• 대한조선학회논문집
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• 제52권4호
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• pp.315-322
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• 2015

In this paper, the theory of rectangular plate on the elastic foundation is used to get the relation equation between the effective Young’s modulus and the ice sheet deflection by applying the characteristic length concept, since the model ice sheet is rectangular shape in KRISO (Korea Research Institute for Ships and Ocean Engineering) ice basin. The obtained relation equation is equal to that of using the circular plate theory. A device is made and used to measure the deflection of ice plate using LVDT (Linear Variable Differential Transformer) for several loading cases and the procedure of experiments measuring the deflection used for getting the Young’s modulus is explained. In addition, the flexural strength value obtained through flexural strength experiments is compared with that of finite element analysis using the obtained effective Young’s modulus. Also, a nonlinear FEA (Finite Element Analysis) of cantilever ice beam is done with eroding effect and LS-DYNA result shows the fracture of brittle ice under 1 mm/s velocity load.

• 한국응용과학기술학회지
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• 제32권4호
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• pp.607-615
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• 2015

To investigate the adhesion effect of various kinds and contents of polymeric methylene diphenyl diisocyanates (pMDIs) on adhesion performance, wood adhesives (A-1~5) were synthesized and characterized. As results, when the amount of pMDI increased in adhesives, the dry tensile strength was found to be proportionally increased sustaining at around $16.0{\sim}21.6kgf/cm^2$. The polyurethane (PU) resin, which used M11S as a source of pMDI showed the best wet tensile strength at $11.9kgf/cm^2$ and cyclic boil tensile strength at $8.1kgf/cm^2$, which satisfied the requirement of over $7kgf/cm^2$. Thermal properties of the rice powder (RP) based polyurethane resins were characterized by differential scanning calorimetry (DSC) and Thermal gravimetric analysis (TGA). Thermal stability of polyurethane resins increased to $250^{\circ}C$ with adding pMDIs. The more pMDI (M5S) was added to adhesive, the higher thermal stability of the resin was observed by TGA.

• Carbon letters
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• 제15권1호
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• pp.67-70
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• 2014

In this work, nanocomposites of epoxy resin and chemically reduced graphene oxide (RGO) were prepared by thermal curing process. X-ray diffractions confirmed the microstructural properties of RGO. Differential scanning calorimetry was used to evaluate the curing behaviors of RGO/epoxy nanocomposites with different RGO loading amounts. We investigated the effect of RGO loading amounts on the mechanical properties of the epoxy nanocomposites. It was found that the presence of RGO improved both flexural strength and modulus of the epoxy nanocomposites till the RGO loading reached 0.4 wt%, and then decreased. The optimum loading achieved about 24.5 and 25.7% improvements, respectively, compared to the neat-epoxy composites. The observed mechanical reinforcement might be an enhancement of mechanical interlocking between the epoxy matrix and RGO due to the unique planar structures.

• 한국지반신소재학회논문집
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• 제7권2호
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• pp.1-5
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• 2008

일반적인 콘크리트 건축물이나 도로포장에서 발생되는 부등침하는 건물의 붕괴나 도로의 수명저하로 인한 비용을 증가시킨다. 이에 대하여 침하된 구조물 하부지반에 그라우팅 공법을 이용하여 지반침하복원을 실시한다. 그러나 기존 그라우트 공법의 경우, 강도발현기간이 길고, 보강효과가 지속적이지 못한 단점을 지니고 있다. 이를 보완하기 위한 주입재료로써, 고밀도 팽창 재료의 특성을 평가하였다. 지반상태와 팽창재료의 주입량의 변화에 따른 압축강도의 변화와 화학물질에 대한 안정성 시험 및 SEM 촬영을 통하여 특성을 연구하였다. 압축강도는 다른 물질과의 혼합으로 높은 강도가 발현되었으며, 화학적 저항성은 대부분의 조건에서 반응하지 않았으나 알코올계열에 변화가 발생하였다. SEM 촬영을 통하여 강도발현에 있어서 조직구성이 촘촘할수록 치밀하게 구성된다고 판단하였다.

• Geomechanics and Engineering
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• 제30권4호
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• pp.363-372
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• 2022

One of the most frequent issues in tunnel excavation is the collapse of rock blocks and the dropping of rock fragments from the tunnel face. The tunnel face can be reinforced using a number of techniques. One of the most popular and affordable solutions is the use of face longitudinal dowels, which has benefits including high strength, flexibility, and ease of cutting. In order to examine the reinforced face, this work shows the longitudinal deformation profile and ground response curve for a tunnel face. This approach is based on assumptions made during the analysis phase of problem solving. By knowing the tunnel face response and dowel behavior, the interaction of two elements can be solved. The rock element equation derived from the rock bolt method is combined with the dowel differential equation to solve the reinforced ground response curve (GRC). With a straightforward and accurate analytical equation, the new differential equation produces the reinforced displacement of the tunnel face at each stage of excavation. With simple equations and a less involved computational process, this approach offers quick and accurate solutions. The FLAC3D simulation has been compared with the suggested analytical approach. A logical error is apparent from the discrepancies between the two solutions. Each component of the equation's effect has also been described.

• 대한치과보철학회지
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• 제28권1호
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• pp.137-163
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• 1990

The properties of a investment material can be described by the consistency at the slurry state, the setting time, the compressive strength and the thermal expansion during the casting. In this study the effect of the production parameters which are included the ratio of quartz and cristobalite, the content of binder, the water powder ratio and the content and concentration of additives on the Properties of the gypsum-bonded investments has been investigated with help of the consistency test, the vicat needle test, the compressive strength test, the thermal expansion test, x-ray diffraction and DTA thermal differential test. The experimental results showed that the constitution of a investment with W/P ratio of 0.34, 30% of gypsum, 0.8% aluminium sulfate, 2% magnesium sulfate, 0.6% sodium phosphate was adapted for the properties of the KDA Spec. No. 13 type I investment. The important experimental results are summarized as follows. 1. The consistency of the investment decreased with increasing amount of aluminium sulfate and decreasing amount of sodium phosphate. An addition of magnesium sulfate up to 2% an increase of the consistency was shown. But 3% magnesium sulfate in investment showed a decrease of the consistency. The consistency did not vary significantly with a variation of the content of gypsum and cristobalite and the W/P ratio. 2. Aluminium sulfate and the magnesium sulfate promoted the hardening and the aluminium phosphate delayed the hardening. The setting time increased with amount of gypsum. The effect of the matrix on the setting time was insignificant. With the W/P ratio of 0.34 the setting time was 14 min. 3. The compressive strength decreased with the amount of aluminium sulfate up to 0.25% and increased with the amount of aluminium sulfate greater than 3%. The compressive strength decreased as decreasing the amount of magnesium sulfate and gypsum and as increasing the W/P ratio. The effect of the refractory on the compressive strength was also not significant. With the W/P ratio of 0.34 the compressive strength was $34Kg/mm^2$. 4. The 1st thermal expansion was found at the temperature near and the steady state or the contraction stage was found at the temperature between $250^{\circ}C$ and $500^{\circ}C$. After this stage the 2nd thermal expansion took place at the temperature near $500^{\circ}C$. The amount of thermal expansion increased with decreasing the content of magnesium sulfate, aluminium sulfate and gypsum and the W/P ratio. And the amount of thermal expansion increased as the content of sodium phosphate and cristobalite. With the W/P ratio of 0.34 the amount of total expansion was 1.2%.

• 대한치과보철학회지
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• 제29권1호
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• pp.139-165
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• 1991

The properties of a investment material can be described by the consistency at the slurry state, the setting time, the compressive strength and the thermal expansion during the casting. In this study the effect of the production parameters which are included the ratio of quartz and cristobalite, the content of binder, the water powder ratio and the content and concentration of additives on the properties of the gypsum-bonded investments has been investigated with help of the consistency test, the vicat needle test, the compressive strength test, the thermal expansion test, x-ray diffraction and DTA thermal differential test. The experimental results showed that the constitution of a investment with W/P ratio of 0.34, 30% of gypsum, 0.8% aluminium sulfate, 2% magnesium sulfate, 0.6% sodium phosphate was adapted for the properties of the KDA Spec. No. 13 type I investment. The important experimental results are summarized as follows. 1. The consistency of the investment decreased with increasing amount of aluminium sulfate and decreasing amount of sodium phosphate. An addition of magnesium sulfate up to 2% an increase of the consistency was shown. But 3% magnesium sulfate in investment showed a decrease of consistency. The consistency did not vary significantly with a variation of the content of gypsum and cristobalite and the W/P ratio. 2. Aluminium sulfata and the magnesium sulfate promoted the hardening and the aluminium phoshpate delayed the hardening. The setting time increased with amount of gypsum. The effect of the matrix on the setting time was insignificant. With the W/P ratio of 0.34 the setting time was 14 min. 3. The compressive strength decreased with the amount of aluminium sulfate up to 0.25% and increased with the amount of aluminium sulfate greater than 3%. The compressive strength decreased as decreasing the amount of magnesium sulfate and gypsum and as increasing the W/P ratio. The effect fo the refractory on the compressive strength was also not significant. With the W/P ratio of 0.34 the compressive strength was $34Kg/mm^2$. 4. The 1st thermal expansion was found at the temperature near $250^{\circ}C$ and the steady state or the contraction stage was found at the temperature between $250^{\circ}C$ and $500^{\circ}C$. After this stage the 2nd thermal expansion took place at the temperature near $500^{\circ}C$. The amount of thermal expansion increased with decreasing the content of magnesium sulfate, aluminium sulfate and gypsum and the W/P ratio. And the amount of thermal expansion increased as the content of sodium phosphate ad cristobalite. With the W/P ratio of 0.34 the amount of total expansion was 1.2%.

• 공업화학
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• 제16권3호
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• pp.354-360
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• 2005

본 연구에서는, 방사선 가교와 열처리에 의해 내열특성을 가진 polyvinyl alcohol (PVA) 수화겔을 제조하였다. 제조된 수화겔의 겔화율, 팽윤도와 겔강도 같은 기계적 특성을 측정하였다. DSC와 XRD를 이용하여 구조적 변화를 알아보았다. 수화겔의 겔화율과 겔강도는 방사선 조사 후에 열처리 과정을 했을 경우에 방사선 조사만 했을 때보다 높은 값을 보였다. 또한, 방사선 조사한 수화겔과 방사선 조사 후에 열처리 과정을 한 수화겔이 고온에서의 내열특성이 우수하였다.

• Nuclear Engineering and Technology
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• 제31권6호
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• pp.561-571
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• 1999

Microstructure and mechanical properties of five Cr-Mo steels for nuclear industry applications have been investigated. Transmission electron microscopy, energy dispersive spectrometer, differential scanning calorimeter, hardness, tensile, and impact test were used to evaluate the Cr and W effect on the microstructure and mechanical properties. Microstructures of Cr-Mo steels after tempering are classified into three types : bainitic 2.25Cr-lMo steel, martensitic Mod.9Cr-lMo, HT9M, and HT9W steels, and dual phase HT9 steel. The majority of the precipitates were found to be M$_{23}$C$_{6}$ carbides. As minor phases, fine needle-like V(C,N), spherical NbC, fine needle-like Cr-rich Cr$_2$N, and Cr-rich M$_{7}$C$_3$were also found. Addition of 2wt.% W in Cr-Mo steels retarded the formation of subgrain and dissolution of Cr$_2$N precipitates. Hardness and ultimate tensile strength increased with increasing Cr content. Though Cr content of HT9W steel was lower than that of HT9 steel, the hardness of HT9W was higher due to the higher W content. W added HT9W steel had the highest ultimate tensile strength above $600^{\circ}C$. But impact toughness of W added steel (HT9W) and high Cr steel (HT9) was low.w.w.

• Steel and Composite Structures
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• 제16권3호
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• pp.325-337
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• 2014

The strength and buckling problem of a five layer sandwich beam under axial compression or bending is presented. Two faces of the beam are thin aluminium sheets and the core is made of aluminium foam. Between the faces and the core there are two thin binding glue layers. In the paper a mathematical model of the field of displacements, which includes a share effect and a bending moment, is presented. The system of partial differential equations of equilibrium for the five layer sandwich beam is derived on the basis of the principle of stationary total potential energy. The equations are analytically solved and the critical load is obtained. For comparison reasons a finite element model of the beam is formulated. For the case of bended beam the static analysis has been performed to obtain the stress distribution across the height of the beam. For the axially compressed beam the buckling analysis was carried out to determine the buckling load and buckling shape. Moreover, experimental investigations are carried out for two beams. The comparison of the results obtained in the analytical and numerical (FEM) analysis is shown in graphs and figures. The main aim of the paper is to present an analytical model of the five layer beam and to compare the results of the theoretical, numerical and experimental analyses.