• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.327-330
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• 2003

In this paper, a viscoelastic structural analysis for the spent pressurized water reactor(PWR) nuclear fuel disposal canister is carried out to predict the collapse of the canister while the canister is stored in a deep repository for long time. There may exist some subterranean heat in a deep repository while the nuclear fuel disposal canister is stored for long time. Then, a time-dependent viscoelastic structural deformation may occur in the canister due to the subterrnean heat Hence, the viscoelastic stress variation according to time should be computed to predict the structural strength of the canister. A viscoelastic material model is adopted. Analysis results show that even though some subterrnean heat may exist for quite a long time, the canister structure still endures stresses below the yield strength of the canister. Hence, some subterranean heat cannot seriously affect the structural strength of the canister.

• 소성∙가공
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• 제33권2호
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• pp.123-131
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• 2024

Plastic, the main material of FFF-type 3D printing, exhibits lower strength compared to metal. research aimed at increasing strength is needed for use in various industrial fields. This study analyzed three X-shape infill patterns(grid, lines, zigzag) with similar internal lattice structure. Moreover, tensile test considering weight and printing time was conducted based on the infill line multiplier and infill overlap percentage. The three X-shape infill patterns(grid, lines, zigzag) showed differences in nozzle paths, material usage and printing time. When infill line multiplier increased, there was a proportional increase in tensile strength/weight and tensile strength/printing time. In terms of infill overlap percentage, the grid pattern at 50% and the zigzag and lines patterns at 75% demonstrated the most efficient performance.

• 소성∙가공
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• 제31권5호
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• pp.281-289
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• 2022

Presently, 3D printers manufactured by material extrusion are economical and easy to use, so they are being used in various fields. However, this study conducted a tensile test on the infill pattern and density of the PLA+ material, due to the limitations of long printing time as well as low mechanical strength. The infill area for the infill density change was measured, using a vision-measuring machine for four infill patterns (concentric, zigzag, honeycomb, and cross) in which the nozzle path was the same for each layer. The tensile strength/weight[MPa/g] and tensile strength/printing time[MPa/min] of the tensile specimens were analyzed. In this study, efficient infill density and patterns are suggested, for cost reduction and productivity improvement. Consequently, it was confirmed that the infill area and infill percentage of the four patterns, were not constant according to the infill pattern. And the tensile strength of the infill density 40% of the honeycomb pattern and infill density 20% of the cross pattern, tended to highly consider the weight and printing time. Honeycomb and cross patterns could reduce the weight of the tensile specimen by 19.11%, 28.07%, as well as the printing time by 29.56%, 52.25%. Tensile strength was high in the order of concentric, zigzag, honeycomb, and cross patterns, considering the weight and printing time.

• Structural Engineering and Mechanics
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• 제22권2호
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• pp.197-222
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• 2006

In this paper, the non-linear time-dependent closed-form, discrete and combined solutions for the post-elastic response of a geometrically and physically non-linear suspended cable to a uniformly distributed load considering the creep effects, are presented. The time-dependent closed-form method for the particularly straightforward determination of a vertical uniformly distributed load applied over the entire span of a cable and the accompanying deflection at time t corresponding to the elastic limit and/or to the elastic region, post-elastic and failure range of a suspended cable is described. The actual stress-strain properties of steel cables as well as creep of cables and their rheological characteristics are considered. In this solution, applying the Irvine's theory, the direct use of experimental data, such as the actual stress-strain and strain-time properties of high-strength steel cables, is implemented. The results obtained by the closed-form solution, i.e., a load corresponding to the elastic limit, post-elastic and failure range at time t, enable the direct use in the discrete non-linear time-dependent post-elastic analysis of a suspended cable. This initial value of load is necessary for the non-linear time-dependent elastic and post-elastic discrete analysis, concerning incremental and iterative solution strategies with tangent modulus concept. At each time step, the suspended cable is analyzed under the applied load and imposed deformations originated due to creep. This combined time-dependent approach, based on the closed-form solution and on the FEM, allows a prediction of the required load that occurs in the post-elastic region. The application of the described methods and derived equations is illustrated by numerical examples.

• 콘크리트학회논문집
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• 제16권3호
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• pp.425-431
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• 2004

This paper describes an experimental investigation of how time-dependent deformations of high strength concretes are affected by maximum size of coarse aggregate, curing time, and relatively low sustained stress level. A set of high strength concrete mixes, mainly containing two different maximum sizes of coarse aggregate, have been used to investigate drying shrinkage and creep strain of high strength concrete for 7 and 28-day moist cured cylinder specimens. Based upon one-year experimental results, drying shrinkage of high strength concrete was significantly affected by the maximum size of coarse aggregate at early age, and become gradually decreased at late age. The larger the maximum size of coarse aggregate in high strength concrete shows the lower the creep strain. The prediction equations for drying shrinkage and creep coefficient were developed on the basis of the experimental results, and compared with existing prediction models.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1994년도 가을 학술발표회 논문집
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• pp.223-228
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• 1994

The strength development of polymer concrete using an unsaturated polyester polymer varies depending on many factors. However, the strength development is mostly dependent upon the age and curing temperature if the mixture ratios are the same. This study conducted to experimentally describe the relationship between the strength development and maturity which is defined as a function of $\Sigma$(time $\times$ temperature). The research result may be applied to predict the compressive, tensile and splitting strengths of the polymer concrete by computing the maturinty of the concrete.

• 한국터널지하공간학회 논문집
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• 제9권2호
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• pp.109-120
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• 2007

대형 대단면 터널의 시공시 지반 변형을 억제시키고 지반의 강성을 증가시키며 차수 및 지수를 확보하기 위해 다양한 사전 보강공법들이 굴착전 막장 천단부 전방에 적용되고 있으나 물성치 결정 및 시공단계 해석에 있어서 여러 오류를 안고 있다. 본 연구에서는 탄성파를 이용하여 사전보강영역의 시간 의존적 강도 및 강성 특성을 분석하는 기법을 제시하였다. 실내실험을 통해 획득한 탄성파속도와 전단강도는 경화시간에 따라 증가하며, 전단강도와 전단강도정수는 탄성파 속도와 일정한 관계를 갖는 것으로 분석된다. 재령에 따른 탄성계수와 점착력을 터널의 시공단계에 따른 시뮬레이션에 적용하여 경시효과가 터널 변위 거동에 미치는 영향을 분석하였다. 해석결과 $1{\sim}2$일 강도 및 강성을 적용한 결과가 경시효과를 고려한 경우와 갱구부에서 유사한 거동을 하며, 특히 초기 시공부분 및 갱구부에서 터널의 안정성에 큰 영향을 미치는 것으로 분석된다. 본 연구에서 제안된 기법을 통해 향후 사전보강영역의 경시효과를 고려한 터널 거동해석을 위해 실내실험과 수치해석을 병용하여 신뢰성 있는 터널 해석 및 설계를 수행하는 것이 바람직 할 것이다.

• 대한인간공학회지
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• 제30권3호
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• pp.381-387
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• 2011

Objective: The aim of this study was to investigate the maximal grip strength for the combinations of resting time and trial and to provide guideline of resting time for the maximum gripping task associated with the number of trials. Background: Despite many previous researches for the maximal grip strength, few studies have considered the effect of both trials and rest time on the maximum grip strength. Methods: A total of thirty subjects participated in the study. The average of maximum grip strength was measured using JAMAR hydraulic hand dynamometer. The testing position was same as the position recommended by the American Society of Hand Therapists. The between-subject experimental design has been conducted in this study. Trials(1~20 trials) and rest time(2, 3, and 4min) were considered as independent variables, and the maximum grip strength was considered as dependent variable, respectively, in this study. Results: According to the result of the number of trials, the maximal grip strength decreased gradually as the number of trials increased. The ANOVA result showed that the main effect was significant for both resting time(p<.0001) and trial(p<.0001), and the interaction was significant(p<0.0086). Conclusions: The maximal grip strength decreased gradually as the number of trials increased. Thus, basic guideline of resting time was suggested for the number of trials of maximal grip strength tests in this study.

• Nuclear Engineering and Technology
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• 제34권5호
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• pp.445-454
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• 2002

The sorption of U(Vl) on a domestic granite is studied as a function of experimental conditions such as contact time, solution-solid ratio, ionic strength, and pH using a batch procedure. The distribution coefficients, $K_{d}$＇s, of U(VI) are about 1-100mL/g depending on the experimental conditions. The sorption of U(VI) onto granite particles is greatly dependent upon the contact time, solution-solid ratio, and pH, but very little is dependent on the ionic strength. It is noticed that an U(VI)-carbonate ternary surface complex can be formed in the neutral range of pH. In the alkaline range of pH above 7, U(VI) sorption onto granite particles is greatly decreased due to the formation of anionic U(VI)-carbonate aqueous complexes.s.

• 한국건축시공학회지
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• 제15권5호
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• pp.457-464
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• 2015

지속적으로 증가하고 있는 이산화탄소 배출량을 저감시키기 위한 국제사회의 노력과 더불어 건설업계, 특히 시멘트 산업에서 알칼리 활성화제를 첨가한 알칼리 활성 슬래그를 활용하고자 하는 연구가 다수 수행되고 있다. 연구결과로 알칼리 활성 슬래그 모르타르의 고강도화 가능성이 밝혀지면서 초고층 구조물에 대한 적용가능성이 검토되고 있다. 그러나 초고층 구조물의 부재로 사용되기 위해서는 시간의 존 변형 거동에 관한 연구가 중요함에도 불구하고 굉장히 미흡한 실정이다. 따라서 본 연구에서는 OPC와 AAS를 이용한 콘크리트 시험체를 제작하여 크리프와 건조수축을 측정하고 도출된 결과값을 ACI 209R-92, CEB-FIP(1990)의 예측모델을 이용한 비선형 회귀분석을 통해 시간의존 변형 특성을 분석하였다. 각각의 열분석 및 SEM촬영을 통해 변형 발생 메카니즘을 규명하고자 하였다.