• Journal of the Society of Naval Architects of Korea
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• v.48 no.1
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• pp.42-48
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• 2011

To define ice as a solid material, mathematical and physical characteristics and their application examples are investigated for several materials' yield functions which include isotropic elastic, isotropic elastic-plastic, classical Drucker-Prager, Drucker-Prager Cap, Heinonen's elliptic, Derradji-Aouat's elliptic, and crushable foam models. Taking into account brittle failure mode of ice subject to high loading rate or extremely low temperature, isotropic elastic model can be better practicable than isotropic elastic-plastic model. If a failure criterion can be properly determined, the elastic model will provide relatively practicable impact force history from ice-hull interactions. On the other hand, it is thought that the soil models can better predict the ice spalling mechanism, since they contain both terms of shear stress-induced and hydrostatic stress-induced failures in the yield function.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.50-59
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• 2006

The risk of fault reactivation in the Gippsland Basin was calculated using the FAST (Fault Analysis Seal Technology) technique, which determines fault reactivation risk by estimating the increase in pore pressure required to cause reactivation within the present-day stress field. The stress regime in the Gippsland Basin is on the boundary between strike-slip and reverse faulting: maximum horizontal stress $({\sim}\;40.5\;Mpa/km)$ > vertical stress (21 Mpa/km) ${\sim}$ minimum horizontal stress (20 MPa/km). Pore pressure is hydrostatic above the Campanian Volcanics of the Golden Beach Subgroup. The NW-SE maximum horizontal stress orientation $(139^{\circ}N)$ determined herein is broadly consistent with previous estimates, and verifies a NW-SE maximum horizontal stress orientation in the Gippsland Basin. Fault reactivation risk in the Gippsland Basin was calculated using two fault strength scenarios; cohesionless faults $(C=0;{\mu}=0.65)$ and healed faults $(C=5.4;\;{\mu}=0.78)$. The orientations of faults with relatively high and relatively low reactivation potential are almost identical for healed and cohesionless fault strength scenarios. High-angle faults striking NE-SW are unlikely to reactivate in the current stress regime. High-angle faults oriented SSE-NNW and ENE-WSW have the highest fault reactivation risk. Additionally, low-angle faults (thrust faults) striking NE-SW have a relatively high risk of reactivation. The highest reactivation risk for optimally oriented faults corresponds to an estimated pore pressure increase (Delta-P) of 3.8 MPa $({\sim}548\;psi)$ for cohesionless faults and 15.6 MPa $({\sim}2262\;psi)$ for healed faults. The absolute values of pore pressure increase obtained from fault reactivation analysis presented in this paper are subject to large errors because of uncertainties in the geomechanical model (in situ stress and rock strength data). In particular, the maximum horizontal stress magnitude and fault strength data are poorly constrained. Therefore, fault reactivation analysis cannot be used to directly measure the maximum allowable pore pressure increase within a reservoir. We argue that fault reactivation analysis of this type can only be used for assessing the relative risk of fault reactivation and not to determine the maximum allowable pore pressure increase a fault can withstand prior to reactivation.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.204-213
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• 2008

This paper presents the analysis about the stability of the Pohang deep geothermal borehole drilled in 2006. Severe wellhole instability problems such as collapse and tight hole occurred in weak rocks while drilling. Optimal mud pressure (mud window) required to prevent instability problems during drilling is obtained from analysis on in-situ stress and rock strength. The window is bounded by vertical stress in its upper limit and by either collapse pressure or pore pressure in its lower limit. Mud window varies with different types of rocks. In the top-most semi-consolidated mudstone formation, no mud window can secure borehole stability. In some weak rock types (basic dyke and crystal tuff), the borehole pressure needs to be higher by $50{\sim}60%$ than hydrostatic pressure. That means a mud density of 1.5 g/$cm^3$ or higher should be applied during drilling in order to prevent excessive collapse around the borehole.

• Journal of the Korean Geotechnical Society
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• v.26 no.4
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• pp.27-36
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• 2010

In this study, a series of flat dilatometer tests are performed for Busan sand reconstituted in a large calibration chamber to evaluate the state parameter ($\Psi$). Experimental result shows that the horizontal amplification factor ($K_D/K_0$) is linearly related with state parameter in semi-logarithmic space, but the $K_D/K_0$ of OC specimen is smaller than that of NC specimen because of the horizontal residual stress by stress history of OC specimen. The relation between the normalized dilatometer modulus ($E_D/\sigma_m'$) and the state parameter is also linearly expressed in semi-logarithmic space, and the effect of stress history is relatively insignificant in this relation. However, the variation in $E_D/\sigma_m'-\Psi$ relation of NC state is slightly higher than that of OC state due to the effect of the stress level, and the correlation curve is descending with increase of confining stress. The comparison of test result with previous results of Ticino and Toyoura sands shows that the $E_D/\sigma_m'-\Psi$ relation of Toyoura sand is located on upper side than that of Busan and Tieino sands due to the effect of the higher compressibility, whereas the $K_D/K_0-\Psi$ relation of each sand is irregularly distributed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.29-37
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• 2000

The effect of a ceramic ball inclusion on densification behavior of a metal powder compact was investigated under cold isostatic pressing, pressureless sintering and hot isostatic pressing. To simulate those processes, proper constitutive models were implemented into a finite element program (ABAQUS). Measured density distributions of metal powder compacts were also compared with finite element results and showed the same trend with simulated results. Residual stress distributions were calculated by finite element analysis to study the effect of ceramic ball inclusions with different thermal expansion coefficients. The higher residual stress was observed in a metal powder compact when the difference between thermal expansion coefficients for a ceramic ball and metal powder became larger. Samples produced by Wing showed more uniform density distributions and lower residual stresses compared to those by sintering after cold isostatic pressing. For various sizes of ceramic ball inclusions, densification and deformation of powder compacts were also studied during hot isostatic pressing.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.65-78
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• 2012

Elastic moduli and behavioral characteristics changes of very widely according to stress level resulting from uniaxial compressive test of sedimentary rock. This means that elastic moduli do not indicate constants but variables. More appropriate and reasonable outcome will be accepted through loading-reloading test in design and construction progress. An attention for behavioral characteristics of elastic moduli shown in low level of stress should be paid.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.329-334
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• 1992

It has been shown that the application of hydrostatic pressure during superplastic forming of 8090A1 can prevent the cavitaiton normally encountered at atmospheric pressure and cavity growth rate factor .eta. in the plane strain state is greater than that in the equibiaxial stress state. .eta. value shows some difference compared to the theoretical value, which seems to be due to the continuous nucletion and coalescence of voids during superplastic deformation. Scatter of measured data of cavity volume fraction seems to be on preferential nucleation of viods on non-uniformly distributed second phase particles in the deforming matrix.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.4
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• pp.118-125
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• 1992

Theoretical equations for hoop stress, longitudinal or meridian stress and Von Mises stress of an axismmetric conical pressure vessel and a frustum of conical pressure velle, both of which are pressuized by hydrostatic loading, are derived from equilibrium equations. The membrane stresses conputed by theoretical equations for a conical pressure vessel and a frustum of conical pressure vessel are compared with the values obtained from finite elelment method. Based on the fact that the computational values by theoretical equations are well agreed with the finite element results, derived equations are proved to be valid and it is possible for those equations to be conveniently used for structural analysis or design of frustum of conical pressure vessel which is a part of silo body.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.5
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• pp.61-68
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• 2021

Movable weirs with multi-stage control are necessary in many Korean rivers to actively control the water storage level. A mesh dependency test was performed to determine the appropriate number of meshes for structural analysis of movable weirs. The standing angles of movable weirs were set to 60°, 45°, 30°, and 15° for stress analysis. The standing angle of 0° was excluded from the analysis because it was unloaded. Changes in the standing angle led to changes in the water depth, maximum pressure, maximum strain, and maximum stress. The maximum average stress and the structural safety of the multi-stage control movable weir were computed and tested using the Ansys FEA software package.

• Journal of the Korean Society for Railway
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• v.13 no.1
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• pp.84-91
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• 2010

We built multi-purpose large triaxial testing system that can test and evaluate various geotechnical design parameters such as shear strength, deformation modulus and stress-strain behaviour for large diameter granular materials, which are the most commonly used construction materials in the railway, road embankments. The details of the built testing system and the results obtained from static triaxial test carried out for gneiss ballast material are discussed within the scope of this paper. Ballast is hardly saturated and is confined at low overburden pressure, since the depth is shallow and the permeability is very high. Herein we ascertained that the confining pressure can effectively be controlled by vacuum. The rational trend could be checked up through triaxial test results such as shear strength, deformation, and particle breakage. And the shear strength envelope could be non-linearly represented with the parent rock strength, confining pressure of the triaxial test and proper parameters.