• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.55-66
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• 2012

To investigate the hysteresis of the suction stress in unsaturated weathered mudstone soils (CL), matric suction and volumetric water content were measured in both drying and wetting processes using Automated Soil-Water Characteristics Curve Apparatus. The drying and wetting processes in unsaturated soils were reproduced in the test; the drying process means to load matric suction to spill pore water from the soils, and the wetting process means to unload matric suction to inject pore water into the soils. Based on the measured result, Soil Water Characteristic Curve(SWCC)s were estimated by van Genuchten model (1980). SWCCs have nonlinear relationship between effective degree of saturation and matric suction. The hysteresis in SWCCs between drying and wetting processes occurred. As a result of estimating Suction Stress Characteristic Curve(SSCC) using Lu and Likos model (2006), the suction stress rapidly increased in the low level of matric suction and then increased slightly. Also, the hysteresis in SSCCs between drying and wetting processes occurred. In order to design geo-structures and check its stability considering unsaturated soil mechanics, therefore, it is more reasonable that the SSCC of drying process should be applied in the condition of rainfall infiltration and the SSCC of wetting process in the condition of evaporation or drainage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.183-194
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• 2004

It's essential process to study non-linear material function related to characteristics of compressibility and permeability when we predict the consolidation behavior of soft clay ground. In this study, laboratory tests were conducted to find out the material function using marine clay. Standard oedometer test and Rowe cell test were performed with conditions, which were classified into vertical drainage only, radial drainage only and vertical-radial drainage case. Modified oedometer test equipment was developed to find out the material function and special extrusion device was originated to minimize the sample disturbance effect. Reliability of the results in modified oedometer test could be confirmed by comparing with the Rowe cell's one. Effective stress - void ratio - permeability relations were analyzed using all testing results. As a result, void ratio with effective stress level could be expressed by the power function and permeability with void ratio could be expressed by exponential function. In soft clay with high initial water content and low shear strength, non-linear characteristics related to compressibility and permeability varied with wide range by the effective stress levels. It's important to note that non-linearity of the material function should be considered at prediction of the consolidation behavior.

• Geotechnical Engineering
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• v.5 no.2
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• pp.45-56
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• 1989

The influence of stress path on the deformation characteristics of clay has been studied through a series of stress-path controlled triaxial tests on artificially sedimented and normally con- solidated Kaolinite. It has been found that there exists a critical stress increment ratio, Kc, in which stress·strain characteristics possesses a linear relationships and beyond Kc, strain hardening. A modified hyperbolic constitutive model for the strain hardening behavior has been formulated based on the Drnevich's hyperbolic function. And, a method of settlement analyses has been Proposed wherein the effect of stress path during consolidation is taken into account.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.4
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• pp.321-327
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• 2014

Structural light weight aggregate concrete are made with both coarse and fine light weight aggregates, but it is common with the high strength concrete to replace all or part with normal weight sand be called class 1 structural light weight aggregate concrete. Fire resistance of structural light weight aggregate concrete are determined by properties of high water content ratio and explosive spalling. Especially, structural light weight aggregate concrete is occurred serious fire performance deterioration by explosive spalling stem from thermal stress and water vapor pressure. This study is concerned with experimentally investigating fire resistance of class 1 structural light weight concrete. From the test result, class 1 structural light weight concrete is happened explosive spalling. The decrease of cross section caused by explosive spalling made sharp increasing gradient of inner temperature.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.143-150
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• 2009

Material functions about effective stress, permeability, coefficient of consolidation and coefficient of volume change has important role to predict consolidation velocity and settlement of soft ground. Modified oedometer for radial drainage is adapted to find out material functions on laboratory tests. Undisturbed sample for laboratory tests were taken from construction sites of industrial complexes on southern coastal area which consists of upper dredged fill and lower original clay layer. For different drainage condition in consolidation process void ratio, effective stress, permeability, coefficient of consolidation and coefficient of volume change has been assessed with results of existing standard oedometer tests. It is worthwhile to note that consolidation material functions could be expressed as regression equation by Stark (2005), heterogeneity for permeability could be assessed from these relationships.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.5 no.2
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• pp.107-120
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• 1993

This paper presents a new modal solution of linear three-dimensional hydrodynamic equations using similarity transform technique. The governing equations are first separated into external and internal mode equations. The solution of the internal mode equation then proceeds as in previous modal models using the Galerkin method but with expansion of arbitrary basis functions. Application of similarity transform to resulting full matrix equations gives rise to a set of uncoupled partial differential equations of which the unknowns are coefficients of mode vector. Using the transform technique a computationally efficient time integration is possible. In present from the model use Chebyshev polynomials for Galerkin solution of internal mode equations. To examine model performance the model is applied to a homogeneous, rectangular basin of constant depth under steady, uniform wind field.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.381-387
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• 2016

In this paper, the methodology applied to the improvement of stress analyses is extended to free vibration and buckling analyses. The essence of the methodology is the Saint-Venant's principle that is applicable to beam and plate models. The principle allows one to dimensionally reduce three-dimensional elasticity problems. Thus the methodology can be employed to vibration and buckling as well as stress analysis. First, the principle is briefly revisited, and then the formations of classical beam theories are presented. To improve the predictions, the perturbed terms (unknowns) are introduced together with the warping functions that are calculated by stress equilibrium equations. The unknowns are then calculated by applying the equivalence of stress resultants (i.e., Saint-Venant's principle). As numerical examples, cantilever and simply supported beams are analytically solved. The results obtained are compared with those of the classical beam theories. It is shown that the methodology can be used to improve the predictions without introducing shear correction factors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.91-98
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• 2003

In the structural analysis of a launch vehicle, the construction of loading functions and the determination of responses to them are very important. Among many kinds of loads, acoustic load generated by exhaust is a random load that can be described in a statistical manner. In this study, loading functions corresponding to the acoustic loads are constructed and applied to the structural analysis of launch vehicle. Acoustic loading functions are constructed using source allocation method. Structural analyses are carried out by using finite element modelling and frequency response function of finite element model. The stresses resulting from acoustic loads and acceleration power spectral density functions at interfaces of each section are calculated. These analyses are essential for the development of environmental test specifications and associated dynamic design requirements which are necessary to ensure overall vehicle reliability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.67-75
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• 2013

The flow stress of zircaloy-4 used in the spacer grid supporting a nuclear fuel rod was determined by the Johnson-Cook model, and model parameters were determined using reverse engineering. Parameters such as A, B, n and $\dot{\varepsilon}_0$ were determined by the tensile test result. To obtain the parameters C and m, a slot milling test and numerical simulation were performed. The objective functions were defined as the difference between the experimental and the simulation results, and then, the parameters were determined by minimizing the objective function. To verify the validity of the determined parameters, cross-verification for each case was conducted through a shearing test and simulation. The results tend to show agreement with the experimental results, such as the features of sheared edges and maximum punch force, with the correlation coefficients exceeding at least 0.97.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.133-140
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• 2018

This paper is concerned with the 2-D micostructure generation for $Ni-A{\ell}_2O_3$ dual-phase composite materials and the numerical analysis of mechanical characteristic of hierarchical models of microstructure which are defined in terms of the scale of microstructure. The microstructures of dual-phase composite materials were generated by applying the mathematical RMDF(random morphology description functions) technique to a 2-D RVE of composite materials. And, the hierarchical models of microstructure were defined by the number of Gaussian points. Meanwhile, the volume fractions of metal and ceramic particles were set by adjusting the level of RMD functions. The microstructures which were generated by RMDF technique are definitely random even though the total number of Gaussian points is the same. The randomly generated microstructures were applied to a 2-D beam model, and the variation of normal and shear stresses to the scale of microstructure was numerically investigated. In addition, through the crack analyses, the influence of RMDF randomness and Gauss point number on the crack-tip stress is investigated.