• 한국철도학회:학술대회논문집
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• 한국철도학회 1999년도 추계학술대회 논문집
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• pp.437-446
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• 1999

The structural behavior of the composite material light rail vehicle body are investigated. Composite material is very useful for light rail vehicle structure due to its high specific strength and lightweight characteristics. The main carbody is made of aluminum alloy. The side wall and roof with composite panels can reduce total vehicle weight about 2000kg. In addition, with the lower density of the foam, enhances lightness in the panel and to save the operation expenses. The finite element analysis code, ANSYS is used to evaluate the stability of the body structure under the various load conditions.

• 한국자동차공학회논문집
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• 제6권1호
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• pp.143-150
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• 1998

The evaluation of joint fatigue strength of light weight materials for electrical vehicle body has been performed through single lap joint tests with the design parameters such as joint style, adherend, bonding overlap length and bonding thickness. Fatigue strength was evaluated through 5-Hz, tension-tension, load controlled test with the stress ratio zero value. It is experimentally observed that fatigue strength of joint increases for the increase of overlap length. The combinations of Al-Al and Al-FRP adherends show that fatigue strength of joint is hardly changed for the increase of bonding thickness, but FRP-FRP adherend specimen shows that fatigue strength of joint increases after decreases for the increase of bonding thickness. Al-Al adherend specimen has much higher fatigue length than Al-FRP and FRP-FRP adherend specimens. Riveting at adgesive bonded joint gives little effect on fatigue strength.

• 한국지반공학회논문집
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• 제18권4호
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• pp.75-83
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• 2002

본 연구에서는 준설토, EPS 그리고 고화재를 혼합한 경량혼합토의 역학적 특성을 일축 및 삼축압축시험을 통하여 고찰하였다. 역학적 특성은 다양한 준설토의 초기 함수비, EPS 함유율, 시멘트 함유율 그리고 양생압력에 대한 경량혼합토의 압축강도에 대하여 연구하였다. 삼축압축상태에서 EPS를 함유한 경량혼합토의 압축강도는 유효구속압에 의존 하지 않는 것으로 나타났다. EPS 함유율이 감소할수록($A_E$<2%) 그리고 시멘트 함유율이 증가할수록($A_c$>2%) 삼축압축강도-변형 거동특성은 극한 압축강도를 지나 급격한 압축강도의 감소를 보이는 시멘트 혼합토의 압축강도-변형 거동특성과 유사한 것으로 나타났다. 200kpa 이상의 압축강도를 요구하는 개량지반에 본 경량혼합토를 적용하는 경우에서 적절한 준설토의 초기함수비, EPS 함유율은 각각 약 165%~175%이상 그리고 3%~4%이상으로 제시할 수가 있었다. 삼축 및 일축압축상태에서 극한 압축강도는 시멘트 함유율이 2%이상에서 거의 증가하지 않음으로서 한계 시멘트 함유율은 2%로 제시할 수가 있었다.

• 대한치과보철학회지
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• 제44권3호
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• pp.333-342
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• 2006

Statement of problem. Although many studies have been carried out to investigate the correlation between the degree of conversion and the flexural strength of composite resins, there is minimal information in the literature attempting to compare degree of conversion, flexural strength and their correlation between restorative composite resins and flowable composite resins. Purpose. The purposes of this study were to measure the degree of conversion and flexural strength of composite resins with different rheological behavior and to correlate the two properties. Materials and methods. Four restorative (Vit-1-escence, Z-250, Tetric ceram, Esthet-X) and four flowable (Aeliteflo, Admiraflow, Permaflo, Revolution) light-curing composite resins were investigated. The degree of conversion(DC) was analyzed with Fourier transfer infra-red spectroscopy(FTIR) spectrum by a potassium bromide(KBr) pellet transmission method. The spectrum of the unpolymerized specimen had been measured before the specimen was irradiated for 60s with a visible light curing unit. The Poiymerized specimen was scanned for its in spectrum. The flexural strength(FS) was measured with 3-point bending test according to ISO 4049 after storage in water at $37^{\circ}C$ for 24 hours. The data were statistically analyzed by an independent sample t-test and one-way ANOVA at the significance level of 0.05. The dependence of flexural strength on the degree of conversion was also analyzed by regression analysis. Results. Mean DC and FS values ranged from 43% to 61% and from 84.7MPa to 156.7MPa respectively. DC values of the flowable composite resins were significantly higher than those of restorative composite resins (P < 0.05). The FS values of restorative composite resins were greater than those of flowable composite resins. No statistically significant correlation was observed between the DC and the FS tested in any of the composites. The dependence of FS on DC in restorative or flowable composite resins was not significant. Conclusion. It can be concluded that radical polymerization of the organic matrix is not a major factor in determining flexural strength of the commercially available composite resins.

• The Journal of Advanced Prosthodontics
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• 제5권2호
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• pp.104-109
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• 2013

PURPOSE. Among the surface treatment methods suggested to enhance the adhesion of resin cement to fiberreinforced composite posts, conflicting results have been obtained with silanization. In this study, the effects of silanization, heat activation after silanization, on the bond strength between fiber-reinforced composite post and resin cement were determined. MATERIALS AND METHODS. Six groups (n=7) were established to evaluate two types of fiber post (FRC Postec Plus, D.T. Light Post) and three surface treatments (no treatment; air drying; drying at $38^{\circ}C$). Every specimen were bonded with dual-curing resin cement (Variolink N) and stored in distilled water for 24 hours at $37^{\circ}C$. Shear-bond strength (MPa) between the fiber post and the resin cement were measured using universal testing device. The data were analyzed with 1-way ANOVA and by multiple comparisons according to Tukey's HSD (${\alpha}$=0.05). The effect of surface treatment, fiber post type, and the interactions between these two factors were analyzed using 2-way ANOVA and independent sample T-tests. RESULTS. Silanization of the FRC Postec Plus significantly increased bond strength compared with the respective non-treated control, whereas no effect was determined for the D.T. Light Post. Heat drying the silane coupling agent on to the fiberreinforced post did not significantly improve bond strength compared to air-syringe drying. CONCLUSION. The bond strength between the fiber-reinforced post and the resin cement was significantly increased with silanization in regards to the FRC Postec Plus post. Bond strength was not significantly improved by heat activation of the silane coupling agent.

• Restorative Dentistry and Endodontics
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• 제22권1호
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• pp.267-277
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• 1997

The purpose of this study was to evaluate the shear bond strength of light-cured glass ionomer cements to dentin surface according to curing time induced by argon laser. In this study, 160 extracted human molars with sound crown were used. The dentin surface of these teeth were exposed with high speed diamond bur under water spray and polished with 120, 320, 400, 800, 1200 grits sand paper. 160 extracted human molars were randomly assigned into four groups (control, experimental 1, 2 & 3) with 40 teeth each. Control group used a visible light curing unit, XL 1000(3M Co., U.S.A) and experimental groups used argon laser($SPECTRUM^{TM}$). And then each group subdivided into two groups (A, B) according to filling materials. Subdivided A group used Fuji II LC(GC Co., Japan), B group used Vitremer(3M Co., U.S.A). The curing units and curing time of each group were as follows : Control group : visible light, 40 seconds Experimental group 1 Experimental group 2 Experimental group 3 : argon laser, 10 seconds : argon laser, 20 seconds : argon laser, 30 seconds The glass ionomer cements were bonded to dentin surface of each specimen. The specimens were stored in 100% relative humidity at 37"c for 7days. And then, the shear bond strength were measured by universal testing machine(Shimatzu Co. Japan) at crosshead speed of 5mm/min and 100kg in full scale and analyzed statistically. The following results were obtained : 1. Experimental group 2-A showed the highest shear bond strength with $9.87{\pm}1.24$ kgf and control group B showed the lowest shear bond strength with $4.08{\pm}0.78$ kgf(P<0.01). 2. The Fuji II LC showed higher shear bond strength with $9.49{\pm}1.24$ kgf than that of the Vitremer with $4.23{\pm}1.24$ kgf. There was significant difference between Fuji II LC and Vitremer(p<0.01). 3. There was no significant differences among experimental groups according to curing time induced by argon laser. 4. There was no significant differences between control group and experimental groups according to curing units.

• Restorative Dentistry and Endodontics
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• 제23권1호
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• pp.68-93
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• 1998

The physical properties of polymer are greatly influenced by the extent to which a resin cures. The presence of un reacted monomer can, have a plasticizing effect on the polymer, thereby altering the physical and mechanical properties of dentin bonding agent (DBA). If the DBA does not polymerize sufficiently, it will leave a weak bonding layer and lead to lower bond strength. The purpose of this study was to evaluate the shear bond strengths(SBS) and the degree of conversion (DC) of 4 commercialy avilable dentin bonding systems which are composed of 2 multi-bottle systems [Scotchbond Multi-Purpose (SMP), AeliteBond(AB)] and 2 onebottle systems [SingleBond(SB), One-Step(OS)]. For shear bond strength measurement, labial surfaces of freshly extracted bovine incisors were ground with # 600 grit SiC paper to expose dentin. Four different groups of samples were formed, with 10 samples. being made for each of the 4 commercial DBA in each group according to the curing sequences of DBA and overlayer thickness of composites: Group I (standard cure and 1mm thick composites) : The DBA was light cured and the composites of 1mm thickness was applied ; Group II (standard cure and 2mm thick composites) : The DBA was light cured and the composites of 2mm thickness was applied; Group III (simultaneous cure and 1mm thick composites) : The DBA was not light-cured and simultaneously cured with composites of 1mm thickness; Group N (simultaneous cure and 2mm thick composites) : The DBA was. not light-cured and simultaneously cured with composites of 2mm thickness. The SBS was measured immediately after the composites was bonded to the bovine dentin using an Instron machine. The DC of the DBA was examined in a thin film under simulated conditions of the experimental groups according to the curing sequences and overlayer thickness of composites in the SBS test. using a Fourier transform Infrared(FTIR) spectrometer. The following results were obtained from SBS tests and DC measurements 1. In SBS tests, the multi-bottle DBA(SMP, AB) had a generally higher bond strength values than the one bottle DBA(SB, OS). In DC measurements, the one bottle DBA(SB, OS) had a significantly higher DC than the multi-bottle DBA(SMP, AB). 2. In all DBAs except OS, there was no significant difference between the bond strength of group I (standard cure and 1mm thick composites) and that of group III (simultaneous cure and 1mm thick composites). SMP, SB in Group I had a significantly higher DC than those in group III, but AB, OS in group I had a significantly lower DC than those in group III 3. All DBAs in Goup II (standard cure and 2mm thick composites) had significantly higher bond strength and DC than those in Group N (simultaneous cure and 2mm thick composites). 4. In all DBAs, there was no significantly different SBS and DC between Group I and Group II, but all DBAs in Group III had significantly higher SBS and DC than those in Group IV.

• 생물환경조절학회지
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• 제5권1호
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• pp.23-33
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• 1996

시설하우스에 이용되는 시설자재의 규격화와 품질개선을 유도하기 위하여 피복자재의 종류별, 두께별로 물리적 기계적 특성을 시험 분석하였다. 피복재의 물리적 기계적 특성은 충격강도, 인장 인열강도 및 파장별 투과율을 측정하였으며, 시험한 결과를 요약하면 다음과 같다. 1. 다트식 낙추시험에서 연질필름의 충격 강도는 피복재가 두꺼울수록 파괴하중이 증가하여 50% 파괴수준의 하중이 158-213g 범위에 있었으며, LDPE 필름이 대체로 높게 나타났다. 2. 충격파괴정도를 보면 전혀 파괴되지 않는 최대 충격하중이 62-192g 범위였으며, 0.05mm에 비해 0.1mm 두께의 필름이 충격에 견디는 힘이 1.8-3.2배 더 강한 것으로 나타났다. 3. 인장하중은 0.95-2.22kg 범위로 피복재 길이 방향이 높고, LDPE 필름이 높게 나타났으며, 신장율은 345-1020% 범위로 길이보다 폭방향이 1.4-2.7배 더 신장되는 것으로 나타났다. 4. 인열강도는 80.S-121.7kg/cm의 범위로 LDPE 필름이 높고 EVA가 낮은 것으로 나타났으며, 길이방향보다 폭방향이 더 큰 값으로 나타났다. 5. 연질필름의 종류별 광투과특성은 자외선 영역에서 87-92%로 큰 차이가 나타나지 않았으나 가시광선 영역에서 높은 투광율을 나타내었다.

• 한국재료학회지
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• 제26권10호
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• pp.542-548
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• 2016

The influence of NiCrAlY bond coating on the adhesion properties of an Fe thermal coating sprayed on an Al substrate was investigated. By applying a bond coat, an adhesion strength of 21MPa was obtained, which was higher than the 15.5MPa strength of the coating without the bond coat. Formation of cracks at the interface of the bond coat and the Al substrate was suppressed by applying the bond coat. Microstructural analysis of the coating interface using EBSD and TEM indicated that the dominant bonding mechanism was mechanical interlocking. Mechanical interlocking without crack defects in the coating interface may improve the adhesion strength of the coating. In conclusion, the use of an NiCrAlY bond coat is an effective method of improving the adhesion properties of thermal sprayed Fe coatings on Al substrates.

• 한국분말재료학회지
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• 제13권2호
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• pp.102-107
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• 2006

Recycling industrial wastes such as fly ash from a coal burning heat power plant and shell from an oyster farming were investigated to prevent environment contamination as well as to enhance the value of recycling materials. In this study, the lightweight aggregates and the red bricks were fabricated from fly ashes with other inorganic materials and wastes. The starting materials of the lightweight aggregate were fly ash powder and water glass, and the compacts of these materials were heat treated at $1100^{\circ}C$. The fabricated lightweight aggregates had low bulk density, $0.9-1.2\;g/cm^3$, hence floated on the water and had the strength of 7.0-11.0 MPa and the modulus of 2900-3300 MPa which indicates it has enough strength as the aggregate. Another type of the light weight aggregate was prepared from fly ashes, shell powders and clays. The bulk density, porosity, and compressive strength of these aggregates were $1.19-1.34\;g/cm^3,\;18.3{\sim}56.1%$ and 5-12 MPa, respectively. The addition of a small amount of fly ash powder prevented hydration of the light weight aggregates. The red brick was also fabricated from the fly ash containing materials. It is suitable for the brick facing of a building as it has moderate strength and low water absorption rate.