• 한국세라믹학회지
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• 제56권1호
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• pp.77-83
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• 2019

MgO-C refractories are used in basic furnaces and steel ladles due to their many desirable properties, such as excellent thermal shock resistance via low thermal expansion, and high thermal conductivity. However, the mechanical and thermal properties of the refractory continuously deteriorate by spalling phenomena and pore generation due to the oxidation of graphite, used as a carbon source, indicating that the characteristics and performance of MgO-C refractories need to be improved by using a new material or composition. In this study, the use of a Hertzian indentation test as a method for determining the damage and fracture behavior of an MgO-C refractory is described. The results highlight that Hertzain indentation tests can be one of the important evaluation tools for quasi-plastic damage accumulation of MgO-C refractories during falling process of scrap metal.

• Advances in concrete construction
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• 제11권2호
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• pp.163-171
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• 2021

This paper studies the effect of using multi-scale reinforcement additives on mechanical strengths, damage performance, microstructure, and water absorption of cementitious composites. Small dosages of carbon nanotubes (CNTs) or polypropylene (PP) microfibers; 0.05%, 0.1%, and 0.2% by weight of cement; were added either separately or simultaneously into cement mortar. The experimental results show the ability of these additives to enhance the mechanical behavior of the mortar. The best improvement in compressive and flexural strengths of cement mortar reaches 28% in the case of adding a combination of 0.1% CNTs and 0.2% PP fibers for compression, and a combination of 0.2% CNTs and 0.2% PP fibers for flexure. Adding CNTs does not change the brittle mode of failure of plain mortar whereas the presence of PP fibers changes it into ductile failure and clearly enhances the fracture energy of the specimens. Scanning electron microscopic (SEM) images of the fracture surfaces highlights the role of CNTs in improving the adhesion between the PP fibers and the hydration products and thus enhance the ability of the fibers to mitigate cracks propagation and to enhance the mechanical performance of the mortar.

• 대한기계학회논문집A
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• 제33권2호
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• pp.108-113
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• 2009

The mixing of two dissimilar aluminum alloys in friction stir welding (FSW) was investigated using etching. The results show that the materials from the retreating side mixed into the advancing side in rather narrow and elongated bands whereas the materials from the advancing side mixed into the retreating side in the form of thick bands and lobes. A computational method using smoothed particle hydrodynamics (SPH) is introduced as a way to properly describe the complex mixing behavior in FSW.

• Composites Research
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• 제29권6호
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• pp.395-400
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• 2016

최근에는 이온 전도도의 감소없이 높은 기계적 물성을 가진 구조 복합재를 개발하기 위하여 에폭시 매트릭스를 기반으로 하여 전해질을 함유한 다기능성 구조 전해질에 대한 연구가 활발히 진행 중이다. 구조 전해질의 최적 함량 및 소재 선정에 대해서는 많이 연구되고 있는 반면, 경화 거동에 따른 특성 분석에 관한 연구는 더디게 진행되고 있기 때문에 본 연구에서는 구조 성능과 에너지 저장 성능을 동시에 가진 고체 전해질을 함유한 에폭시 기반의 구조 전해질을 다양한 경화 시간 및 온도에 따라 제조하고 기계적 특성 및 이온 전도도 특성을 측정하였다. 그리하여 전해질의 열 분해가 일어나지 않는 온도 범위 내에서 에폭시가 충분히 경화할 수 있는 경화 조건을 통해 115 MPa와 $6{\times}10^{-5}S/cm$의 값을 동시에 가지는 구조 전해질을 얻었다.

• 한국분말재료학회지
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• 제10권3호
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• pp.172-175
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• 2003

Mechanically-alloyed NiAl powder was sintered by Spark-Plasma Sintering (SPS) process. Densification and behavior mechanical property were determined from the experimental results and analysis ,such as changes in linear shrinkage, shrinkage rate, microstructure, and phase during sintering process, Victors hardness, and transver.ie-rupture-strength (TRS). Above 97% relative density was obtained after sintering at 115$0^{\circ}C$ for 5 min. Crystallite size determined by the Scherrer method was approximately 50 nm. From the X-ray diffraction analysis it was confirmed that the sintered bodies were composed mainly of NiAl phase together with Ni$_3$Al phase. Measured Vickers hardness and TRS value were 555$\pm$10 $H_v$ and 1393$\pm$75 MPa , respectively.

• Advances in materials Research
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• 제6권2호
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• pp.93-128
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• 2017

In this paper, thermal vibration behavior of nanoscale beams made of functionally graded (FG) materials subjected to various types of thermal loading are investigated. A Reddy shear deformation beam theory which captures both the microstructural and shear deformation effects without the need for any shear correction factors is employed. Material properties of FG nanobeam are assumed to be temperature-dependent and vary gradually along the thickness according to the power-law form. The influence of small scale is captured based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived through Hamilton's principle and they are solved applying analytical solution. The comparison of the obtained results is conducted with those of nonlocal Euler-Bernoulli beam theory and it is demonstrated that the proposed modeling predict correctly the vibration responses of FG nanobeams. The effects of nonlocal parameter, material graduation, mode number, slenderness ratio and thermal loading on vibration behavior of the nanobeams are studied in detail.

• 대한기계학회논문집A
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• 제26권4호
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• pp.660-666
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• 2002

It has many variables and factors to design the friction materials for automotive brake pads. The purpose of this study is to develop the proper method for design of low-cost and to know friction characteristics of each raw materials. For the purpose of examining the effect of each major raw materials, we used the Taguchi L9(3$^4$)orthogonal matrix and 1/5 scale dynamo machine for evaluation of the friction characteristics of composite brake pads. By adapting the Taguchi method, it is easy to investigate the influence of each component in complicated composites friction materials. After analyzing the testing results by the Taguchi method, the effect of factors and levels influenced friction behavior was studied.

• Advances in nano research
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• 제10권4호
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• pp.327-337
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• 2021

In this review, composite structures are used for many industries for at least four decades. Polymeric composites are one of the important structures in the aerospace and aviation industry because of their high strength and low weight. In this comprehensive review, mechanical behaviors, physical and mechanical properties of polymeric composites, different types of reinforcements, different methods to fabricate polymeric composites, historical structural composite materials for aviation and aerospace industries, and also different methods for the characterization are reported. How to use various methods of composite preparation using different nanofillers as reinforcements and its effect on the physical properties and mechanical behavior of composites are discussed as well.

• Structural Engineering and Mechanics
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• 제59권5호
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• pp.885-899
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• 2016

The energy-based approach to predict the fatigue crack growth behavior under constant and variable amplitude loading (VAL) of the aluminum alloy 2024 T351 has been investigated and detailed analyses discussed. Firstly, the plastic strain energy was determined per cycle for different block load tests. The relationship between the crack advance and hysteretic energy dissipated per block can be represented by a power law. Then, an analytical model to estimate the lifetime for each spectrum is proposed. The results obtained are compared with the experimentally measured results and the models proposed by Klingbeil's model and Tracey's model. The evolution of the hysteretic energy dissipated per block is shown similar with that observed under constant amplitude loading.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.40.2-40.2
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• 2009

Using the favorable resorption behavior of amorphous Calcium phosphate (CaP) we fabricated a gelatin basednano fibrous mat by electrospinning for using as a fast healing patch for minorbone defects. Bone is predominantly formed by an inorganic phase of nano-crystalline HAp materials and nano fibrous protein material of collagen. The osteoblast cells, which are the bone formation cells and are key to the new bone formation, receive these materials to form new bone. Taking these considerations we make a new nano fibrous mat of amorphous CaP and gelatin, which is derived from collagen itself. A polymer carrier of poly caprolactone(PCL) was used in the system to stabilize the materials in biological condition. The electrospinning conditions were optimized for smooth mat without any droplet formation. The fabricated mat was characterized for its morphologyby SEM. Mechanical properties like tensile strength was evaluated. To investigate the bio-compatibility we performed the MTT assay and investigated its resorption behavior and apatite formation behavior by SBF immersion.