• Structural Engineering and Mechanics
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• 제62권3호
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• pp.373-380
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• 2017

Concrete structures are often subjected to long-term static and short-term dynamic loads. Due to a relatively low tensile strength and energy dissipating characteristics, the impact resistance of concrete is considered poor. This study investigates the feasibility of using polypropylene fibers to improve the impact resistance of reinforced concrete slabs. Fourteen polypropylene fiber reinforced concrete slabs were fabricated and tested using a drop weight test. The effects of slab thickness, fiber volume fractions, and impact energy on the dynamic behaviors were evaluated mainly in terms of impact resistant, crack patterns, and failure modes. The post impact induced strains versus time responses were obtained for all slabs. The results showed that adding the polypropylene fiber at a dosage of 0.90% by volume of concrete leads to significant improvement in the overall structural behavior of the slabs and their resistance to impact loading. Interestingly, the enhancement in the behavior of the slabs using a higher fiber dosage of 1.2% was not as good as achieved with 0.90%.

• Composites Research
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• 제29권4호
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• pp.173-178
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• 2016

Graphene oxide (GO) was concurrently reduced and functionalized using long alkyl chain dodecyl amine (DA). The DA functionalized GO (DA-G) was assumed to disperse homogenously in linear low density polyethylene (LLDPE). Subsequently, DA-G was used to fabricate DA-G/LLDPE composites by melt mixing technique. Fourier transform infrared spectra analysis was performed to ascertain the simultaneous reduction and functionlization of GO. Field emission scanning electron microscopy analysis was performed to ensure the homogenous distribution and dispersion of DA-G in LLDPE matrix. The enhanced storage modulus value of the composites validates the homogenous dispersion of DA-G and its good interfacial interaction with LLDPE matrix. An increased in tensile strength value by ~ 64% also confirms the generation of good interface between the two constituents, through which efficient load transfer is possible. However, no significant improvement in glass transition temperature was observed. This simple technique of fabricating LLDPE composites following industrially viable melt mixing procedure could be realizable to developed mechanically strong graphene based LLDPE composites for future applications.

• 한국강구조학회 논문집
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• 제28권4호
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• pp.281-292
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• 2016

본 연구에서는 HSA800 60mm 강재의 FCAW 용접성, 용접자세 및 이음성능을 확인하기 위해 용접자세 1G와 3G에 대한 FCAW 공시체를 제작하여 10종의 시험을 실시하였다. FCAW 1G 및 3G의 시험결과는 HSA800 강재의 KS 및 강도의 균질성에 대한 기준을 만족하며, 양호한 용접부로 나타났다. 그러나 용접부 평판 인장시험결과 FCAW 3G의 경우 용접기술 및 방법의 개선이 필요하다고 판단된다.

• 한국의류산업학회지
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• 제11권3호
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• pp.496-501
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• 2009

In this study, a kiwifruit-produced protease was used to improve the quality of the wool and silk fabrics. The wool and silk were treated with the actinidin from kiwifruit. Following this protease treatment, changes in the surface of a single yarn of the fabrics were observed via both an optical microscope and a scanning electron microscope (SEM). In order to determine the amount of dye uptake in the fabric, changes in the K/S value of the wool and silk were measured by spectrophotometric analysis. Also, we performed a tensile strength examination to determine variation in their mechanical properties. By increasing the protease treatment time to 48h, the dyeing properties of fabrics were enhanced, and the surfaces of the single yarns of the fabrics became smoother, because of the removal of soil and scale in them. However, no mechanical changes were detected in the fabrics. Thereby, we suggest that the kiwifruit-produced actinidin treatment can improve the quality of the fabrics.

• 한국포장학회지
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• 제5권2호
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• pp.1-8
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• 1999

The state of compatability of poly(vinyl alcohol)(PVA) and methyl cellulose(MC), prepared by an aqueous solution casting, were investigated over the entire compositions by dynamical mechanical analyzer(DMA) and differential scanning calorimetry(DSC). The glass transition temperatures of the blends, estimated by DMA, indicate that the blends of PVA and MC showed a definite degree of partial miscibility by showing two glass transition temperatures below 80 wt % MC contents in the blends and one glass transition temperature above 80 wt % of MC contents. The DSC results show a depression of melting point and crystallization temperature of PVA in the blends containing more than 80 wt % MC. This indicates that a considerable compatibility in the blend above 80 wt % MC contents may be attribute to the presence of interaction of hydroxyl groups of component polymers through hydrogen bonding. The DMA study of the effect of plasticizer on the polymers showed that water was a good plasticizer for PVA and PEG400 for MC. The addition of water and PEG400 in the blends showed a synergic plasticizing effect on these blends, which resulted in the large extent of the improvement of the compatibility. The elongation of PVA, MC and blonds was found to increase with addition of PEG400 in the blends, but the tensile strength to decrease with addition of plasticizer.

• Journal of Welding and Joining
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• 제30권5호
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• pp.34-39
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• 2012

This study was conducted to investigate the microstructure and mechanical properties of friction stir lap joints. Invar 42 and SS 400 were selected as the experimental materials, and friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. The application of friction stir welding to Invar 42 effectively reduced the grain size in the stir zone; the average grain size of Invar 42 was reduced from $11.5{\mu}m$ in the base material to $6.4{\mu}m$ in the stir zone, which resulted in an improvement in the mechanical properties of the stir zone. The joint interface between Invar 42 and SS 400 showed a relatively sound weld without voids and cracks, and the intermetallic compounds with $L1_2$ type in lap jointed interface were partially formed with size of 100 nm. Moreover, the hook in the advancing side of Invar 42 was formed from SS 400, which contributed to maintenance of the tensile strength. The evolution of microstructures and mechanical properties of friction stir lap jointed Invar 42 and SS 400 are also discussed herein.

• 펄프종이기술
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• 제34권3호
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• pp.46-52
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• 2002

To produce the raw material used for printing and writing paper or high quality tissue, MOWs that were consisted of white ledger, colored ledger and old newspaper were bleached with EoP and EoPY(FAS) method, the EoP bleaching process gave the improvement in brightness and a high color removal efficiency. Especially, MOW B(initial brightness: 59.1％ ISO) that contained much old newspaper showed the higher bleaching efficiency than those of MOW A(initial brightness: 68.3%). After EoPY(FAS) bleaching, MOW's brightness was increased from 68.3% ISO to 84.3∼84.0% ISO, and from 59.1% ISO to 78.7∼79.2% ISO, respectively. Also the tensile and burst index of bleached pulps decreased by 10∼30%. The tear index slightly decreased or halted at the same range as unbleached pulps.

• 한국주조공학회지
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• 제30권6호
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• pp.210-216
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• 2010

The aim of this study is to characterize a thixoextruded 7075 Al wrought alloy bar in terms of its isotropic behavior through the optical microscope, mechanical test and electron back scattered diffraction. It is also discussed of the extrudability improvement for 7075 Al wrought alloy by thixoextrusion, with emphasis on controlling thixoextrusion parameters. Hot extrusion shows that the maximum extrusion pressure depends on their characteristics in terms of flow stress and hot workability. In the contrary, thixoextrusion demonstrates that the maximum extrusion pressure is almost uniform regardless of the experimental parameters, such as initial ram speed, die bearing length and thixoextrusion temperature. The hot extruded microstructures become elongated to extrusion direction, while the thixoextruded microstructures are isotropic and homogeneously distributed due to the existence of liquid phase between solid grains during the process. The grain refinement due to dynamic recrystallization during thixoextrusion has been also occurred. Subsequent recrystallization would lead to the strengthening of mechanical properties, as observed in the study. The important point is that the values of tensile, yield strength and elongation of the thixoextruded bar without plastic deformation are similar to those of the hot extruded bar with severe plastic deformation.

• 폴리머
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• 제37권2호
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• pp.232-239
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• 2013

A series of novel imidazole-blocked diisocyanate bioadhesives (IBAs) were synthesized from reaction of toluene 2, 4-diisocyanate (TDI), isophorone diisocyanate (IPDI), hydroxyl-terminated polylactide (HO-PLA-OH), 1,1,1-trimethylolpropane (TMP), and imidazole. Synthesis of IBAs was confirmed by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) revealed that the TDI-based IBA had lower thermal dissociation temperature and a faster deblocking rate than IBA based on IPDI. Hydroxyl-terminated polyurethane (HPU) was introduced to study the adhesive effect of the synthesized IBAs. Improvement on elastic modulus, tensile strength and water resistance of IBA-modified HPU in comparison with neat HPU suggested the good adhesive effect of IBA due to the strong chemical reaction between released NCO groups from IBA and hydroxyl groups from HPU.

• Elastomers and Composites
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• 제43권2호
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• pp.72-81
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• 2008

포장도로의 소성변형을 줄여보고자 개질아스팔트가 나타나고 있다. 본 연구에서는 타이어 고무 등을 이용하여 개질된 아스팔트의 물성을 알아 보았다. 마샬안정도와 인장강도가 각각 98% 및 43% 증가하여 타이어 고무의 개질효과를 알 수 있었다. 점도, 침입 및 열 분석에서 아스팔트의 변형저항성이 향상되었음을 알 수 있었다. IR 및 GPC 실험에서 개질제의 구조가 아스팔트의 구조와 유사할 경우 두 화합물 사이에 화학결합이 발생하여 분자들의 크기가 증가함으로써 개질효과가 커짐을 알 수 있었다.