• Composites Research
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• v.32 no.6
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• pp.335-341
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• 2019

In this study, an acrylic acid (AAc) was grafted on a polypropylene (PP) nonwoven fabric using electron beam irradiation. Electron beam grafting was carried out under various conditions to produce AAc grafted PP (PP-g-AAc) nonwoven fabric having a grafting yield of about 50% at radiation dose of 100 kGy and a monomer concentration of 60%. The physical and chemical properties of PP-g-AAc nonwoven fabric were evaluated by SEM, ATR-FTIR, thermal analysis and tensile strength. The morphology of PP and PP-g-AAc nonwoven fabric confirmed by SEM showed no significant change, and it was judged that AAc was introduced into PP nonwoven fabric from ATR-FTIR. PP-g-AAc nonwoven fabric showed an increase in tensile strength and a decrease in tensile strain compared to PP nonwoven fabric. However, since change of value is not significant, it is considered that there is no significant influence on the physical characterization. Adsorption experiments of PP-g-AAc nonwoven fabric on various ions showed selective adsorption behavior for lead ion. In conclusion, the electron beam radiation-induced PP-g-AAc nonwoven fabric is expected to be applied as an effective adsorbent for the adsorption of lead ions.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.3
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• pp.172-180
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• 1998

It is attempted to verify the Quantitative relationship between fracture mechanical parameters (${\Delta}K$, $K_{max}$) and X-ray parameters (residual stress, half-value breadth) of A12009-15v/o $SiC_w$ composite, and normalized SS41 steel. In this study, fatigue crack propagation test were carried out and X-ray diffraction was applied to fatigue fractured surface in order to investigate the change of residual stress and half-value breadth on fatigue fractured surface. And it is loaded prestrain to each tensile specimen, A12009-15v/o $SiC_w$ composite(0.3, 0.5, 1, 1.5, 2%) and normalized SS41 steel(0.63, 2.25, 7.50, 13.7, 20%), for investigating plastic strain rate using nondestructive measurement method. X-ray diffraction was applied to the prestrained tensile specimens in order to measure the change of residual stress and half-value breadth.

• Journal of the Korea Concrete Institute
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• v.18 no.1 s.91
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• pp.47-56
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• 2006

The repeated loading responses of four shear-critical reinforced concrete beams with two different shear span-to-depth ratios, were studied. One series of beams was reinforced using pairs of bundled stirrups with $90^{\circ}$ standard hooks, haying free end extensions of $6d_b$. The companion beams contained shear reinforcement made with larger diameter headed bars anchored with 50mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that beams containing headed bar stirrups have a superior performance to companion beams containing bundled standard stirrups with improved ductility, larger energy absorption and enhanced post-peak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.

• International Journal of Highway Engineering
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• v.8 no.4 s.30
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• pp.115-124
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• 2006

The objectives of this paper are to develop the structural condition evaluation technique using Falling Weight Deflectometer deflections and propose the structural condition criteria for asphalt pavements. To figure out correlation between surface deflections and critical pavement responses, the synthetic database has been established using the finite element pavement structural analysis program. A regression approach was adopted to develop the pavement response model that can be used to compute the stresses and strains within pavement structure using the FWD deflections. Based on the pavement response model, the procedure for assessing the structural condition of pavement layers was proposed in this study. To validate the condition evaluation procedure for asphalt pavements, the FWD test, dynamic cone penetrometer test, and repeated triaxial compression test were conducted on 11 sections of national highway and 8 sections of local road. Test results indicate that the tensile strain at the bottom of AC layer and AC elastic modulus were good indicators for estimating the stiffness characteristics of AC layer. For subbase layer, the BDI value and compressive strain on top of the subbase layer were appropriate to predict the structural capacity of subbase layer. The BCI value and compressive strain on top of the subgrade were found to be good indicators for evaluating the structural condition of the subgrade. The evaluation criteria for structural condition in asphalt pavements was also proposed in this paper.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.1
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• pp.1-5
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• 2019

In this paper, the experimental study and finite elements analysis were conducted on homogeneous and dissimilar metals single lap-shear bonded joints to investigate the factor that affect the joint failure load. It was found that factors which have the significant effects on the failure load of the joint was stiffness of the adherends. And from experimental results, it can be confirmed that the failure load increases linearly with overlap length increases. And the failure load of dissimilar metal joints is approximately 1KN(10~17%) larger than homogeneous metal joints. In order to confirm this phenomenon, the stress distribution and strain distribution of the specimens were analyzed through the finite element analysis. The difference between homogeneous metals joints and dissimilar metals joints is that stress and strain in adhesive are concentrated at the end of the overlap zone close to aluminium which has lower rigidity than aluminium in case of dissimilar metals joints. From high rigidity of steel, the stress concentration in bonds are decreased and it cause increase of the failure strength at dissimilar metal joints.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.807-818
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• 2004

Experimental tests and theoretical methods of the analysis of the concrete shrinkage behaviors of steel-concrete composite girders are described herein. Steel-concrete composite test specimens were fabricated in the laboratory, and long-term behaviors such as deflections, curvatures, and strains were measured for one year. Test results were compared to the analytical results obtained by using the age-adjusted effective modulus method (AEMM). In addition, composite girders have been analyzed to investigate the effects of several parameters on the concrete shrinkage behaviors. From the long-term test results, it could be used to validate AEMM for the evaluation of the shrinkage behavior of composite girders. Because the shrinkage of the reinforced concrete slab in composite girders may lead to large tensile stresses in the concrete section, the transverse cracking of the slab could occur both in the positive and negative regions. Therefore, if the cracking of concrete would be ignored,it might lead to an overestimation of the stresses of the steel section of composite girders. Based on this research, it is proposed that the effect of transverse concrete cracking on the shrinkage behavior of steel-concrete composite bridges be considered.

• International Journal of Highway Engineering
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• v.10 no.1
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• pp.11-18
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• 2008

The behavior of pavement and waterproofing layer on the steel bridge deck system under traffic loading was analyzed using a finite element method in this paper. In the finite element analysis, the othotropic steel bridge deck is represented by equivalent plate using solid element instead of shell element and the interface is assumed perfect bonding state. The effects of several parameters such as thickness of deck, Young's modulus of deck, thickness of pavement, different braking loading, and temperature on the stresses and strain in the interface are investigated for bridge deck pavement. The shear stress of waterproof layer increases with decrease of bridge deck thickness and stiffness. The change of shear stress is negligible when the bridge deck thictaess is greater than 150mm and stiffness is greater than $2{\times}10^{5}MPa$. As the pavement thickness and temperature decrease, the shear stress in the waterproof layer tends to be increased. The tensile strain at the bottom asphalt layer decreases as the temperature and thickness increase.

• Polymer(Korea)
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• v.27 no.3
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• pp.249-254
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• 2003

The variation of chemical structure and physical properties of crosslinked polyethylene (XLPE) during thermal aging process was investigated. The formation of carbonyl functional group resulting from thermal oxidation reaction of XLPE was monitored using X-ray photoelectron spectroscopy and near infrared (NIR) spectroscopy. It was observed that the intensity of carbonyl peak observed at 1715 nm linearly increased with aging time in NIR spectroscopy. The linear relationship between NIR peak absorbance and aging time confirmed that NIR spectroscopy might be used as a proper tool for monitoring the aging process of polymeric materials. Also the formation of crosslinks during the aging process was monitored using thermal mechanical analysis, stress-strain test, and Shore hardness test. The change in the physical properties, such as the increase in the glass transition temperature from 110 to 132$^{\circ}C$, the decrease in the strain from 265 to 110%, as well as the increase in the shore D hardness from 32 to 50, was observed during the aging process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.727-734
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• 2014

This paper describes multi-scale based ductile fracture simulation using finite element (FE) damage analysis. The maximum and crack initiation loads of cracked components were predicted using proposed virtual testing method. To apply the local approach criteria for ductile fracture, stress-modified fracture strain model was adopted as the damage criteria with modified calibration technique that only requires tensile and fracture toughness test data. Element-size-dependent critical damage model is also introduced to apply the proposed ductile fracture simulation to large-scale components. The results of the simulation were compared with those of the tests on SA333 Gr. 6 full-scale pipes at $288^{\circ}C$, performed by the Battelle Memorial Institute.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.281-290
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• 2000

In this study, we have quantitatively estimated the mechanical properties of structural welding steels widely used in steel structures after correcting the millsheets of the steels using statistical technique. From this result, in present, the mechanical properties of the steels produced in domestics have satisfied the prescribed values in Korean Standards. The mechanical properties of the steels were dependent upon the plate thickness & class of the steels. Also, there have been linear relations between the plate thickness & class of the steels and the mechanical properties of the steels. And the results of this study have shown the similar tendencies with the existing results. Because the upper limit value of yield strength is not prescribed at Korean Standards in present, it is necessary to prescribe the upper limit value of yielding ratio(or yield strength) in order to assure the deformation performance of the steels.