• 분석과학
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• 제37권3호
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• pp.143-154
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• 2024

건강기능식품공전은 기능성 원료의 지표(기능)성분에 대해 시험법을 고시하고 있다. 본 연구에서는 공전에서 제공하는 비타민C 시험법을 개선하고 정량을 위한 크로마토그래프법 조건의 조정 가능 범위에 대한 데이터를 검토하였다. 우선적으로 이동상 조건인 용매 조성, 염 농도, pH, 컬럼 온도를 조정해 보았으며, 특히 pH의 조절에 따라 완충용액으로부터 유래한 피크가 목적 성분인 비타민C와 명확히 분리될 수 있음을 개선된 시험법으로 확인하였다. 고정상 규격인 컬럼 내경, 컬럼 길이 및 고정상 입자 크기의 조정에 따라 성분의 머무름시간이 일부 조정되었으나, 이론단수는 유사한 수치를 나타냄으로써 목적 성분의 분리 및 정량적 분석에 영향을 주지 않았다. 변경된 컬럼 규격에 따른 유량 변경식은 USP <621> Chromatography 및 국내 식품의약품안전처의 [의약품 등 시험방법 밸리데이션 가이드라인 해설서]에서 제시하는 공식을 근거로 컬럼 규격(내경, 길이, 입자 크기)을 고려한 새로운 공식을 도출하였으며, 비타민 복합제에 대한 적용성 평가 결과, 변경된 고정상 및 유량에도 비타민C에 대한 높은 선택성을 보였다. 결론적으로, 크로마토그래프법 조건 일부의 변경을 통해서 비타민C를 최적으로 분리 및 검출할 수 있음을 확인하였으며, 등용매 용리를 활용하는 시험법에서 액체크로마토그래피의 이동상 및 고정상 조건을 조정 가능함을 확인하였다.

• Structural Engineering and Mechanics
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• 제66권5호
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• pp.569-582
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• 2018

Effects of crack separation, bridge area, on the tensile behaviour of concrete are studied experimentally and numerically through the Brazilian tensile test. The physical data obtained from the Brazilian tests are used to calibrate the two-dimensional particle flow code based on discrete element method (DEM). Then some specially designed Brazilian disc specimens containing two parallel cracks are used to perform the physical tests in the laboratory and numerically simulated to make the suitable numerical models to be tested. The experimental and numerical results of the Brazilian disc specimens are compared to conclude the validity and applicability of these models used in this research. Validation of the simulated models can be easily checked with the results of Brazilian tests performed on non-persistent cracked physical models. The Brazilian discs used in this work have a diameter of 54 mm and contain two parallel centred cracks ($90^{\circ}$ to the horizontal) loaded indirectly under the compressive line loading. The lengths of cracks are considered as; 10 mm, 20 mm, 30 mm and 40 mm, respectively. The visually observed failure process gained through numerical Brazilian tests are found to be very similar to those obtained through the experimental tests. The fracture patterns demonstrated by DEM simulations are mostly affected by the crack separation but the tensile strength of bridge area is related to the fracture pattern and failure mechanism of the testing samples. It has also been shown that when the crack lengths are less than 30 mm, the tensile cracks may initiate from the cracks tips and propagate parallel to loading direction till coalesce with the other cracks tips while when the cracks lengths are more than 30 mm, these tensile cracks may propagate through the intact concrete itself rather than that of the bridge area.

• Structural Engineering and Mechanics
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• 제67권5호
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• pp.493-504
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• 2018

In this paper, the tensile failure behaviour of transversally bedding layers was numerically simulated by using particle flow code in two dimensions. Firstly, numerical model was calibrated by uniaxial, Brazilian and triaxial experimental results to ensure the conformity of the simulated numerical model's response. Secondly, 21 circular models with diameter of 54 mm were built. Each model contains two transversely bedding layers. The first bedding layer has low mechanical properties, less than mechanical properties of intact material, and second bedding layer has high mechanical properties, more than mechanical properties of intact material. The angle of first bedding layer, with weak mechanical properties, related to loading direction was $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, $75^{\circ}$ and $90^{\circ}$ while the angle of second layer, with high mechanical properties, related to loading direction was $90^{\circ}$, $105^{\circ}$, $120^{\circ}$, $135^{\circ}$, $150^{\circ}$, $160^{\circ}$ and $180^{\circ}$. Is to be note that the angle between bedding layer was $90^{\circ}$ in all bedding configurations. Also, three different pairs of the thickness was chosen in models; i.e., 5 mm/10 mm, 10 mm/10 mm and 20 mm/10 mm. The result shows that In all configurations, shear cracks develop between the weaker bedding layers. Shear cracks angel related to normal load change from $0^{\circ}$ to $90^{\circ}$ with increment of $15^{\circ}$. Numbers of shear cracks are constant by increasing the bedding thickness. It's to be note that in some configuration, tensile cracks develop through the intact area of material model. There is not any failure in direction of bedding plane interface with higher strength.

• 한국터널지하공간학회 논문집
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• 제18권2호
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• pp.129-142
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• 2016

지표침하를 발생시키는 다양한 원인 중에 하나로 알려진 지하에서 발생되는 공동은 지반의 불연속적 특징이다. 그러므로 기존의 연속체해석으로 분석하기에는 한계가 있을 것으로 판단된다. 본 연구에서는 지표침하를 발생시키는 구형지하공동에 대해서 개별요소법을 활용하여 분석하였다. 지표침하에 영향을 미치는 구형지하공동의 특성인자로서 지반의 물성치, 구형지하공동의 심도 및 크기를 선택하였고, 각 특성인자들의 값의 변화가 지표침하에 미치는 영향에 대해 분석하였다. 또한 지하공동의 직경에 대한 상대적 깊이와 지표침하의 관계를 분석하였고, 이를 통해 지하공동의 붕괴 예측 및 보강유무를 결정하기 위한 근간을 제시하였다.

• 한국지반환경공학회 논문집
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• 제13권10호
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• pp.55-62
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• 2012

본 연구에서는 개별요소해석 프로그램인 $PFC^{3D}$를 이용하여 대입경 조립재료의 특정 입도분포를 구현하는 알고리즘을 개발하였다. 기존의 입자 형상이나 입도를 구현하기 위해 사용되었던 clump logic 또는 cluster logic을 사용하지 않으며 요소의 경계면 이탈 현상과 경계면 파괴 등을 방지할 수 있는 초기 개별요소 모델링 기법을 고안하였다. 최종적으로 대입경 조립재료에 대한 대형 삼축압축시험을 수치 모델링하고 실내시험 결과와 비교하였다. 해석 결과, 실제 시료의 입도분포와 매우 흡사한 분포의 개별요소를 생성할 수 있었고, 적정 미시물성치 산정 과정(calibration)을 통해 다양한 구속응력 조건에 대한 대입경 조립재료의 특정 입도분포하에서의 전체적인 수치 모델링이 가능하였다.

• Geomechanics and Engineering
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• 제22권5호
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• pp.385-396
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• 2020

A uniaxial compression test was performed to analyse the mechanical properties and macroscale and mesoscale failure mechanisms of sandstone with pyrite concretions. The effect of the pyrite concretions on the evolution of macroscale cracks in the sandstone was further investigated through numerical simulations with Particle Flow Code in 2D (PFC2D). The results revealed that pyrite concretions substantially influence the mechanical properties and macroscale and mesoscale failure characteristics of sandstone. During the initial loading stage, significant stress concentrations occurred around the edges of the pyrite concretion accompanied by the preferential generation of cracks. Meanwhile, the events and cumulative energy counts of the acoustic emission (AE) signal increased rapidly because of friction sliding between the concretion and sandstone matrix. As the axial stress increased, the degree of the stress concentration remained relatively unchanged around the edges of the concretions. The cracks continued growing rapidly around the edges of the concretions and gradually expanded toward the centre of the sample. During this stage, the AE events and cumulative energy counts increased quite slowly. As the axial stress approached the peak strength of the sandstone, the cracks that developed around the edges of the concretion started to merge with cracks that propagated at the top-left and bottom-right corners of the sample. This crack evolution ultimately resulted in the shear failure of the sandstone sample around the edges of the pyrite concretions.

• Structural Engineering and Mechanics
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• 제60권6호
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• pp.939-952
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• 2016

A compression to tensile load transforming (CTT) device was developed to determine indirect tensile strength of concrete material. Before CTT test, Particle flow code was used for the determination of the standard dimension of physical samples. Four numerical models with different dimensions were made and were subjected to tensile loading. The geometry of the model with ideal failure pattern was selected for physical sample preparation. A concrete slab with dimensions of $15{\times}19{\times}6cm$ and a hole at its center was prepared and subjected to tensile loading using this special loading device. The ratio of hole diameter to sample width was 0.5. The samples were made from a mixture of water, fine sand and cement with a ratio of 1-0.5-1, respectively. A 30-ton hydraulic jack with a load cell applied compressive loading to CTT with the compressive pressure rate of 0.02 MPa per second. The compressive loading was converted to tensile stress on the sample because of the overall test design. A numerical modeling was also done to analyze the effect of the hole diameter on stress concentrations of the hole side along its horizontal axis to provide a suitable criterion for determining the real tensile strength of concrete. Concurrent with indirect tensile test, the Brazilian test was performed to compare the results from two methods and also to perform numerical calibration. The numerical modeling shows that the models have tensile failure in the sides of the hole along the horizontal axis before any failure under shear loading. Also the stress concentration at the edge of the hole was 1.4 times more than the applied stress registered by the machine. Experimental Results showed that, the indirect tensile strength was clearly lower than the Brazilian test strength.

• Geomechanics and Engineering
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• 제24권2호
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• pp.179-191
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• 2021

In this study, the strength and failure mechanism of red sandstones with combined defects were investigated by uniaxial compression tests on red sandstones with different crack angles using two-dimensional particle flow code numerical software, and their mechanical parameters and failure process were studied and analyzed. The results showed that the mechanical characteristics such as peak strength, peak strain, and elastic modulus of the samples with prefabricated combined defects were significantly inferior than those of the intact samples. With increasing crack angle from 15° to 60°, the weakening area of cracks increased, elastic modulus, peak strength, and peak strain gradually reduced, the total number of cracks increased, and more strain energy was released. In addition, the samples underwent initial brittle failure to plastic failure stage, and the failure form was more significant, leading to peeling phenomenon. However, with increasing crack angle from 75° to 90°, the crack-hole combination shared the stress concentration at the tip of the crack-crack combination, resulted in a gradual increase in elastic modulus, peak strain and peak strength, but a decrease in the number of total cracks, the release of strain energy reduced, the plastic failure state weakened, and the spalling phenomenon slowed down. On this basis, the samples with 30° and 45° crack-crack combination were selected for further experimental investigation. Through comparative analysis between the experimental and simulation results, the failure strength and final failure mode with cracks propagation of samples were found to be relatively similar.

• Geomechanics and Engineering
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• 제30권1호
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• pp.93-105
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• 2022

With the exploitation of natural resources in China, underground resource extraction and underground space development, as well as other engineering activities are increasing, resulting in the creation of many defective rocks. In this paper, uniaxial compression tests were performed on rocks with double holes and fractures at different angles using particle flow code (PFC2D) numerical simulations and laboratory experiments. The failure behavior and mechanical properties of rock samples with holes and fractures at different angles were analyzed. The failure modes of rock with defects at different angles were identified. The fracture propagation and stress evolution characteristics of rock with fractures at different angles were determined. The results reveal that compared to intact rocks, the peak stress, elastic modulus, peak strain, initiation stress, and damage stress of fractured rocks with different fracture angles around holes are lower. As the fracture angle increases, the gap in mechanical properties between the defective rock and the intact rock gradually decreased. In the force chain diagram, the compressive stress concentration range of the combined defect of cracks and holes starts to decrease, and the model is gradually destroyed as the tensile stress range gradually increases. When the peak stress is reached, the acoustic emission energy is highest and the rock undergoes brittle damage. Through a comparative study using laboratory tests, the results of laboratory real rocks and numerical simulation experiments were verified and the macroscopic failure characteristics of the real and simulated rocks were determined to be similar. This study can help us correctly understand the mechanical properties of rocks with defects and provide theoretical guidance for practical rock engineering.

• Structural Engineering and Mechanics
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• 제85권3호
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• pp.337-351
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• 2023

In this paper, the shear behavior of soft filling in rectangular-hollow concrete specimens was simulated using the 2D particle flow code (PFC2D). The laboratory-measured properties were used to calibrate some PFC2D micro-properties for modeling the behavior of geo-materials. The dimensions of prepared and modeled samples were 100 mm×100 mm. Some disc type narrow bands were removed from the central part of the model and different lengths of bridge areas (i.e., the distance between internal tips of two joints) with lengths of 30 mm, 50 mm, and 70 mm were produced. Then, the middle of the rectangular hollow was filled with cement material. Three filling sizes with dimensions of 5 mm×5 mm, 10 mm×5 mm, and 15 mm×5 mm were provided for different modeled samples. The parallel bond model was used to calibrate and re-produce these modeled specimens. Therefore, totally, 9 different types of samples were designed for the shear tests in PFC2D. The shear load was gradually applied to the model under a constant loading condition of 3 MPa (σc/3). The loading was continued till shear failure occur in the modeled concrete specimens. It has been shown that both tensile and shear cracks may occur in the fillings. The shear cracks mainly initiated from the crack (joint) tips and coalesced with another one. The shear displacements and shear strengths were both increased as the filling dimensions increased (for the case of a bridge area with a particular fixed length).