• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.160-162
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• 2017

When rubber elastomer has contact with fuel, since the component and additive having low molecular weight can flow out, the physical properties of both elastomer and fuel could be hindered. In order to predict the life of the rubber elastomer, this study is to determine the change of weight, thickness, hardness, strain, and compression set as mechanical properties of the sealant rubber O-ring, which was dependent on volume, temperature, and storage time of the contacted fuel. We also determined purity of fuel via GC analysis and measured gross heat of combution. The results could be used as a reference to evaluate the life of the rubber elastomer.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.24-24
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• 2022

토양 수분은 육상 생태계를 지배하는 핵심 변수로 널리 간주되어 왔다. 따라서 토양 수분을 모니터링하고 추정하는 것은 수문, 농업, 생화학적, 및 기후 역학을 평가하는 데 필수적이다. 그러나 최대 토양 접촉을 요구하는 기존의 토양 수분 모니터링 방법은, 토양 교란을 최소화하여 토양의 고유 특성을 보전하지 못하는 한계가 있다. 이 문제를 극복하기 위해 본 연구에서는 비접촉 초음파 시스템을 이용하여 토양 수분을 평가 방법을 개발하였다. 이 시스템은 공기-토양 조인트 절반 공간에서 누설 레일리파(Rayleigh wave)를 측정하도록 설계되었다. 토양 수분의 변화에 대한 누설 레일리파의 측정은 통제된 실험 설계에서 모래, 실트, 점토와 같은 세 가지 토양 유형에서 평가하였다. 본 연구 결과에서 세 가지 토양 사례 모두, 누설 레일리파의 에너지와 토양 수분 사이에 밀접한 관계가 있음을 보였다. 그러나 모래에서 얻은 동적 매개변수의 특성은 실트 및 점토의 특성과 다른 형태를 보였다. 이러한 결과는 미세한 토양 입자와 대조적으로 굵은 토양 입자는 증발 과정에서 감소된 토양 강도로 설명될 수 있다. 관측된 누설 레일리파에서 얻은 동적 매개변수를 기반으로 토양 수분을 평가하기 위해 랜덤 포레스트 모형을 이용하였다. 예측된 토양 수분의 정확도는 모든 데이터 및 토양 유형에 관계없이 높은 정확도를 보였다(R² ≥ 0.98, RMSE ≤ 0.0089 m³ m^-3). 즉, 본 연구에서는 레일리파가 토양 교란 없이 토양 수분 변화를 지속적으로 평가할 수 있는 큰 잠재력을 가지고 있음을 보여주었다.

• The Journal of Korean society of community based occupational therapy
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• v.6 no.1
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• pp.1-11
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• 2016

Purpose : By confirming the relationship of the Social Network Service(SNS) strength and social participation, it tries to present the basic data of the social participation of the university students. Method : Students that department of Occupational Therapy in K University was done to target 136 people. SNS strength was measured to be stored in the mobile phone SNS friends and KakaoTalk average call times. measurement tool of social participation was used Maastricht Social Participation Profile(MSPP) as modifed by Godelief et al.(2009). MSPP is composed of formal social participation(undertaking) and informal social participation(contact with friends and acquaintances and contact with family) item. Results : The study shows a significant correlation between the number of SNS friends and Undertaking item and between KakaoTalk average call times and Contact with friends and acquaintances item(${\alpha}=0.05$). Conclusion : College student SNS strength and social participation showed a correlation. Therefore, The higher the SNS strength and social participation is determined to have a positive impact on the daily life of college students.

• Journal of the Korea Convergence Society
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• v.11 no.11
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• pp.233-237
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• 2020

In this study, the thermal analysis on the brake disc of electric kickboard was analyzed. The different heat is transmitted depending on the pad contact surface of brake disc. The trend that the temperature decreases at the part away from the contact surface was almost constant. And model A showed a slightly lower temperature distribution than model B. Model A has a maximum equivalent stress of 7% higher than model B. By being applied with the higher heat transfer above the contact surface, it is thought that model B has a greater strength than model A if the design takes into account the corner of the brake disc. If this study result is utilized to the design of electric kickboard, the design of brake disc with better strength is considered to be established. The durability of brake against the heat can be evaluated by applying this study result to the brake disc of electric kickboard. And it is seen that the result can be the design of brake with strength and the aesthetic convergence.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.223-232
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• 2003

In this study, a constitutive model called the disturbed state concept (DSC) was modified to be applied to the interface shear stress-displacement relationship between geosynthetics. The DSC model is comprised of two reference states, namely the relative intact (RI) and the fully adjusted (FA) state, and one function, namely the disturbance function. This model is a unified approach and can allow for various models as an RI state such as elastic-perfectly plastic model, hierarchical model, and so on. In addition, by using this model, the elastic and plastic displacements can be considered simultaneously. Comparisons between the measured data and predicted results through the parameters determined from four sets of large direct shear tests showed good agreements with each other, especially for the smooth geomembrane-involved interface. Although there are slight differences at peak shear strength for textured geomembrane-involved interface, this model can still be useful to predict the position of displacement at peak strength and the large displacement (or residual) shear strength.

• Polymer(Korea)
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• v.26 no.2
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• pp.279-286
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• 2002

For surface modification of polymers with hydrophilic functional groups, acrylic acid was grafted and immobilized on the surface of polyethylene(PE) by cold-plasma treatment using Ar gas. The modifications were identified by analysis of ATR-IR spectrum and by the measurement of contact angles. Compared to virgin PE significant decreases in contact angle were observed for both the grafted PE and the immobilized PE. The decreases of contact angle were in the range of 47~$53^{\circ}$ for grafted PE and 23~$26^{\circ}$ for immobilized PE. The degree of hydrophilicity depended strongly on the plasma-treating time and discharge power. For the case of grafting it has show that the longer plasma-treating time, the higher hydrophilic character. For the case of immobilization, whereas, higher discharge power and longer exposure to plasma have shown the detrimental effect for the preparation of hydrophilic PE surface due to the decrease of carboxyl group by ablation effect. The decrease in adhesion strength of immobilized PE. compared to grafted PE, was also attributed to the ablation of carboxyl group.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.78-85
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• 2020

The scaffolding system, which is a construction workbench of the cargo containment for a membrane LNG carrier, is a large truss structure composed of various members. To shorten the installation period and process of the scaffolding system, it is effective to enlarge the mounting unit from the existing two stages to eight stages. Owing to the increase in lifting load according to the large size of the module, the stresses around the pin and hole will be increased significantly. In this study, a tensile strength test and contact stress analysis were performed to confirm the structural safety. The relatively large hole deformation was observed visually near the average load generated in the vertical pipe at the top through tensile strength tests. A contact stress calculation confirmed the stress distribution around the hole. The contact problem was dealt with in terms of the Herzian contact stress. The possibility of 8-stage loading was examined by comparing the yield strength and contact stresses of failure critical locations. As a result, the 8-stage loading method of the existing scaffolding material was inadequate, and a new loading method with proper safety is proposed.

• Journal of Adhesion and Interface
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• v.23 no.4
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• pp.122-129
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• 2022

In this study, the hydrophilicity of the metal fiber is improved by introducing an oxygen-containing functional group to the fiber surface after treatment of the metal fiber using the oxygen plasma treatment time as an experimental variable. For the surface modification of metal fibers, changes in surface properties before and after plasma treatment were observed using SEM and x-ray photoelectron spectroscopy (XPS). In order to observe the effect of the plasma treatment time on the surface of the metal fiber, the change in contact angle of the metal fiber with respect to a polar solvent and a non-polar solvent was measured. After calculating the change in surface free energy using the measured contact angle, the contact angle and the surface free energy for metal fibers before and after oxygen plasma treatment were compared, and the correlation with the adhesion work was also considered. The microdroplet specimens were prepared to investigate the effect of surface changes of these metal fibers on the improvement of shear strength at the interface when combined with other materials and the interfacial shear strength was measured, and the correlation with the adhesion work was also identified. Therefore, the oxygen plasma treatment of the metal fiber results in an increase in the physical surface area on the fiber surface and a change in contact angle and surface energy according to the introduction of the oxygen-containing functional group on the surface. This surface hydrophilization resulted in improving the interfacial shear strength with the polymer resin.

• Journal of the Korean GEO-environmental Society
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• v.8 no.1
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• pp.49-55
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• 2007

In order to utilize treads of waste tire as reinforcement material it is necessary to know the interface friction angle between tread surfaces and soil and tensile strength of connection joint of tire treads. In this research large direct shear tests were performed to get the interface friction angle between the inner and outer surfaces of treads and soil for different degree of compaction. From the large direct shear tests, the ratio of interface friction angle to the shear friction angle of sand, ${\delta}/{\phi}$, were 1.06 in outside surface of tire tread and 0.93 in inside surface of tire tread. For weathered granite soil the ratio of interface friction angle was 0.98 and 0.92 for outside and inside of tread, respectively. Also tensile tests were performed using universal testing machine for the connection joint of treads and Tirecell units using bolts. The tensile strength of connection joint increased with the number of bolts and with the sizes of washers. Connection by polypropylene ropes showed lower strength than those of bolts.

• Journal of the Korean GEO-environmental Society
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• v.14 no.12
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• pp.23-30
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• 2013

Bearing capacity of pile is governed by only skin friction in frozen ground condition, while it is generally governed both by skin friction and end bearing capacity in typically unfrozen ground condition. Skin friction force, which arises from the interaction between pile and frozen soils, is defined as adfreeze bond strength, and adfreeze bond strength is one of the most important key parameters for design of pile in frozen soils. Many studies have been carried out in order to analyze adfreeze bond strength characteristics over the last fifty years. However, many studies for adfreeze bond strength have been conducted with limited circumstances, since adfreeze bond strength is sensitively affected by various influence factors such as intrinsic material properties, pile surface roughness, and externally imposed testing conditions. In this study, direct shear test is carried out inside of large-scaled freezing chamber in order to analyze the adfreeze bond strength characteristics with varying freezing temperature and normal stress. Also, the relationship between adfreeze bond strength and shear strength of the frozen soil obtained from previous study was analyzed. The coefficient of adfreeze bond strength was evaluated in order to predict adfreeze bond strength based on shear strength, and coefficients suggested from this and previous studies were compared.