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Showing papers on "Epoxy published in 1991"


Journal ArticleDOI
TL;DR: In this paper, the static strength of reinforced concrete beams strengthened by gluing glassfiber reinforced reinforcedplastic GFRP plates to their tension flanges was investigated, and five rectangular beams and o...
Abstract: The static strength of reinforced concrete beams strengthened by gluing glassfiberreinforcedplastic GFRP plates to their tension flanges is experimentally investigated. Five rectangular beams and o...

565 citations


Journal ArticleDOI
TL;DR: In this paper, the surface of sisal fibres has been modified by mercerization and silane treatment to improve adhesion characteristics and moisture resistance, which is most effective in reducing moisture uptake of fibres in humid environments.

405 citations


Journal ArticleDOI
TL;DR: A series of networks of diverse crosslink density were prepared using bifunctional epoxide prepolymers of different molecular weight, crosslinked with diamine diphenyl sulphone, and their fracture behaviour investigated as discussed by the authors.
Abstract: A series of networks of diverse crosslink density were prepared using bifunctional epoxide prepolymers of different molecular weight, crosslinked with diamine diphenyl sulphone, and their fracture behaviour investigated. The same set of resins was also modified with a reactive rubber. The fracture toughness regularly decreased on increasing the crosslink density for all formulations. The addition of the rubber gave rise to a marked increase in toughness, though it magnified the influence of the molecular weight of the prepolymer. Tests performed with blunt notches showed that the fracture toughness was maximum at medium crosslink densities. A dispersion of rubber particles caused a toughness increase through the formation of microcavities ahead of the crack tip. Failure was preceded by a rapid volume increase caused by void coalescence.

228 citations


Journal ArticleDOI
TL;DR: A simple equation to model the dependence of the glass transition temperature (T g ) on the extent of reaction in highly cross-linked thermosetting polymers has been derived in this article, assuming that the increase in T g is caused by decrease in chain-end concentration, formation of effective cross-links, and further decrease in the configurational entropy due to departure from Gaussian behavior at high cross-link densities.
Abstract: A simple equation to model the dependence of the glass transition temperature (T g ) on the extent of reaction in highly cross-linked thermosetting polymers has been derived. The model assumes that the increase in T g is caused by (a) decrease in chain-end concentration, (b) formation of effective cross-links, and (c) further decrease in the configurational entropy due to departure from Gaussian behavior at high cross-link densities

227 citations


Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this article, bisphenol A-based epoxy resins were modified with either phenolic hydroxyl or aromatic amine functionally-terminated poly(arylene ether sulphone) oligomers and thermally cured with 4,4′ diaminodiphenyl sulphone.

224 citations


Journal ArticleDOI
TL;DR: Differential scanning calorimetry in dynamic and isothermal modes was used to study the cure kinetics of the commercial epoxy system Narmco 5208, whose main components are bis [4-(diglycidylamino)-phenyl] methane and bis (4-aminophenyl) sulfone as mentioned in this paper.
Abstract: Differential scanning calorimetry in dynamic and isothermal modes was used to study the cure kinetics of the commercial epoxy system Narmco 5208, whose main components are bis [4-(diglycidylamino)-phenyl] methane and bis (4-aminophenyl) sulfone. The data were analyzed in terms of a new mechanistic approach described in the preceding paper

198 citations


Journal ArticleDOI
TL;DR: An optimum level of interfacial bond strength between reinforcing fiber and a polymeric matrix in which it is placed is essential for acceptable composite mechanical properties and performance as discussed by the authors. But this is not the case for all materials.
Abstract: An optimum level of interfacial bond strength between reinforcing fiber and a polymeric matrix in which it is placed is essential for acceptable composite mechanical properties and performance. The...

189 citations


Journal ArticleDOI
TL;DR: In this paper, a progressive damage analysis was developed to study tensile failure of laminated composites containing an open hole, and good agreements were found between the calculations and the data.
Abstract: An investigation was conducted to study tensile failure of laminated composites containing an open hole This investigation was especially concerned with determining the response, type and extent of damage in composites as a function of applied load Both an analysis and experiments were performed for graphite/epoxy composites during the study A progressive damage analysis was developed to study the problem The analysis was verified by an extensive comparison between the numerical calculations based on the analysis and the experimental data obtained during the investigation as well as from published literature Different graphite/epoxy composite materials were considered in the study Overall, good agreements were found between the calculations and the data Based on the study, it was found that the types and extent of internal damage in the notched composites strongly depend on the ply orientation of the laminates The types and the size of damage directly affect the strength and failure mode of the co

186 citations


Journal ArticleDOI
TL;DR: The morphology of a system consisting of a bisphenol A digrycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration.
Abstract: The morphology of a system consisting of a bisphenol A digrycidylether (DGEBA) based epoxy, cured with a cycloaliphatic diamine (4,4'-diamino-3,3'-dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration

164 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental investigation was performed to establish the relationship between fiber-matrix adhesion as determined by single fiber interfacial shear strength tests with the inplane and interlaminar shear properties of graphite/epoxy composites.
Abstract: An experimental investigation was performed to establish the relationships between fiber-matrix adhesion as determined by single fiber interfacial shear strength tests with the inplane and interlaminar shear properties of graphite/epoxy composites. ±45°-tension, Iosipescu, and short beam shear tests were conducted on three identical sets of composites differing only in their fiber-matrix interfacial shear strength. The fiber-matrix interphase and consequently the interfacial shear strength was varied by using the same graphite fiber was different surface modifications, namely untreated, surface treated, and surface treated and coated with a thin layer of epoxy. The surface modification changed the interfacial shear strength by more than a factor of two, while the properties of fibers remained unchanged. The experimental results showed that both inplane and interlaminar shear strengths increased approximately in the same ratio as the interfacial shear strength, however, the inplane shear modulus was relati...

144 citations


Journal ArticleDOI
TL;DR: In this paper, the stiffness reduction as a result of multiple transverse cracking in cross-ply laminates and the crack density dependence on the applied tensile stress are analyzed by linear elastic fracture mechanics.
Abstract: The stiffness reduction as a result of multiple transverse cracking in cross-ply laminates and the crack density dependence on the applied tensile stress are analyzed by linear elastic fracture mechanics. The stress field distribution is obtained by the principle of minimum complementary energy. Two models are suggested which describe the non-uniform stress distribution in the thickness direction of the 0° layer. They contain the variational approach presented by Hashin as a particular case. Elastic ply properties and the Mode I critical strain energy release rate GIc for transverse cracking are the experimental data needed. Model predictions are compared with experimental data for glass fiber/epoxy, AS4/3502, and AS/3501-06 carbon fiber/epoxy cross-ply laminates. The predictions from the suggested models describe both the constraint effect and the crack saturation phenomenon.

Journal ArticleDOI
TL;DR: In this paper, the feasibility of using remote FT-IR spectroscopy to monitor the gelation reaction of an epoxy resin used in advanced composite materials has been studied, and it was found that the primary amine band at 5067 cm−1 was the most sensitive for rapid and accurate real-time monitoring of the cure reaction up to gelation.
Abstract: The feasibility of using remote FT-IR spectroscopy to monitor the gelation reaction of an epoxy resin used in advanced composite materials has been studied. The commercial epoxy resins MY720 and MY721, consisting mostly of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) were cured with diaminodiphenylsulfone (DDS) in a microcapillary cell connected to an FT-IR spectrometer by single silica fiber optics. By operating in the near-IR, direct measurement of the consumption of epoxide and primary amine and growth in hydroxyl groups was possible. It was found that the primary amine band at 5067 cm−1 was the most sensitive for rapid and accurate real-time monitoring of the cure reaction up to gelation. The temperature dependence of amine consumption from 135 to 180°C gave an activation energy of 70 kJ mol−1 for the cure reaction in agreement with DSC. Several artefacts involved in using fiber optic FT-IR in this way have been identified.

Journal ArticleDOI
TL;DR: In this article, the Horie model for describing the cure kinetics of epoxy amine systems is extended to explicitly include the etherification reaction, which becomes significant when there is an excess of epoxide with respect to amine and when the cure is performed at higher temperatures.
Abstract: The Horie model for describing the cure kinetics of epoxy amine systems is extended to explicitly include the etherification reaction, which becomes significant when there is an excess of epoxy with respect to amine and when the cure is performed at higher temperatures

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this article, a series of tough thermosetting resins based on the incorporation of amine-terminated poly(aryl ether ketone) oligomeric derivatives into commercial epoxy/amine resins, through a solventless process, have been evaluated.

Journal ArticleDOI
TL;DR: In this paper, a hybrid composite (CARALL) consisting of thin layers of carbon fiber/ epoxy prepreg sandwiched between aluminium sheets was developed, and it was shown that this class of materials offers higher modulus, higher tensile strength and lower density than 2024-T3 alloy in the longitudinal direction.

Patent
27 Feb 1991
TL;DR: In this paper, an epoxy resin composition comprises an vicinal polyepoxide and a Mannich condensation reaction product curing agent, which are useful in coatings, adhesives, encapsulations and composite matrices.
Abstract: EPOXY RESIN COMPOSITIONS (D#80,775-F) ABSTRACT OF THE DISCLOSURE An epoxy resin composition comprises an vicinal polyepoxide and a Mannich condensation reaction product curing agent. The curing agent is the Mannich condensation reaction product of a phenol, formaldehyde and a polyoxyethylenediamine of the formula: NH2(CH2CH2O)x-CH2CH2NH2, and wherein: x ranges from 1 to 3. These epoxy resin compositions are useful in coatings, adhesives, encapsulations and composite matrices. RM\80775.app

Journal ArticleDOI
TL;DR: In this paper, the authors examined the toughness properties of grafted-rubber concentrate (GRC), dispersed acrylic rubber (DAR), and Proteus rubber-modified brittle epoxy (i.e., highly crosslinked) systems using scanning electron microscopy and optical microscopy techniques.
Abstract: The toughening mechanisms in grafted-rubber concentrate (GRC), dispersed acrylic rubber (DAR), and Proteus rubber-modified brittle epoxy (i.e., highly crosslinked) systems are examined using scanning electron microscopy, optical microscopy and transmission electron microscopy techniques. The toughening of the GRC-modified brittle epoxy system is found to be due to cavitation of the GRC rubber particles, followed by formation of limited shear yielding when the crack propagates. Crack bifurcation and crack deflection are also observed in this system. Only crack bifurcation, crack deflection, and possibly crack/particle bridging mechanisms are operative in the DAR-modified brittle epoxy system. In the case of the Proteus rubber-modified system, the rubber appears to be rigid (Tg ≈ 28°C). As a result, the crack/particle bridging mechanism is not observed. Only crack deflection and crack pinning mechanisms are found. These observations are in agreement with the toughness measurement results (see Part I), which indicate that the GRC rubber provides the most effective toughening, followed by the DAR rubber, and then by the Proteus rubber. An approach for toughening brittle epoxies is also discussed.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this paper, the effect of particle size on the fracture behavior of cured epoxy resin filled with angular-shaped silica was studied and it was shown that the damage zone was formed at the crack tip by particle fracture and by crack diverging.

Journal ArticleDOI
C Jones1
TL;DR: In this article, an improved plasma treatment method was proposed to obtain a greater degree of control over interfacial properties in carbon fiber/epoxy composites, which can be used to improve the interfacial shear strength.

Journal ArticleDOI
TL;DR: In this paper, the effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described, but the extent of the reduction is less than that used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Sepcifications.
Abstract: The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests included beam end and splice specimen testing. The results are compared with the splice tests that were used to establish the epoxy coated bar provisions in the 1989 ACI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coating are found to reduce bond strength significantly, but the extent of the reduction is less than that used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Sepcifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern; bars with relatively larger rib-bearing areas with respect to the bar cross section are affected less by the coating than bars with smaller bearing areas.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this paper, the mechanical and viscoelastic properties of epoxy networks based on the diglycidyl ether of bisphenol A epoxy prepolymer cured with various aromatic diamines, viz. 4,4′- and 3,3′-diaminodiphenylsulphone, 4, 4′-and 3, 3′-dimethylmethane, bis(4-(4-aminophenoxy)phenyl)-propane, and (4-(aminophenox)-propANE, were studied.

Journal ArticleDOI
TL;DR: In this article, the dependence of the interfacial shear strength on the bulk material matrix properties using model compounds based on epoxy/amine chemistry was evaluated using AS4, carbon fibers were used as the subject for these measurements with both a difunctional epoxy (DGEBA) system as well as a tetra functional epoxy system.
Abstract: Experiments were conducted to determine the dependence of the interfacial shear strength on the bulk material matrix properties using model compounds based on epoxy/amine chemistry. AS4, carbon fibers were used as the subject for these measurements with both a difunctional epoxy (DGEBA) system as well as a tetrafunctional epoxy (MY720) system. Amine curing agents were carefully chosen to produce matrices which produced a range of matrix properties from brittle, elastic to ductile, plastic. The fiber-matrix interfacial chemistry was constant throughout this study by always using a stoichiometric amount of curing agent. The results indicate that, for both the difunctional as well as the tetrafunctional epoxy system, the interfacial shear strength (as determined by the fragmentation test) decreases nonlinearly with decreasing modulus of the matrix. Linear elastic analysis yields a nearly linear relationship, for both systems, between the interfacial shear strength and the product of strain to final break and the square root of the matrix shear modulus. A linear relationship is also found between the difference in test temperature and glass transition temperature of the cured matrix and the interfacial shear strength. Additionally, the failure mode is seen to remain interfacial as the ductility of the matrix changes.

Journal ArticleDOI
TL;DR: In this article, a modified epoxy resins with poly(phthaloyl diphenyl ether) (PPDE), soluble in the uncured epoxy resin without using solvents, was prepared by the Friedel-Crafts reaction of phthaloyl chloride and diphenly ether.
Abstract: Poly(aryl ether ketone)s were used as modifiers for bisphenol-A diglycidyl ether epoxy resin (AER 331) cured with methyl hexahydrophthalic anhydride. Poly(phthaloyl diphenyl ether) (PPDE), soluble in the uncured epoxy resin without using solvents, was prepared by the Friedel-Crafts reaction of phthaloyl chloride and diphenyl ether. The mechanical, thermal, and dynamic viscoelastic properties of the modified resins with PPDE were examined and compared to the parent resin (AER 331). The fracture toughness, KIC, for the modified resins increased at no expense to their mechanical and thermal properties on 10 wt % addition of PPDE with molecular weights of more than 17,000. The toughening mechanism is discussed based on the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system.

Patent
20 Feb 1991
TL;DR: In this paper, a method for forming a structure comprising a layer of polymeric material containing epoxy groups having preselected regions of differing degrees of polymerization and differing refractive indices is presented.
Abstract: A structure comprising a layer of polymeric material containing epoxy groups having preselected regions of different degrees of polymerization and different refractive indices; and a method for forming a structure comprising a layer of polymeric material containing epoxy groups having preselected regions of differing degrees of polymerization and differing refractive indices which comprises providing a polymeric material containing epoxy groups on a support and selectively modifying the refractive index in said material.


Journal ArticleDOI
TL;DR: In this paper, a bisphenol A-based epoxy adhesive was modified by polyblending with Kraft Lignin (L) and the possibility of an enhanced degree of bonding between L and the epoxy network was discussed.
Abstract: A bisphenol A based epoxy adhesive (EP) was modified by polyblending with Kraft Lignin (L). A systematic investigation of the thermally cured EP-L polyblends with up to 40% by weight L was undertaken. Adhesive shear tests, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and solid-state CP-MAS NMR spectroscopy were performed to establish the effect of L on the mechanical properties of the polyblends and on the morphology of these crosslinked structures. The possibility of an enhanced degree of bonding between L and the EP network is discussed. This bonding can arise from a chemical reaction between L and some unreacted amine groups present in the hardener.

Journal ArticleDOI
TL;DR: In this article, the mechanical properties of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3 dimethyldicyclohexyl-methane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration.
Abstract: The mechanical properties of a system consisting of a bisphenol A diglycidylether (DGEBA) expoxy, cured with a cycloaliphatic diamine (4,4′-diamino-3,3 dimethyldicyclohexyl-methane, 3DCM), in the presence of an epoxy-terminated butadiene-acrylonitrile random copolymer (ETBN), was studied as a function of the cure schedule and the initial rubber concentration. Fracture toughness (KIc) and fracture energy (GIc) were increased, while Young's modulus and yield strength decreased slightly with increasing volume fraction of the dispersed phase. We show that there is no significant influence of the precure schedule and of the various observed particle diameters on the mechanical properties for a constant rubber volume fraction. In our case, the main deformation process in the rubber-modified epoxy networks is shear yielding while cavitation is negligible.

Journal ArticleDOI
TL;DR: In this paper, the interlaminar shear strength of unidirectional ultra-high-modulus polyethylene composites was measured as a means of accessing the level of fibre/epoxy resin adhesion for a number of different reinforcing yarns, produced by melt and gel-spinning.
Abstract: The interlaminar shear strength of unidirectional ultra-high-modulus polyethylene composites was measured as a means of accessing the level of fibre/epoxy resin adhesion for a number of different reinforcing yarns, produced by melt and gel-spinning. The fibres were shown to possess poor adhesive properties due partly to inadequate wetting associated with the inert polyolefine surface and also because of a weak boundary layer, formed by the segregation of low molecular weight impurities to the surface during fibre formation. The interlaminar shear strength was significantly increased by pretreating the reinforcement with an oxygen plasma. This improved wetting by producing oxygen-containing groups on the fibre surface and removed the weak boundary layer by the formation of a cross-linked skin. For a fixed fibre volume fraction, the interlaminar shear strength was found to be inversely proportional to the filament diameter. The other mechanical properties were shown to be largely independent of fibre/resin adhesion, with plasma treatment having little or no effect.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the dependence of glass transition Tg on both crosslink density and network chain flexibility and determined the viscoelastic coefficients Cg1 and C which are related to some free volume characteristics on the molecular scale.
Abstract: Six epoxy networks with various structures built up from a diepoxy prepolymer, DGEBA, and three different diamines or mixtures of a monoamine and a diamine were studied by dynamic mechanical analysis in the glass transition region. The systems were designed in order to investigate the dependence of glass transition Tg on both crosslink density and network chain flexibility. The time (frequency)—temperature superposition principle (WLF equation) was used to determine the viscoelastic coefficients Cg1 and C which are related to some free volume characteristics on the molecular scale. Cg1, related to the free volume fraction available at Tg depends mainly on crosslink density, even though the product Cg1C, related to the free volume expansion coefficient, is dependent on both chain flexibility and crosslink density. Thus, viscoelastic properties determined over large temperature and frequency ranges are shown to yield more precise information on epoxy network structure than the simple analysis of glass transition temperature.

Journal ArticleDOI
01 Jan 1991-Polymer
TL;DR: In this article, the six-bond aliphatic link segment formed when diglycidyl ether of bisphenol-A (DGEBA) is cured with aromatic amines is analyzed using molecular mechanics.