed by investigating the amplitude and number of counts per event for corresponding applied strain. Loading and unloading tests were conducted separately. AE results showed Kaiser effect in the crossply composite laminates and ultrasonic results supported the AE results.

• Composites Research
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• v.36 no.5
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• pp.303-309
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• 2023

In this paper, a Progressive Damage and Failure Analysis (PDFA) modeling method was developed using ABAQUS/EXPLICIT to predict in-plane damage and delamination for Open-Hole Compression (OHC) testing. The proposed PDFA model was constructed based on Hashin criteria and cohesive behavior. The strength and stiffness of OHC specimens with three types of stacking sequences [(45/-45/0₂)₃]_s , [(45/0/-45/90)₃]_s and [45/-45/0/45/-45/90/(45/-45)₂]_s were compared to comprehensively evaluate the validity of the Finite Element(FE) model of PDFA. The strength and stiffness of the OHC specimens were predicted relatively well, with less than a percentage error 10.0 %. For the numerical simulation case for each layup, the damage initiation/evolution of OHC specimens were evaluated for delamination and tension/compression matrix damage before and after failure.

• Composites Research
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• v.29 no.6
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• pp.321-327
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• 2016

In this study, tests and finite element analyses were performed regarding compression after impact strength for laminated composite structures of unidirectional carbon fiber reinforced plastic widely used in structural materials. Two lay-up sequences of composite laminates were selected as test specimens and four impact energy conditions were applied respectively. Impact and compressive strength tests were conducted in accordance with ASTM standards. Impact damages in test specimens were analyzed by using non-destructive inspection method of C-Scan, and compression after impact strengths were calculated with compressive test results. Progressive failure analysis method that can progressively simulate damages and fractures of fiber/matrix/lamina/laminate level was used for impact and compressive strength analyses. All analysis results including contact force, deflection, impact damages, compressive strengths, etc. were compared to test results, and the validity of analysis method was verified.