• Smart Structures and Systems
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• 제34권1호
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• pp.33-40
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• 2024

We aimed to assess the evolution of small-strain stiffness and relative density in non-compacted embankment layers. We developed embedded type in-situ soil stiffness measurement devices for monitoring small-strain stiffness occurring after filling at a test site and conducted comprehensive laboratory compaction tests using an oedometer cell with a bender element. However, direct comparison is extremely difficult because the shear wave velocity measured in the field and laboratory depend on depth and effective stress, respectively. Therefore, we propose a method for establishing a relationship between effective stress and depth using a compressibility model. In this study, the shear wave velocity measured in the field was compared to the estimated shear wave velocity-depth profiles for completely dry and saturated conditions with different relative densities. The relative density under saturated soil conditions may vary between 50% and 90% and tends to be closer to 95%. Under dry soil conditions, the relative density of the embankment can vary from 30% to 70% and tends to approach 76%. For model validation, the relative density estimated from shear wave velocity-depth profiles was compared to that estimated from DCPI data. In other words, the results analyzed in the context of an effective stress-depth model enable the prediction of engineering properties such as the small-strain stiffness and relative density of embankment layers. This study demonstrates that physics-based data analyses successfully capture the relative density of non-compacted embankment layers.

• Bulletin of the Korean Chemical Society
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• 제5권2호
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• pp.73-78
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• 1984

Superplastic alloys generally exhibit a three-stage sigmoidal variation of stress (f) with strain rate (s), the stages being named region 1, 2 and 3 according to the increasing order of stress or strain rate. In the recent years, two different types of papers have been published on the plastic deformation of Zn-22% Al eutectoid in region Ⅰ differing in strain-rate sensitivity m (= dln f/dln s). In this paper, the data of the two groups have been analysed by applying Kim and Ree's theory of superplastic deformation. (1) We obtained the parametric values of $X_{gj}/{\alpha}_{gj}\;and\;{\beta)_{gj}$ (g: grain boundary, j = 1,2 indicating flow units) appearing in Kim and Ree's theory [Eq. (2a)]. (2) It was found that the value of $X_{g^2}/{\alpha}_{g^2}$ is small for the group data with small m, i.e., ${\alpha}_{g^2}$, which is proportional to the size of flow unit g2, is large whereas ${\alpha}_{g^2}$ is small for the groups data with large m, i.e., the size of the flow unit g2 is small. In other words, the two types of behavior occur by the size difference in the flow units. (3) From the ${\beta}_{gj}$ value, which is proportional to the relaxation time of flow unit gj, the ${\Delta}H_{gj}^{\neq}$ for the flow process was calculated, and found that ${\Delta}H_{g^2}^{\neq}$ is large for the group data with small m whereas it is small for the group data with large m. (4) The flow-unit growth was studied, but it was concluded that this effect is not so important for differentiating the two groups. (5) The difference in ${\alpha}_{g^2}$ and in the growth rate of flow units is caused by minute impurities, crystal faults, etc., introduced in the sample preparation.

• 항공우주시스템공학회지
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• 제18권2호
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• pp.12-20
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• 2024

초소형 위성체의 태생적 공간 제약으로 탑재 전장품은 발사진동환경 하 구조건전성 확보를 위한 보강설계 적용에 한계가 존재하며, 피로파괴에 취약한 고집적 소자의 실장으로 고신뢰도의 평가기법이 요구된다. 종래 전장품 구조건전성 평가를 위해 Steinberg 피로파괴 이론이 적용되고 있으나 최근 연구들에서 이론적 한계점들이 보고되고 있다. 본 논문에서는 상기 이론의 한계점을 극복한 임계변형률 이론기반 방법론을 적용하여 초소형 SAR 군집위성 S-STEP(Small SAR Technology Experimental Project)의 X대역 SAR 탑재체 구성품 중 DCU(Digital Control Unit)를 설계하였다. 설계 유효성 검증을 위해 단순화된 모델링 기법을 기반으로 모드 해석, 랜덤 해석을 수행하였다. 적용한 방법론을 기반으로 해석 결과분석 및 안전여유 도출과 발사진동환경시험 전후 기능시험을 통해 최종적으로 전장품의 구조건전성이 확보됨을 입증하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1430-1433
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• 2003

Transducers, which are incorporated in control devices for fixed wing aircraft, land vehicles. and weapon systems were designed and manufactured by use of semiconductor strain gages. These transducers consist of three parts; flange mounts, sensing rods, and semiconductor strain gages. In this investigation, we designed cylindrical sensing rods with high sensitivity and developed installation procedures of semiconductor strain gages. The semiconductor strain gage has hish gage factor such that it can produce high resistance change in spite of low strain, but it is so small and fragile that one should handle carefully and sophisticated installation method is needed for good performances. The prototype transducers are manufactured, and then tested about three important factors: sensitivity, linearity, and hysteresis. We got results or 0.084 V/N sensitivity, 0.2% nonlinearity, and 0.5% hysteresis.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.299-308
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• 2003

In order to investigate the dynamic deformation properties of rockfill materials in small strain level, cyclic triaxial tests were conducted using the large cyclic triaxial testing apparatus, which was developed by Water Resources Research Institute of KOWACO in 2001. Two types of rockfill materials consisting of granite and shale-sandstone were tested in this study. The test results show that G/G$\_$max/ of granite specimen decreases more than that of shale-sandstone with the increase of shear strain and the increase ratio in the maximum shear modulus G$\_$max/ of granite is bigger than the ratio of shale-sandstone.

• 자원환경지질
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• 제24권1호
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• pp.27-41
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• 1991

Taebaeg-Hajang area, in the northern part of Taebaeg city, comprises of Paleozoic sedimentary sequences and Cretaceous intrusive and volcanoclastic rocks. The rocks in the area are affected by folding and thrusting during the Bulgugsa Orogeny. In Taebaeg area, geologic structures related with thrust movement are dominant. These structures are small scale of klippe and window, back thrust, and asymmetric folds related with blind thrust. Tear fault or compartment fault due to differential movement of thrust sheets have "en echelon" arrays. Small scale transpression effects occurred along these faults and produced the flower structure. According to strain measurement using by ooids from limestone and quartz grains from quartzite, strain ratios are very low and strain ellipsoids are apparent oblate type.

• Geomechanics and Engineering
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• 제36권3호
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• pp.295-301
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• 2024

Understanding the post-liquefaction shear behavior is crucial for predicting and assessing the damage, such as lateral flow, caused by liquefaction. Most studies have focused on the behavior until liquefaction occurs. In this study, we performed undrained multi-stage tests on clean sand, sand-silt mixtures, and silty soils to investigate post-liquefaction shear strain based on soil compressibility. The results confirmed that it is necessary to consider the soil compressibility and the shape of soil particles to understand the post-liquefaction shear strain characteristics. Based on this, an index reflecting soil compressibility and particle shape was derived, and the results showed a high correlation with post-liquefaction small resistance characteristic regardless of soil type and fine particle content.

• 한국해양공학회지
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• 제10권1호
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• pp.53-64
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• 1996

In this paper, rotating bending fatigue tests have been carried out to investigate the growth behabiors of surface fatigue crack initiated from a small artificial surface defect, that might exist in real structures, on 2024-T3 and 6:4 brass. The test results are analysed in the viewpoints of both strength of materials and fracture mechanics, it can be concluded as follows. The effect of a small artificial surface defect upon the fatigue strength is very large. The sensitivity of 2024-T3 on the defect is higher than that of 6:4 brass. The growth behavior of the surface fatigue crack of 2024-T3 is different from that of 6:4 brass. The growth rate of the surface fatigue crack of 2024-T3 is considerably rapid in the early stage of the fatigue life and apt to decrease in the later stage. It was impossible to establish a unifying approach in the analysis of crack growth begabior of 2024-T3 and 6:4 brass using the maximum stress intensity factor because of their dependence on stress level. But if the elastic strain and cyclic total strain intensity factor range were applied to obtain the growth rate of surface fatigue cracks of the materials, the data were found to be nearly coincided.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.331-340
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• 2009

This study evaluates the relationship between cone tip resistance ($q_c$) and small-strain shear modulus ($G_{max}$) of cemented sand. For this purpose, a series of miniature cone penetration and bender element tests are performed in calibration chamber specimens with various gypsum contents. Experimental results show that both $q_c$ and $G_{max}$ of sand increase with increasing cementation level as well as relative density and vertical confining stress. However, the relative density and vertical confining stress has more significant influence on $G_{max}$ and $q_c$ of uncemented sand than those of cemented sand. It is observed that the $G_{max}/q_c$ ratio of cemented sand decreases with increasing relative density. This result means that state variables have more affect on $q_c$ than $G_{max}$ of cemented sand. Test results also show that the effect of vertical stress on $G_{max}-q_c$ relation is reduced by cementation effect.

• Geomechanics and Engineering
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• 제16권5호
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• pp.547-558
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• 2018

Studies of soil dynamic properties in Malaysia are still very limited. This study aims to investigate the dynamic properties of two selected tropical residual soils (i.e., Sandy Clay and Sandy Silt) and a sand mining trail (Silty Sand) in Peninsular Malaysia using 1g shaking table test. The use of 1g shaking table test for soil dynamic testing is often constrained to large strain level and small confining pressure only. Three new experimental setups, namely large laminar shear box test (LLSBT), small chamber test with positive air pressure (SCT), and small sample test with suction (SSTS) are attempted with the aims of these experimental setups are capable of evaluating the dynamic properties of soils covering a wider range of shear strain and confining pressure. The details of each experimental setup are described explicitly in this paper. Experimental results show that the combined use of the LLSBT and SCT is capable of rendering soil dynamic properties covering a strain range of 0.017%-1.48% under confining pressures of 5-100 kPa. The studied tropical residual soils in Malaysia behaved neither as pure sand nor clay, but show a relatively good agreement with the dynamic properties of residual soils in Singapore. Effects of confining pressure and plasticity index on the studied tropical residual soils are found to be insignificant in this particular study.