• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.3
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• pp.105-110
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• 2015

The fiber-reinforced endodontic posts were prepared using a photocurable resin and a glass fiber. The mechanical property of the posts increased with increasing density of glass fiber and the micro-pores in the post were removed by a vacuum impregnation process. To improve the interfacial adhesion between glass fiber and polymer, silane coupling agent was used. The surface treatment of glass fiber increased the surface wettability of resing on glass fiber and increased the adhesion property with resin, consequently improved the mechanical property of posts.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.577-582
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• 2016

In this study, a multiscale method for solving a thermoelasticity problem for interphase in the polymeric nanocomposites is developed. Molecular dynamics simulation and finite element analysis were numerically combined to describe the geometrical boundaries and the local mechanical response of the interfacial region where the polymer networks were highly interacted with the nanoparticle surface. Also, the micrmechanical thermoelasticity equations were applied to the obtained equivalent continuum unit to compute the growth of interphase thickness according to the size of nanoparticles, as well as the thermal phase transition behavior at a wide range of temperatures. Accordingly, the equivalent continuum model obtained from the multiscale analysis provides a meaningful description of the thermoelastic behavior of interphase as well as its nanoparticle size effect on thermoelasticity at both below and above the glass transition temperature.

• Advances in materials Research
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• v.8 no.1
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• pp.47-73
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• 2019

Joining of Mg/Ti hybrid structures by welding for automotive and aerospace applications has attracted great attention in recent years due mainly to its potential benefit of energy saving and emission reduction. However, joining them has been hampered with many difficulties due to their physical and metallurgical incompatibilities. Different joining processes have been employed to join Mg/Ti, and in most cases in order to get a metallurgical bonding between them was the use of an intermediate element at the interface or mutual diffusion of alloying elements from the base materials. The formation of a reaction product (in the form of solid solution or intermetallic compound) along the interface between the Mg and Ti is responsible for formation of a metallurgical bond. However, the interfacial bonding achieved and the joints performance depend significantly on the newly formed reaction product(s). Thus, a thorough understanding of the interaction between the selected intermediate elements with the base metals along with the influence of the associated welding parameters are essential. This review is timely as it presents on the current paradigm and progress in welding and joining of Mg/Ti alloys. The factors governing the welding of several important techniques are deliberated along with their joining mechanisms. Some opportunities to improve the welding of Mg/Ti for different welding techniques are also identified.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.381-387
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• 2000

Si3N4/stainless steel 316 joints with Ni buffer layer were fabricated by direct active brazing method (DIB) using Ag-Cu-Ti brazing alloy only and double brazing method (DOB) using Ag-Cu brazing alloy with Si3N4 pretreated with Ag-Cu-Ti brazing alloy. For the joint brazed by DIB method, Ti was segregated at the Si3N4/brazing alloy interface, but was not enough to form a stable joint interface. In addition, large amounts of Ni-Ti inter-metallic compounds were formed in tehbrazing alloy near the joint interface, which could deplete the contents of Ti involved in the interfacial reaction. However, for the joint brazed by DOB method, segregation of Ti at the joint interface were enough to enhance the formation of stable interfacial reaction products such as TiN and Ti-Si-Ni-N-(Cu) multicompounds, which restricted the formation of Ni-Tio inter-metallic compounds in the brazing alloy during brazing with Ni buffer layer. Fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was much improved by using DOB method rather than DIB method. It could be deduced that the differences of fracture strength of the joint with Ni buffer layer depending on brazing process adapted were directly affected by the formation of stable joint interface and the change in microstructure of the brazing alloy near the joint interface. It was found that fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was gradually reduced as the thickness of interface. It was found that fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was gradually reduced as the thickness of Ni buffer layer in the joint was increased from 0.1 mm to 10 mm. It seems to due to the increased residual stress in the joint as the thickness of Ni buffer layer is increased. The maximum fracture strength of Si3N4/S.S 316 joints with Ni buffer layer was 386 MPa, and the fracture of joint was originated at Si3N4/brazing alloy joint interface and propagated into Si3N4 matrix.

• Composites Research
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• v.20 no.3
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• pp.55-62
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• 2007

Interfacial evaluation and durability of Jute and Hemp fibers/polypropylene (PP) composites were investigated. Moisture content of various treated conditions were measured by thermogravimetic analyzer (TGA). After boiling water test, mechanical properties and IFSS between Jute, Hemp fibers and PP matrix decreased. On the other hand, work of adhesion increased due to swelled fibril by water. Surface energies of Jute and Hemp fibers before and after boiling water test were obtained using dynamic contact angle measurement. IFSS was not always consistent with thermodynamic work of adhesion. In boiling water case, since Jute and Hemp fibers could be swelled by water, surface area and moisture infiltration space increased. Environmental effect on microfailure modes of Jute or Hemp fibers and Jute or Hemp fibers/PP composites were obtained by observing via optical microscope and by monitoring acoustic emission (AE) events and their AE parameters. After boiling water test, unlike Hemp fiber, microfailure process of Jute fiber could occur due to low tensile strength by swelled fibril. In addition, AE events occurred more and AE amplitude and energy became lower than those of before boiling water test.

• Composites Research
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• v.18 no.4
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• pp.21-26
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• 2005

Nondestructive damage sensing and load transfer mechanisms of carbon nanotube (CNT) and nanofiber (CNF)/epoxy composites have been investigated by using electro-micromechanical technique. The electrospun PVDF nanofibers were also prepared as a piezoelectric sensor. The electro-micromechanical techniques were applied to evaluate sensing response of carbon nanocomposites by measuring electrical resistance under an uniform cyclic loading. Composites with higher volume content of CNT showed significantly higher tensile properties than neat and low volume$\%$ CNT composites. CNT composites showed humidity sensing within limited temperature range. CNT composites with smaller aspect ratio showed higher apparent modulus due to high volume content in case of shorter aspect ratio. Thermal treated electrospun PVDF nanofiber showed higher mechanical properties than the untreated case due to crystallinity increase, whereas load sensing decreased in heat treated case. Electrospun PVDF nanofiber web also showed sensing effect on humidity and temperature as well as stress transferring. Nanocomposites and electrospun PVDF nanofiber web can be applicable for sensing application.

• Applied Chemistry for Engineering
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• v.16 no.3
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• pp.422-426
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• 2005

Visible-light activated polymer nanocomposites (PNC) were designed to be used for dental restoration. Hybrid-filler composed of barium silicate and nano-sized silica was adopted as a filler system. To improve the interfacial be havior of the resin matrix of bisphenol A glycerolate methacrylate/triethyleneglycol dimethacrylate, the surface of filler was hydrophobically treated with a silane coupling agent. Mechanical properties of PNC were investigated by measuring the abrasion resistance, and it was discovered that PNC showed excellent properties with an increase of nanofiller content. However, the polymerization shrinkage was consistently maintained under 3 vol% and the shrinkage continued even after photo-polymerization. In addition, a slight color difference between PNC specimens was observed with increase of nanofiller content.

• Polymer(Korea)
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• v.35 no.2
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• pp.124-129
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• 2011

Wood plastic composites (WPCs) are attracting a lot of interest recently. In this study, wood flour/polyethylene (PE) composites panels comprised of a coupling agent and nanoclay were prepared by melt-blending followed by compression molding. Five maleic anhydride grafted polyethylene (MAPE) coupling agents were tested, and the best choice and its optimum content were determined. The mechanical properties of the WPCs were measured by UTM, and the thermal properties were measured by TGA, DMA, DSC, and TMA. Adding just a small amount (1 phr) of organoclay made the tensile and flexural strength and the crystallinity of the WPC somewhat increase and the storage modulus and dimensional stability of the WPC largely increase. SEM images showed that the coupling agent drastically improved wood flour/PE interfacial bonding. Selecting the best coupling agent optimized content and adding a small amount of organoclay resulted in a high performance wood flour/PE composite.

• Polymer(Korea)
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• v.32 no.1
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• pp.77-84
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• 2008

The thermal properties, morphology, mechanical properties and gas permeability of the blends of poly (amic acid) (PAA) and poly (o-hydroxyamides) (PHAs) having pendant group was investigated. The 5% weight loss and major weight loss of the b)ends occurred in the ranges of $348{\sim}407^{\circ}C$ and $589{\sim}615^{\circ}C$ upon a heating process. After a thermical annealing, the tensile strength and initial modulus of blends increased $3.7{\sim}52.9%$ and $34.4{\sim}70%$ from the value of pure PAA, respectively. Especially the tensile strength and modulus of the PAA/MP-PHA=9/1 showed the highest values (97.5 MPa and 2.67 GPa, respectively), which were 53 and 70% higher than those of pure PAA. The fine PHA domains were found to be uniformly dispersed. The interfacial adhesion between PAA and PHA was identified to be good. The gas permeabilities of PAA/M-PHA blend increased with M-PHA contents.

• Elastomers and Composites
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• v.51 no.1
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• pp.17-23
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• 2016

In this study, the reclaimed polypropylene (RPP) and waste ground rubber tire (WGRT) were used to simulate the thermoplastic vulcanizate (TPV) for cost reduction and resources recycling. Also, we examined the effects of dicumyl peroxide (DCP) and 2,5-dimethyl-2,5-di-(tert-butylperoxy)-hexane (DTBPH) as peroxide type cross-linking agents to enhance the properties of TPV's. The components of RPP and WGRT were fixed at 30 and 70 wt%, and DCP and DTBPH were added in the concentrations from 0.5 to 1.5 phr, respectively. RPP/WGRT composites with different contents of DCP and DTBPH were prepared by a modular intermeshing co-rotating twin screw extruder. The Young's modulus of composites were decreased with increasing peroxides contents. On the other hand, tensile strength, elongation at break, and impact strength of the composites were increased with peroxide contents. We also confirmed that interfacial adhesion between RPP and WGRT was considerably improved by adding the peroxides. Taken together, DTBPH added RPP/WGRT composites exhibited better mechanical properties rather than those of DCP added composites.