• Geotechnical Engineering
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• v.9 no.4
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• pp.65-82
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• 1993

A series of torsion shear tests were performed to study the drained stress -strain behavior of medium dense Santa Monica Beach sand under various stress paths. The torque was applied to both clockwise and counterclockwise directions at the end of hollow cylinder specimen. Two clip gages had been previously used to measure the changes in wall thickness and diameter of the specimen. In this study, however, the lateral strain was determined by measuring volume changes in specimen. Specimens were prepared by the air pluviation method and gaseous carbon deozide( CO2) was used to measure precisely volumetric strain in specimen. The drained stress -strain behavior of cohesionless Boils during rotation of principal stress directions was analysed based on the results of torsion shear tests. The coupling of mal stress were applied. It was also found from the test results that the atrial strain at failure decreased with increasing value.

• The Journal of Engineering Geology
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• v.8 no.1
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• pp.75-86
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• 1998

Eighteen oriented samples from the Jeongsun limestone of the Joseon Supergroup are collected. The orientations of C-axis of calcite and e twin plane, the average thickness, numbers of twins and the widths of calcite grains in 10 samples are measured. Then, the twin strain, mean width, intensity of twin and relative magnitude and orientations of principal stresses are calculated using Calcite Strain Gauge program. Twin strain, mean width and intensitv rainge between 0.801%~10.927%, $0.43{\mu\textrm{m}}~2.03{\mu\textrm{m}}$, and 33.5~113.4twim/mm, respectively. Metamorphic temperatures calculated from twin show below $70^{\circ}C$, indicating that twins were developed within 2.3km depth. In five samples, two events with different orientations of principal stress produced calcite twins, while only one event produced calcite twins in five samples. The direction of the maximum stress is almost horizontal and the minimum is almost vertical, indicating that the stress regirne is identical with thrust fault. E-W and NW-SE are the most dominant directions of comressive stress and N-S and NE-SW directions are also shown. Comparision between paleostress orientations measured in the study and others indicates that the maximum horizontal stress oriented to E-W may represent the paleostress of period either from the Silurian to the Triassic or from the Silulian to the Permian. Paleostress oriented to NW-SE may be the major direction of stress during the Daeho orogeny.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.35-47
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• 2003

In the conventional axial load transfer analysis for composite piles (i.e., steel pipe pile filled with concrete), it was assumed that the concrete's strain is same as the measured steel's strain and the elastic modulus of the steel and the concrete calculated by formular as prescribed by specification is used in calculation of pile axial load. But, the pile axial load calculated by conventional method had some difference with the actual pile load. So, the behavior of a composite pile could not be analyzed exactly. Thus, the necessity to measure the strain for each pile components was proposed. In this study, the verification test for DRS (Deformable Rod Sensor) developed to measure the strain of each pile component (i.e., the steel and the concrete) was performed. In the calculation of pile axial load using the DRS, elastic modulus of concrete could be determined by the uniaxial compression test for the concrete cylinder samples made in the test site and an average tangential modulus in the stress range of (0.2∼0.6)f$_ck$ was taken.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.1
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• pp.17-23
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• 1990

When a thin walled member is subjected to compression in a condition such as collision, the energy is mainly absorbed by axial crumpling. In this case, dynamic crushing strength of the member is increased due to the effects of strain-rate compared with the static strength, even though the inertia effect is neglected. In this paper, the method of predicting the static crushing for tubular members is presented using the kinematic method of plasticity. Since, a predicted crushing load, taking account of the dynamic yield stress, usually overestimates the effects of strain-rate, the average plastic flow stress for the effects of strain-rate is used to obtain the dynamic crushing load for tubular members. The analytical results are compared with the experiments published in references, and a good correlation is observed.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.33-42
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• 2017

This study conducted uniaxial tension tests on D10, D19, D29, and D35 SD400 steel-grade rebar and evaluated the strain distributions and necking regions to provide basic data for resolving differences between evaluation methods. Owing to the limitations of the existing measurement methods, this study conducted detailed evaluations of the strain of the rebar and necking regions using image processing, which is almost limitless on the measurement range and can easily distinguish measurement regions. The strain was concentrated at the region where necking occurred when the rebar approached its ultimate strength, which was successfully confirmed through image processing. The correlation between the length of the necking region and the diameter of the rebar could be analyzed by evaluating the necking region that occurs during the ultimate behavior of the rebar. According to the results, the length of the necking region is around 1.5~2.5 times the diameter of the rebar.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.745-751
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• 2011

This study proposes finite element modeling of dislocation punching at cooling after consolidation in order to calculate the strength of particle-reinforced aluminum composites. The Taylor dislocation model combined with strain gradient plasticity around the reinforced particle is adopted to take into account the size-dependency of different volume fractions of the particle. The strain gradients were obtained from the equivalent plastic strain calculated during the cooling of the spherical unit cell, when the dislocation punching due to CTE (Coefficient of Thermal Expansion) mismatch is activated. The enhanced yield stress was observed by including the strain gradients, in an average sense, over the punched zone. The tensile strength of the SiCp/Al 356-T6 composite was predicted through the finite element analysis of an axisymmetric unit cell for various sizes and volume fractions of the particle. The predicted strengths were found to be in good agreement with the experimental data. Further, the particle-size dependency was clearly established.

• Geotechnical Engineering
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• v.14 no.4
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• pp.47-60
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• 1998

A series of conventional tests and CRS consolidation tests with different rates of strain were performed to investigate the consolidation characteristics of marine clay. Preconsolidation pressures were evaluated by applying previously proposed methods for both the conventional tests and CRS tests results in order to check the legitimacy of those methods. The effects of strain rate on effective consolidation stress strain relationship, porewater pressure, and preconsolidation pressure were also discussed It was found that the effective stress strain relationship and the preconsolidation pressure are a function of strain rate imposed during consolidation test, but compression index isn't. The preconsolidation pressure ratio ($a_2=\sigma'_{pCRS}/\sigma'_{pConv}$)of marine clay appears proportional to the logarithm of strain rate, with average values ranging from 1.11 to 1.30 for strain rates between $1\timesx10^{-4} %/sec\; and\; 4\times10 %/sec$. The porewater pressure ratio during CRS teats does not exceed 6.0% except when the strain rate is $6.67\times10^{-4} %/sec$. Coefficient of consolidation or coefficient of permeability at normally consolidated range was not affected by the type of consolidation tests and the strain rate. Typical values of compression index (C.), coefficient of consolidation(c.), and coefficient of permeability (k.) at normally consolidated range were 0.56-0.95, $0.56\times10^{-4}~3.0\times10^{-4}cm2/sec,\; and\; 2.0\times10^{-8}~7.0\time10^{-4}cm/sec,$ respectively.

• Journal of the Korean Society for Railway
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• v.16 no.5
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• pp.386-393
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• 2013

In this study, the so-called repeated plate load bearing test (RPBT) used to get $E_{v2}$ values in order to check the degree of compaction of subgrade, and to get design parameters for determining the thickness of the trackbed foundation, is investigated. The test procedure of the RPBT method is scrutinized in detail. $E_{v2}$ values obtained from the field were verified in order to check the reliability of the test data. The $E_{v2}$ values obtained from high-speed rail construction sites were compared to converted modulus values obtained from resonant column (RC) test results. For these tests, medium-size samples composed of the same soils from the field were used after analyzing stress and strain levels existing in the soil below the repeated loading plates. Finite element analyses, using the PLAXIS and ABAQUS programs, were performed in order to investigate the impact of the strain influence coefficient. This was done by getting newly computed $I_z$ to get the precise strain level predicted on the subgrade surface in the full track structure; under wheel loading. It was verified that it is necessary to use precise loading steps to construct nonlinear load-settlement curves from RPBT in order to get correct $E_{v2}$ values at the proper strain levels.

• Composites Research
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• v.33 no.3
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• pp.125-132
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• 2020

The polymerization shrinkage behavior of dimethacrylate-based composite (Clearfil AP-X, Kuraray) and silorane-based composite (Filtek P90, 3M ESPE) used for dental composite restorations was measured using digital image correlation method. The stress distribution on the surface of specimen was calculated by finite element analysis with equivalent elastic modulus and was compared with the measured shrinkage distribution. Camera images were monitored by a CCD camera during and after the irradiation of light. As a result of the DIC analysis, a non-uniform shrinkage distribution was observed in both composite resins, and the resin core inside the ring specimen had free flowability, leading to in greater shrinkage strain than the resin/ring interfacial region. It was observed that as the distance from the center of the resin increased, the radial average shrinkage strain decreased. The radial average shrinkage strain during light irradiation occurred to be 33% for P90 and 57% for AP-X of the entire strain at the end of the test. The shrinkage behavior of P90 and AP-X was measured to be significantly different from each other during light irradiation. In the resin near the resin/ring interface, it was confirmed that the tensile strain rapidly formed to increase after light irradiation, causing a tensile stressed, interface weak.

• Geotechnical Engineering
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• v.8 no.2
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• pp.71-80
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• 1992

A new constitutive model is proposed for normally consolidated clays. A main skeleton of the proposed model is based on the concepts of the incremental stress-strain theory by Roscoe and Poorooshasb. The equation of the undrained stress path is formulated by introducing the new pore pressure parameter(C), which is the slope of the linear line in the plot of the normalized pore pressure against the stress ratio. Once the stress increment along the constant stress ratio path (followed by untrained stress path) is know, the volumetric strains are calculated from the linear characteristics between void ratio and logarithm of the mean normal stress for any stress ratio. Then the incremental shear strains are successfully predicted by applying the flow rule derived in the modified theory by Roscoe and Burland.