• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.1-9
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• 2008

Fiber Reinforced Polymer (FRP) composites are used extensively in aerospace, marine, automotive, infrastructure, chemical processing and sporting good applications. A concern with using FRP composites in some engineering structures is their high flammability and poor fire resistance In this research, material properties of FRP composites at increasingly high temperatures was measured and verified. The obtained mechanical properties of FRP composites were performed according to ASTM D3039/D3039M and tested to a wide range of heat conditions with temperatures from Room-temp. to 300 for times up to 30 min. It is found that the mechanical properties of FRP composites dropped with increasing heat or temperature. The reduction to the properties was due mainly to thermal degradation and combustion of the polymer matrix.

• Structural Engineering and Mechanics
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• v.13 no.5
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• pp.557-568
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• 2002

For the evaluation of the capability of a tubular member of an offshore structure to absorb the collision energy, a simple method can be employed for the collision analysis without performing the detailed analysis. The most common simple method is the rigid-plastic method. However, in this method any characteristics for horizontal movement and rotation at the ends of the corresponding tubular member are not included. In a real structural system of an offshore structure, tubular members sustain a certain degree of elastic support from the adjacent structure. End fixity has influences in the behaviors of a tubular member. Three-dimensional FEM analysis can include the effect of end fixity fully, however in viewpoints of the inherent computational complexities of the 3-D approach, this is not the recommendable analysis at the initial design stage. In this paper, influence of end fixity on the behaviors of a tubular member is investigated, through a new approach and other approaches. A new analysis approach that includes the flexibility of the boundary points of the member is developed here. The flexibility at the ends of a tubular element is extracted using the rational reduction of the modeling characteristics. The property reduction is based on the static condensation of the related global stiffness matrix of a model to end nodal points of the tubular element. The load-displacement relation at the collision point of the tubular member with and without the end flexibility is obtained and compared. The new method lies between the rigid-plastic method and the 3-demensional analysis. It is self-evident that the rigid-plastic method gives high strengthening membrane effect of the member during global deformation, resulting in a steeper slope than the present method. On the while, full 3-D analysis gives less strengthening membrane effect on the member, resulting in a slow going load-displacement curve. Comparison of the load-displacement curves by the new approach with those by conventional methods gives the figures of the influence of end fixity on post-yielding behaviors of the relevant tubular member. One of the main contributions of this investigation is the development of an analytical rational procedure to figure out the post-yielding behaviors of a tubular member in offshore structures.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1325-1348
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• 2015

Real-time hybrid testing (RTHT) involves virtual splitting of the structure into two parts: physical substructure that contains the key region of interest which is tested in a laboratory and numerical substructure that contains the remaining part of the structure in the form of a numerical model. This paper numerically assesses four step-by-step integration methods (Central difference method (CDM), Operator splitting method (OSM), Rosenbrock based method (RBM) and CR-integration method (CR)) which are widely used in RTHT. The methods have been assessed in terms of stability and accuracy for various realistic damping ratios of the physical substructure. The stability is assessed in terms of the spectral radii of the amplification matrix while the accuracy in terms of numerical damping and period distortion. In order to evaluate the performance of the methods, five carefully chosen examples have been studied - undamped SDOF, damped SDOF, instantaneous softening, instantaneous hardening and hysteretic system. The performance of the methods is measured in terms of a non-dimensional error index for displacement and velocity. Based on the error indices, it is observed that OSM and RBM are robust and performs fairly well in all the cases. CDM performed well for undamped SDOF system. CR method can be used for the system showing softening behaviour. The error indices indicate that accuracy of OSM is more than other method in case of hysteretic system. The accuracy of the results obtained through time integration methods for different damping ratios of the physical substructure is addressed in the present study. In the presence of a number of integration methods, it is preferable to have criteria for the selection of the time integration scheme. As such criteria are not available presently, this paper attempts to fill this gap by numerically assessing the four commonly used step-by-step methods.

• Polymer(Korea)
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• v.26 no.1
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• pp.1-8
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• 2002

In this study, poly(arylene ether sulfone) (PAES) having thermal stability and excellent mechanical properties was synthesized to be useful for the matrix of anion exchange resin. $1^{\circ}$-Aminated poly(arylene ether sulfone) ($1^{\circ}$-APAES) was prepared by reduction reaction after lithiation of PAES. Then $3^{\circ}$-APAES was Prepared by alkylation of the amino group of $1^{\circ}$-APAES. The structures of PAES and APAESs were confirmed with FT-IR and $^1H-NMR$ spectroscopy. Also, thermal properties of the resins were characterized by DSC and TG analysis. The introduction of amine groups in PAES resulted in the increase of glass transition temperature and decrease of initial thermal degradation temperature. The ion exchange capacities of $1^{\circ}$-APAES and $1^{\circ}$-APAES were 1.19 and 1.45 meq/g, respectively.

• Journal of Adhesion and Interface
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• v.14 no.2
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• pp.75-81
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• 2013

Epoxy matrix based composites were fabricated by adding SiC nano fillers. The interfacial properties of composites were varied with different shapes of SiC nano fillers. To investigate the shape effects on the interfacial properties, beta and whisker type SiC nano fillers were used for this evaluation. The dispersion states of nano SiC-epoxy nanocomposites were evaluated by capacitance measurements. FE-SEM was used to observe the fracture surface of different structures of SiC-epoxy nanocomposites and to investigate for reinforcement effect. Interfacial properties between carbon fiber and SiC-epoxy nanocomposites were also evaluated by ILSS (interlaminar shear strength) and IFSS (interfacial shear strength) tests. The interfacial adhesion of beta type nanocomposites was better than whisker type.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.95-102
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• 2017

The friction pendulum system(FPS) is a kind of seismic isolation devices for isolating structures from an earthquake. To analyze the effect of friction materials used in the friction pendulum system, fragility analysis of LNG tank with seismic isolation system was conducted. In this study, titanium dioxide($TiO_2$) nanoparticles were incorporated into polyvinylidene fluoride(PVDF) matrix to produce friction materials attached to the FPS. The base moment of the concrete outer tank and the acceleration of the structure were evaluated from different mixing ratios of constituents for the friction materials. The seismic fragility curves were developed based on two types of limit state. It is confirmed that evaluation of combined fragility curves with several limit states can be applied to select the optimum friction material satisfying the required performance of the FPS for various infrastructure.

• Polymer(Korea)
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• v.30 no.6
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• pp.545-549
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• 2006

Blends of poly(acrylic acid- co-maleic acid) (PAM) with poly (vinyl alcohol) (PVA) were pre -pared in distilled water PVA/PAM/saponite (PVA/PAM/SPT) nanocomposite films were prepared with various clay contents by using the solution intercalation method. The variations of the dispersion, morphology, and thermo-mechanical properties of the nanocomposites with clay content in the range 0 to 9 wt% were examined. Up to 3 wt% clay loading, the clay particles were homogeneously dispersed in the PVA/PAM blends. However, some agglomerated structures form in the polymer matrix above a clay content of 7 wt%. The thermal stability of the hybrids was increased linearly with increasing the clay loading up to 9 wt%. The maximum strength and modulus were obtained at a clay content of 7 wt%. Thus, the addition of small amounts of clay to the PVA/PAM blends produced PVA/PAM nano-composites with improved the thermo-mechanical properties.

• Journal of Welding and Joining
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• v.29 no.4
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• pp.85-92
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• 2011

Microstructures and tensile properties in arc brazed joints of ferritic stainless steel, 429EM using Cu-8.6%Al insert metal was investigated as function of brazing current. The brazing speed was fixed at 800mm/min and brazing current varied in the range of 80A to 120A. The initial phase of filler metal was Cu single phase. However, the insert metal structures of brazed joints was composed of Cu matrix and intermetallic compound such as ${\gamma}_1(Al_4Cu_9)$, and flower-shape Fe-Cr. The fraction of ${\gamma}_1(Al_4Cu_9)$ phase was similar with 80A and 100A brazing currents while that of brazed with 120A was decreased. On the other hand, the fraction of Fe-Cr phase increased with increasing of the brazing current. A reaction layer at the base metal/insert metal interface was observed and this reaction layer was thickened with increasing of the brazing current. In the brazed joints with the current lower than 100A, crack was grew up along the interface which was perpendicular to the tensile stress, and then, passed through the insert metal in the final stage of fracture. As the brazing current increased to 120A, fracture occurred at the base metal.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.555-559
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• 2016

A biodegradable nanofiber scaffolds using electrospining provide fibrous guidance cues for controlling cell fate that mimic the native extracellular matrix (ECM). It can create a pattern using conventional electrospining method, but has a difficulty to generate one or more pattern structures. Femtosecond(fs) laser ablation has much interested in patterning on biomaterials in order to distinguish the fundamental or systemic interaction between cell and material surface. The ablated materials with a short pulse duration using femtosecond laser that allows for precise removal of materials without transition of the inherent material properties. In this study, linear grooves and circular craters were fabricated on electrospun nanofiber scaffolds (poly-L-lactide(PLLA)) by femtosecond laser patterning processes. As parametric studies, pulse energy and beam spot size were varied to determine the effects of the laser pulse on groove size. We confirmed controlling pulse energy to $5{\mu}J-20{\mu}J$ and variation of lens maginfication of 2X, 5X, 10X, 20X created grooves of width to approximately $5{\mu}m-50{\mu}m$. Our results demonstrate that femtosecond laser processing is an effective means for flexibly structuring the surface of electrospun PLLA nanofibers.

• The Korea Journal of Herbology
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• v.32 no.1
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• pp.83-89
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• 2017

Objectives : The present study was designed to determine the effects of mixture of Achyranthis Japonicae Radix, Scutellariae Radix, and Acanthopanacis Cortex on monosodium iodoacetate (MIA)-induced osteoarthritis in rats. The mixture was composed of Achyranthis Japonicae Radix, Scutellariae Radix, and Acanthopanacis Cortex extracts. Methods : Arthritis was induced by injection of MIA into knee joints of rats. At the end of experiment, gross examination on the articular structures of knee joints were performed. Proteoglycan (PG) contents in articular cartilages were analysed as well. Tumor necrosis $factor-{\alpha}$($TNF-{\alpha}$) and $interleukin-1{\beta}$ ($IL-1{\beta}$) contents in synovial fluids were measured by ELISA method and matrix metalloproteinase 2 (MMP2), MMP9, and tissue inhibitors of metalloproteinase 1 (TIMP1) mRNA were measured by a realtime PCR. Results : The surfaces of the articular cartilage were observed. The severity of osteoarthritis in the treated group were alleviated compared with control group. PG contents in articular cartilages of the treated group were increased compared with control group. $IL-1{\beta}$ contents in synovial fluids of the treated group were significantly decreased compared with control group. MMP2 and MMP9 mRNA contents in articular cartilages were significantly decreased compared with control group and TIMP1 mRNA contents were increased compared with control group. Conclusions : On the basis of these results, we concluded that Achyranthis Japonicae Radix-containing mixture treatment has anti-arthritic effects on the MIA-induced osteoarthritis in rats. And the effects were related with the reduction of $IL-1{\beta}$ in synovial membranes and the consequent reduction of MMP2 and MMP9 expressions.