• 치위생과학회지
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• 제10권5호
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• pp.335-340
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• 2010

This study was performed to evaluate the fracture strength of the dental zirconia veneering ceramics for zirconia ceramic core. Six commercial zirconia veneering ceramics were used in this study, namely E-Max(Ivoclar vivadent, Inc, Liechtenstein), Creation ZI(KLEMA Dental produckte GmbH, Austria), Cercon ceram kiss(Degudent, GmbH, Hanau-Wolfgang, Germany), Triceram(Dentaurum, Ispringen, Germany), Zirkonzahn(Zirkonzahn GmbH, Italy), Zirmax(Alpadent, korea). All samples were prepared according to the relevant instructions of manufacture. Disc specimens were prepared to the final dimensions of 17 mm in diameter and 1.5 mm in thickness. The biaxial flexure strength test was conducted using a ball-on-three-ball method. All specimens were tested in a moisture-free environment. Average flexural strengths were analyzed with Weibull analysis and one-way analysis of variance(ANOVA). Significant differences were founded between the mean flexural strength values of five commercials zirconia veneering ceramics and the other. The flexural strengths and Weibull modulus were similar to those of five groups E-Max(EM), Creation ZI(CR), Cercon ceram kiss(CE), Triceram(TR), Zirkonzahn(ZI) with the exception of Zirmax(ZM). The biaxial flexural strength from Cercon ceram kiss(CE) was higher than those of other groups. Fracture analysis showed similar results for these five groups.

• 콘크리트학회논문집
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• 제12권2호
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• pp.89-98
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• 2000

The mechanical properties of specialty cellulose fiber reinforced concrete and the contribution of specialty cellulose fiber to drying shrinkage crack reduction potential of concrete and theirs evaluation are presented in this paper. The effects of differing fiber volume fraction(0.03%, 0.06%, 0.08%, 0.1%, 0.15%, 0.2%) were studied. The results of tests of the specialty cellulose fiber reinforced concrete were compared with plain and polypropylene fiber reinforced concrete. Flexural performance(flexural strength and flexural toughness) test results indicated that specialty cellulose fiber reinforcement showed an ability to increase the flexural performance of normal- and high- strength concrete(as compared to plain and polypropylene fiber reinforced concrete). Optimum specialty cellulose fiber reinforced concrete were obtianed using 0.08% fiber volume fraction. Drying shrinkage cracking test results confirmed specialty cellulose fibers are effective in reducing the drying shrinkage cracking of normal and high-strength concrete(as compared to popylene fiber reinforced concrete).

• 콘크리트학회논문집
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• 제20권2호
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• pp.139-146
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• 2008

본 연구에서는 콘크리트의 이축 휨인장 특성을 일축 휨인장 특성과 실험적으로 비교, 분석하였다. 이를 위하여 일축 휨인장강도는 현재 많이 사용되고 있는 콘크리트 휨강도 실헙 방법을 사용하여 측정하였으며, 이축 휨강도의 경우는 지광습 외, Zi and Oh에 의해 제안된 새로운 이축 휨강도 실험 방법을 사용하였다. 골재의 크기에 따른 휨파괴강도 변화를 분석하기 위하여 세 가지 크기의 실험체를 제작하였다. 또한 통계적 특성 분석을 위하여 각 변수별로 32개의 실험체를 제작하여 실험을 수행하였다. 실험 결과 평균 이축 휨파괴강도가 일축의 경우보다 20% 정도 큰 것으로 나타났으나, COV의 경우에는 이축의 경우가 18% 큰 것으로 해석되었다. 이는 이축 휨균열 확률이 일축 보다 클 수도 있음을 의미한다.

• 한국안전학회지
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• 제34권2호
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• pp.40-47
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• 2019

The Half-depth precast deck is a structural system that utilizes pre-cast panels pre-built at the factory as formwork at the construction stage and as a major structural member at the same time after completion. These systems have joints between segments, and the detail and performance of the joints are factors that have a very large impact on the quality, such as the constructability and durability of the bridge decks. In this study, strength performance evaluation was performed for improved joints using connecting rebar by experimental method. Static loading tests were conducted on the test specimen with improved joint, those with existing joint and those without joint. The test results of the specimens were compared to each other, and the flexural strength required by the design was compared. The flexural strength required in the design was presented by finite element analysis. It has been shown that the flexural strength of the specimens with joints were more than twice that required by the design. But the flexural strength of the specimen with existing joint was about 84% of that without joint. The flexural strength of the specimen with improved joints was a nearly similar degree of that compared to the specimen without joint. And a comparison of the moment-deflection relationship curves of the two specimens also shows a very similar flexural behavior. It is confirmed that improved joint has sufficient flexural strength. In addition to strength, the bridge decks require serviceability, such as deflection and cracking, and in particular, fatigue resistance due to repetitive live loads is an important performance factor. Therefore, further verification studies are required.

• 대한치과보철학회지
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• 제43권4호
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• pp.478-486
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• 2005

Statement of problem : Fracture and dimensional change of an acrylic resin denture are a rather common occurrence. Purpose : The purpose of this study was to compare differences in dimensional changes and flexural strength of separate maxillary complete dentures after immediate deflasking by injection molding and conventional compression processing. Material and method: To evaluate dimensional stability, the maxillary dentures were fabricated by using different materials and methods. Lucitone 199(Dentsply Trubyte. york, pennsylvania, USA) and Vertex(Dentimex, zeist, Netherlands) were used as materials. Compression and injection packing methods were used as processing methods. The impression surface of the dentures was measured by 3D Scann-ing System(PERCEPTRON USA) and overlapped original impression surface of the master cast. To evaluate flexural strength, resin specimens were made according to the different materials, powder/liquid ratio and processing methods. Flexural strength of the complete resin specimens (64mm$\times$10mm$\times$3.3mm) were measured by INSTRON 4467. (INSTRON, England) The data was analyzed by ANOVA, t-test and Tukey test. (p<.05 level of significance) Result: The results were as follows 1. There was no significant differences between master model and denture base for each group in overall dimensional changes. 2. Palatal area was more stable than flange or alveolar area in dimensional stability. but. there was no significant differences among each area. 3. Materials and power/liquid ratio had an effect on flexural strength. (P<.05) Especially materials was most effective. (P<.05) 4. Lucitone 199(powder/liquid ratio followed by manufacturer's direction) showed higher flexural strength than Vertex. Conclusion : Dimensional stability or flexural strength are affected by materials rather than packing techniques.

• 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.

• 콘크리트학회논문집
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• 제26권4호
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• pp.483-489
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• 2014

이 연구에서는 ASTM C 1609을 따라서 비정질 강섬유보강콘크리트의 휨실험을 수행하였고, 이를 바탕으로 휨성능을 평가하였다. 비정질 강섬유는 기존의 일반 강섬유와 달리 얇은 두께, 거친 표면의 특성을 가지고 있다. 주요한 실험변수는 섬유 종류(비정질 강섬유, 일반 강섬유), 섬유 혼입률(0.25, 0.50, 0.75%) 그리고 콘크리트 압축강도(27, 50 MPa)이다. 실험 결과에 근거하여 비정질 강섬유와 일반 강섬유보강콘크리트의 휨강도와 휨인성을 분석하였고, 그 결과 일반 강섬유보강콘크리트의 경우 주로 휨인성이 증가하였으나 비정질 강섬유보강콘크리트의 경우 휨강도와 인성을 모두 증가하는 것으로 나타났다.

• 콘크리트학회논문집
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• 제20권6호
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• pp.731-739
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• 2008

이 연구에서는 강섬유 보강 초고강도 콘크리트의 타설방법에 따라 섬유의 방향성이 인장강도에 미치는 영향을 파악하고자 섬유의 방향성을 정량적으로 평가할 수 있는 이미지 프로세싱 기법을 개발하였으며, 개발한 기법을 적용하여 섬유의 방향성을 평가하였다. 또한 휨인장실험을 수행하여 섬유의 방향성이 균열발생강도 및 휨인장강도에 미치는 영향을 파악하였다. 이 연구에서 개발한 이미지 프로세싱 기법은 섬유 방향성 이외에 분산성 계수, 단위면적당 섬유의 개수 등, 분포 특성을 정량적으로 평가하고 있으며, 타설방법에 따라 섬유 분포 특성에 상당한 차이가 있음을 확인할 수 있었다. 그리고 섬유의 방향 분포특성은 강섬유 보강 초고강도 콘크리트의 균열발생강도에는 크게 영향을 미치지 않으나, 휨인장강도에 미치는 영향은 아주 큰 것으로 나타났으며, 이론적인 휨강도 모델식에 실제 섬유 방향성을 적용하여 예측한 결과, 실험 결과와 잘 일치하는 것으로 나타났다.

• 대한치과기공학회지
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• 제33권3호
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• pp.193-202
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• 2011

Purpose: The aim of this study was to evaluate the effect of pre-treatment of core and hydrothermal treatment on the bond strength and flexural strength of ceramic veneered zirconia. Methods: 3Y-TZP specimens(KaVo Zr, $25mm{\times}3mm{\times}1mm$)were prepared by five pre-treatment methods and divided into seven groups including control two groups, subsequently the specimens veneered with the E-MAX ceram according to manufacturer's information(total specimen thickness 1.5mm). Two groups from ceramic-zirconia specimens(n=105, n=15 per group)were assigned into two experimental fatigue conditions, namely storage in an autoclave at $134^{\circ}C$ for 5h, thermo-cycling(3,000cycles, between 5 and $55^{\circ}C$, dwell time 45s, transfer time 2s). A flexural strength test was performed in a universal testing machine(crosshead speed: 0.5mm/min). Data were statistically analyzed using one-way ANOVA and Tukey's test(${\alpha}$=0.05). Results: The ceramic-zirconia bond strength value for liner application group(LLW, $27.3{\pm}3.8$) were significantly lower than those of the pre-treatment groups($30.72{\pm}5.3$). The ceramic-zirconia bond strength and zirconia flexural strength was not affected by thermo-cycling(p>0.05), whereas it was affected by storage in an autoclave at $134^{\circ}C$ for 5h(p<0.05). Conclusion: The results indicated that the ceramic-zirconia bond strength and zirconia flexural strength was affected by low temperature degradation.

• 한국안전학회지
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• 제28권2호
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• pp.55-59
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• 2013

The analytical model was constituted to evaluate the flexural strength of UHPFRC(ultra high performance fiber reinforced concrete) member. The analytical approach was attemped to study the effect of the joint and the result compared with the experimental study to verify the analytical model. The calculated value tends to underestimate about 23%~25% in comparison with the experimental result of the jointed test member because the bond stress between precast UHPFRC and cast-in-place UHPFRC surface is not considered in the analytical model. But in the case of the continuous test member, the analytical model provides reasonable results for the flexural strength of UHPFRC member.