• 한국재료학회지
• /
• 제30권1호
• /
• pp.38-43
• /
• 2020

Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/㎠. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/㎠, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.

• 한국전기전자재료학회논문지
• /
• 제25권11호
• /
• pp.886-894
• /
• 2012

In order to develop electrical insulation materials, epoxy-nanosilica-microsilica mixture composites (ENMC) was synthesized, and mechanical properties such as their tensile and flexural strength, and AC insulation breakdown strength were investigated. Properties of mechanical strength and AC insulation breakdown strength are analyzed as scale and shape parameter with respect to weibull plot. Their tensile and flexural strength, AC insulation breakdown strength were compared original epoxy or EMC to ENMC. The 4 phr nano-silica addition and the 65 wt% micron-silica mixture composite (ENMC) was found to have the highest tensile and flexural strength. In the tensile strength was improved 29%, and flexural strength was improved 60.9% higher than those of the original epoxy. In the insulation breakdown strength, ENMC_4 phr was improved 17% and ENMC_5 phr was improved 15.8% higher than those of the EMC.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
• /
• pp.475-480
• /
• 2003

Latex modification of concrete provides the material with higher flexural strength. This increase in flexural strength can attribute to the crack-arresting action of polymer in concrete, and also to the bonding they provide between the matrix and aggregates. This experimental study presents the fracture behavior of 12 flexural reinforced concrete beams repaired or strengthened by latex-modified concrete with the main experimental variables such as overlay thickness, strength thickness, and shear reinforcement. The results are as follow: All beam specimens having shear reinforcement were failed by delamination rupture at concrete interface at about 80% of ultimate loading after flexural cracking. All specimens overlayed and strengthened by latex-modified concrete (LMC) showed higher ultimate flexural strength than OPC control specimen, but lower than LMC control specimen. This increase in flexural strength could attribute to the high bonding they provide between the matrix and aggregates. All specimens except two shear unreinforced showed quite similar and consistent displacement behavior. The effect of overlay and strength thickness on the load-displacement relationship were a small at this study.

• 한국건축시공학회:학술대회논문집
• /
• 한국건축시공학회 2021년도 봄 학술논문 발표대회
• /
• pp.239-240
• /
• 2021

In this study, we conducted a study to evaluate the more accurate mechanical properties of concrete damaged by fire. In relation to this, in this study, the results of compressive strength and biaxial flexural strength were compared for concrete that received high temperature heat. As a result, both the compressive strength and the biaxial bending strength decreased as the heating temperature increased. As a result of examining the correlation between the compressive strength and the biaxial flexural strength, the biaxial flexural strength was smaller than the compressive strength.

• 한국농공학회논문집
• /
• 제58권2호
• /
• pp.83-90
• /
• 2016

This study was performed to evaluate the effective analysis of flexural performance for polypropylene fiber (PF) reinforced EVA concrete that can be used in marine bridge, tunnel and agricultural structures under flexural load. The control design was applied in ready mixed concrete using 10 % fly ash of total binder weight used in batch plant. On the basis of the control mix design, there was designed mix types that contained PF ranged from 0 % to 0.5 % by volume ratio into two mix types of using 0 % and 5.0 % EVA contents of total binder weight. Before evaluating the flexural performance, we tested compressive strength and flexural strength to evaluate whether polypropylene fiber reinforced concrete could be used or not in site. The method of flexural performance evaluation was applied by ASTM C 1609. These results showed the maximum compressive strength and flexural strength was measured at each E5P1 and E5P2. Concrete reinforced with PF exhibited deflection-softening behavior. In the concrete reinforced with 0.4 % PF contents and containing 5.0 % EVA, the flexural performance was the best.

• Carbon letters
• /
• 제17권1호
• /
• pp.33-38
• /
• 2016

In the present study, exfoliated graphite nanoplatelets (xGnP) with different particle sizes were coated onto polyacrylonitrile-based carbon fibers by a direct coating method. The flexural properties, interlaminar shear strength, and the morphology of the xGnP-coated carbon fiber/phenolic matrix composites were investigated in terms of their longitudinal flexural strength and modulus, interlaminar shear strength, and by optical and scanning electron microscopic observations. The results were compared with a phenolic matrix composite counterpart prepared without xGnP. The flexural properties and interlaminar shear strength of the xGnP-coated carbon fiber/phenolic matrix composites were found to be higher than those of the uncoated composite. The flexural and interlaminar shear strengths were affected by the particle size of the xGnP, while the particle size had no significant effect on the flexural modulus. It seems that the interfacial contacts between the xGnP-coated carbon fibers and the phenolic matrix play a role in enhancing the flexural strength as well as the interlaminar shear strength of the composites.

• The Journal of Advanced Prosthodontics
• /
• 제11권4호
• /
• pp.209-214
• /
• 2019

PURPOSE. The purpose of this study was to evaluate the effect of two coloring liquids (aqueous and acid-based coloring liquids) and the position of multilayered zirconia on the flexural strength of multilayered zirconia. MATERIALS AND METHODS. The multilayered zirconia specimens were divided into upper and lower positions. The specimens were divided into three subgroups (n=10): non-shaded, acid-based coloring liquid, and aqueous coloring liquid. The specimens were cut using a milling machine and were immersed in either a acid-based coloring liquid or aqueous coloring liquid 2 times for 5 seconds. The specimens were sintered in a sintering furnace according to the manufacturer's introduction. The flexural strength of the specimen was measured using a universal testing machine and the surface of the specimen was observed using a field emission scanning electron microscope. RESULTS. The flexural strength of multilayered zirconia was 400 - 500 MPa. There was no statistically significant difference among all groups (P>.05).The flexural strength of the multilayered zirconia was not influenced by the kind of coloring liquid used (P>.05). The flexural strength of the multilayered zirconia colored with the coloring liquids was not influenced by its position (P>.05). CONCLUSION. The different coloring liquid application did not affect the flexural strength of multilayered zirconia of all positions.

• 콘크리트학회논문집
• /
• 제28권1호
• /
• pp.95-104
• /
• 2016

강섬유가 보강된 콘크리트의 지반 바닥슬래브는 소성해석법인 항복선 이론을 바탕으로 평균강도 개념인 등가 휨 강도비로서 설계 휨강도를 평가하였다. 최근 유럽의 설계기준에서는 강섬유에 의한 인장성능을 균열이후의 잔류 휨강도를 직접 평가하도록 하였다. 따라서, 본 연구에서는 기존의 등가 휨강도비와 잔류 휨강도에 따른 인장성능을 실험적으로 평가하고, 하중의 등가 접촉반경과 상대강성반경 비에 의해 하중 위치별 휨 내력을 평가하였다. 설계 휨 내력은 ACI 360R-10 기준이 TR 34 (2003 & 2013)에 비해 과소 평가하였다. 또한, 잔류 휨강도로서 평가하는 TR 34 (2013)은 등가 휨강도비로 계산되어진 TR 34 (2003)의 휨 내력에 비해 다소 작게 평가하고 있지만, 그 차이는 크지 않았다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제13권3호통권55호
• /
• pp.155-163
• /
• 2009

본 연구에서는 콘크리트의 휨인장강도 특성과 함께 구콘크리트와 신콘크리트 사이의 부착강도 특성을 규명하고자 하였다. 구콘크리트와 신콘크리트를 이용하여 제작한 빔 시편 실험을 통하여 콘크리트와 콘크리트 사이의 부착강도 및 인장강도를 실험적으로 연구하였다. 신 구 콘크리트 사이의 부착강도는 인장강도에 비해 훨씬 작게 나타나며, 그 비율은 15~27% 범위이다. 또한, 신 구콘크리트 사이의 부착강도는 양생 조건에 영향을 받는 것으로 나타난다. 또한, 인장강도 실험자료의 분석으로부터 콘크리트의 휨인장강도를 예측할 때, ACI 363 위원회의 제안식을 적용하는 것이 가장 합리적이라고 사료된다.

• 대한치과기공학회지
• /
• 제30권2호
• /
• pp.65-69
• /
• 2008

Recently, zirconia is widely used in the field of dental ceramics thanks to the proliferation of CAD/CAM systems. Accordingly, different types of zirconia block are being solid in the market. However, there are no precise, objective standards for properties of zirconia. This study concerns the flexural strength of zirconia ceramic for CAD/CAM block. The test specimens used for this study were ZirBlank(Acucera), ZirBlank shade(Acucera), VITA, Cercon(Densply) and Cerasys. The test results suggest that ZirBlank shade block shows the highest flexural strength and density among the zirconia blocks tested. Its flexural strength was $971{\pm}58MPa$ and its density was 99.89%. On the other hand, Cerasys block shows the lowest flexural strength of $576{\pm}36MPa$ and the lowest density of 94.85%. Given all, the density of the specimens is found to be directly proportional to strength and inversely to grain size.