Showing papers on "Epoxy published in 1988"

Impact-Induced Delamination—A View of Bending Stiffness Mismatching

Abstract: Fiber-reinforced composite materials are very susceptible to impact loading. The damage characteristics of a composite material subjected to subperforation impact can be classified as indentation, fiber breakage, matrix cracking, fiber-matrix debonding and delamination. Among these damage modes, delamination has been found to be important for all cases of loading. In this study, the damage characteristics of many composite plates made of glass/epoxy, Kevlar/epoxy, and graphite/epoxy were investigated. Delaminations in the impacted composite plates were inspected by high-intensity light, X-ray radiog raphy, ultrasonic imaging system and edge replication. It was found that delamination in every interface of impacted composite plates had a peanut-like shape. Since membrane ef fect could be ignored in this study, stresses caused by bending were the major stresses which should be responsible for the delamination. Although the interlaminar stresses had been analyzed by many investigators for the determination o...

Process and compositions for reinforcing structural members

Abstract: A two-part system for reinforcing a hollow structural member and its method of use are provided. Part A of the two-part system is formed by adding a filler and unexpanded, thermally-expandable microspheres to a liquid thermosetting resin, such as an epoxy resin, in a quantity sufficient to produce a dough-like mass which can be readily kneaded. Part B is formed by adding a filler and a colorant, such as carbon black, to a liquid curing agent, again forming a dough-like mass. The curing agent is compatible with the thermosetting resin to promote cross-linking of the thermosetting resin upon contact with the curing agent. A hollow structural member is cleared of debris of the like and may be preheated to enhance the rate at which the thermosetting resin cross-links. The two parts are blended together until a reactive third dough of substantially uniform mixture is formed. The uniformity of the blending is confirmed when the reactive third dough attains a uniform color intermediate the color between the colors of part A and part B. The blended reactive dough is then packed into the cavity of the cleaned structural member. The cavity is then preferably closed with a closure plate. As the curing agent promotes the cross-linking reaction of the thermosetting resin, the exothermic reaction generates heat which is transferred to the unexpanded, thermally-expandable microspheres, causing the microspheres to expand. The expansion of the microspheres causes the reactive dough to rise, substantially filling the cavity. As the reactive dough cures, it bonds rigidly to the surfaces which it contacts. The reactive dough is allowed to fully cure, whereupon a solid lightweight reinforcement member rigidly bonded to the structural member is formed. The reinforced structure has good strength and energy absorption characteristics. The present system is particlarly suitable for use in reinforcing motor vehicle structure which have been cold-worked during repair of collision damage.

Measurements of Matrix Cracking and Delamination Caused by Impact on Composite Plates

Abstract: Tests were performed measuring the locations and extents of delaminations and matrix crackings in 3-in. by 3-in. Fiberite T300/934 graphite/epoxy plates impacted by 1/2-in. diameter aluminum spheres. Plates with six ply orientations were tested. The impactor speeds ranged from 700 to 1300 in/sec. The plates were inspected by C-scan both before and after impact. The plates were also dissected after impact and examined visually for damage. In addition, the longitudinal and transverse tensile, compressive, and shear properties of the material were measured.

Residual Strength of a Carbon/Epoxy Composite Material Subjected to Repeated Impact:

Abstract: The residual tensile and compressive strengths of specimens cut from composite plates subjected to repeated impact at various energy levels were measured. The 16-ply quasi- isotropic composite plates were 2 mm thick, fabricated from Hercules AS4/3501-6 car bon/epoxy prepreg. Impact energy level and number of impacts were found to be major factors influencing strength degradation. However, strength degradation was limited to the region near the impact point.

The effect of fiber-matrix stress transfer on the strength of fiber-reinforced composite materials

Abstract: A model for the mechanism of tensile failure in oriented fiber composites based on random fragmentation of the reinforcing fibers biased by stress concentrations at fracture sites has been developed. Single-fiber composites and composite strands of 34 to 36 volume percent fiber were prepared from an epoxy resin reinforced with Hercules AS4, HMS4, and IM6G carbon fibers. Fiber strength distributions and single-fiber composite fragmentation data were used to calculate theoretical composite tensile strengths, which were then compared with experimental values. The fractures in single-fiber composites were observed in situ under cross-polarized light, and the mechanisms of interfacial failure were discussed.

Photosensitive thermosetting resin composition and method of forming solder resist pattern by use thereof

Abstract: A photosensitive thermosetting resin composition, comrpising (A) a photosensitive prepolymer containing at least two ethylenically unsaturated bonds in the molecular unit thereof, (B) a photoinitiator, (C) a photopolymerizable vinyl monomer and/or an organic solvent as a diluent, (D) a finely powdered epoxy compound containing at least two epoxy groups in the molecular unit thereof and exhibiting sparing solubility in the diluent to be used, and optionally (E) a curing agent for epoxy resin, excels in developing property and sensitivity and enjoys a long shelf life. By subjecting this photosensitive thermosetting resin composition to coating, exposure, development, and post-­curing, there can be formed a solder resist pattern which excels in adhesion,insulation resistance, resistance to electrolytic corrosion, resistance to soldering temper­ature, resistance to chemicals, and resistance to plating.

Characterization and role of an elastomeric interphase on carbon fibers reinforcing an epoxy matrix

Abstract: Oxidized carbon fibers were coated using an on-line filament winding process with an elastomeric adduct crosslinkable and compatible with an epoxy matrix. The coating and modifications of the epoxy network were studied by dynamic mechanical measurements. Assuming that apparent activation energies of the secondary relaxation βe of the epoxy network and main relaxation αa of adduct are very different, it is possible at low frequencies to separate the two peaks. The composite material can be described as a three phase system: an epoxy network as matrix, carbon fibers, and a soft interlayer. The mechanical behavior of unidirectional composite materials studied by impact and bending tests is strongly dependent on the presence and the thickness of the coating at the carbon fiber surface.

Ultraviolet curable conductive resin

Abstract: A UV curable electrically conductive adhesive has been developed with low resistivity, adequate lap shear strength, good thermal stability, and very stable conductivity at high temperatures of about 100° C. and high humidity. The adhesive may be applied by silk screen printing and cured by UV in about 8 seconds. The adhesive may also be used as a replacement of solder in automated surface mount technology for electronic circuit fabrication. The adhesive is a mixture of (A) a blend of an acrylate epoxy and a urethane, a copolymer of an acrylate epoxy and a urethane, or mixtures thereof; (B) a polyfunctional acrylate monomer; (C) a photoinitiator, and (D) a conductive filler. Optionally, adhesion promoters and flow control agents may be used.

Fatigue behaviour of hybrid composites

Abstract: A study has been made of the fatigue behaviour in repeated tension of unidirectional and [(±45, 0, 0)2]s hybrid laminates composed of XAS carbon fibres and E-glass fibres in the same 913 epoxy resin. The ordinary mechanical properties of these composites are close to those predicted by simple, conventional models of hybrid behaviour. For the unidirectional materials, the fatigue stress for a given life is not a linear function of composition, showing a substantial positive deviation from the rule of mixtures. This behaviour closely mirrors that of unidirectional carbon-Kevlar hybrids reported in Part 1 of this work. In terms of strain-life comparisons, results for all hybrid compositions and plain carbon fibre reinforced plastic fall within a single scatter-band. These features are also reflected in the fatigue behaviour of the more complex hybrid laminate.

Epoxy resin composition

Abstract: PURPOSE:To obtain a resin composition capable of sufficiently maintaining the mechanical properties and adhesive strength even in a high-temperature atmosphere and having excellent workability and applicable as a heat-resistant paint and adhesive, by mixing an epoxy resin with a specific amount of a polymetallocarbosilane. CONSTITUTION:100pts.wt. of an epoxy resin is compounded with 5-200pts. of a polymetallocarbosilane. The polymetallocarbosilane is a polymer composed of (A) a carbosilane bond unit of formula I (R1 and R2 are lower alkyl,, phenyl or H) and (B) a metalloxane bond unit of formula II (M is Ti, Zr, Mo or Cr) wherein the units A and B are randomly bonded in the skeleton of main chain and/or a polycarbosilane segment composed of the chain of the unit A is crosslinked with the B. The ratio of the total number of A of the total number of B is preferably (1-10):1 and the number-average molecular weight of the polymetallocarbosilane is preferably 400-50,000. The flexibility and adhesive strength of an adhesive layer can be improved by adding 10-900pts. of a silicone resin to 100pts. of the polymetallocarbosilane.

Aqueous epoxy resin compositions and metal substrates coated therewith

Abstract: This invention relates to aqueous epoxy resin-containing compositions and to such compositions which are particularly useful for depositing coatings on metallic substrates in order to protect substrates against corrosion. The aqueous compositions generally comprise (A) an organic resin component consisting essentially of at least one water-dispersible or emulsifiable epoxy resin or a mixture of resins containing more than 50% by weight of at least one water-dispersible or emulsifiable epoxy resin, (B) chromium trioxide, and (C) water, said composition further characterized as being substantially free of strontium chromate. The aqueous compositions may also contain other ingredients including zinc and/or ferro alloys. These aqueous compositions are useful as pretreatment coatings on metal surfaces, and in particular, on steel and on galvanized and aluminized metal substrates. This pretreatment coating can then be coated with weldable or non-weldable primer coatings followed by the application of decorative topcoats such as appliance topcoats or automotive topcoats. The invention also relates to metal substrates which have been coated with the pretreatment coating and, optionally, the weldable or non-weldable primer coatings.

Epoxy resin composition

Abstract: An epoxy resin composition consisting essentially of (A) an epoxy resin, (B) a curing agent, (C) a curing promoter, (D) a polyphenylene ether resin, and (E) a filler.

Cross-linked polymers : chemistry, properties, and applications

Abstract: Cross-Linking and Structure of Polymer Networks Intramolecular Reaction: Effects on Network Formation Selective Quenching of Large-Scale Molecular Motions Rubber Elasticity Modulus Star-Branched Nylon 6 Urethane and Melamine-Formaldehyde Coatings Effect of Ionizing Radiation on Epoxy Adhesive Frequency-Dependent Dielectric Analysis Fluorescence Optrode Cure Sensor Deformation Kinetics of Cross-Linked Polymers Plastic Deformation in Epoxy Resins Fractoemission Fatigue Behavior of Acrylic Networks Epoxy Resins Cured with m-Phenylene Diamines Cross-Linking of an Epoxy with a Mixed Amine Thermal Stress Development Recycling of Cured Epoxy Resins Semiinterpenetrating Networks Development of Multiphase Morphology Polyurethane-Acrylic Coatings Ionomer Interpenetrating Polymer Network Coatings Liquid Crystalline Oligoester Diols Cross-Linkable Heterogeneous Oligoester Diols Benzocyclobutene in Polymer Synthesis Bisbenzocyclobutene High-Temperature Resin Bismaleimidodiphenyl Methane Cobalt(II) Chloride-Modified Films Tetraethyleneglycol Diacrylate Polydimethacrylates: Dental Applications Monomer Interaction: Effects on Polymer Cure Amide-Blocked Monomers Cross-Linkable Substrate-Reactive Copolymers

Novolac coated ceramic particulate

Abstract: Ceramic particulate useful as a proppant in hydraulic fracturing and in gravel packing operations is provided which comprises a ceramic (sometimes vitreous) core surrounded by an epoxy resin coating Novolac epoxy resin compounds without any substantial acid soluble filler are used The result is a product which combines the excellent solvent resistance of the ceramics with the acid resistance of the resin The resin coating gives the added benefits of lower specific gravity and improved crush resistance

Resin-encapsulated semiconductor device

Abstract: A resin encapsulated semiconductor device sealed with an epoxy resin molding material particularly containing a brominated epoxy resin as a flame retardant with the bromine content of 0.5% by weight or less, antimony oxide as a flame retardant in an amount of 2.0% by weight or more and a quaternary phosphonium tetrasubstituted borate as a curing accelerator is excellent in connection reliability at Au/Al junctions and heat resistance.

Environmental degradation of the electrical and thermal properties of organic insulating materials

Abstract: The sorption behaviour of water molecules in epoxy-based thermosetting networks is discussed and related to the modifications of the polymer properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental liquid-sorption tests, differential scanning calorimetry (DSC), and electrical analyses. Two modes of moisture sorption are assumed: a sorption leading to an increase in the free volume of the system, and adsorption of the water molecules due to hydrogen bonding to hydrophilic groups present in the network and to the surfaces of “holes” which make up the excess free volume of the glassy polymer. Electrical investigation improved the understanding of the hygrothermal ageing phenomena. Water conditioning of the composites modified the surface and bulk resistivities as a consequence of microstructural damage and plasticization.

Material having a resistivity with a positive temperature coefficient

Abstract: The invention relates to an electrically conductive, polymer based material with electrical resistivity having a positive temperature coefficient The material comprises a matrix of thermosetting polymer having conductive particles in the form of fibers distributed through the polymer The polymer can be an epoxy resin, polyimide, unsaturated polyester, silicone, polyurethane or phenolic resin, and the fibers can be carbon fibers, carbon fibers coated with metal or metal alloy, graphite fibers, graphite fibers coated with metal or metal alloy, graphite intercalation compound fibers, metal fibers, ceramic fibers, or ceramic fibers coated with a metal or metal alloy

A new technique for ultrasonic-nondestructive evaluation of thin specimens

Abstract: Combining standard FFT methods with conventional ultrasonics, a method has been developed for measuring the phase velocity, the group velocity and the attenuation in ultrathin specimens (submillimeter or subwavelength in thickness). A detailed description of this technique is given. The technique was used on four disparate materials: aluminum, an epoxy, a particulate composite and a graphite-fiber/epoxy composite. The method works equally well for thin or thick specimens, and for dispersive as well as nondispersive media.

Epoxy resin compositions for use in low temperature curing applications

Abstract: Compositions comprising a mixture of (A) an epoxy resin composition consisting essentially of (1) at least one epoxy resin which has an average of not more than 2 vicinal epoxy groups per molecule; (2) at least one epoxy resin which has an average of more than 2 vicinal epoxy groups per molecule and (3) at least one rubber or elastomer; and (B) optionally, a low viscosity reactive diluent, are useful in preparing low temperature curable compositions. Also claimed is low temperature curable compositions containing the above components (A) and (B); (C) at least one cycloaliphatic amine hardener and (D) optionally, an accelerator for component (D).

The influence of the interphase on composite properties: Poly(ethylene‐co‐acrylic acid) and poly(methyl vinyl ether‐co‐maleic anhydride) electrodeposited on graphite fibers

Abstract: The electrodeposition of saturated copolymers onto carbon fibers is investigated, focusing particular attention on improvement of shear and impact properties of the corresponding composites. Carbon fibers are electrocoated with poly(ethylene-co-acrylic acid) and poly(methyl vinyl ether-co-maleic anhydride) from aqueous media, and fabricated into epoxy composites. The results of interlaminar shear strength (ILSS) tests, initially employed to assess fibermatrix adhesion, are vitiated by the occurrence of mixed-mode failure. Interfacial shear strength (IFSS) is hence evaluated by stressing single-fiber composite specimens to obtain ultimate aspect ratios of the fiber fragments. The data are combined with fiber strengths by a recently developed statistical theory (1) to yield a distribution for IFSS. Both copolymer interphases improve fiber-matrix bonding to an extent greater even than that obtained with commercial fiber surface treatment. Good fiber-matrix adhesion is further apparent from SEM studies of fractured ILSS test specimens. A key to this improved adhesion is the interpenetration of matrix resin and interphase polymer, revealed by electron microprobe analysis (2). Notched Izod impact strength is also increased over uncoated-fiber composites. These copolymer interphases behave as deformable interlayers, absorbing impact energy and blunting the growing crack tip. Further energy is absorbed in deflecting the crack through a more tortuous path. Simultaneous improvements in impact and shear strengths are thus obtained, which may be further enhanced by optimizing the electrodeposition parameters and the coating thickness. The influence of the interphase on composite properties is better understood from this study, paving the way for refinement in interphase design.

Mechanical behaviour of polymer concrete systems

Abstract: The mechanical behaviour of epoxy and polyester polymer concrete systems was studied under different loading conditions at various temperatures, resin content, and glass fibre content. While polymer content varied between 10 and 20% of the total weight of polymer concrete, the fibre content was limited to 4% by weight. The temperature was varied between 22 and 110°C, depending on the glass transition temperature of the resin. Compared to vibration, the compaction method of preparation reduces the void content and enhances the strength and modulus of polymer concrete. The compressive and flexural strength and stiffness of the polymer concrete systems increase up to a certain limit of polymer content at which they exhibit maximum strength and stiffness. They subsequently decrease or remain almost constant with further increase in polymer content. The strength and stiffness of polymer concrete are very much dependent on the temperature. The stiffness model, based on inclusion theory, yields satisfactory results for the three-phase polymer concrete. Using this model, the compression and flexural modulus of polymer concrete can be predicted from the properties of the constituents and their composition. Incremental strength and stiffness models developed in this study are effective in predicting the increase in strength and stiffness of glass-fibre-reinforced polymer concrete.

Fractography of unfilled and particulate-filled epoxy resins

Abstract: The objective of this work was to analyse and understand the types of fracture surface morphology found in unfilled and particulate-filled epoxy resins in the light of the thermomechanical history of the specimen (loading rate or duration of loading, temperature, strain at break). Short-term tensile tests and long-term creep tests were conducted at four different temperatures. The fracture surface features were analysed using the scanning electron and optical microscopes and, where suitable, an image analyser. In order to correlate these morphologies with certain regimes of crack velocity, fracture mechanics tests were also conducted, varying the crack speed between 10−7 and 102 m sec−1. In the case of the filled resin, the lifetime under static loading is governed by a phase of slow, sub-critical crack growth which is manifested by resin-particle debonding. Thereafter, the crack accelerates and finally may reach terminal velocities depending on the amount of stored elastic energy available at the moment of fracture.

Epoxy resin composition

Abstract: PURPOSE:To obtain the titled composition, having excellent operability and productivity without precipitating and solidifying an inorganic filler during transportation and storage, by adding an anionic surfactant and silane based coupling agent to an epoxy resin containing the inorganic filler. CONSTITUTION:The aimed composition obtained by adding (B) an anionic surfactant (e.g. sodium polyoxyethylene lauryl ether sulfate) and (C) a silane coupling agent (e.g. gamma-glycidoxypropyltrimethoxysilane) to (A) an epoxy resin containing an inorganic filler, such as silica powder, alumina, talc or calcium carbonate. Furthermore, the amounts of the blended components based on 100pts.wt. epoxy resin are preferably 5-700pts.wt. inorganic filler, 0.05-1pt.wt. component (B) and 0.01-1pt.wt. component (C).

Thermal conductivity of boron nitride filled epoxy resins: temperature dependence and influence of sample preparation

Abstract: Castable particulate-filled epoxy resins exhibiting excellent thermal conductivity have been prepared using hexagonal boron nitride (BN) as filter. The thermal conductivity of BN filled epoxies is influenced by the sample preparation procedures, due to agglomeration effects of the particles in the matrix. The temperature dependence of the thermal conductivity of resins is measured as a function of the volume content of filler. The thermal conductivity in percolative systems depends in a complex way on the filler concentration and on the temperature. The mechanisms leading to the observed behavior are discussed. >