• 한국농공학회지
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• 제31권1호
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• pp.106-116
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• 1989

This study aims at scrutinizing the long4errn consolidation characteristics of peats sampled at three different regions of Chonbuk province. The standard consolidation test and the single load consolidation test were performed about these samples and especially in case of the latter the loading period was 350 days. The main condusions analyzed are as follows. 1. Void ratio showed much greater values than that of the general clay and was decresed greatly according to the increase of the load. 2. In case of the relationship between the sefflement and the long-term settlement time the rate of settlement increment became great according to the increase of the load step and the long4erm settlement became linely proportional to the logarithm of time alter 10 minutes. 3. The linear correlation was showed between the long4erm settlement time and the void ratio and therefore equations by regression analysis were derived in order to estimate the long-term settlement The slope of straight lines increased according th the increase of the load step and secondary consolidation coefficients ranged from 0.04-0.27. 4. The secondary consolidation coeffcient became linealy proportional to the compression index and the ratio of Ca to CC was 0.072. 5. The period required in ending the primary consolidation was about 10 minutes and alter that the secondary consolidation coefficient appeared to have constant value. Therefore the secondary consolidation coefficient was judged to be used as a significant factor in estimating the long4erm settlement. 6. In case of the single load consolidation test the secondary consolidation coefficient showed the tendancy increasing according to the increase of the consolidation pressure.

• 터널과지하공간
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• 제13권2호
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• pp.100-107
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• 2003

본 암석에 외력을 가하면 내부 응력이 발생하고, 이로 인해 변형이 발생하게 된다. 암석재료에서 크리프 변형이 장기간 지속되어 어느 한계에 도달하면 급작스런 파괴로 이어진다. 따라서 구조물의 장기적 안정성 검토 시에 지반의 크리프 특성 파악이 필수적이라 할 수 있다. 본 논문에서는 일축압축강도의 40% 50%, 60%, 70%에 해당하는 하중을 가하여 변형률을 측정하였다. 크리프 특성을 비교 . 분석한 결과로써 변형률 속도의 경우 하중 이 증가함에 따라 변형률 속도 상수$\alpha$ , ${\gamma}$ 도 증가하는 경향이 나타났다. 크리프 곡선에서 Griggs가 제안한 식이 Li와Xia, Singh식 보다 적합하였으며, Burger's model을 적용하여 구한상수 G$_2$는 응력수준의 증가에 파라 감소하며, η$_1$,η$_2$, G$_1$의 경우 불규칙하게 나타났다.

• 한국지반공학회지:지반
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• 제2권2호
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• pp.17-28
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• 1986

전북도내 3개시역에서 채취한 유기물함량 15%인 저유기질토(LL:95%)와 유기물함량 68%인 고유기질토(LL:400%)의 압밀특성을 조사분석하기 위해서 표준압밀시험과 단일하중압밀시험을 실시하였다. 공소비는 저유기질토 보다 고유기질토가 현저하게 큰 경향을 보였으며 e-log P 곡선에서 저유기질토는 하중이 증가함에 따라서 공소비 감소경향이 완만하였으나 고유기질토에서는 현저하게 감소하였다. 압밀량과 장기압밀시간과의 관계에서 고유기질토의 경우 약 5분경 부터 시간대수에 따라 직선적으로 증가하였고 저유기질토는 일반정성토와 같은 경향을 보였다. 고유기질토의 2차압밀표수는 상기추밀시간에 따라 일정한 경향을 나타내고 있으므로 장기롱밀량추정에 중요한 인자로 이용될 수 있다.

• 한국안전학회지
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• 제27권5호
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• pp.117-125
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• 2012

In recent years, polymer concrete based on polyester resin have been widely generalized and the research of polymer concrete have been actively pursued by the technical innovations. Polymer concrete is a composite consisting of aggregates and an organic resin binder that hardens by polymerization. Polymer concrete are stronger by a factor of three or more in compression, a factor of four to six in tension and flexural and a factor of two in impact when compared with portland cement concrete. In view of the growing use of polymer concrete, it is important to study the physical characteristics of the material, emphasizing the short term properties as well as long term mechanical behavior. If polymer concrete is to be used in flexural load-bearing application such as in beam, it is imperative to understand the deformation of the material under sustained loading conditions. This study is proposed to empirical and mechanical model of polymer concrete tension creep using long-term experimental results and mathematical development. The test results showed that proposed model has been used successfully to predict creep deformations at a stress level that was 20 percent of the ultimate strength and viscoelastic behavior of recycled-PET polymer concrete is linear of stress level up to 30 percent. It is expected that the present model allows more realistic evaluation of varying stresses in polymer concrete structures with a constant loading.

• 지질공학
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• 제20권1호
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• pp.89-100
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• 2010

암석의 손상상태를 평가하기위한 여러 방법들이 제안되어 있으나, 일부의 방법은 명확한 손상기준을 제시하기도 하지만 일부의 방법은 매우 모호하여 분석자의 주관에 따라 값이 달라지기도 한다. 그러므로 이 연구에서는 황등화강암을 대상으로 현재까지 제안된 모든 손상기준 결정방법을 적용하여, 각 방법의 적용성, 오차 및 최적의 손상기준결정 방법 등을 연구하였다. 또한 암석의 균열발달 및 파괴특성의 규명에 가장 중요한 손상기준인 균열개시응력과 균열손상응력을 FSR 및 장기 정하중 시험을 이용하여 검정하였다. 황등화강암의 균열닫힘응력과 균열개시응력은 각각 57.5 MPa, 77.6 MPa이며 균열체적변형률에서 측정하는 것이 가장 정확한 것으로 판단된다. 2차 균열개시응력은 90.6 MPa로 측정되었으며, 미소파괴음 계수 및 계수율이 균열개시응력의 측정에 가장 효과적인 것으로 판단된다. 균열결합응력 측정은 체적강성곡선, 미소파괴음 계수 및 미소파괴음 계수율이 가장 효과적인 방법으로 판단되며, 균열결합응력은 110.3 MPa이다. 균열손상응력은 체적강성곡선 및 미소파괴음 계수율에서 가장 명확히 측정되며, 약 127.5 MPa이다. 일축압축강도에 대한 비로서 나타낸 균열개시응력은 0.47로 FSR 값 0.46과 매우 유사하며, 균열손상응력은 0.77로 장기 정하중 시험을 통하여 측정된 장기 강도비 0.75~0.8과 거의 일치하여 균열개시응력 및 균열손상응력 값이 정확함을 검정하였다.

• 대한치과보철학회지
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• 제43권6호
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• pp.717-726
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• 2005

Statement of problem. One of the common problems of provisional crown and fixed partial denture materials is that when they are subjected to constant loads for a long period of time, they exhibit a dimensional change (creep). Purpose. The aim of this study was to investigate the viscoelastic behaviour of polymer-based provisional crown and fixed partial denture materials with time at constant compressive load. Material and methods. Three dimethacrylate-based materials (Protemp 3 Garant, Temphase, Luxatemp) and one monomethacrylate-based material (Trim) were selected. Dimensional changes of the specimens were recorded by a LVDT to evaluate their viscoelastic behavior and creep strain. For all specimens, two loading procedures were used. At first, static compressive stress of 4 MPa was applied for 30 minutes and followed by 1 hour of strain recovery. Then, after 24 hours of water storage, the specimens were loaded again. The creep values between materials were statistically analyzed using one-way ANOVA and multiple comparison $Scheff\acute{e}$ test. Independent samples t-test was also used to identify the difference of creep strain between first and secondary loading conditions at the significance level of 0.05. Results. Following application of the first loading, Trim showed the highest maximum creep strain (32.7%) followed by Luxatemp, Protemp 3 Garant and Temphase, with values of 3.78%, 2.86% and 1.77%, respectively. Trim was significantly different from other materials (P<0.05), while there were no significant differences among Luxatemp, Protemp 3 Garant and Temphase (P>0.05). The highest recovery and permanent set of Trim, were significantly different from those of others (P<0.05). At the secondary loading of the dimethacrylate-based materials, creep deformation, recovery and permanent set decreased and the percentage of recovery increased, while in Trim, all values of the measurements increased. This result showed that the secondary loading at 24 hours produced a significant creep magnitude. Conclusion. The dimethacrylate-based provisional crown and fixed partial denture materials showed significantly higher creep resistance and lower deformation than the monomethacrylate-based material. Thus, monomethacrylate-based materials should not be used in long-term stress-bearing situations.

• 폴리머
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• 제36권1호
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• pp.88-92
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• 2012

일정 하중에 지속적으로 노출되는 고분자의 장기간 사용을 위해서는 재료의 수명을 평가할 수 있는 가속화된 시험 방법이 필요하다. 반복 피로하중 시험법은 이러한 방법들 중 하나로 많은 관심을 받고 있다. 본 연구에서는 X-선 회절법을 이용하여 고밀도 폴리에틸렌의 반복 피로하중에 의한 구조적 변화와 크리프 변형을 비교하고자 하였다. 이를 위하여 별도의 인장시험기를 제조, X-선 회절기에 부착하여 장시간 변형 과정을 성공적으로 관찰하였다. 그 결과 크리프와 반복 피로하중 사이의 거시적이고 뚜렷한 차이에도 불구하고 결정화도, 결정크기 및 면간거리와 같은 결정의 미세구조는 두 방법에서 거의 동일하게 관찰되었다. 그러나 항복점 전(BYP), 항복점(YP) 그리고 항복점 후(AYP)로 각각 변형시킨 후 시험한 시료의 경우 AYP와 다른 두 시료간 뚜렷한 구조적 차이를 확인할 수 있었다.

• Journal of the Korean Wood Science and Technology
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• 제34권5호
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• pp.11-18
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• 2006

This study was carried out to evaluate the mechano-sorptive deflection of shear creep of drift pin jointed solid wood. Specimens were the solid wood of Pinus densiflora. The joint was composed with steel plate and drift pin, 85mm in length and 10mm in diameter. The creep tests were conducted under the constant loads in an variable environment. Five different shearing loads were applied parallel to the grain of specimens. The shearing loads applied were 170, 340, 510, 680 and 850 kgf. The stress levels were 10, 20, and 30, 40 and 50% of the bearing strength obtained from the tension-type lateral strength test. The creep tests for specimens were carried out for 10300 hours. A few general conclusions could be drawn from this study: The mechano-sorptive deflection (${\delta}$ ms) is defined as ${\delta}\;ms={\delta}\;t-({\delta}\;c+{\delta}\;sh)-{\delta}\;o$, where ${\delta}$ t is the total deflection, ${\delta}$ c is the pure creep, ${\delta}$ sh is shrinkage-swelling behavior, and ${\delta}$ o is the initial deflection. Changes of relative humidity may cause more severe creep deflection than those of constant humidity, especially during the drying process. The mechano-sorptive behaviors of specimens, except the effects of shrinkage and swelling, gradually increased with increasing time. The deflection is increased in desorption process and recovered in adsorption process. The deflections of drift pin jointed solid wood under different loads showed almost same tendency in all specimens. Although the creep deflection tendencies of each series are very similar, the specimens subjected to a large shearing load exhibit large creep deflections in the desorption process than do those to the small shearing load specimens.

• 한국해양공학회지
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• 제26권6호
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• pp.19-26
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• 2012

Recently the world has been suffering from difficulties related to the demand and supply of energy due to the democratic movements sweeping across the Middle East. Consequently, many have turned their attention to never-developed extreme regions such as the polar lands or deep sea, which contain many underground resources. This research investigated the strength and initial elastic modulus values of eternally frozen ground through a uniaxial compression test and indirect tensile test using frozen artificial soil specimens. To ensure accurate test results, a sandymud mixture of standard Jumunjin sand and kaolinite (20% in weight) was used for the specimens in these laboratory tests. Specimen were prepared by varying the water content ratio (7%, 15%, and 20%). Then, the variation in the strength value, depending on the water content, was observed. This research also established three kinds of environments under freezing temperatures of $-5^{\circ}C$, $-10^{\circ}C$, and $-15^{\circ}C$. Then, the variation in the strength value was observed, depending on the freezing environment. In addition, the tests divided the loading rate into 6 phases and observed the variation in the stress-strain ratio, depending on the loading rate. The test data showed that a lower freezing temperature resulted in a larger strength value. An increase in the ice content in the specimen with the increase in the water content ratio influenced the strength value of the specimen. A faster load rate had a greater influence on the uniaxial compression and indirect tensile strengths of a frozen specimen and produced a different strength engineering property through the initial tangential modulus of elasticity. Finally, the long-term strength under a constant water content ratio and freezing temperature was checked by producing stress-strain ratio curves depending on the loading rate.

• 한국산학기술학회논문지
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• 제21권10호
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• pp.283-290
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• 2020

본 연구에서는 수상 태양광 발전설비를 위한 부유체 개발에 대하여 연구하였다. 부유체는 단위 모듈로 이루어진 금속재질의 프레임과 상부의 태양광 패널들을 수상에서 부력을 이용하여 지지하는 부품이다. 단위 모듈화된 프레임의 구조와 태양광 패널의 설치 환경을 고려하여 부유체에 작용하는 하중을 산출하였다. 부유체의 형상은 수압과 부력을 고려하여 바깥쪽으로 둥근 형태를 가지도록 하였으며, 유한요소해석을 수행하여 부유체의 세부 형상과 두께를 설계하였다. 설계된 부유체는 선형저밀도폴리에틸렌 플라스틱을 사용하여 회전성형법으로 제작하였다. 부유체의 압축강성을 측정한 결과, 제작된 부유체는 최대하중 322.7 kgf의 4배 이상에서도 붕괴를 일으키지 않고 강성을 유지하는 것으로 나타났다. 부유체의 장기 압축 시험을 수행하기 위하여 중력을 이용한 무게추 방식의 장기 하중 인가 장치를 제작하였다. 부유체에 무게추를 올린 후 7일 간 부유체의 압축량을 측정한 결과, 작은 하중에서도 지속적인 압축 변형이 발생하였다. 그러나 상시 하중 100 kgf 에 대하여 10년 압축량을 예측한 결과 약 4.64 mm 의 작은 변형이 예측되었다. 이와 같이 개발된 부유체는 수상 태양광 발전시스템에 사용이 가능한 것으로 나타났다.