• International Journal of Highway Engineering
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• v.13 no.1
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• pp.239-249
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• 2011

The behavior of the fiber reinforced concrete (FRC) base under environmental loads was analyzed numerically as a fundamental study to develop a high structural and functional performance composite pavement system in which the base was formed using FRC and the asphalt or cement concrete surface was placed on it. A two-dimensional finite element model of the FRC base was developed and the sensitivity study was performed with the variables including slab thickness of base, thermal expansion coefficient, elastic modulus, and tensile and compressive strengths. The crack spacing and crack width were selected as representatives of the base behavior. The effects of the selected variables on the crack spacing and crack width were analyzed and the sensitive variables were determined. The results of this study could be useful to determine the optimal material properties of the FRC base for combining well with the surface materials.

• Polymer(Korea)
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• v.24 no.2
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• pp.141-148
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• 2000

Polycaprolactone (PCL) was blended with corn starch to produce biodegradable compost films and the biodegradability and mechanical properties were investigated. As the compatibilizer for the immiscible PCL/starch blend, 2-hydroxyethylmethacrylate (HEMA)-PCL macromer was grafted onto starch by initially grafting HEMA to starch and then grafting of PCL onto HEMA via ring opening polymerization of $\varepsilon$-caprolactone. When biodegradability of the PCL grafted starch-g-DEMA copolymers was compared with that of starch by the modified Sturm test, graft copolymers degraded at much slower rates due to the presence of the non-degradable HEMA. With the addition of the graft copolymer up to 5 wt% to the blend, the elongation-at-break of the starch/PCL blend increased substantially, while the tensile strength and modulus did not change much. SEM observation of the blend containing 2 wt% copolymer clearly indicated that the interfacial adhesion between the starch and PCL was strengthened by the copolymer.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.154-161
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• 2004

The flat dilatometer test(DMT) is a geotechnical tool to estimate in-situ properties of various types of ground materials. The undrained shear strength is known to be the most reliable and useful parameter obtained by DMT. However, the existing relationships which were established for other local deposits depend on the regional geotechnical characteristics. In addition, the flat dilatometer test results have been interpreted using three intermediate indicesmaterial index($I_p$), horizontal stres index($K_p$), and dilatometer modulus($E_p$) and the undrained shear strength is estimated only by using the horizontal stress index($K_D$). In this paper, an artificial neural network was developed to evaluate the undrained shear strength by DMT and the ANN, based on the $p_0,\;p_1,\;p_2,\;{\sigma}'_v_0$, and porewater pressure. The ANN which adopts the back-propagation algorithm was trained based on the DMT data obtained from Korean soft clay. To investigate the feasibility of ANN model, the prediction results obtained from data which were not used to train the ANN and those obtained from existing relationships were compared.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.129-138
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• 2010

Technical ceramics, due to their unique physical properties, are excellent candidate materials for engineering applications involving extreme thermal and chemical environments. When ceramics are rapidly cooled, they receive thermal shock. The thermal shock parameter is defined as the critical temperature difference. The critical temperature difference for ceramic parts is influenced by its size, the convective heat transfer coefficient, etc. The thermal shock for a component is analyzed by using the transient thermal stress. If the transient thermal stress exceeds the modulus of rupture (MOR), cracking by thermal shock is initiated. The critical temperature difference for water is less than the critical temperature difference for air. The three-way catalyst substrate used in this study has an adequate performance against thermal shock because its radial and axial temperature differences existed below the critical temperature differences.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.2 s.25
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• pp.35-44
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• 2007

Plowable fill is generally a mixture of sand, fly ash, a small amount of cement and water. Sand is the major component of most flowable fill mixes. Marine dredged soil was adopted for flowable fill instead of fly ash. Natural sea sand and in-situ soil were used for comparison. The flow behavior, hardening characteristics, and ultimate strength behavior of flowable fill were investigated. The unconfined compression test necessary to sustain walkability as the fresh flowble fill hardens was determined and the strength at 3-days appeared to correlate well with the water-to-cement ratio. The strength parameters, like cohesion and internal friction angle, was determined along the curing time. The creep test for settlement potential was conducted. Also, potable falling weight deflectometer(PFWD) test has been carried out for elastic modulus of each controlled low strength materials(CLSM). The data presented show that marine dredged soil and in-situ soil can be successfully used in CLSM.

• Journal of the Korean Wood Science and Technology
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• v.42 no.6
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• pp.700-707
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• 2014

The effect of steam and ozone pretreatments on fibrillation efficiency by wet disk-milling was investigated. Hemicellulose (40%) and lignin (42%) of Korean white pine were partially removed by steam and ozone pretreatments, respectively. With increasing wet disk-milling time, the diameter of fibers was significantly decreased and its size distribution became narrow. Especially, the average diameters of lignocellulose nanofibers after steam and ozone pretreatments were 19 nm and 12 nm, respectively. Thus-obtained lignocellulose nanofibers-reinforced polyurethane composite was prepared. Tensile strength and elastic modulus were drastically improved with increasing wet disk-milling time and lignocellulose nanofiber content. Nanocomposite reinforced by lignocellulose nanofibers after two pretreatments showed higher tensile properties, compared to that reinforced by lignocellulose nanofiber without pretreatment, at the similar wet disk-milling time.

• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.71-78
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• 2005

This study focuses on finding out engineering characteristics of asphalt concrete mixtures using mineral fillers with recycled waste lime, which is a by-product in the Soda Ash(Na2CO3) production course. The materials tested in this study were made with 25%, 50%, 75% and 100% of mixing ratio based on the conventional mineral filler ratio to analyze the recycle possibility of the waste lime. The asphalt concrete mixtures with recycled waste lime and hydrated lime, and conventional asphalt concrete mixtures were evaluated through their fundamental engineering properties such as Marshall stability, indirect tensile strength, resilient modulus, permanent deformation characteristics, moisture susceptibility and fatigue resistance. The results indicate that the application of recycled waste lime as mineral filler improves the permanent deformation characteristics, stiffness and fatigue endurance of asphalt concrete mixtures at the wide range of temperatures. It is also found that the mixtures with recycled waste lime show higher resistance against stripping than conventional asphalt concrete mixtures. It is concluded from various test results that the waste lime can be used as mineral fillers and especially can greatly improve resistance to permanent deformation of asphalt concrete mixtures at high temperatures.

• Structural Engineering and Mechanics
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• v.37 no.2
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• pp.149-162
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• 2011

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.765-768
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• 2008

Silica fume is a very important gradient in UHPC(Ultra High Performance Concrete) and its amount is normally over 25% of cement(wt.%). But we surely need to comprehend the influence of the amount of silica fume on the UHPC. In this paper, it was investigated how the amount of silica fume influence on the properties such as fluidity, compressive strength, elastic modulus, and flexural strength. Furthermore, it was examined the internal micro structure on UHPC through the test of SEM and MIP. In results, If we properly use silica fume in UHPC, fluidity and strength of UHPC was increased. It can be ascertained through the test of MIP that silica fume effectively increased density of UHPC by posolanic reaction and acting as filler. Especially, In case of Cement to silica fume ratio$0.1{\sim}0.25%$, we can be concluded that UHPC has similar to mechanical property.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.55-62
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• 2019

Stiffness-gradient stretchable electronic packages of the soft PDMS/hard PDMS/FPCB structure were processed using the polydimethylsiloxane (PDMS) as the base substrate and the more stiff flexible printed circuit board (FPCB) as the island substrate. The elastic characteristics of the stretchable packages were estimated and their long-term reliabilities on stretching cycles and bending cycles were characterized. With 0.28 MPa, 1.74 MPa, and 1.85 GPa as the elastic moduli of the soft PDMS, hard PDMS, and FPCB, respectively, the effective elastic modulus of the soft PDMS/hard PDMS/FPCB package was estimated as 0.6 MPa. The resistance of the stretchable packages varied for 2.8~4.3% with stretching cycles ranging at 0~0.3 strain up to 15,000 cycles and for 0.9~1.5% with 15,000 bending cycles at a bending radius of 25 mm.