• Geomechanics and Engineering
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• 제21권4호
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• pp.391-399
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• 2020

Brittleness is one of the most important properties of rock which has a major impact not only on the failure process of intact rock but also on the response of rock mass to tunneling and mining projects. Due to the lack of a universally accepted definition of rock brittleness, a wide range of methods, including direct and indirect methods, have been developed for its measurement. Measuring rock brittleness by direct methods requires special equipment which may lead to financial inconveniences and is usually unavailable in most of rock mechanic laboratories. Accordingly, this study aimed to develop a new strength-based index for predicting rock brittleness based on the obtained base form. To this end, an innovative algorithm was developed in Matlab environment. The utilized algorithm finds the optimal index based on the open access dataset including the results of punch penetration test (PPT), uniaxial compressive and Brazilian tensile strength. Validation of proposed index was checked by the coefficient of determination (R²), the root mean square error (RMSE), and also the variance for account (VAF). The results indicated that among the different brittleness indices, the suggested equation is the most accurate one, since it has the optimal R², RMSE and VAF as 0.912, 3.47 and 89.8%, respectively. It could finally be concluded that, using the proposed brittleness index, rock brittleness can be reliably predicted with a high level of accuracy.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 추계학술대회 논문집 전기물성,응용부문
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• pp.128-130
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• 2003

As toughness-investigation to improve brittleness of existing epoxy resin, elastic-factor of elastic epoxy using TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis) and FESEM (Field Emission Scanning Electron Microsope) for structure-images analysis were investigated. A range of measurement temperature of the TMA, DMTA was changed from -20[$^{\circ}C$] to 200[$^{\circ}C$]. When modifier was ratio of 0[phr], 20[phr], 35[phr], glass transition temperature (Tg) of elastic epoxy was measured through thermal analysis devices. Also, it was investigated thermal expansion coefficient ($\alpha$), modulus and loss factor through DMTA. In addition, it was analyzed structure through FSSEM and made sure elastic-factor of elastic epoxy visually. As thermal analysis results, 20[phr] was superior than 30[phr] thermally and mechanically. Specially, thermal expansion coefficient, modulus, damping properties were excellent. By structure-images analysis through FESEM, we found elastic-factor of elastic epoxy that is not existing epoxy, and proved high impact.

• 한국식품과학회지
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• 제38권3호
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• pp.337-341
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• 2006

다시마를 Vibrio sp.로 분해하여 제조한 SCD를 첨가하여 수산 연제품을 만들어 그 특성을 분석하였다. 원료의 최적 배합 비율을 구하기 위하여 mixture program의 modified distance design을 적용하였다. 수리미와 SCD의 첨가량이 증가할수록 hardness와 cohesiveness 값은 감소 후 증가하였다. SCD의 첨가량이 증가할수록 hardness의 값은 증가 후 감소하였으나 cohesiveness 값은 감소 후 증가하였다. 수리미와 물의 첨가량이 증가할수록, SCD의 첨가량이 감소할수록 gumminess와 brittleness의 값은 증가하였다. SCD의 첨가량이 증가할수록, 물의 첨가량이 감소할수록 수분보유력과 백색도의 값은 증가하였다. 수리미의 첨가량이 증가할수록 백색도의 값은 증가한 반면, 수분보유력은 감소하였다. ANOVA 분석에 의한 다시마 SCD 어육 gel의 Hardness 및 cohesiveness는 nonlinear model(Quadratic model)이 결정되었으며, gumminess, brittleness, 수분보유력 및 백색도는 linear model이 결정되었다. Constraint coefficient 값의 분석 결과 수리미는 hardness 및 백색도에 가장 큰 영향을 미쳤고, cohesiveness, gumminess, brittleness에서는 SCD가, 수분보유력에서는 물이 가장 큰 영향을 미쳤다. Hardness는 surimi-SCD의 상호작용이 있었으며 cohesiveness에서는 surimi-water의 상호작용이 나타났다. Modified distance design에 의한 다시마 SCD 어육 gel의 수리미, 물 및 SCD의 최적배합 비율은 각각 36.80, 57.05 및 4.14%이었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.137-140
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• 2008

FRP rebar와 콘크리트의 취성적인 재료특성때문에 FRP rebar를 사용한 콘크리트 휨 부재는 균형 보강비 이하의 저보강 설계시 극한상태에서 FRP rebar의 파단에 따른 급작스런 취성파괴가 발생한다. 따라서 일반철근콘크리트와 달리 균형보강비 이상으로 설계한다. 또한 부족한 연성을 보완하고 충분한 예비강도를 확보하기 위하여 철근콘크리트보다 안전한 휨 강도감소계수가 요구된다. ACI 440.1R-06에서는 FRP rebar의 사용한 콘크리트 휨 부재의 파괴형태에 따라 서로 다른 휨 강도감소계수를 제안하고 있으며, 또한 다양한 재료로 개발되어진 모든 FRP rebar에 동일한 휨 강도감소계수를 적용하고 있다. 이는 FRP rebar로 균형보강비 이상 보강된 콘크리트 휨부재의 휨 강성 증대효과를 고려하지 못하는 것이며, 다양한 FRP rebar 사용을 제한하는 것이라 할 수 있다. 따라서 다양한 FRP rebar의 종류와 보강비의 변화에 따라 다른 휨 강도감소계수를 적용하는 것이 바람직한 것으로 판단되며, 본 논문에서는 GFRP rebar로 보강된 콘크리트보의 휨 강도감소계수 보정식을 신뢰성해석을 통하여 제안하였다.

• Geomechanics and Engineering
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• 제33권3호
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• pp.279-289
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• 2023

Brittleness index (BI) is an important property of rocks because it is a good index to predict rockburst. Due to its importance, several empirical and soft computing (SC) models have been proposed in the literature based on the punch penetration test (PPT) results. These models are very important as there is no clear-cut experimental means for measuring BI asides the PPT which is very costly and time consuming to perform. This study used a novel Multivariate Adaptive regression spline (MARS), M5P, and white-box ANN to predict the BI of rocks using the available data in the literature for an improved BI prediction. The rock density, uniaxial compressive strength (σ_c) and tensile strength (σ_t) were used as the input parameters into the models while the BI was the targeted output. The models were implemented in the MATLAB software. The results of the proposed models were compared with those from existing multilinear regression, linear and nonlinear particle swarm optimization (PSO) and genetic algorithm (GA) based models using similar datasets. The coefficient of determination (R²), adjusted R² (Adj R²), root-mean squared error (RMSE) and mean absolute percentage error (MAPE) were the indices used for the comparison. The outcomes of the comparison revealed that the proposed ANN and MARS models performed better than the other models with R² and Adj R² values above 0.9 and least error values while the M5P gave similar performance to those of the existing models. Weight partitioning method was also used to examine the percentage contribution of model predictors to the predicted BI and tensile strength was found to have the highest influence on the predicted BI.

• 한국식품조리과학회지
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• 제2권2호
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• pp.68-75
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• 1986

무우 김치를 $17{\sim}20^{\circ}C$의 온도에서 숙성시키면서 텍스쳐의 변화와Dietary fiber(식이성 섬유)의 함량 변화를 측정했다. 숙성이 진행됨에 따라 무우 정치의 경도와 Brittleness는 감소하였으며, 그 변화는 Brittleness에 있어서 더욱 뚜렷하였다. 섬유소와 헤미셀루로오스의 양은 숙성기간동안 뚜렷한 변화를 보이지 않았으며, AIS 함량은 조금 감소하였다. 무우 김치 중의 펙틴질은 숙성이 진행됨에 따라 수용성 펙틴은 소량 증가하고, protopectin은 소량 감소하는 경영을 보였다. 텍스쳐에 영영을 주는 fiber는 펙틴질이었으며, 특히 Protopectin 함량은 경도와 0.85의 상관 관계를 보였다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권4호
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• pp.192-199
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• 2004

Elastic-factor of elastic epoxy were investigated by TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis), TGA (Thermogravimetric Analysis) and FESEM (Field Emission Scanning Electron Microscope) for structure-images analysis as toughness-investigation to improve brittleness of existing epoxy resin. A range of measurement temperature of the TMA and DMTA was changed from -20($^{\circ}C$) to $200^{\circ}(C)$, and TGA was changed from $0^{\circ}(C)$ to $600^{\circ}(C)$. Glass transition temperature (Tg) of elastic epoxy was measured through thermal analysis devices with the content of 0(phr), 20(phr) and 35(phr). Also, thermal expansion coefficient (a), high temperature, modulus and loss factor were investigated through TMA, TGA, and DMTA. In addition, the structure of specimens was analyzed through FESEM, and then elastic-factor of elastic epoxy was visually showed by FESEM. As thermal analysis results, 20(phr) was more excellent than 30(phr) thermally and mechanically. Specially, thermal expansion coefficient, high temperature, modulus, and damping properties were excellent. By structure-images analysis through FESEM, we found elastic-factor of elastic epoxy that is not existing epoxy, and proved high impact.

• 한국생활과학회지
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• 제6권2호
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• pp.157-166
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• 1997

묵의 형성과 그의 물리적 특성을 구명하기 위하여 동두전분을 포함한 9가지 전분의 겔 텍스쳐를 비교 분석하였고, 아밀로오스와 아밀로펙틴이 묵의 특성에 미치는 영향에 대하여 시험하였다. 10%의 전분으로 제조한 동부, 녹두, 도토리 및 메밀 전분 겔의 겔 지표는 2.11-2.37 범위로서 이들 상호간에 유의한 차이가 없었고, 탄성 한계는 0.60이상이었다. 겔 강도 계수는 녹두 전분 겔이 1400으로서 가장 높았고, 동부, 도토리, 메밀 전분 겔은 약 700-1000범위에서 상호간에 유의한 차이가 없었으며, 절단성은 동부 전분 겔은 0.23이었고, 다른 전분 겔들은 0.46-0.62범위였다. 묵의 텍스쳐 특성에 있어서 아밀로펙틴은 겔 지표와 탄성한계에, 아밀로오스는 겔 강도 계수와 절단성에 기여하며, 이 두 분획은 어느 한 쪽 만으로는 묵을 형성할 수 없고 두 분획이 알맞은 비율로 배합되어 있을 때 비로소 묵이 될 수 있다는 것을 알 수 있었다. 또한 곡류와 감자 전분으로부터 분리한 아밀로오스를 동부 전분이나 동부 아밀로펙틴에 첨가하면 그 효과가 다르게 나타났으며, 곡류 전분에 동부 아밀로오스를 첨가하면 겔 강도 계수와 절단성은 증가되었지만 겔 지표와 탄성 한계는 향상되지 않았다. 그러나 감자 전분은 동부 아밀로오스의 첨가에 의하여 겔 강도 계수가 증가되고 절단성이 생김으로써 묵과 비슷한 텍스쳐 특성치를 나타냈다.

• Structural Engineering and Mechanics
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• 제28권3호
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• pp.295-316
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• 2008

In the present paper a mechanical model to predict the compressive response of high strength short concrete columns with square cross-section confined by transverse steel is presented. The model allows one to estimate the equivalent confinement pressures exercised by transverse steel during the loading process taking into account of the interaction of the stirrups with the inner core both in the plane of the stirrups and in the space between two successive stirrups. The lateral pressure distributions at hoop levels are obtained by using a simple model of elastic beam on elastic medium simulating the interaction between stirrups and concrete core, including yielding of steel stirrups and damage of concrete core by means of the variation in the elastic modulus and in the Poisson's coefficient. Complete stress-strain curves in compression of confined concrete core are obtained considering the variation of the axial forces in the leg of the stirrup during the loading process. The model was compared with some others presented in the literature and it was validated on the basis of the existing experimental data. Finally, it was shown that the model allows one to include the main parameters governing the confinement problems of high strength concrete members such as: - the strength of plain concrete and its brittleness; - the diameter, the pitch and the yielding stress of the stirrups; - the diameter and the yielding stress of longitudinal bars; - the side of the member, etc.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권5호
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• pp.230-235
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• 2004

In this paper, epoxy elasticity factors were investigated by TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis) and FESEM (Field Emission Scanning Electron Microscope) to improve toughness and reduce brittleness of existing epoxy resin. Dumbbell shaped specimens were made and tested at rates of 0, 20 and 35phr (part per hundred resins). TMA temperatures ranged from -2$0^{\circ}C$ to 20$0^{\circ}C$. Tg (glass transition temperature) of elastic epoxy was measured by thermal analysis. Also investigated were thermal expansion coefficient ($\alpha$), modulus and Tan$\delta$ (loss factor). And we analyzed structure through FESEM, could find elastic-factors of elastic epoxy that is not existing-epoxy. In addition, we measured permittivity and Tan$\delta$ for investigation of the electrical properties of elastic epoxy. Permittivity and Tan$\delta$ depend on elastomer composition. Namely, permittivity and Tan$\delta$ increase according to the elastomer contents. For experimental analysis results, 20phr was considered an excellent specimen.