• Title/Summary/Keyword: flexural fracture toughness

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Effect of Crack Propagation Directions on the Interlaminar Fracture Toughness of Carbon/Epoxy Composite Materials (탄소섬유/에폭시 복합재료의 층간파괴인성에 미치는 균열진전각도의 영향)

  • Hwang, Jin-Ho;Hwang, Woon-Bong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.23 no.6 s.165
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    • pp.1026-1038
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    • 1999
  • Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.

The relationship between reinforcing index and flexural parameters of new hybrid fiber reinforced slab

  • Cao, Mingli;Xie, Chaopeng;Li, Li;Khan, Mehran
    • Computers and Concrete
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    • v.22 no.5
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    • pp.481-492
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    • 2018
  • In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

A Study on the Strength and Fracture Toughness of High Strength Hardened Cement Paste (고강도 시멘트 경화체의 강도 및 파괴인성에 관한 연구)

  • 김정환
    • Magazine of the Korea Concrete Institute
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    • v.6 no.6
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    • pp.151-158
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    • 1994
  • In this work, in order to inrprove the flexural strength of hardened portlarid cerncrit paste, mix ing water was reduced to water ccrnent ratio of 0.1 aid water soluble polymer such as hydroxy propyl methyl cellulose was adclelri to the paste to obtain a better dispersion. The paste was kneaded by the twin roll mill for cornpact and homogeneous mixing. The high strength mechanism of the hardened cement paste may be due to the removal of macropores larger than 100${\mu}m$, the reduction of capillary pores acting as the passage of crack propagation, the increase of Young's moculus with iticrease of unhytlratcci cenxxnt ard the incicasc of fracture toughnevs with the crack toughening mechanism (grain bridging, polymer fibril bridging and fritional inter-locking).

Comparison of mechanical properties of a new fiber reinforced composite and bulk filling composites

  • Abouelleil, Hazem;Pradelle, Nelly;Villat, Cyril;Attik, Nina;Colon, Pierre;Grosgogeat, Brigitte
    • Restorative Dentistry and Endodontics
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    • v.40 no.4
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    • pp.262-269
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    • 2015
  • Objectives: The aim of this study was to evaluate the mechanical and physical properties of a newly developed fiber reinforced dental composite. Materials and Methods: Fiber reinforced composite EverX Posterior (EXP, GC EUROPE), and other commercially available bulk fill composites, including Filtek Bulk Fill (FB, 3M ESPE), SonicFill (SF, Kerr Corp.), SureFil (SDR, Dentsply), Venus Bulk Fill (VB, HerausKultzer), Tetric evoceram bulk fill (TECB, Ivoclar Vivadent), and Xtra Base (XB, Voco) were characterized. Composite samples light-cured with a LED device were evaluated in terms of flexural strength, flexural modulus (ISO 4049, n = 6), fracture toughness (n = 6), and Vickers hardness (0, 2, and 4 mm in depth at 24 hr, n = 5). The EXP samples and the fracture surface were observed under a scanning electron microscopy. Data were statistically analyzed using one-way ANOVA and unpaired t-test. Results: EXP, FB, and VB had significantly higher fracture toughness value compared to all the other bulk composite types. SF, EXP, and XB were not statistically different, and had significantly higher flexural strength values compared to other tested composite materials. EXP had the highest flexural modulus, VB had the lowest values. Vickers hardness values revealed SF, EXP, TECB, and XB were not statistically different, and had significantly higher values compared to other tested composite materials. SEM observations show well dispersed fibers working as a reinforcing phase. Conclusions: The addition of fibers to methacrylate-based matrix results in composites with either comparable or superior mechanical properties compared to the other bulk fill materials tested.

FRACTURE TOUGHNESS OF SELF-CURING DENTURE BASE RESINS WITH DIFFERENT POLYMERIZING CONDITIONS (의치상용 자가중합레진의 중합조건에 따른 파괴인성)

  • Jeong Soo-Yang;Kim Ji-Hye;Yang Byung-Deok;Park Ju-Mi;Song Kwang-Yeob
    • The Journal of Korean Academy of Prosthodontics
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    • v.43 no.1
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    • pp.52-60
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    • 2005
  • Purpose. The intent of this study was to evaluate the effects of curing conditions on self-curing denture base resins to find out proper condition in self-curing resin polymerization. Materials and methods, In this study, 3 commercial self-curing denture base resins are used Vertex SC, Tokuso Rebase and Jet Denture Repair Acrylic. After mixing the self curing resin, it was placed in a stainless steel mold(3$\times$6$\times$60mm). The mold containing the resin was placed under the following conditions: in air at 23$^{\circ}C$; or in water at 23$^{\circ}C$; or in water at 23$^{\circ}C$ under pressure(20psi); or in water at 37$^{\circ}C$ under pressure(20psi) or in water at 50$^{\circ}C$ under pressure(20psi) , or in water at 65$^{\circ}C$ under pressure(20psi), respectively. Also heat-curing denture base resin is polymerized according to manufactures' instructions as control. Fracture toughness was measured by a single edge notched beam(SENB) method. Notch about 3mm deep was carved at the center of the long axis of the specimen using a dental diamond disk driven by a dental micro engine. The flexural test was carried out at a crosshead speed 0.5mm/min and fracture surface were observed under measuring microscope. Results and conclusion . The results obtained were summarized as follows : 1. The fracture toughness value of self-curing denture base resins were relatively lower than that of heat-curing denture base resin. 2. In Vertex SC and Jet Denture Repair Acrylic, higher fracture toughness value was observed in the curing environment with pressure but in Tokuso Rebase, low fracture toughness value was observed but there was no statistical difference. 3. Higher fracture toughness value was observed in the curing environment with water than air but there was no statistical difference. 4. Raising the temperature in water showed the increase of fracture toughness.

Mechanical Properties of Zirconia Reinforced Glass-Ceramic (지르코니아 강화형 Glass-Ceramic의 기계적 성질)

  • Park, Eun-Eui;Dong, Jin-Keun;Lee, Hae-Hyoung;Song, Ki-Chang;Oh, Sang-Chun
    • Journal of Dental Rehabilitation and Applied Science
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    • v.17 no.3
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    • pp.199-204
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    • 2001
  • This study was to investigate the reused possibility of zirconia reinforced glass-ceramic(IPS Empress Cosmo ceramic) with sprue button in the flexure strength and fracture toughness. 40 disk-shaped ceramic specimens (20 specimens: as-pressed material; 20 specimens: reused material) with approximately 1.7 mm thickness and 15 mm diameter were prepared by "lost wax" technique. The remnants(sprue buttons) were used for repressing. The surface treatments for the discs were gradually abraded with 320, 800, 1200, and 2000 grit SiC sandpaper. The specimens were evaluated their flexure strength with the biaxial flexure jig(ball-on-three balls) and their fracture toughness with Vickers Indentation-microfracture test. The Weibull moduli were calculated for biaxial flexural strength. The mean flexure strength and fracture toughness of each group were $122.2{\pm}18.3MPa$, $1.00{\pm}0.09MPa{\cdot}m^{0.5}$ (as-pressed ceramics), and $122.2{\pm}20.3MPa$, $1.01{\pm}0.10MPa{\cdot}m^{0.5}$ (reused ceramics). There were no significant differences in the strength and the fracture toughness between the as-pressed and the reused IPS Empress Cosmo ceramic (P>0.05). This implied zirconia reinforced glass-ceramic(IPS Empress Cosmo ceramic) could be used one more time by reusing of sprue button in the flexure strength and fracture toughness.

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Evaluation of Mode II Interlaminar Fracture Toughness for Carbon Fabric/Epoxy Composite for Tilting Train (틸팅차량용 탄소섬유직물/에폭시 복합재의 모우드 II 층간파괴인성 평가)

  • Lee Eun Dong;Yoon Sung Ho;Shin Kwang Bok;Jeong Jong Cheol
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2004.10a
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    • pp.189-192
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    • 2004
  • In this study, mode II interlaminar fracture phenomena of carbon fabric/epoxy composite for tilting train were investigated. The end notched flexural specimen containing an artificial crack with the thickness of 12.5fl11l was used. The mode II interlaminar fracture toughness was evaluated through a three point bending test and the fractured surfaces were examined through a scanning electron microscope. The experimental results obtained in this study would be applicable in the design and structural analysis of the composite structures.

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Experimental and numerical simulation study on fracture properties of self-compacting rubberized concrete slabs

  • Wang, Jiajia;Chen, Xudong;Bu, Jingwu;Guo, Shengshan
    • Computers and Concrete
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    • v.24 no.4
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    • pp.283-293
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    • 2019
  • The limited availability of raw materials and increasing service demands for pavements pose a unique challenge in terms of pavement design and concrete material selection. The self-compacting rubberized concrete (SCRC) can be used in pavement design. The SCRC pavement slab has advantages of excellent toughness, anti-fatigue and convenient construction. On the premise of satisfying the strength, the SCRC can increase the ductility of pavement slab. The aim of this investigation is proposing a new method to predict the crack growth and flexural capacity of large-scale SCRC slabs. The mechanical properties of SCRC are obtained from experiments on small-scale SCRC specimens. With the increasing of the specimen depth, the bearing capacity of SCRC beams decreases at the same initial crack-depth ratio. By constructing extended finite element method (XFEM) models, crack growth and flexural capacity of large-scale SCRC slabs with different fracture types and force conditions can be predicted. Considering the diversity of fracture types and force conditions of the concrete pavement slab, the corresponding test was used to verify the reliability of the prediction model. The crack growth and flexural capacity of SCRC slabs can be obtained from XFEM models. It is convenient to conduct the experiment and can save cost.

Study on properties of geopolymer-polyurethane sponge composite

  • Chen, Zhilei;Lee, Sang-Jin
    • Journal of Ceramic Processing Research
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    • v.19 no.5
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    • pp.419-423
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    • 2018
  • A newly conceived geopolymer composite was fabricated by a combination of the geopolymer and polyurethane sponge. The density and porosity of hardened geopolymer composite, corresponded to different pore sizes of polyurethane sponge, exhibited no significant differences from each other. However, the mechanical behavior, the compressive strength and flexural strength, showed slight differences accordingly. Fracture of the geopolymer composite exposed to high compressive load was not observed from all specimens containing polyurethane sponge. The toughness enhancement of the geopolymer composite, due to spontaneous elasticity of polyurethane sponge, crack spread, and crack diffraction, was identified through the stress-strain curve and microstructure of fracture surface. The newly designed geopolymer composite having a 3-dimensional sponge skeleton showed relatively higher flexural strength of 8.0 MPa than other conventional geopolymer composites.

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.