Showing papers on "Epoxy published in 1975"

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

Abstract: The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy1. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ∼4000J/m2 (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryc) in that was a maximum when bond thickness was equal to 2 ryc. At bond thicknesses less than 2 ryc, there was a restraint on the development of the plastic zone resulting in lower values.

Photocurable epoxy compositions containing group Va onium salts

Abstract: Cationic polymerization of epoxy resin such as epoxy monomers or prepolymers, can be achieved by use of certain radiation sensitive aromatic onium salts of Group Va elements. Curable compositions are provided which can be used as sealants, coating compounds, encapsulants, etc.

The concept of one polymer composites modelled with high density polyethylene

Abstract: One polymer composite materials have been prepared using a difference in melting points between the components. This depends on the fact that aligned and extended chains provide thermodynamically more stable crystals, which thus will have higher melting points than conventionally crystallized melts. The growth of transcrystalline regions in the melt matrix at the interface plus an observed partial melting between fibre and matrix are indications of a strong and intimate interfacial bond with a gradient in morphologies for the system studied, high-density polyethylene. The pull-out test is a simple and adequate method for evaluating the interfacial shear strength of one polymer composites. The value for the high-density polyethylene composite falls between the strengths for glass-reinforced polyester and epoxy resins. However, the interfacial strength in the polyethylene composites is due mainly to the unique epitaxial bonding rather than the radial forces from compressive shrinkage. The low critical aspect ratio for the filaments in these polyethylene composites suggests possible advantageous uses as short fibrereinforced materials where the interfacial strength is a controlling factor.

Curing Stresses in Composite Laminates

Abstract: Analysis of curing stresses in resin matrix composite laminates involves a temperature range over which variation of elastic moduli is appreciable. A method based on total stress-strain-temperature relations is formulated and applied to determine the curing stresses in boron/epoxy composite laminates. This method is shown to be preferable to the incremental method because the former requires the thermal strains and the stress-strain relations only at the final temperature of interest. The use of incremental constitutive equations is also discussed, and it is shown that proper care must be exercised to insure inclusion of interaction terms that have no counterparts in linear theories.

Photocurable compositions containing group via aromatic onium salts

Abstract: Cationic polymerization of epoxy resin materials, such as epoxy monomers or prepolymers, can be achieved by use of certain radiation sensitive aromatic onium salts of Group VIa elements. Curable compositions are provided which can be used as sealants, coating compounds, encapsulants, etc.

Process for electrodepositing cationic compositions

Abstract: It has been found that aqueous coating compositions comprising a blocked organic polyisocyanate, an amine adduct of an epoxy group-containing resin, and optionally a catalyst for urethane formation can be electrodeposited. These compositions deposit on the cathode to provide coatings having excellent properties.

Characterization of the time-temperature-viscosity behavior of curing B-staged epoxy resin

Abstract: The work described herein was initiated in order to generate resin characterization data that could describe a B-staged epoxy material via the viscosity-time-temperature interactions that are inherently related to the nature of thermoset processing. The technique of chemorheology is explored as a means of characterizing the viscosity-time-temperature behavior of the B-staged epoxy resins. The resins studied are typical of those available as glass-impregnated prepreg bonding sheets used to manufacture multilayer printed wiring boards. The B-staged resins were characterized isothermally at various curing temperatures. Their isothermal behavior was correlated via an empirical viscosity expression in the form of a dual Arrhenius model. Experiments were then conducted in a nonisothermal temperature mode, measuring viscosity as a function of both time and temperature. The viscosity model was taken into the nonisothermal temperature mode by introducing a time-temperature integral. Good correlations between measured and predicted dynamic viscosity profiles are presented. Deviations are explained in terms of resin chemistry. The generalizations of behavior are discused. Calculations are presented which allow the comparison of the various B-staged resins in terms of their viscosity behavior under the influence of an actual lamination thermal profile.

Deformation of a carbon-epoxy composite under hydrostatic pressure

Abstract: This paper describes the behaviour of a carbon-fibre reinforced epoxy composite when deformed in compression under high hydrostatic confining pressures. The composite consisted of 36% by volume of continuous fibres of Modmur Type II embedded in Epikote 828 epoxy resin. When deformed under pressures of less than 100 MPa the composite failed by longitudinal splitting, but splitting was suppressed at higher pressures (up to 500 MPa) and failure was by kinking. The failure strength of the composite increased rapidly with increasing confining pressure, though the elastic modulus remained constant. This suggests that the pressure effects were introduced by fracture processes. Microscopical examination of the kinked structures showed that the carbon fibres in the kink bands were broken into many fairly uniform short lengths. A model for kinking in the composite is suggested which involves the buckling and fracture of the carbon fibres.

Fracture toughness and mechanical behaviour of an epoxy resin

Abstract: The variation of fracture and mechanical properties of epoxy resin Epikote 828, cured with diaminodiphenyl-methane by variation of the resin/amine ratio has been determined. Observations of the crack tip have shown that fracture toughness variations can be attributed to the different blunting characteristics of the various resin/amine compositions. A systematic variation in the thermal transitions of the resins also occurs as a function of composition. Investigations by chemical etching and small angle X-ray scattering have failed to reveal a structural entity which can be invoked to explain the trends in fracture and mechanical properties. It has been found that care must be taken when choosing the method of evaluation of fracture parameters in order that meaningful comparisons can be made between different resin compositions.

Environmental effects on deformation, strength, and degradation of unidirectional glass-fiber reinforced plastics. II. Experimental study

Abstract: Glass-fiber reinforced epoxy (GRP) and unfilled epoxy specimens were exposed to different environmental conditions consisting of hot- and cold-water absorption and subsequent drying. Effects of the environmental history on deformational and strength characteristics of the composite material were investigated. GRP specimens exposed to hot water undergo pronounced degradation, which sets in shortly after exposure and is associated with a significant irrecoverable weight loss. Degraded specimens are characterized by higher void content and lower strength compared with their cold-water and reference counterparts. The degradation process is attributed to penetration of water into the matrix-fiber interfaces and is followed by an attack, at high temperatures, on the glass-fibers surface and coupling agent. As a result, glass constituents are leached out and then removed from the system by diffusion. The degradation effect was also confirmed by micro-observation of the fractured surfaces and by infra-red spectroscopy. A simple and effective testing method is recommended, permitting detection of degradation onset and its progress by simultaneous measurement of weight and dimensional changes with time.

Methods for Improving the Impact Resistance of Composite Materials

Abstract: A three-phase program to improve the impact resistance of composite materials was undertaken. In the first phase, the Charpy impact test was investigated for its utility in characterizing impact performance. It was found that the results of the standard Charpy test can be misleading, but the addition of instrumentation to provide load and energy histories can make this test a useful one. The importance of differentiating between initiation energy and propagation energy is shown, and a new parameter (the "Ductility Index") is proposed, along with maximum stress and total energy, as a useful measure for comparing impact behavior of materials. The instrumented Charpy test was used to investigate impact behavior of unidirectional, epoxy-matrix composites reinforced with fibers of E-glass, Kevlar 49, and graphite. In addition, two unidirectional hybrid composite materials consisting of graphite and Kevlar 49 fibers in epoxy were investigated. Comparisons were made with quasi-static three-point bend tests. It was found that the hybrid materials had significantly higher impact energies, ductility indices, and maximum stresses than the all-graphite fiber material. Impact behavior of [′45] graphite/epoxy and hybrid Kevlar 49-graphite/epoxy panels, representative of aircraft fuselage shear panels, was studied using a ball-drop test. Results indicate a significant improvement in impact resistance with hybrid construction.

Well treating process for consolidating particles with aqueous emulsions of epoxy resin components

Abstract: Particles are resin-coated in a remote location, such as a subterranean reservoir or a sand or gravel pack, by contacting them with a cationic aqueous emulsion which contains a resin-forming mixture of a polyepoxide and a relatively water-soluble tertiary-amine that is capable of both catalyzing the polymerization of the polyepoxide and oil-wetting of solid surfaces

Crack Growth Resistance of Random Fiber Composites

Abstract: Crack growth resistance of a random glass fiber composite has been studied by applying the concepts of Linear Elastic Fracture Mechanics. The crack growth resistance curves (R-curves) for epoxy and polyester composites have been developed to study the total fracture behavior of these composites. It is shown that the R-curve approach is suitable for these type of materials. An attempt has been made to use the information from the R-curves to predict the fracture strength of plate specimens with a hole at the center and subjected to tensile loading.

Powder coating compositions comprising a blend of coreactive polymers - II E

Abstract: Powder coating compositions are disclosed which comprise a blend of coreactable, thermosettable copolymers each of which have at least two different functional groups Ordinarily, these polymers will be qualitatively difunctional, although they may contain more than two different functional groups, and quantitatively polyfunctional At least one of the copolymers has epoxy functionality as one of its two or more different functionalities Thus, in the preferred embodiments, the first copolymer of the blend has epoxy functionality and a second functionality selected from amide functionality, anhydride functionality and hydroxy functionality and is crosslinkable with the second copolymer through at least two different types of functional groups on the first copolymer The second copolymer also is crosslinkable with the first copolymer through at least two different types of functional groups on the second copolymer and may be (a) anhydride functional and carboxy functional, (b) carboxy functional and amide functional, (c) carboxy functional and hydroxy functional, (d) epoxy functional and amide functional or (e) epoxy functional and anhydride functional The second copolymer is advantageously employed in an amount such that its functionality of greatest concentration provides about 03 to about 12 functional groups per functional group on the first copolymer and the functionality of lesser concentration provides about 01 to about 04 functional groups per functional group on the first copolymer

Glass fiber sizing composition for the reinforcement of resin matrices and method of using same

Abstract: A glass fiber size is provided which contains a phenolic epoxy resin, the reaction product of the partial ester of a polycarboxylic acid containing one or more unesterified carboxyl groups with a compound containing more than one epoxy group, an amino silane coupling agent, a methacryloxy alkyl trialkoxy silane, and a non-ionic surface active agent. A method of sizing glass fibers and glass fibers sized with the aforementioned composition are also provided.

Method of electrodepositing quaternary sulfonium group-containing resins

Abstract: Synthetic resins containing quaternary sulfonium base groups are prepared by reacting an epoxy-group containing material with a sulfide in the presence of an acid. The resins may contain epoxy groups or they may be essentially epoxy-group free, and may optionally contain oxyalkylene groups. When dispersed in water, the aqueous dispersion preferably contains boron. The resultant dispersion can be applied to a wide variety of substrates by electrodeposition and will deposit on the cathode to provide coatings of unique properties, including high resistance to corrosion and staining.

Plugging subterranean regions with acrylic-epoxy resin-forming emulsions

Abstract: A subterranean region is plugged by flowing into it an aqueous emulsion containing a polyepoxide, a polycarboxy polymer, and a material for controlling the rate of the interaction of said polymers, with the proportions of said materials arranged to cause the emulsion to become a resinous plug after being emplaced.

Aqueous coating composition from aminoplast and reaction product of tertiary amine and polymer containing terminal epoxy groups

Abstract: A water-borne thermosetting coating composition comprising a stable dispersion or solution of: (A) a terminally functional epoxy resin reacted with (B) a tertiary amine; and (C) a nitrogen resin Is provided. Such composition is useful for spray-, flow-, dip-, roller-, and electro-coating metal and paper substrates and provides coatings of improved properties, including high degree of flexibility during machining and stamping of the coated articles, corrosion resistance, gloss, hydrolytic stability, and non-adulterating of foods and beverages in contact therewith.

Removal of glass coverslips from cultures flat embedded in epoxy resins using hydrofluoric acid.

Abstract: SUMMARY A technique is described by which the glass coverslip of a culture, flat embedded in epoxy resins can be removed easily using hydrofluoric acid. Removal by this method leaves the surface of the resin quite smooth and suitable for subsequent thin or ultrathin sectioning for electron microscopy.

Hardenable epoxy resin compositions and process for making the same

Abstract: A curable composition comprising a mixture of an epoxy resin and a hardener can be prepared by dissolving the resin and curing agent in a low boiling solvent and flashing off the solvent at temperatures in excess of 400° F, the evaporating solvent cooling the composition and minimizing precure of the resin. Reinforced composites can be prepared by passing a supporting material such as a continuous web strand or roving through the resin solution and thereafter heating at temperatures above 400° F to remove the solvent without appreciably precuring the resin. The curable epoxy compositions can be used for molding, laminating and the like.

Low flow, vacuum bag curable prepreg material for high performance composite systems

Abstract: A composite prepreg material comprising a carboxy-terminated polybutadiene, an epoxy novolak resin, a carboxylic acid accelerator and an epoxy catalyst. When reinforced with well known reinforcing fibers or filaments, the material is eminently suitable for use in the fabrication of structural composites.

Epoxy modified acrylic latices and method of producing same

Abstract: Acrylic latices containing epoxy resins are prepared by emulsion polymerization in which an epoxy resin (polyepoxide) is incorporated into at least one of the monoethylenic monomers, including an epoxy-reactive monomer, and the monomers including the epoxy resin are emulsified into water containing surfactant to provide the oil phase of an oil-in-water emulsion. The monomers are then polymerized in the aqueous emulsion using a free radical polymerization catalyst and a reaction temperature which does not cause premature reaction between the epoxy groups and the reactive monomer. This provides thermosetting latex particles of fine particle size in the presence of less emulsifying agent than is normally needed.

Early Fatigue Damage Detection in Composite Materials

Abstract: Detection of early fatigue damage in composite materials by nondestructive inspection (NDI) techniques has been demonstrated for ±45° Glass/Epoxy, and ±45°/0° Graphite/Glass/Epoxy. Dynamic axial mo...

Interfacial Crack Propagation

Abstract: Interfacial crack propagation studies were conducted on specimens of epoxy bonded to aluminum under both tensile and bending loads. The effect of surface roughness of the aluminum on fracture toughness was measured for four different surface finishes: polished, milled, glass-peened and sandblasted. It was found that increased surface roughness resulted in greater fracture toughness and that the interfacial cracks replicated the surface features of the aluminum. Microscopic studies of the failure surfaces indicated that crack propagation occurs in the epoxy near the interface, and that a residue of epxoy remains bonded to the aluminum. The magnitude of the residual stresses due to casting and curing of the epoxy was determined by photoelastic techniques. Methods were developed for analyzing the birefringent pattern in the epoxy to determine the magnitude of the elastic residual stress and the frozen stress. It was found that the residual stresses contributed 15 to 20% of the strain required for cr...