• Journal of the Korean Institute of Landscape Architecture
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• v.31 no.5
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• pp.1-10
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• 2003

The purpose of this study was to verify the shore margin protection effect of a root system developed from direct sticking of Salix gracilistyla Miq., focusing on the reinforcement of soil shear strength. The materials were 20cm long sticks whose average diameter and weight were 7.52mm and 14.58g respectively, and sandy loam(Sand 60.36%, Silt 28%, Clay 11.64%), whose maximum dry weight(${\gamma}$$_{dmax}$) was 1.59gf/㎤ at the water ratio( $W_{opt}$) 13.8%. The direct shearing test(KS F 2343) was applied to cylindric columms(diameter 132mm) of pure soil and two years old root reinforced soil. At each condition of vertical stress, 10N/$ extrm{cm}^2$, 14.41N/$\textrm{cm}^2$ and 18.82 N/$\textrm{cm}^2$, five soil+root columns were sheared. After shear tests, the root area ratio and soil moisture on the shear plane were measured. The results of this research were as follows: 1. The average of root area ratio was 1.86% and the soil moisture 14.67%. 2. Two years old root system was found to increase the soil shear strength of pure soil in terms of Cohesion(C) and Inner friction Angle($\phi$) as follows. 3. The relationship between root area ratio and the increased shear strength can be presented with the following equation, $\Delta$S ≒ 0.33ㆍ TrㆍAs/A $\Delta$S : Increased Shear Strength Tr : Average Tension Strength of Root, Ar/A : Root Area Ratioioage Tension Strength of Root, Ar/A : Root Area Ratio

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.175-187
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• 2003

The earth pressure acting on the cylindrical retaining wall in cohesionless soils is different from that on the retaining wall in plane strain condition due to three dimensional arching effect. Accurate estimation of earth pressure is required for the design of vertical cylindrical retaining wall. Failure modes of the ground behind vertical shaft are dependent on ground in-situ stress conditions. Failure modes are actually divided into two modes of cylindrical failure mode and funnel-shaped mode with truncated cone surface. Several researchers have attempted to estimate the earth pressure on cylindrical wall for each failure mode, but they have some limitations. In this paper, several equations for estimating the earth pressure on cylindrical wall in cohesionless soils are investigated and new formulations for two failure modes are suggested. It rationally takes into account the overburden pressure, wall friction, and force equilibriums on sliding surface.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1243-1251
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• 1994

The implicit finite difference program was developed to evaluate the relationship between time and consolidation ratio within the zone of vertical drain effective radius. In the evaluation, the excess pore water pressure was considered to dissipate in two directions, namely, vertical and radial flow direction. To calculate subsoil stress increments in the soil due to multi-step embanking, the foundation soil was assumed to be an isotropic and homogeneous elastic medium and the initial excess pore water pressure was estimated by using Skempton's parameters whose condition is plane strain and elastic phase of pore pressure response within the soft ground. Regarding to the settlement estimation, immediate and primary consolidation settlements were calculated. The secondary or delayed consolidation settlement was not considered. Numerically calculated excess pore water pressure and settlements were similar to the measured data in situ. Thus, this method can be used to predict the time-consolidation ratio of each layer treated by vertical drain method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.10
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• pp.3199-3210
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• 1996

The buckling and postbuckling behaviors were sutdied analytically and experimentally for stiffened laminated composite panels under compression loading. The panels with I-, blade, -and hat-shapeed stiffeners were investigated. In the analysis, the stiffened panels were anlyzed using the nonlinear finite element method combined with an improved arc-length method. The progressive failure analysis was done by adopting the maximum stress criterion and complete unloading failure model. The effects of the fiber angles were investigated on the buckling and postbuckling behaviors. In the experiment, the web and the lower cap of each stiffener were formed by the continuous lay-up of the skin for cocuring the stiffened panels. Therefore, the separation between stiffener and skin was not found in the junction part even after postbuckling ultimate load and the stiffened panels had excellent postbuckling load carrying capacity. A shadow moire thchnique was used to monitor the out-of-plane deformations of the panels. The piezoelectric films were attached to the panels to get the failure characteristics of the panel. The analytical results on the buckling load, postbuckling ultimate load, and failure pattern showed good agreement with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.717-723
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• 2010

Many researchers have studied woven fabric carbon-fiber-reinforced composite (CFRP) materials but the study of fatigue crack propagation in composites has been insufficient. It has known that the crack propagation behavior differs depending on the load and the fiber direction. In this study, the fatigue crack propagation along two different fiber array directions ($0^{\circ}$, $45^{\circ}$) in plain woven CFRP composite was investigated. Fatigue crack propagation tests were conducted on the woven CFRP composite under a sinusoidal waveform load with stress ratios of 0.1 at a frequency of 10 Hz. Once the results of the tests were obtained, fatigue crack propagation rates (da/dN) were plotted against the energy release rate amplitude (${\Delta}G$), and it was observed that either mode I crack propagation or mixed mode crack propagation occurs depending on the fiber array direction.

• Journal of the Korean Society for Precision Engineering
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• v.6 no.2
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• pp.40-46
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• 1989

Recently, the researches on cutting the new material have been done for development of aerospace industrial engineering. Especially, titanium ally is well known as heat resisting, antiwear, anticorrosion and difficult-to-machine materials. Many studies on the analysis of shear angle have been done for improving productivity in cutting these materials. In case of titanium alloy, the saw-toothed type of chip which has wave surface of a triangular form, an eccentric from of a continuous type of chip that is produced in the cutting process, was checked. Nakayama supposed that a maximum shear strewss plane and the shear crack in the free surface made an angle of $45^{\circ}$ .deg. , but it's usually much larger than that. In this paper, the author analyzed the shear conditions of the cutting process in the quick-stopping device with the help SEM-photographs, and measured the hypotenuse angle directly in the photographs of the chips. In conclusion, the author tried to find the shear angle in the cutting process with the saw-toothed chip and compared it with the shear angles which can be calculated from the theories established by others. The results obtained are as follows. 1. In case of the saw-toothed chips, the equivalent cutting ratio can be calculated by using the chip thickness to two-thirds of ramp height. 2. The theory of Ernst-Merchant is not applicable to the titanium and its alloys which does not fractured in accordance with the theory of maximum shear stress. 3. When we cut the titanium alloys which produced the saw-toothed chips, the shear angle can be found with the theories of Rowe-Spick, P.K. Wright and the measurement of hypotenuse angle.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.189-195
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• 2002

This paper deals with the free vibration of horizontally curved beams with transition currie. Based on the dynamic equilibrium equations of a curved beam element subjected to the stress resultants and inertia forces, the governing differential equations are derived for the out-of-plane vibration of curved beam with variable curvature. These equations are applied to the beam having transition curve in which the clothiod curve is chosen in this study. The differential equations are solved by the numerical methods lot calculating the natural frequencies and mode shapes. For verifying theories developed herein, the frequency parameters obtained from this studs and ADINA are compared with each other. As the numerical results, the various parametric studies effecting on natural frequencies are investigated and those results are presented in tables and figures.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.1-12
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• 2002

To obtain more accurate responses of laminated composite structures, the effect of transverse shear deformation, transverse normal strain/stress and a nonlinear variation of in-plane displacements with respect to the thickness coordinate need to be considered in the analysis. The improved higher-order theory is used to determine the deflections and natural frequencies of laminated composite structures. A quasi-elastic method is used for the solution of viscoelastic analysis of the laminated composite plates and sandwiches. Solutions of simply-supported laminated composite plates and sandwiches are obtained and the results are compared with those by the 3D elasticity theory and other theories. The improved theory proposed in this paper is shown to predict the deflections and natural frequencies more accurately than all other theories.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.145-145
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• 1999

La-Ca-Mn-O (LCMO) 박막에서 초거대 자기 저항 효과와 발견된 이후 자기 센서와 고밀도 자기 저장 매체로서 응용하기 위한 연구가 진행되고 있다. 그러나 현재 대부분의 증착은 타겟과 박막간의 조성의 일치를 위하여 PLD 방법을 이용하고 있으며 RF magnetron sputtering 법으로 증착한 예는 많이 보고되고 있지 않으며 특히 적층 성장시킨 예는 아직 보고되지 있지 않다. 또한 LCMO와의 낮은 격자 상수 불일치를 보이는 SrTiO3와 LaAlO3 기판에 LCMO 박막을 성장시킬 경우 LaAlO3의 경우 XRD rocking curve의 curve의 FWHM 값이 SrTiO3 상에 증착시킨 것의 10배 이상의 값을 보인다는 것은 주목할 만한 사실이다. RF magnetron sputtering 법을 이용하여 LaAlO3 기판상에 145nm MCMO 박막을 적층성장시켰다. XRD $ heta$-2$\theta$ scan을 통해 박막이 c-축 배향한 것을 확인할 수 있었으며 RBS 분석결과 4.98%의 minimumyield를 보였으며 이로부터 박막이 적층성장한 것을 확인할 수 있었다. LCMO (200) peak의 XRD $\theta$-rocking 결과 FWHM의 값은 0.311$^{\circ}$를 보였으나 2개의 피크가 존재하는 것을 볼 수 있었다. 따라서 기판의 (200) 피크를 XRD $\theta$-2$\theta$ scan에서 0.3$^{\circ}$ 간격으로 두 개의 피크를 관찰할 수 있었는데 이는 기판과 박막간의 stress로 인한 tetragonal distortion에 의한 것으로 알려져 있었다. 따라서 기판상에 박막이 어떤 식으로 적층 성장되었는지를 RBS를 이용하여 <001>과 <011> 방향으로 2MeV He++를 주입하여 0.1$^{\circ}$ 간격으로 틸팅을 해본 결과 <001> 방향에서는 1.12$^{\circ}$의 차이를 보였다. 이는 기판과의 compressive stress로 인해 c축 방향으로 늘어났으며 stress relaxed layer는 XRD 결과와는 달리 관찰할 수 없었다. 이러한 현상의 기판 자체의 twin 구조로 인한 것으로 생각된다. RBS 분석후 고분해능 XRD를 이용해 LCMO (200) peak의 $\theta$-rocking 결과 이제R지 laAlO3 상 증착한 LCMO의 값으로는 제일 작은 0.147$^{\circ}$를 나타내었다.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.183-196
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• 2003

This paper evaluates the effects of haunches and the characteristic differences of haunch design regulations through design of pier and box structures with/without haunches. The design of the pier and box structures was conducted by using the linear elastic plane stress finite element analysis, the DIN 1045 and ACI 318-99 codes, the suggested experimental design equations, and the strut-tie model approach. To prove the validity of design results obtained by the strut-tie model approach, the ultimate strength of two haunched reinforced concrete beams tested to failure was evaluated by using the approach. According to the comparison and evaluation of the design results, it is concluded that the design results of haunched reinforced concrete structures by using conventional and design codes need to be complemented with those by using the strut-tie model approach that reflected the effects of haunches in design comparatively well through the actions of arch and direct transfer of applied loads.