• Journal of the Korean Wood Science and Technology
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• v.41 no.6
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• pp.535-543
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• 2013

The objective of this study was to analyse the residual stress in Larix kaempferi board during and after kiln-drying. The boards were primarily intended for using as laminar of cross laminated timber (CLT). In this study, the equivalence of moisture content by equalizing treatment was proved and reduction of residual stress by conditioning treatment was quantified. Prong test and slice test were carried out to analyse the residual stress in wood during drying. Transverse casehardening was measured immediately after making prong sample. Residual stress of four parts in wood from surface to center was analyzed quantitatively based on elastic deformation after just cutting slices from board. Tensile stress and compressive stress on the surface of board during drying did not exceed 2.2 MPa when boards were dried by kiln-drying schedule of T10-C4 and T12-D5. Because the tensile strength and compressive strength of transverse direction of Larix kaempferi lumber are 2.65 MPa and 4.60 MPa, application of more severe drying schedule can be recommended. Cup and twist were reduced by about 40% by equalizing and conditioning treatments after drying.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.267-273
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• 2006

We have prepared PP/Ba-ferrite composite fabrics by a melt-blown spinning method and investigated the relationship between the properties of PP/Ba-ferrite composite fabrics and melt-blown processing factors. A PP composite containing Ba-ferrite as a magnetic particulate filler was prepared in the form of pellet from PP resin and Ba-ferrite powder by melt compounding using a single extruder. Screw turning force (rpm), DCD (die-to-collector distance), and Ba-ferrite content were changed. We measured diameters of fiber, mechanical, thermal, and magnetic properties for the composited PP fabrics. The elongation was increased and a fiber diameter and tensile strength were decreased as the spinning distance increased or screw turning force decreased. The crystallinity was increased with increasing spinning distance according to XRD. It was assumed that the orientation of crystalline domain in the neat PP without ferrite was increased by drawing in mechanical direction, however, the orientation in the PP composite was decreased according to XRD analysis. We measured a magnetic property of PP nonwoven fabric containing Ba-ferrite powder. A coercive force, maximum magnetization, and residual magnetization are reduced with the spinning distance. According to the result of TGA measurement, the heat resistance was increased with the Ba-ferrite powder content and with decreasing the spinning distance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.3
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• pp.92-103
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• 2015

Development of new concrete bridge deck system with FRP plank using as a permanent formwork and the main tensile reinforcement recently has been actively conducted. Concurrent use as a reinforcing material and a permanent formwork, it is possible to reduce the construction time and construction costs than the usual concrete slab. In this study, an experiment was carried out for the bond stress between cast-in-place concrete and the type of FRP plank using as a permanent formwork. The interfacial fracture energy that can be one of the most important parameters were evaluated for adhesion performance and bond stress to know the characteristics of the failure mechanism of the adhesion surface. Interfacial fracture energy of normal concrete is 0.24kN/m of GF11 case, in the case of GF21, 0.43kN/m appears, in the case of CF11 and GF31, 0.44kN/m and 0.46kN/m respectively it appeared. In case of RFCON, 0.52kN/m appears from GF12, the CF12 and GF22, 0.51kN/m and 0.36kN/m appeared each case.

• Applied Chemistry for Engineering
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• v.28 no.1
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• pp.42-49
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• 2017

To replace phthalate plasticizer for PVC, acetylated monoglyceride (AMG) plasticizers were prepared from plant oil and their plasticization effects were also investigated. Transesterification of coconut oil by glycerol followed by acetylation with acetic anhydride gave AMG-CoCo (Coco : Coconut Oil). In addition, AMG-GMO (GMO : Glycerol monooleate) and AMG-GMO-Epoxy were synthesized by acetylation and epoxidation with glycerol monooleate. It was found that the thermal stability of AMG plasticizers increased in the following order: AMG-GMO-Epoxy > AMG-GMO > AMG-CoCo and all three plasticizers were thermally more stable than those of common petroleum-based plasticizer DOP (Dioctyl phthalate). The tensile strain values of the PVC containing AMG compounds were ca. 770~810%, while tensile strength values were ca. 19~22 MPa, which were higher than those of PVC containing DOP. DMA (Dynamic Mechanical Analysis) results showed that the miscibility of AMG-GMO-Epoxy in PVC was excellent and the $T_g$ of PVC containing AMG-GMO-Epoxy at 50 phr decreased down to $24^{\circ}C$. Finally, the leaching experiment result showed that the weight loss values of PVC containing AMG-GMO and AMG-GMO-Epoxy at 50 phr were as low as 2 and 1%, respectively, indicating that they have high water migration resistance. The above findings suggested that AMG-GMO-Epoxy could be one of plant oil-based PVC plasticizers to replace DOP.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.12
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• pp.733-740
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• 2017

'The facilities standards of water supply' issued by the Ministry of Environment in 2004 indicates that expansion joints cannot be used in welding water supply steel pipes. However, their reason is not clear and it is difficult to confirm the stability of the steel pipe for a water supply pipeline. The purpose of this study is to determine whether or not an expansion joint is necessary to improve the stability of water supply in steel pipe through a displacement analysis of the pipework. The test results are as follows. Firstly, it was found that expansion and contraction of the water supply steel pipe (D 2,400 mm) occur repeatedly in 4 cycles per year, and the maximum expansion and contraction amount of the pipe is 13.03 mm in 1.24 km pipelines. Secondly, the thermal stress caused by expansion and contraction of the steel pipe is $13.7{\sim}36.1kgf/cm^2$ according to the burial depth (0~4 m). The main comparison factors to determine the stability of the steel pipe (STWW 400) were the allowable tensile strength and the fatigue limit, which were computed to be $4,100kgf/cm^2$ and $1,840kgf/cm^2$, respectively. Finally, the thermal stress of the steel pipe is very small compared to the allowable tensile stress and fatigue stress. Therefore, thermal stress does not affect the stability of the steel pipe, although the expansion and contraction of the steel pipe occurs by temperature changes. In conclusion, the study demonstrated that expansion joints are not required in water supply steel pipelines.

• Polymer(Korea)
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• v.25 no.4
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• pp.486-495
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• 2001

Degradable poly(butylene succinate) (PBS)/poly(TEX>${\varepsilon}$-caprolactone) (PCL) copolyesters were prepared by using transesterification between poly(butylene succinate) and poly(TEX>${\varepsilon}$-caprolactone). The thermal and mechanical properties of copolyesters were investigated using differential scanning calorimetry and tensile testing. Interchange reaction between PBS and PCL molecules could be identified from proton NMR spectra. The reduced viscosity of the PBS/PCL copolyesters increased with reaction time except for a series of PBS/PCL (50/50 wt%) copolyesters. For all the compositions, the melting point and crystallization temperature of high-$T_m$ component (PBS) decreased as reaction time increased. From the results of tensile testing, it was found that stress and strain at break of the PBS/PCL copolymers containing less than 40 wt% PCL improved as compared to those of pure PBS, but at 50 wt% PCL stress at break of PBS/PCL copolymers was lowered due to decrease of crystallinity. On the other hand, Young's moduli of all the copolyesters decreased with both reaction time and PCL content.

• Elastomers and Composites
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• v.46 no.3
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• pp.211-217
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• 2011

Wood Polymer Composite (WPC) has attracted a great deal of attention in environmental industries due to renewable resources, processability, excellent physical properties and logging regulations for application to housing units and engineering construction materials. In this study, commercial WPCs were prepared by using a modular intermeshing co-rotating twin screw extruder. The effect of three main factors such as wood flour contents, coupling agent concentrations and pre-treatment of wood flour on the properties of WPCs was extensively investigated. It was found that tensile strength and thermal stability were decreased with increasing wood flour contents whereas the water absorption was increased. Addition of maleic anhydride grafted polypropylene (PP-g-MA) into WPC exhibited better physical properties. On the contrary, the water absorption was slightly decreased with PP-g-MA. Finally the sample, which was prepared with pre-treated wood flour, represented the highest tensile strength. However, the water absorption of the sample was increased due to the transition of crystalline structure of cellulose.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.313-316
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• 2008

Corrosion of steel in the reinforced concrete structures is one of the main reason of degradation. It causes that lifetime of structures is shortened and maintenance cost is increased. And it also causes degradation of structures like bridges which are under repeated load. So, many research have been performed about FRP rebar. But there are few research about FRP rebar under fatigue. This study is to examine flexural characteristic of concrete beam reinforced with FRP(CFRP, GFRP) rebar under static and fatigue for considering the application. The specimens that used in this study are designed by ACI 440.1R-06 and reinforced with CFRP(CR) or GFRP(GR) overly. In the result of static bending test, all specimens were failed at compression phase. In fatigue test, the fatigue stress level was 60%, 70% or 80% of the static bending strength. Most of the specimens seemed to be compressive failure, but CR-60 and CR-70 specimens were failed with rupturing of tension bar.

• Elastomers and Composites
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• v.41 no.2
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• pp.97-107
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• 2006

The recycled polyethylene composites with various ratio of ground waste tire powder were manufactured by using a fully intermeshing co-rotating twin screw extruder for the reuse of waste tire scrap. In this investigation, the ground waste tire powders (GWTP) were blended with virgin HDPE and recycled polyethylene in the weight ratio of 0 to 50 wt.%. Mechanical properties such as tensile strength, elongation at break and impact strength were measured by using ASTM standard. The experimental results for the various composite showed that the tensile strength of composites decreased with increasing GWTP ratio, while elongation at break increased with the amounts of GWTP. On the other hand, the impact strength for the three kinds of composites showed maximum at the 30 wt.% of GWTP and then decreased. Morphology of the fracture surface tends to be rough with increasing waste tire powder content. Rheological properties were investigated by measuring the shear viscosity against shear rates and softening temperatures. They showed that melt viscosity of rubber composites in this study subsequently increased with increasing GWTP content as a result of increase of flow resistance against external stress and followed a Power-law behavior.

• Membrane Journal
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• v.15 no.3
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• pp.247-254
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• 2005

Chitosan film has potential applications in agriculture, food, and pharmacy. However, films made only from chitosan lack gas barrier and have poor mechanical properties. For enhanced gas barrier and mechanical properties, chitosan/clay nanocomposites have been prepared with montmorillonite (MMT) which is a layered structure of clays and chitosan. The cationic biopolymer, chitosan is intercalated into $Na^+-montmorillonite$ through cationic exchange and hydrogen bonding process. Diluted acetic acid is used as solvent f3r dissolving and dispersing chitosan. Chitosan was intercalated or exfoliated in MMT and it was confirmed by X-ray diffraction method. D-spacing of the characteristic peak from MMT plate in chitosan/clay nanocomposites was moved and diminished. The thermal stability and the mechanical properties of the nanocomposites are measured by TGA and Universal Testing Machine. Gas permeability through the chitosan/clay nanocomposites films decreased due to increased tortuosity made by intercalation of clay in chitosan.