• Title/Summary/Keyword: 4-point Bending Strength

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Characterization of crack self-healing of silicon carbide by hot press sintering (열간가압소결법으로 제조한 탄화규소의 균열자기치유 특성)

  • Kim, Seong-Hoon;Kim, Kyung-Hun;Dow, Hwan-Soo;Park, Joo-Seok;Kim, Kyung-Ja;Shim, Kwang-Bo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.26 no.2
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    • pp.62-66
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    • 2016
  • In this study, it was investigated that characteristic of crack-self-healing of hot-pressed SiC. SiC ceramics was sintered with $Al_2O_3$ and $Y_2O_3$ sintering additive by hot press. Sintering was performed in hot-press furnace in flowing argon (Ar), holding for 3 hr under $1950^{\circ}C$ and 50 MPa. The sintered SiC was machined into 3-point bending strength specimen of $3{\times}4{\times}40mm$, and introduced pre-crack by Vickers indentation at 49.6 N. Specimens were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), 3-point bending strength after heat treatment at $1200{\sim}1400^{\circ}C$ for 1~10 hr. The best crack-self-healing ability was achieved 770 MPa 3-point bending strength by heat treatment at $1300^{\circ}C$ for 5 hr.

Effect of morphology and diameter of implant fixture-abutment connection on mechanical failure of implants (임플랜트 고정체-지대주 연결부의 형태와 직경이 임플랜트의 기계적 실패에 미치는 영향)

  • Yun, Bo-Hyeok;Shin, Hyon-Mo;Yun, Mi-Jung;Huh, Jung-Bo;Jeong, Chang-Mo;Kang, Eun-Sook
    • The Journal of the Korean dental association
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    • v.53 no.9
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    • pp.644-655
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    • 2015
  • Purpose: This study was conducted to evaluate the effect of the fixture abutment connection type and diameter on the screw joint stability in external butt joint for 2nd surgery and internal cone connected type implant system for 1st and 2nd surgery using ultimate fracture strength. Materials and Methods: USII system, SSII system and GSII system of Osstem Implant were used. Each system used the fixture with two different diameters and cement-retained abutments, and tungsten carbide / carbon coated abutment screws were used. Disc shaped stainless steel metal tube was attached using resin-based temporary cement. The experimental group was divided into seven subgroups, including the platform switching shaped specimen that uses a regular abutment in the fixture with a wide diameter in USII system. A static load was increased to the metal tube at 5mm deviated point from the implant central axis until it reached the compression bending strength at a rate of 1mm/min. Then the deformations and patterns of fracture in threaded connection were compared. Results and Conclusion: 1. In the comparison between the Regular diameter, compression bending strength of SSII system was higher than USII system and GSII system. There was no significant difference between USII system and GSII system. 2. In the comparison between wide diameter, compression bending strength was increased in the order of GSII system, USII system, and SSII system. 3. In comparison between the implant diameter, compression bending strength of the wide diameter was greater than the regular diameter in any system(P<0.05). 4. There was no significant difference between the platform switching (III group) and the regular diameter (I group) in USII system. 5. In USII system, fracture of abutment screw and deformation of both fixture and abutment were observed in I, II and III subgroups. 6. Failure pattern of SSII system, which was the fracture of abutment screw and deformation of the abutment and fixture, was observed in both IV and V subgroups. Fracture of some fixtures was observed in subgroup V. 7. Failure pattern of GSII system, which was the fracture of the abutment screw and deformation of the fixture and the abutment, was observed in both VI and VII subgroups. Apart from other subgroups, subgroup VII demonstrated no bending neither the fracture at the top of the fixture. The compressive deformation of internal slope in the fixture was the only thing observed in subgroup VII.

A Study on Static Behavior of 60 m span Half-Decked PSC Girder (Half-Deck을 포함한 60 m 경간 PS 콘크리트거더의 정적 거동 연구)

  • Kim, Tae Min;Park, Jong Heon;Kim, Moon Kyum;Lim, Yun Mook
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.32 no.2A
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    • pp.65-73
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    • 2012
  • In this study, we tested structural performance of Half-Decked PSC girder which was developed for applying to long span bridge. We operated 4 point bending test with 60 m span full scale girder designed as simple bridge with hinge-roller boundary condition. Actuators were set on the both sides of girder, 5.5 m away from the center, and 4 stages of cyclic loading was applied at rate of 1 kN/sec. Through stages 1 to 4, loading and unloading 1,000 kN, 1,200 kN, 1,500 kN, and 2,000 kN were repeated and displacement, strain of concrete and steel, crack of girder were checked. From these results, the strength of girder was assessed and resilience and ductility were observed after removing the load. Since initial flexural crack occurred in the vicinity of 1,400 kN, non-linearity of load-displacement curve appeared and definite residual strain was measured at that point. The test result showed that initial cracking load was over twice the DB-24 load which means the developed girder had sufficient strength. To verify the experimental results, we numerically analyze the test and confirmed that the data were similar with results from the test above. Half-Decked PSC type of 60 m-girder developed in this study showed its adequate structural capacity through static loading test, which proved that possibility of applying the girder to actual bridges practically.

Experimental Study of Flexural Behavior in Flexural Members Based on Repair Thickness of ECC (ECC 재료보강 두께에 따른 휨 부재의 휨 거동에 관한 실험적 연구)

  • Kyoung Min Su;Kim Dong Wan;Bae Byung Won;Jun Kyung Suk;Lim Yun Mook;Kim Jang Ho
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.05a
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    • pp.192-195
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    • 2004
  • Recently, the development of construction materials is rapidly advancing. Especially, the rate of development of cement based construction materials is much quicker than steel or composite materials. In order to optimize the ductility and strength of cement based materials, Micro-mechanics based fiber concrete called Engineered Cement Composite (ECC) is developed and studied extensively by many researchers in the field. Due to ECC's remarkable flexural strain and strength capacities, many leading nation (i.e., US, Japan, and European countries) are currently using ECC in actual constructions. In this study, ECC with internationally competitive material capacities is manufactured using domestic materials. Then, unreinforced concrete beams are repaired using ECC with $10\%,\;20\%,\;30\%$ of concrete specimen height Using 4 point bending test, the flexural strength of repaired flexural members are determined. The results show that ECC manufactured with domestic materials can be effectively used for repairing materials.

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Toughening of Ni Bonded $Cr_3C_2$ by Mo Particulates (Mo 입자에 의한 Ni 결합 $Cr_3C_2$의 고인성화)

  • 한동빈;장철우;백성기;박병학
    • Journal of the Korean Ceramic Society
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    • v.30 no.6
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    • pp.429-432
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    • 1993
  • Cr3C2 material is characterized by high chemical stability and poor sinterability with low strength [50~150MPa]. In his study, low melting temperature nickel powder was used to improve sinterability as well as strength. In addition, molydenum particles were added to the Ni-bonded Cr3C2 cermet pseudomatrix to increase resistance to fracture. The specimens made by hot-pressing under vacuum and strength was measured by 4-point bending. Indentation cracking and fractographic examination were conducted to study the interaction of the indentation cracks with the reinforcing particles. Toughening mechanisms and failure will be discussed in terms of crack/particle interactions and compared with previous works.

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The Solid State Bonding or ZrO2/NiTi: (I) Optimizating of Bonding Condition and its Strength (ZrO$_2$와 NiTi 합금의 고상접합 : (I)접합의 최적조건 및 접합강도)

  • Kim, Young-Jung;Kim, Hwan
    • Journal of the Korean Ceramic Society
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    • v.28 no.8
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    • pp.654-660
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    • 1991
  • Stabilized Zirconia (3 mol % Yttria, 3Y-TZP) was joined with intermetallic compound NiTi which has similar thermal expansion coefficient. The optimum bonding condition was determined by the Taguchi Method. Under the optimum bonding condition, the 4-point bending strength was as high as 400 MPa. bonding interfaces were examined by optical microscope, SEM, and TEM; reaction products were identified by XRD and TEM, The relationship between products and strength was examined.

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Effect of basalt fibers on fracture energy and mechanical properties of HSC

  • Arslan, Mehmet E.
    • Computers and Concrete
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    • v.17 no.4
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    • pp.553-566
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    • 2016
  • Fracture energy is one of the key parameters reveal cracking resistance and fracture toughness of concrete. The main purpose of this study is to determine fracture behavior, mechanical properties and microstructural analysis of high strength basalt fiber reinforced concrete (HSFRC). For this purpose, three-point bending tests were performed on notched beams produced using HSFRCs with 12 mm and 24mm fiber length and 1, 2 and $3kg/m^3$ fiber content in order to determine the value of fracture energy. Fracture energies of the notched beam specimens were calculated by analyzing load versus crack mouth opining displacement curves by the help of RILEM proposal. The results show that the effects of basalt fiber content and fiber length on fracture energy are very significant. The splitting tensile and flexural strength of HSFRC increased with increasing fiber content whereas a slight drop in flexural strength was observed for the mixture with 24mm fiber length and $3kg/m^3$ fiber content. On the other hand, there was no significant effect of fiber addition on the compressive strength and modulus of elasticity of the mixtures. In addition, microstructural analysis of the three components; cement paste, aggregate and basalt fiber were performed based on the Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy examinations.

Steel fibre and transverse reinforcement effects on the behaviour of high strength concrete beams

  • Cucchiara, Calogero;Fossetti, Marinella;Papia, Maurizio
    • Structural Engineering and Mechanics
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    • v.42 no.4
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    • pp.551-570
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    • 2012
  • An experimental program was carried out to investigate the influence of fibre reinforcement on the mechanical behaviour of high strength reinforced concrete beams. Eighteen beams, loaded in four-point bending tests, were examined by applying monotonically increasing controlled displacements and recording the response in terms of load-deflection curves up to failure. The major test variables were the volume fraction of steel fibres and the transverse steel amount for two different values of shear span. The contribution of the stirrups to the shear strength was derived from the deformations of their vertical legs, measured by means of strain gauges. The structural response of the tested beams was analyzed to evaluate strength, stiffness, energy absorption capacity and failure mode. The experimental results and observed behaviour are in good agreement with those obtained by other authors, confirming that an adequate amount of steel fibres in the concrete can be an alternative solution for minimizing the density of transverse reinforcement. However, the paper shows that the use of different theoretical or semi-empirical models, available in literature, leads to different predictions of the ultimate load in the case of dominant shear failure mode.

An Experimental Study on the Damage Mechanism of Particle Impact in a Scratched Glass (표면거칠기를 가진 유리의 입자충격 손상기구에 관한 실험적 연구)

  • Suh, Chang-Min;Chung, Seong-Muk;Lee, Mun-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2196-2204
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    • 1996
  • The damage mechanism by the impact of steel ball on the soda-lime glass having a different surface roughness was investigated. An initiation and a propagation behavior of cracks formed by each impact velocity were quantitatively studied. A 4-point bending test was carried out to evaluate the remaining bending strength of a scratched soda-lime glass which impacted by the steel ball. As the surface roughness was increased, the shape of cracks became more irregular rather than those of the smooth specimens. The phenomenon of turning up in the wing of cone cracks occurred even at the lower velocity than the critical velocity caused the crushing. The threshold velocity of cracks initiation generally became lower than those of smooth specimen. An initiation and a propagation behavior of radial cracks had no relation with the direction of scratch on the surface. The remaning benidng strength of the scratched specimen according to impact velocity had no big difference compared with those of the smooth specimen.

Mode-I fracture toughness of carbon fiber/epoxy composites interleaved by aramid nonwoven veils

  • Beylergil, Bertan;Tanoglu, Metin;Aktas, Engin
    • Steel and Composite Structures
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    • v.31 no.2
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    • pp.113-123
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    • 2019
  • In this study, carbon fiber/epoxy (CF/EP) composites were interleaved with aramid nonwoven veils with an areal weight density of $8.5g/m^2$ to improve their Mode-I fracture toughness. The control and aramid interleaved CF/EP composite laminates were manufactured by VARTM in a [0]4 configuration. Tensile, three-point bending, compression, interlaminar shear, Charpy impact and Mode-I (DCB) fracture toughness values were determined to evaluate the effects of aramid nonwoven fabrics on the mechanical performance of the CF/EP composites. Thermomechanical behavior of the specimens was investigated by Dynamic Mechanical Analysis (DMA). The results showed that the propagation Mode-I fracture toughness values of CF/EP composites can be significantly improved (by about 72%) using aramid nonwoven fabrics. It was found that the main extrinsic toughening mechanism is aramid microfiber bridging acting behind the crack-tip. The incorporation of these nonwovens also increased interlaminar shear and Charpy impact strength by 10 and 16.5%, respectively. Moreover, it was revealed that the damping ability of the composites increased with the incorporation of aramid nonwoven fabrics in the interlaminar region of composites. On the other hand, they caused a reduction in in-plane mechanical properties due to the reduced carbon fiber volume fraction, increased thickness and void formation in the composites.