• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.102-112
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• 1994

The drying shrinkage of concrete has a close relation to the water movement. Since the diffusion process of water in concrete is strongly dependent on the temperature and the pore humidity, the process is highly nonlinear phenomena. This study consists of two parts. The first is the development of a finite element program which is capable of simulating the rnoisture distri- ,bution in concrete, and the other is the estimation of the differential drying shrinkage and stress considering creep by using the modified elastic modulus due to inner temperature change and maturity. It is shown that the analytical results of this study are in good agreement with experlimental data in the literatures, and results calculated by BP-KX model. The internal stress caused by moisture distribution which was resulted from the diffusion process, was calculated :quantitatively. The tensile stress which occured in the drying outer zone mostly exceeded the tensile strength of concrete, and necessarily would result in crack formation.

• Geophysics and Geophysical Exploration
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• v.21 no.3
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• pp.162-170
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• 2018

The purpose of this study is to understand the ground change of large scale mountainous region and to estimate the active weak zone using geophysical exploration (electrical resistivity and refraction seismic explorations) in large scale deep landslide area located in Wanjugun, Jeollabukdo. We also analyzed the characteristics of deep landslides occurred in metamorphic rocks region and confirmed the approximate scale. As a result of comparative analysis of N-value by standard penetration test (SPT), low resistivity anomaly, and tension crack identified from field investigation, a discontinuity in soil layer was estimated at 10 ~ 15 m below the surface. Based on this results, the distribution pattern of active weak zone was confirmed between the discontinuity in soil layer and estimation line of bedrock.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.76-84
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• 1985

Mechanical property enhancing mechanisms of $Al_2O_3-ZrO_2$ two phase ceramic composites were studied for several compositions of different $ZrO_2$/$Al_2O_3$ ratio. Microstructural analysis of $Al_2O_3-ZrO_3$(pure) composites indicated that pre-existing microcrack due to larger $ZrO_2$ particle at grain boundary extended along alumina grain boundaries within process zone. Microcracks also nucleated when very small $ZrO_2$ particles at the grain boundaries transformed to monoclinic phase at near of main crack tip. These types of microcracks could contribute to the toughening achieved by creating additional crack surface area during crack propagation. Microstructural analyses also showed that the average grain size and abnormal grain size of $Al_2O_3$ were decreased with increasing $ZrO_2$ vol% in $Al_2O_3$ matrix. As a result it could be concluded as follows In TEX>$Al_2O_3-ZrO_3$(pure) system 1. Microcrack nucleation (stress-induced microcracking) and extension was effective mechanism for absorpiton of fracture energy 2, More narrow distribution and smaller grain size of $Al_2O_3$ due to $ZrO_2$particles mainly contributed to main-tatin the strength and hardness.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.114-122
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• 1994

X-ray stress constant, K, was determined for the diffraction line of (211)plane by using Cr-K$\alpha$ radiation. K was -340.87 MPa/deg. Fatigue crack propagation tests of SS41 steel were conducted under stress ratios of 0.1, 0.3 and 0.5. The half-value breadth of X-ray diffraction profile was measured at and beneath the fracture surface. The half-value breadth, B, on the fracture surface was found to increase with increasing $K_max$. The value of B was influenced by stress ratio in SS41 steel. The half-value breadth took the maximum value at the borden of reversed plastic zone, while it approached to the initial (pre-fatigue) value near the boundary of monotonic plastic zone. The maximum depth of the plasticzone was evaluated on the basis of the half-value breadth distribution. The depth $\omega$$_y$ is related to $K_max$by the following equation : $\omega$$_y$ = $\alpha$($K_max$/$\sigma$$_y$$)^2$ where .sigma.$\sigma$$_y$ is the yield strength obtength obtained in tension test .alpha.is 0.136 for SS41 steel.

• Geomechanics and Engineering
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• v.23 no.2
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• Geomechanics and Engineering
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• v.34 no.6
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• pp.683-696
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• 2023

The destruction and fracture of rock masses are crucial components in engineering and there is an increasing demand for the study of the influence of rock mass heterogeneity on the safety of engineering projects. The numerical manifold method (NMM) has a unified solution format for continuous and discontinuous problems. In most NMM studies, material homogeneity has been assumed and despite this simplification, fracture mechanics remain complex and simulations are inefficient because of the complicated topology updating operations that are needed after crack propagation. These operations become computationally expensive especially in the cases of heterogeneous materials. In this study, a heterogeneous model algorithm based on stochastic theory was developed and introduced into the NMM. A new fracture algorithm was developed to simulate the rupture zone. The algorithm was validated for the examples of the four-point shear beam and semi-circular bend. Results show that the algorithm can efficiently simulate the rupture zone of heterogeneous rock masses. Heterogeneity has a powerful effect on the macroscopic failure characteristics and uniaxial compressive strength of rock masses. The peak strength of homogeneous material (with heterogeneity or standard deviation of 0) is 2.4 times that of heterogeneous material (with heterogeneity of 11.0). Moreover, the local distribution of parameter values can affect the configuration of rupture zones in rock masses. The local distribution also influences the peak value on the stress-strain curve and the residual strength. The post-peak stress-strain curve envelope from 60 random calculations can be used as an estimate of the strength of engineering rock masses.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.68-76
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• 1999

The welding residual stresses produced by the welding frequently caused a crack and promote stress corrosion etc. in HAZ(heat affected zone) contained with external load and weakness of material. Therefore, PWHT(post welding heat treatment) is widely used to reduce wekdubg residuss, to relax hardening of heat affected zone and to get rid of impurity. In this study, in order to define the effect on shappes of T-welded joint, during the post welding heat treatment, we have carried out numerical analyses on the several test pieces by using computer program which was based on thermal-elasto-plato-plasto-creep theories for the study. The main results obtained form this study is as follows: 1) The mechanical difference for change the thickness of plate and groove angle did not appear. 2) The distribution modes of welding residual stresses are same on the all test specimens during the post welding heat treatment. 3) In a mecharical point of view, minimum groove groove angle($40^{circ}$) is more suitable than maximum groove angle($60^{circ}$). 4) Therefore, it is appropriate to minimize the size of groove shape in strength and safety.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.2
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• pp.77-82
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• 1992

When a crystal is grown by FZ process, the melt zone is located at between the solid of upper and lower side and is kept by the solid-liquid interface tension. On the surface of the melt zone, a surface tension gradient is occured by the difference of temperature and solute concentration, it is the driving force of marangoni flow. The crystal even in the steady state growth can become imperfect for the dislocation distribution and the solute concentration in the peripheral region of the crystal are higher than those in the inner part and the probability of the formation of the defects such as voids, bubble penetration, secondary phase creation and crack is high near the solid-liquid interface. This is because the solid -liquid interface becomes irregular because of the local variation of temperature in that region due to marangoni convection.

• Computers and Concrete
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• v.15 no.2
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• pp.305-319
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• 2015

On mesoscopic level, concrete can be treated as a three-phase composite material consisting of mortar, aggregates and interfacial transition zone (ITZ) between mortar and aggregate. A lot of research has confirmed that ITZ plays a crucial role in the mechanical fracture process of concrete. The aim of the present study is to propose a numerical method on mesoscale to analyze the failure mechanism of reinforced concrete (RC) structures under mechanical loading, and then it will help precisely predict the damage or the cracking initiation and propagation of concrete. Concrete is meshed by means of the Rigid Body Spring Model (RBSM) concept, while the reinforcing steel bars are modeled as beam-type elements. Two kinds of RC members, i.e. subjected to uniaxial tension and beams under bending, the fracture process of concrete and the distribution of cracks, as well as the load-deflection relationships are investigated and compared with the available test results. It is found that the numerical results are in good agreement with the experimental observations, indicating that the model can successfully simulate the failure process of the RC members.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.841-850
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• 2004

The modeling of uplift pressure within dam, on the foundation on which it was constructed, and on the interface between the dam and foundation is a critical aspect in the analysis of concrete gravity dams, i.e. crack stability in concrete dam can correctly be predicted when uplift pressures are accurately modelled. Current models consider a uniform uplift distribution, but recent experimental results show that it varies along the crack faces and the procedures for modeling uplift pressures are well established for the traditional hand-calculation methods, but this is not the case for finite element (FE) analysis. In large structures, such as dams, because of smaller size of the fracture process zone with respect to the structure size, limited errors should occur under the assumptions of linear elastic fracture mechanics (LEFM). In this paper, the fracture behaviour of concrete gravity dams mainly subjected to uplift Pressure at the crack face was studied. Triangular type, trapezoidal type and parabolic type distribution of the uplift pressure including uniform type were considered in case of evaluating stress intensity factor by surface integral method. The effects of body forces, overtopping pressures are also considered and a parametric study of gravity dams under the assumption of LEFM is performed.