• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.485-492
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• 2001

Weathered soil is one of the most representative soils in Korea. In this study, a series of cyclic triaxial tests was carried out to predict the post-cyclic deformation behavior of weathered soils in case of non-liquefaction. Excess pore pressure response during cyclic loading and volumetric strain during the dissipation of excess pore pressure were measured varying the confining pressure, relative density and cyclic stress ratio. Based on the test results, it Is found that the modified excess pore pressure ratio, excess pore pressure ratio normalized by cyclic stress ratio, is uniquely correlated with the number of cycles irrespective of confining pressure and cyclic stress ratio. Using the newly proposed MEPPR(modified excess pore pressure ratio) concept, it is possible to easily evaluate the excess pore pressure and the settlement of weathered soils due to cyclic loading by greatly reduced number of tests. It is also verified that the reconsolidation volumetric strain is independent of the way how the excess pore pressure was generated.

• 한국연소학회지
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• 제19권2호
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• pp.8-14
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• 2014

Experiments were conducted to clarify role of the outermost edge flame on low-strain-rate flame extinction in buoyancy-suppressed non-premixed methane flames diluted with He and $N_2$. The use of He curtain flow produced a microgravity level of $10^{-2}-10^{-3}g$ in $N_2$- and He-diluted non-premixed counterflow flame experiments. The critical He and $N_2$ mole fractions at extinction with a global strain rate were examined at various burner diameters (10, 20, and 25 mm). The results showed that the extinction curves differed appreciably with burner diameter. Before the turning point along the extinction curve, low-strain-rate flames were extinguished via shrinkage of the outermost edge flame with and without self-excitation. High-strain-rate flames were extinguished via a flame hole while the outermost edge flame was stationary. These characteristics could be identified by the behavior of the outermost edge flame. The results also showed that the outermost edge flame was not influenced by radiative heat loss but by convective heat addition and conductive heat losses to the ambient He curtain flow. The numerical results were discussed in detail. The self-excitation before the extinction of a low-strain-rate flame was well described by a dependency of the Strouhal number on global strain rate and normalized nozzle exit velocity.

• 한국지반공학회지:지반
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• 제10권2호
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• pp.85-96
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• 1994

공진주 실험기는 전단탄성계수, 영계수 및 감쇠비로 표현되는 지반의 동적물성치를 연구하기 위한 중요한 실내 실험법으로 널리 사용되어 왔다. 본 연구에서는 Stokoe식 공진주 실험기를 이용하여 전단 변형률 10-4%-10-1% 범위에서 대표적인 국내 노상토의 동적 물성치를 연구하였다. 전단탄성계수와 감쇠비는 한계변형률 Ix10-3%부근에서 부터 변형률의 영향을 받기 시작 하였다. 한계 변형률 이하에서 최대 전단탄성계수(Gmin)는 구속압 (Qc)에 따라 (Qc)0.61에 비례하여 증가하였고 최소감쇠 비(Dmin)는 1%-5.7% 범위에 분포하였다. 한계 변형률 이상에서 정규화 탄성계수 감소곡선은 Ramberg-Osgood식으로 잘 나타낼 수 있으며 Seed와 Idriss가 사질토 를 이용하여 얻은 감소곡선과 거의 일치하였다.

• 대한기계학회논문집
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• 제11권5호
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• pp.740-745
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• 1987

본 연구에서는 파괴조건(4)와 유사하게 임계 스트레인 조건을 사용하나 기존 스트레인이 없는 재료의 날카로운 균열선단을 가진 시편의 파괴인성실험치(.delta.$_{IC}$)로 부터 재료의 고유상수인 특성길이를 결정하는 방법이 제안되었다.이 파괴조건을 이 용하여 처음노치선단의 유한한 반경과 재료의 기존 스트레인이 시편의 파괴개시에 미 치는 영향을 예측하고자 한다.

• 대한기계학회논문집A
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• 제27권2호
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• pp.239-246
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• 2003

This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

• 한국농공학회지
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• 제36권3호
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• pp.90-99
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• 1994

To investigate the undrained shear strength characteristics of marine soils with high water content, high compressibility and weak bearing capacity, a series of undrained triaxial tests with pore pressure measurements on undisturbed and disturbed Banwol marine clay in normally consolidated and overconsolidated states is carried out. The results and main conclusions of this study are summarized as follows : 1 . When the consolidation pressure is increased, the maximum deviator stress of disturbed and undistubed clay in normally consolidated state is increased. Pore pressure parameters and internal friction angle of undisturbed clay are greater than those of disturbed clay. 2. The relationship between pore pressure and axial strain of undisturbed clay in normally consolidated state can be expressed as a hyperbolic function like stress-strain relation proposed by Kondner. 3. In the pore pressure-axial strain relation of disturbed clay in normally consolidated state, failure ratio R'f is greatly deviated in the range of 0.7~0.9 proposed by Christian and Desai. 4. For overconsolided clay, when overconsolidation ratio (OCR) is increased, normalized maximum deviator stress is increased and maximum pore pressure is decreased gradually. 5. Cohesion of overconsolidated clay is greater than that of nomally consolidated clay and internal friction angle slightly is decreased. 6. Pore pressure parameter at failure (Af) of overconsolidated clay is varied with OCR, Af becomes negative values with increment in OCR

• 한국해양공학회지
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• 제31권4호
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• pp.288-298
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• 2017

A study of the damage evolution laws for ductile materials was carried out to predict the ductile fracture behavior of a marine structural steel (EH36). We conducted proportional and non-proportional stress tests in the experiments. The existing 3-D fracture strain surface was newly calibrated using two fracture parameters: the average stress triaxiality and average normalized load angle taken from the proportional tests. Linear and non-linear damage evolution models were taken into account in this study. A damage exponent of 3.0 for the non-linear damage model was determined based on a simple optimization technique, for which proportional and non-proportional stress tests were simultaneously used. We verified the validity of the three fracture models: the newly calibrated fracture strain model, linear damage evolution model, and non-linear damage evolution model for the tensile tests of the asymmetric notch specimens. Because the stress evolution pattern for the verification tests remained at mode I in terms of the linear elastic fracture mechanics, the three models did not show significant differences in their fracture initiation predictions.

• 한국광물학회지
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• 제31권4호
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• pp.277-285
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• 2018

상온에서 남동석($Cu_3(CO_3)_2(OH)_2$)에 대한 고압 거동 연구를 하였다. 대칭형 다이아몬드 앤빌기기를 이용하여 21.52 GPa까지 압력을 증가시키면서 각분산 X-선 회절법과 방사광을 이용하여 고압회절 데이터를 얻었으며, 시료에 가해준 압력은 루비 형광파의 파장 변화를 측정하여 결정하였다. 본 실험에서 시행한 압력의 범위 내에서 상변이는 관찰되지 않았으며, 정압상태에서 체적탄성률($K_0$)은 ${K_0}^{\prime}$이 4일 때, 54.4 GPa로 계산되었다. 상온상태에서 얻은 남동석의 체적탄성률에 대한 신뢰도를 정규화압력 및 정규화응력변형 분석을 통해 검증하였다.

• Smart Structures and Systems
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• 제30권6호
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• pp.673-686
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• 2022

Deep learning algorithms for Structural Health Monitoring (SHM) have been extracting the interest of researchers and engineers. These algorithms commonly used loss functions and evaluation indices like the mean square error (MSE) which were not originally designed for SHM problems. An updated loss function which was specifically constructed for deep-learning-based structural damage detection problems has been proposed in this study. By tuning the coefficients of the loss function, the weights for damage localization and quantification can be adapted to the real situation and the deep learning network can avoid unnecessary iterations on damage localization and focus on the damage severity identification. To prove efficiency of the proposed method, structural damage detection using convolutional neural networks (CNNs) was conducted on a truss bridge model. Results showed that the validation curve with the updated loss function converged faster than the traditional MSE. Data augmentation was conducted to improve the anti-noise ability of the proposed method. For reducing the training time, the normalized modal strain energy change (NMSEC) was extracted, and the principal component analysis (PCA) was adopted for dimension reduction. The results showed that the training time was reduced by 90% and the damage identification accuracy could also have a slight increase. Furthermore, the effect of different modes and elements on the training dataset was also analyzed. The proposed method could greatly improve the performance for structural damage detection on both the training time and detection accuracy.

• 한국지반공학회논문집
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• 제15권1호
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• pp.151-160
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• 1999

광양만의 해저에서 채취한 점성토시료의 물리적 성질과 역학적 특성을 규명하기 위한 일련의 실내시험을 수행하였다. 주요 시험내용은 제반 물리적 성질시험, 표준압밀시험, 비배수 및 배수 삼축시험(CIU, CID) 등이다. 통일분류에 의하면 CL, CH로 구분되는 광양만 점토는 자연함수비, 38.3~84.6%, 액성지수, 0.71~0.98 이고 과압밀비가 1.06~l.60인 실질적인 정규압밀상태라고 볼 수 있다. 비배수 삼축시험에서의 유효응력경로는 (q, p)공간에서 등방압밀응력($p_0$) 으로 규준화되고, 등 전단변형률선은 원점을 통과하며 선형적이다. 비배수 전단변형률($\varepsilon$)은 응력비($\eta$) 만의 함수이고, ($\varepsilon/\eta, \eta$) 공간에서 절편값을 갖는 직선으로 나타났다. 또한, 등방압밀응력으로 규준화된 간극수압도 응력비에 대하여 직선이고, 그 구배, C는 간극수압 매개변수로 정의될 수 있다. 이상에서 기술된 경향을 근거로 하여 비배수 응력경로 및 전단변형률을 예측할 수 있는 계산식을 제안하였고, 제안식에 의하여 계산된 응력경로와 전단변형률은 기존의 Cam-clay이론 보다 실측치에 더 가까운 값을 주는 것으로 나타났다. 배수시험 결과에서 얻어진 응력경로 상의 파괴점은 비배수 응력경로의 한계상태선과 동일 선상에 위치하며, 이 사실은 한계상태이론의 기본 개념과 일치한다.