• Title/Summary/Keyword: Critical Strain Energy Release Rate

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A comparative study for beams on elastic foundation models to analysis of mode-I delamination in DCB specimens

  • Shokrieh, Mahmood Mehrdad;Heidari-Rarani, Mohammad
    • Structural Engineering and Mechanics
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    • v.37 no.2
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    • pp.149-162
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    • 2011
  • The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

Effect of Surface Treated SiC on Thermal Stability and Mechanical Interfacial Properties of Carbon Fiber/Epoxy Resin Composites (탄소섬유 강화 에폭시 수지 복합재료의 열안정성 및 기계적 계면특성에 미치는 SiC 표면처리 영향)

  • 박수진;오진석;이재락;이경엽
    • Composites Research
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    • v.16 no.3
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    • pp.25-31
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    • 2003
  • In this work the effect of surface treated SiC on thermal stability and mechanical interfacial properties of carbon fiber/epoxy resin composites. The surface properties of the SiC were determined by acid/base values and contact angles. The thermal stabilities of carbon fiber/epoxy resin composites were investigated by TGA. The mechanical interfacial properties of the composites were studied in ILSS, critical stress intensity factor ($\textrm{K}_{IC}$), and critical strain energy release rate($\textrm{G}_{IC}$) measurements. As a result, the acidically treated SiC(A-SiC) had higher acid value than untreated SiC(V-SiC) or basically treated SiC(B-SiC). According to the contact angle measurements, it was observed that chemical treatments led to an increase of surface free energy of the SiC surfaces, mainly due to the increase of the specific(polar) component. The mechanical interfacial properties of the composites including ILSS, $\textrm{K}_{IC}$, and $\textrm{G}_{IC}$ had been improved in the specimens treated by chemical solutions. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between SiC and epoxy resin matrix.

Effect of Anodic Oxidation of H2SO4/HNO3 Ratio for Improving Interfacial Adhesion between Carbon Fibers and Epoxy Matrix Resins (탄소섬유와 에폭시 기지의 계면강도 증가를 위한 황산/질산 양극산화에 관한 영향)

  • Moon, Cheol-Whan;Jung, Gun;Im, Seung-Soon;Nah, Changwoon;Park, Soo-Jin
    • Polymer(Korea)
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    • v.37 no.1
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    • pp.61-65
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    • 2013
  • In this work, the anodic oxidation of carbon fibers was carried out to enhance the mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites. The surface characteristics of the carbon fibers were studied by FTIR, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Also, the mechanical interfacial properties of the composites were studied with interlaminar shear strength (ILSS), critical stress intensity factor ($K_{IC}$), and critical strain energy release rate ($G_{IC}$). The anodic oxidation led to a significant change in the surface characteristics of the carbon fibers. The anodic oxidation of carbon fiber improved the mechanical interfacial properties, such as ILSS, $K_{IC}$, and $G_{IC}$ of the composites. The mechanical interfacial properties of the composites anodized at 20% sulfuric/nitric (3/1) were the highest values among the anodized carbon fibers. These results were attributed to the increase of the degree of adhesion at interfaces between the carbon fibers and the matrix resins in the composite systems.

Studies on Cure Behavior and Thermal Stability of Epoxy/PMR-15 Polyimide Blend System (에폭시/PMR-15 폴리이미드 블렌드계의 경화동력학 및 열안정성에 관한 연구)

  • Lee, Jae-Rock;Lee, Hwa-Young;Park, Soo-Jin
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2002.10a
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    • pp.265-268
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    • 2002
  • In this work, the blend system of epoxy and PMR-15 polyimide is investigated in terms of the cure behaviors and thermal stabilities. The cure behaviors are studied in DSC measurements and thermal stabilities are also carried out by TGA analysis. DDM (4, 4'-diamino diphenyl methane) is used as curing agent for EP and the content of PMR-15 is varied within 0, 5, 10, 35, and 20 phr to neat EP. As a result, the cure activation energy ($E_a$) is increased at 10 phr of PMR-15, compared with that of neat EP. From the TGA results of EP/PMR-15 blend system, the thermal stabilities based in the initial decomposed temperature (IDT) and integral procedural decomposition temperature (IPDT) are increased with increasing the PMR-15 content. The fracture toughness, measured in the context of critical stress intensity factor ($K_{IC}$) and critical strain energy release rate ($G_{IC}$), shows a similar behavior with $E_a$. This result is probably due to the crosslinking developed by the interactions between intermolecules in the polymer chains.

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Fabrication of unidirectional commingled-yarn-based carbon fiber/polyamide 6 composite plates and their bend fracture performances (일방향 혼합방사형 탄소섬유/폴리아미드 6 복합재료판의 제작조건과 굽힘파괴거동)

  • Choi, Nak-Sam
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.2
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    • pp.416-427
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    • 1998
  • Unidirectional commingled-yarn-based carbon fiber(CF)/polyamide(PA) 6 composite was fabricated under molding pressures of 0.4, 0.6 and 1.0 MPa to study its flexural deformation and fracture behavior. Fiber/matrix interfacial bonding area became larger with an increase of molding pressure from 0.4 to 0.6 MPa. For molding pressures .geq. 0.6 MPa, good flexural performance of similar magnitudes was attained. For the fracture test, four kinds of notch direction were adopted : edgewise notches parallel (L) and transverse (T) to the major direction of fiber bundles, and flatwise notches parallel(ZL) and perpendicular(ZT) to this direction. Nominal bend strength for L and ZL specimens exhibited high sensitivity to notching. ZL specimens revealed the lowest values of the critical stress intensity factor $K_c$ which was slightly superior to those of unfilled PA6 matrix. Enlargement of the compression area for T specimens was analyzed by means of the rigidity reduction resulting from the fracture occurrence.

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.

Experimental Investigations of Mode I Fracture Toughness of a Hybrid Twill Woven Carbon and Aramid Fabric Composite (하이브리드 능직 탄소-아라미드 섬유 복합재의 모드 I 파괴인성에 대한 실험적 연구)

  • Kwon, Woo Deok;Kwon, Oh Heon
    • Journal of the Korean Society of Safety
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    • v.34 no.6
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    • pp.1-6
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    • 2019
  • Carbon fiber has excellent specific strength, corrosion resistance and heat resistance. And p-Aramid fiber has high toughness and heat resistance and high elasticity, and is used in various fields such as industrial protective materials, bulletproof helmets and vests, as well as industrial fields. However, carbon fiber is relatively expensive, and is susceptible to brittle fracture behavior due to its low fracture strain. On the other hand, the aramid fiber tends to decrease in elastic modulus and strength when applied to the epoxy matrix, but it is inexpensive and has higher elongation and fracture toughness than carbon fiber. Thus the twill hybrid carbonaramid fiber reinforced composite laminate composite was investigated for a delamination fracture toughness under Mode I loading by 2 kinds of MBT and MCC deduction. The specimen was fabricated with 20 hybrid fabric plies. The initial crack was made by inserting the teflon tape in the center plane with a0/W=0.5 length. The results show that SERR(Strain Energy Release Rate) as the critical and stable delamination fracture toughness were 0.09 kJ/㎡, 0.386 kJ/㎡ by MBT deduction, and 0.192 kJ/㎡, 0.67 kJ/㎡ by MCC deduction, respectively.

Effect of Plasma Treatment on Mechanical Properties of Carbon Fibers-reinforced Composites (플라즈마 처리가 탄소섬유강화 복합재료의 기계적특성에 미치는 영향)

  • Oh, Jin-Seok;Lee, Jae-Rock;Park, Soo-Jin
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2005.04a
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    • pp.80-83
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    • 2005
  • In this work, effects of oxygen plasma on surface characteristics of carbon fibers were investigated in mechanical properties interfacial of carbon fibers-reinforced composites. The surface properties of the carbon fibers were determined by acid/base values, FT-IR, and X-ray photoelectron spectroscopy (XPS). Also, the mechanical properties of the composites were studied in and critical stress intensity factor ($K_{IC}$) and critical strain energy release rate mode II ($G_{IIC}$) measurements. As experimental results, the $O_{lS}/C_{lS}$ ratio of the carbon fiber surfaces treated by oxygen plasma was increased compared to that of untreated ones, possibly due to development of oxygen-containing functional groups. The mechanical properties of the composites, including $K_{IC}$ and $G_{IIC}$ had been improved in the oxygen plasma on fibers. These results could be explained that the oxygen plasma was resulted in the increase of the adhesion of between fibers and matrix in a composite system.

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Cure Behaviors and Mechanical Interfacial Properties of Epoxy/Polyurethane Blends Initiated by Latent Thermal Catalyst (열잠재성 개시제에 의한 에폭시/폴리우레탄 블렌드의 경화거동 및 파괴인성)

  • Park, Soo-Jin;Seok, Su-Ja;Kang, Jun-Gil;Kwon, Soo-Han
    • Elastomers and Composites
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    • v.39 no.1
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    • pp.42-50
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    • 2004
  • In this work, the diglycidylether of bisphenol A (DGEBA) and modified polyurethane (PU) blends were initiated by N-benzylpyrazinium hexafluoroantimonate (BPH). The cure and fracture toughness of neat DGEBA with the addition of PU were investigated. The cure properties of DGEBA/PU blend system were examined by DSC and near-IR measurements. The fracture touhtness were investigated by measuring the critical stress intensity factor ($K_{IC}$) and the critical strain energy release rate ($G_{IC}$). According to the results, the maximum values of owe activation energy ($E_a$) and conversion (${\alpha}$) were found at 10 phr of PU. Also the $K_{IC}$ showed a similar behavior with the results of conversion. These results were probably due to increase of crosslinking density in the blends resulted from increase of the hydrogen bonding between the hydroxyl groups of DGEBA and isocyanate groups of PU.

Influence of SiC on Thermal Stabilities and Mechanical Interfacial Properties of Carbon Fibers-reinforced Composites (탄화규소의 첨가가 탄소섬유 강화 복합재료의 열안정성 및 기계적 계면특성에 미치는 영향)

  • Oh Jin-Seok;Park Soo-Jin;Lee Jae-Rock;Kim Yeung-Keun
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2004.04a
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    • pp.182-185
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    • 2004
  • In this work, the effect of chemical treatments on surface properties of SiC was investigated in mechanical interfacial properties of carbon fibers-reinforced composites. The surface properties of the SiC were determined by acid/base values and contact angles. The thermal stabilities of carbon fibers-reinforced composites were investigated by thermogravimetric analysis (TGA). Also, the mechanical interfacial properties of the composites were studied in interlaminar shear strength (ILSS) and critical strain energy release rate mode II $(G_{IIC})$ measurements. As a result, tile acidically treated SiC (A-SiC) had higher acid value than that of untreated SiC (V-SiC) or basically treated SiC (B-SiC). According to the contact angle measurements, it was observed that chemical treatments led to an increase of surface free energy of the SiC surfaces, mainly due to the increase of the specific (polar) component. The mechanical interfacial properties of the composites, including ILSS and $(G_{IIC})$, had been improved in the specimens treated by chemical solutions. These results were explained that good wetting played an important role in improving the degree of adhesion at interfaces between SiC and epoxy resin matrix.

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