• Geomechanics and Engineering
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• v.34 no.5
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• pp.481-489
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• 2023

Drained cyclic triaxial tests were conducted on a saturated sand to examine its deformation characteristics under either axial or lateral cyclic loading condition. To apply lateral cyclic loading, the cell pressure was cycled while maintaining a constant vertical stress. The strain accumulations and flow direction in the soil were presented and discussed considering various initial stress ratios (η₀), cyclic stress amplitudes and cyclic stress paths. The results indicate that axial strain accumulation shows an exponential increase with the maximum stress ratio (η^max). The initial deviatoric stress has comparable effects with lateral cyclic stress amplitude on the accumulated axial strain. In contrast, the accumulated volumetric strain is directly proportional to the lateral cyclic stress amplitude but not much affected by η₀ values. Due to the anisotropy of the soil, the accumulated axial and lateral bulging strains are greater in lateral cyclic loading when compared to axial cyclic loading even though η^max is the same. It is also found that η^max affects soil's lateral deformation and increasing the ratio could change the lateral deformation from contraction to bulging. The flow direction depends on η^max in the sand under lateral cyclic loading, regardless of η₀ values and the cyclic stress amplitudes, and a large η^max could lead to great deviatoric strain but a little volumetric strain accumulation.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.1
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• pp.75-83
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• 2017

This study investigated deformation behavior of major nuclear structural materials under cyclic loading conditions via cyclic stress-strain test. The cyclic stress-strain tests were conducted on SA312 TP316 stainless steel and SA508 Gr.3 Cl.1 low-alloy steel, which are used as materials for primary piping and reactor pressure vessel nozzle respectively, under cyclic load with constant strain amplitude and constant load amplitude at room temperature (RT) and $316^{\circ}C$. From the results of tests, the cyclic hardening and softening behavior, stabilized cyclic stress-strain behavior, and ratcheting behavior of both materials were investigated at both RT and $316^{\circ}C$. In addition, appropriate considerations for cyclic deformation behavior in the structural integrity evaluation of major nuclear components under excessive seismic condition were discussed.

• Geomechanics and Engineering
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• v.11 no.3
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• pp.325-343
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• 2016

A total stress-based bounding surface model is developed to predict the undrained behaviour of saturated soft clays under cyclic loads based on the anisotropic hardening modulus field and bounding-surface theories. A new hardening rule is developed based on a new interpolation function of the hardening modulus that has simple mathematic expression and fewer model parameters. The evolution of hardening modulus field is described in the deviatoric stress space. It is assumed that the stress reverse points are the mapping centre points and the mapping centre moves with the variation of loading and unloading paths to describe the cyclic stress-strain hysteresis curve. In addition, by introducing a model parameter that reflects the accumulation rate and level of shear strain to the interpolation function, the cyclic shakedown and failure behaviour of soil elements with different combinations of initial and cyclic stresses can be captured. The methods to determine the model parameters using cyclic triaxial compression tests are also studied. Finally, the cyclic triaxial extension and torsional shear tests are performed. By comparing the predictions with the test results, the model can be used to describe undrained cyclic stress-strain responses of elements with different stress states for the tested clays.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.15-23
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• 2015

An experimental study has been conducted to evaluate the effects of average and cyclic shear stresses on the undrained failure behaviors of dense marine silty sand by using the Cyclic Direct Simple Shear apparatus. The results show that when the average shear stress ratio is zero, symmetric cyclic shear deformation is the major component of deformation, and permanent shear deformation is relatively small. On the other hand, when the average shear stress ratio is larger than zero, asymmetric permanent shear deformation is the major component, and cyclic shear deformation does not change much as the number of cyclic loads increases. The average shear stress ratio has less effects on the number of cyclic loads needed to fail, as compared with the cyclic shear stress ratio. The proposed stress-dependent failure contour can effectively be used to assess the cyclic shear strength of soil beneath the foundation for the design of offshore structures.

• Geomechanics and Engineering
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• v.14 no.2
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• pp.203-209
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• 2018

Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.3
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• pp.177-182
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• 2005

The steady state cyclic mechanism, and the behaviour of Nicoseal(Fe-29Ni-17Co) have been examined under the condition of square wave stress cyclic tension creep test at the temperature, stress and frequency range of $430{\sim}470^{\circ}C$($0.41{\sim}0.43T_m$), 353~383 MPa, and 3 cpm, respectively. Also, the relationship between cyclic creep and static creep have been examined. The stress exponents(n) for the static creep deformation of this alloy were 11.6, 10.0, 8.4 and 7.9 at the temperature of 430, 445, 460 and $470^{\circ}C$, respectively. The apparent activation energies (Q) for the static creep deformation were 54.2, 51.8, 49.7 and 46.8 kcal/mole for the stress of 353, 363, 373 and 383 MPa, From the above results, it could be considered that the cyclic creep accelaration phenomena was obtained and that the cyclic deformation for Nicoseal seemed to be controlled by dislocation climb over the range of experimental conditions. Nicoseal alloy under the cyclic creep conditions was obtained as P=(T+460)(logt+17). The failure plane observed by SEM showed up transgranular fracture at all range.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1458-1465
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• 2010

A lot of dredging and reclaming projects are recently under way in Korea for the efficient use of limiting land space. Saemanguem area is special case of reclaiming by dredged soil. In case of a confined disposal of dredged soils by a pump dredger, generally coarse grained soils are separated from fines with dropping at the near part of the pump dredger. This kind of seperation of fine contents could be a factor of liquefaction by earthquake. In Korea, recently, earthquakes with magnitude of 3.0 or higher are distinctively increasing in 1990. In this study, cyclic shear characterics of Saemanguem Dredged sand depending on fine content were analyzed. A series of undrained cyclic triaxial test with cyclic stress ratio ($\sigma_d/{2\sigma_{{\upsilon}c}}'$) were performed on both isotropic consolidated specimen and sand with fine contents of 0%, 5%, 15%, 30%, 40% under the effective vertical stress of 100kPa and 50% and 60%, 70% of relative density for fine content of 0%, respectively. In the test results, cyclic shear strength increased by increasing of cyclic stress ratio($\sigma_d/{2\sigma_{{\upsilon}c}}'$) with increasing the relative density at the same number of cyclic under the effective confining pressure of 100kPa. It is almost highest the double amplitude(DA) 1%, 3%, 5%, 7.5% and 10% at fine content of 15% between Cyclic stress ratio($\sigma_d/{2\sigma_{{\upsilon}c}}'$) value at cyclic number five and fine content. Number of cyclic is 30 under the effective vertical stress of 100kPa, 70% of relative density for fine content of 15%. when the cyclic stress ratio at each relative density was compared at cyclic number five, the double amplitude(DA) 1%, 3%, 5%, 7.5% and 10%, and the pore-pressure ratio (${\Delta}u/{\sigma'}_c$) 0.95 value were compared; under the relative density of 70% and the effective confining pressure of 100kPa. The pore-pressure ratio (${\Delta}u/{\sigma'}_c$) 0.95 value showed a similar trend to the double amplitude (DA) 5% line.

• Journal of the Korean Ceramic Society
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• v.31 no.10
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• pp.1141-1146
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• 1994

Cyclic fatigue experiment was carried out to predict the life time of alumina ceramics. Four kinds of model were suggested to obtain the adequate representative static stress corresponding to the cyclic stress applied to the alumina specimens. Arithmetic mean stress model gives 21.81 of the crack growth exponent, integrated stress model gives 22.15, maximum stress model gives 24.57, and equivalent static stress model gives 24.43. It is considered that the equivalent static stress model is the most reasonable and gives the best adequate crack growth exponents value.

• Structural Engineering and Mechanics
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• v.16 no.4
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• pp.405-422
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• 2003

Scaled brick masonry panels were tested under cyclic unialxial compression loading to evaluate its deformation characteristics. An envelope stress - strain curves, a common point curves and stability point curves were obtained for various cyclic test conditions. Loops of the stress-strain hysteresis were used to determine the energy dissipation for each cycle. Empirical expressions were proposed for the relations between energy dissipation and envelope and residual strains. These relations indicated that the decay of masonry strength starts at about two-third of peak stress.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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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.