• 한국항공우주학회지
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• 제41권1호
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• pp.17-24
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• 2013

본 논문에서는 복합재료의 미시적 파손모드를 고려하는 복합재 파손예측 프로그램을 개발하였다. 개발된 프로그램의 검증을 위하여 원공이 있는 복합재 적층판 시편의 인장시험 및 정적 파손해석을 수행하였다. 먼저 적층각도별 복합재 시편에 대한 인장시험을 통하여 논문에 사용된 재료에 대한 SIFT 허용치를 산출하였고, 미시역학적 모델인 RVE에 대한 유한요소 해석을 통하여 변형률 증폭계수를 결정하였다. 또한 원공이 있는 복합재 적층판 시편에 대한 인장시험을 수행하고, 실험을 통해 얻어진 파손하중 결과를 바탕으로 유한요소 모델에 대하여 정적 파손해석을 수행하였다. 마지막으로 실험결과를 바탕으로 예측된 파손지수 결과를 평가함으로써 개발된 프로그램의 효용성을 검증하였다.

• 펄프종이기술
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• 제31권5호
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• pp.73-85
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• 1999

Yield and fracture are separated in the tensile failure of paper. Failure in the machine direction of photocopy paper is contrasted with failure in the cross-machine direction . The ratios of distortion (shape change) to dilatation (volume change) for individual elements at yield and fracture are described. The ratios of distortion to dilatation are measured and compared to predicted values of the strain energy density theory. To evaluate the effect of the angle from the principal material direction on the strain energy density theory. To evaluate the effect of the angle from the principal material direction on the strain energy density factor, samples are prepared from machine direction to cross-machine direction in 15 degree intervals. the strain energy density of individual elements are obtained by the integration of stress from finite element analysis with elastic plus plastic strain energy density theory. Poison's ratio and the angle from the principal material direction have a great effect ion the ratio fo distortion to dilatation in paper. During the yield condition, distortion prevails over dilatation . At fracture, dilatation is at a maximum.

• 한국생산제조학회지
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• 제5권3호
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• pp.73-79
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• 1996

In this paper present a new technique (strain-telemetering)for detection of coated tool failure in face milling processes. In the cutter body the strain signals received fro the transmitter is transformed in to frequency modulation(FM) signals in face milling processes. A receiver which is place near by the Vertical milling machine receives the FM signals, then the signals will be sent to a computer which determines whether th tool is failure. And machined surface of workpiece is detected by the SEM. In this paper, A on-line monitoring of the tool failure detection system based on the strain -telemetering apparatus has bee represented.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.436-449
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• 2017

In this paper, the damage and failure behavior of triaxially braided textile composites was studied using progressive failure analysis. The analysis was performed at both micro and meso-scales through iterative cycles. Stress based failure criteria were used to define the failure states at both micro- and meso-scale models. The stress-strain curve under uniaxial tensile loading was drawn based on the load-displacement curve from the progressive failure analysis and compared to those by test and computational results from reference for verification. Then, the detailed failure initiation and propagation was studied using the verified model for both tensile and compression loading cases. The failure modes of each part of the model were assessed at different stages of failure. Effect of ply stacking and number of unit cells considered were then investigated using the resulting stress-strain curves and damage patterns. Finally, the effect of matrix plasticity was examined for the compressive failure behavior of the same model using elastic, elastic - perfectly plastic and multi-linear elastic-plastic matrix properties.

• 한국소음진동공학회논문집
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• 제14권8호
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• pp.757-766
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• 2004

This paper focuses on the formulation and validation of an automatic strategy to select the optimal location and direction of strain gauges for the measurement of the modal response. These locations and directions are important to render the strain measurements as robust as possible when a random mispositioning of the gauges and gauge failures are expected. The approach relies on the evaluation of the signal-to-noise ratios of the gauge measurements from strain data of finite element. The multi-step optimization strategy including genetic algorithm is used to find the strain gauge locations-directions that maximize the smallest modal strain signal-to-noise ratio in the absence of gauge failure or its expected value when gauge failure is possible. A flat Plate is used to prove the applicability of the proposed methodology and to demonstrate the effects of the essential parameters of the problem such as the mispositioning level, the probability of gauge failure, and the number of gauges.

• Geomechanics and Engineering
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• 제24권2호
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• pp.179-191
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• 2021

In this study, the strength and failure mechanism of red sandstones with combined defects were investigated by uniaxial compression tests on red sandstones with different crack angles using two-dimensional particle flow code numerical software, and their mechanical parameters and failure process were studied and analyzed. The results showed that the mechanical characteristics such as peak strength, peak strain, and elastic modulus of the samples with prefabricated combined defects were significantly inferior than those of the intact samples. With increasing crack angle from 15° to 60°, the weakening area of cracks increased, elastic modulus, peak strength, and peak strain gradually reduced, the total number of cracks increased, and more strain energy was released. In addition, the samples underwent initial brittle failure to plastic failure stage, and the failure form was more significant, leading to peeling phenomenon. However, with increasing crack angle from 75° to 90°, the crack-hole combination shared the stress concentration at the tip of the crack-crack combination, resulted in a gradual increase in elastic modulus, peak strain and peak strength, but a decrease in the number of total cracks, the release of strain energy reduced, the plastic failure state weakened, and the spalling phenomenon slowed down. On this basis, the samples with 30° and 45° crack-crack combination were selected for further experimental investigation. Through comparative analysis between the experimental and simulation results, the failure strength and final failure mode with cracks propagation of samples were found to be relatively similar.

• Geomechanics and Engineering
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• 제8권1호
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• pp.33-52
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• 2015

Based on the Mohr-Coulomb failure criterion, a gradient-dependent plastic model that considers the strain-softening behavior is presented in this study. Both triaxial shear tests on conventional specimen and precut-specimen, which were obtained from an ancient landslide, are performed to plot the post-peak stress-strain entire-process curves. According to the test results of the soil strength, which reduces from peak to residual strength, the Mohr-Coulomb criterion that considers strain-softening under gradient plastic theory is deduced, where strength reduction depends on the hardening parameter and the Laplacian thereof. The validity of the model is evaluated by the simulation of the results of triaxial shear test, and the computed and measured curves are consistent and independent of the adopted mesh. Finally, a progressive failure of the ancient landslide, which was triggered by slide of the toe, is simulated using this model, and the effects of the strain-softening process on the landslide stability are discussed.

• Geomechanics and Engineering
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• 제7권4호
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• pp.335-353
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• 2014

The softening hyperelastic model based on the strain energy limitation is of clear concepts and simple forms to describe the failure of materials. In this study, a linear and a nonlinear softening hyperelastic model are proposed to characterize the deformation and the failure in granular materials by introducing a softening function into the shear part of the strain energy. A method to determine material parameters introduced in the models is suggested. Based on the proposed models the numerical examples focus on bearing capacity and strain localization of granular materials. Compared with Volokh softening hyperelasticity and classical Mohr-Coulomb plasticity, our proposed models are able to capture the typical characters of granular materials such as the strain softening and the critical state. In addition, the issue of mesh dependency of the proposed models is investigated.

• 한국해양공학회지
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• 제28권1호
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• pp.34-46
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• 2014

This paper discusses a new formulation for the failure strain in the average stress triaxiaility domain for a low-temperature high-strength steel (EH36). The new formula available at a low average stress triaxiality zone is proposed based on the comparison of two results from tensile tests of flat type specimens and their numerical simulations. In order to confirm the validity of the failure strain formulation, a user-subroutine was developed using Abaqus/Explicit, which is known to be one of the most popular commercial finite element analysis codes. Numerical fracture simulations with the user-subroutine were conducted for all the tensile tests. A comparison of the engineering stress-strain curves and engineering failure strain obtained from the numerical simulation with the user-subroutine for the tensile tests revealed that the newly developed user-subroutine effectively predicts the initiation of failure.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.641-646
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• 2002

FRP-concrete composite slab is consisted of brittle materials and then shows brittle failure mechanism. This study suggests a new design approach that FRP-concrete composite slab leads to ductile failure, and investigates their failure behaviors for two types of section by numerical analysis. Box-type section is higher than I-type section in load capacity to required FRP quantity. Each section was designed so that the strain of FRP plate is 50% to its ultimate strain on initiation of concrete crushing, and it is verified that displacement ductility is more than two. Ductility capacity can be improved by reducing the strain of FRP on initiation of concrete crushing, but as the strain of FRP is reduced load capacity to required FRP quantity is also reduced. Therefore section optimization study is needed considering safety and economical efficiency.