• Journal of the Society of Naval Architects of Korea
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• v.29 no.4
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• pp.87-97
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• 1992

Of various design factors affecting icebreaking capability of an icebreaker, the stem angle(i.e., angle between bow stem and ice sheet) is the most important one under continuous icebreaking operation. This study focuses on the relationship between the bow stem angle of an icebreaker and its icebreaking capability. Considering relatively high loading-rate conditions with typical advancing speed of 3 to 4 knots, the material properties and deformation characteristics of sea ice are regarded as entirely elastic and brittle. In this paper the interaction process of icebreaker with level ice is simplified as a beam of finite length supported by Winkler-type elastic foundation simulating water buoyancy. The wedge type ice beam is loaded by the vertical impact forces due to the inclined bow stem of icebreaking vessels. The numerical model provides locations of maximum bending moment where extreme tensile stress arises and also possible fracture occurs. The model can predict a characteristic length of broken ice sheet upon the given environmental and design parameters.

• Composites Research
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• v.36 no.3
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• pp.211-216
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• 2023

When designing ships and aircraft structures, it is important to design them to satisfy weight reduction and strength. Currently, studies related to topology optimization using 3D printed composite materials are being actively conducted to satisfy the weight reduction and strength of the structure. In this study, structural analysis was performed to analyze the applicability of 3D printed composite materials to the flight control surface, one of the parts of an aircraft or unmanned aerial vehicle. The optimal topology shape of the flight control surface for the bending load was analyzed by considering three types (hexagonal, rectangular, triangular) of the topology shape of the flight control surface. In addition, the bending strength of the flight control surface was analyzed when four types of reinforcing materials (carbon fiber, glass fiber, high-strength high-temperature glass fiber, and kevlar) of the 3D printed composite material were applied. As a result of comparing the three-point bending test results with the finite element method results, it was confirmed that the flight control surface with hexagonal topology shape made of carbon fiber and Kevlar had excellent performance. And it is judged that the 3D printed composite can be sufficiently applied to the flight control surface.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.10
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• pp.688-695
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• 2017

Compared to metal, CFRP has excellent mechanical characteristics in terms of intensity, hardness, and heat resistance as well as its light weight that it is used widely in various fields. Therefore, this material has been used recently in the aerospace field. On the other hand, the material has shortcomings in terms of its extreme vulnerability to damage occurring internally from an external impact. This study examined the intensity up to its destruction from repeated use with the internal impact of a CFRP laminated plate that had also been exposed to external impact obtain design data for the external plate of aircraft used in the aerospace field. For the experimental method, regarding the quasi-isotopic type CFRP specimen and orthotropic CFRP specimen that are produced with a different layer structure, steel spheres with a diameter of 5 mm were collided to observe the resulting impact damage. Through a 3-point flexural fatigue experiment, the progress of internal layer separation and impact damage was observed. Measurements of the flexural fatigue strength after the flexural fatigue experiment until internal damage occurs and the surface impacted by the steel spheres revealed the quasi-isotopic layer structure to have a higher intensity for both cases.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.7
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• pp.693-700
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• 2015

To estimate the fatigue crack propagation behavior of compact tension shear (CTS) specimen under mixed-mode loads, crack path prediction theories and Tanaka's equation were applied. The stress intensity factor at a newly created crack tip was calculated using a finite element method via ANSYS, and the crack path and crack increment were then obtained from the crack path prediction theories, Tanaka's equation, and the Paris' equation, which were preprogrammed in Microsoft Excel. A new method called the finite element crack tip updating method (FECTUM) was developed. In this method, the finite element method and Microsoft Excel are used to calculate the stress intensity factors and the crack path, respectively, at the crack tip per each crack increment. The developed FECTUM was applied to simulate the fatigue crack propagation of a single-edge notched bending (SENB) specimen under eccentric three-point bending loads. The results showed that the number of cycles to failure of the specimen obtained experimentally and numerically were in good agreement within an error range of less than 3%.

• The korean journal of orthodontics
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• v.25 no.2 s.49
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• pp.187-200
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• 1995

To estimate the characteristics of Korean Ni-Ti alloy orthodontic wire, this study investigated compositions, tensile properties, bending properties, heat treatment effects, and ion releasing degrees, and compared these characteristics to those of the imported Ni-Ti alloy wire. The results obtained are as follows ; 1. Ti and -Ni elements in ORTHOLLOY were in a range showing superelasticity, and there was a little difference in the Ni and Ti contents of ORTHOLLOY as compared with those of SENTALLOY. 2. The results of the tensile test concerning ORTHOLLOY exhibited a superelastic effect, indicating an area of a definite amount of stress in spite of the changes in the range from $2\%\;to\;8\%$ in the strain rate. 3. ORTHOLLOY presented higher load values than SENTALLOY in the same deflection values when the wire was tested in three-point bending. A load range displaying a superelastic effect was 80-l00g, 140-l80g, and 130-200g respectively, in wire diameters of 0.014', 0.016', and 0.018' 4. By heat treatments at $400^{\circ}C$ and at $500^{\circ}C$, a load range showing the effect of superelasticitly was lessened by the duration of the heat treatment time. The superelastic effect was destroyed as a result of the 10 minutes heat treatment at $600^{\circ}C$. 5. The quantity of the Ni ion released from ORTHOLLOY, tended to be greater than the amount of released Ni ion in SENTALLOY. The Co ion released was very little(<0.01ppm) in SENTALLOY and ORTHOLLOY irrespective of the lapse of time. Released Ni ions on the 1st day were at the maximum, and the releasing rate showed plateaus after three days. 6. The surface morphology of SENTALLOY was relatively regular irrespective of the lapse of rime, and the corrosion tendency was not observed. However, the surface morphology of ORTHOLLOY was rather irregular and shelved fitting corrosion after immersion.

• Composites Research
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• v.31 no.1
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• pp.37-41
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• 2018

The aim of the current work is to characterise a piecewisely-integrated composite bumper beam based on the IIHS bumper crash protocol. IIHS bumper crash FE analysis for an aluminium type bumper beam was carried out to get the information about the dominant loading types at several regions in the bumper beam during crash. In the meantime, robust stacking sequences against tension and compression have been searched for using FE analysis of a coupon type model. After determining most effective stacking sequences for tension and compression, three-point bending simulation was preliminarily carried out to investigate the combination performance of them. Finally, IIHS bumper crash FE analysis for the piecewisely-integrated composite bumper beam, which consisted of the combination of tension effective stacking sequence and compression efficacious stacking sequence, was conducted and the result was compared with other types of composite bumper beams. It was found that the newly suggested piecewisely-integrated composite bumper beam showed superior crashworthy behaviour to those of uni-modal stacking sequence composite bumper beams.

• The korean journal of orthodontics
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• v.36 no.3 s.116
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• pp.188-197
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• 2006

Fiber reinforced composite (FRC) is usually used as a connector joining a few teeth into one unit in orthodontics. However, fracture often occurs during the two to three years of the orthodontic treatment period due to repeated occlusal loading or water sorption in the oral environment. We simulated the repair by overlapping and attaching portions of two FRC strips in the middle and performed a three-point bending test to investigate the changes of the repair strength among the different FRC groups. The specimens were grouped according to the overlapping lengths of the two FRC strips, which were 1, 2, 3 and 4 mm (group E1, E2, E3 and E4, respectively) and the control group consisted of unrepaired, intact FRC strips. Each group consisted of 6 specimens and were cured with a light emitting diode curing unit. Group E4 showed the highest maximum loads of 2.67 N, then the control group (2.39 N), group E3 (2.35 N), E2 (2.10 N), and E1 (1.75 N) in decreasing order. Group E4 also showed the highest stiffness, which was 2.32 N/mm, however, the stiffness of group E3 (2.06N/mm) was higher than that of the control group (1.88 N/mm). According to the visual examination, the specimens tended to be bent rather than being fractured into two pieces with an increased length of overlapping portions. The above results suggest that a minimum overlapping length of 3 mm was necessary to obtain an adequate repair of a 10 mm length of FRC connector. In addition, the critical section adjacent to the joint area, where the thickness decreased abruptly, should be reinforced with flowable resin to minimize the bending tendency.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.13-13
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• 2009

현재 열간단조 금형을 제작함에 있어 육성용접을 실시하는 방법이 금형강 STD61, STD11 등으로 제작하는 방법에 비해 보수나 비용적인 측면에서 이점을 가지고 있기 때문에 점차적으로 증가하고 있는 추세이다. 열간단조 공정에서 금형은 $1000^{\circ}C$이상의 고온재료와 반복접촉하게 된다. 이때 이형제의 사용은 급속냉각 및 급속가열의 열피로를 가속시킨다. 또한, 금형은 반복충격에 의한 기계적 피로를 받게 된다. 이러한 금형의 사용환경을 고려한 FCW는 종래 고가의 $2.8{\sim}3.2{\Phi}$인 외국산 FCW를 사용하였으나 이를 대체한 $3.2{\Phi}$ 태경 FCW가 국내에서 개발되었다. 하지만 개발된 FCW를 사용하여 제작된 금형의 수명이 부족한 현상이 발생하였다. 이에 금형의 수명을 연장시킬 수 있는 내균열성 및 내열충격성을 확보한 태경 FCW의 개발과 개발된 FCW의 성능평가가 요구되었다. 특히 열간단조 금형에 있어서 중요한 내열충격성의 경우 가열과 냉각의 반복 Cycle에 의한 Thermal shock의 평가가 대부분이며 높은 Cycle로 인해 많은 시간이 걸리며, 또한 가열과 냉각을 오갈 수 있는 고가의 시험장치가 요구된다. 그러므로 개발된 FCW 육성용접부의 내균열성 및 내열충격성을 평가할 수 있는 방법에 대한 연구와 특히 내열충격성을 시간이 적게 걸리면서도 경제적으로 평가할 수 있는 방법에 대한 연구가 필요하다. 본 연구의 목적은 열간단조 금형 육성용접부의 내균열성 및 열충격특성을 평가할 수 있는 방법에 대한 검토와 특히 내열충격성에 대해 J.W.Kim등의 시험방법을 참고하여 시간이 적게 걸리면서 저 비용으로 열 충격특성을 평가할 수 있는 시험법을 고안하는 것이다. 이를 위한 방법으로 육성용접부의 내균열성을 평가하기 위한 상온 Bending을 실시하였고, 내열충격성을 평가하기 위한 염욕로를 이용하는 고온 Bending을 고안하여 실시하였다. 상온 Bending, 고온 Bending 모두 3점 굽힘시험을 적용하였다. 고온 Bending의 가열방법으로는 염욕로를 사용하여 시편이 대기중에서 약 $850^{\circ}C$의 온도가 될 수 있도록 하였다. 시편은 각각 열처리를 하여 요구 경도를 확보하였고, 이를 염욕로에서 5분간 가열 및 유지하여 취출 후 굽힘하중을 가하여 변위의 정도로 열충격을 평가하는 방법을 사용하였다. 상온 Bending은 극한변형량과 파단부 극한응력으로, 고온 Bending은 고온 극한변형량으로 평가를 하였고, 외국산 FCW를 사용한 육성용접부를 비교대상으로 하였다. 평가 결과 개발된 국산 $3.2{\Phi}$ 태경 FCW의 성능은 외국산 FCW와 유사하거나 우수한 것으로 평가되었고, 실제 금형을 제작하여 현장에 적용한 결과 금형의 수명이 연장된 것이 나타났다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1191-1198
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• 2015

In this paper, we develop simplified finite element (FE) models for butt-, lap- and T-welded joints by performing numerical and experimental experiments. Three-point bending tests of butt- and lap-welded specimens are performed to obtain the stiffness of the specimens and the strains at points near the welding beads. Similarly the stiffness and strains of T-welded specimen are measured by applying a point load at the end of the specimen. To develop simplified FE models, we consider the shape parameters of width, thickness and the angle of weld elements in the numerical simulations. The shape parameters of the simplified FE models are determined by building linear regression models for the experimental data sets.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.5
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• pp.103-110
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• 2021

The mounting performance of the GFRP(Glass fiber Reinforced Plastic) beam and the mechanical mounting of the steel bracket was studied to be mounted as a GFRP impact beam on the side door of the passenger car. Moreover, an open-hole tensile test was performed to evaluate breakage tendency based on GFRP stacking conditions. Furthermore, the tightening strength of rivets and bolts was compared using the single lap-shear tension test for the GFRP stacking pattern. Additionally, the GFRP beam and bracket mounting features were designed; moreover, the prototype and bracket were assembled. Additionally, the bracket mounting bending test and the door assembly static bending test were performed to verify the stability of the bracket mounting. In the bracket fastening bending test, no breakage occurred in the connection part between the GFRP beam and the bracket, and it showed 67% (24.4 kN) improved performance compared to steel. In the static bending test of the door assembly, the initial average reaction force increased by 25% compared to the steel, and the performance of all FMVSS-214 regulations was satisfied. The replacement of GFRP impact beams resulted in a 30% weight reduction