Showing papers on "Epoxy published in 1985"

Transverse cracking and stiffness reduction in composite laminates

Abstract: A systematic classification of the effects of transverse cracking on the stress-strain response of composite laminates is presented. Stiffness reductions resulting from transverse cracking in glass/epoxy and graphite/epoxy laminates from crack initiation to crack saturation are predicted using the stiffness-damage relationships developed by the author in a previous work. Good agreement with the experimental results is found. An assessment of the ply discount method for predicting stiffness reductions at crack saturation is also made.

The application of differential scanning calorimetry (DSC) to the study of epoxy resin curing reactions

Abstract: This review is on the use of differential scanning calorimetry as a method of monitoring and investigating the kinetics of epoxy resin curing reactions. Some instrumental and experimental aspects are discussed, including methods of analysing the kinetic data. A brief survey is made of epoxy resin curing reactions and results of DSC studies are reviewed. These results are concerned with the use of carboxylic acid anhydrides, primary and secondary amines, dicyanodiamide, and imidazoles as curing agents.

Chemical Modification of Matrix Resin Networks with Engineering Thermoplastics. 1. Phenolic Hydroxyl Terminated Poly(Aryl Ether Sulfone)-Epoxy Systems,

Abstract: Functionally terminated bisphenol-A polysulfone oligomers were used in the modification of Epon Resin 828/4,4′-diamino-diphenylsulfone (DDS) network system. Phenolic hydroxyl terminated PSF oligomers were first capped with a large excess of bisphenol-A diglycidyl ether or Epon Resin 828 at both ends and then the resulting system was cured with DDS, in a two-step process. During these studies molecular weight and the amount of PSF oligomers incorporated into the network were varied and their effect on the overall properties of the resulting systems were investigated. The capping and curing reactions were followed by using FT-IR and NMR spectroscopy, GPC, HPLC and DSC techniques. As a function of the oligomer molecular weight, SEM studies showed the formation of two-phase structures with ductile PSF particles dispersed in the continuous epoxy matrix. Mechanical characterization and fracture toughness measurements showed a remarkable increase in KIC or gIC values of the modified networks over that of control, without significant loss in the modulus. This work would appear to be one of the first studies where well bonded ductile glassy modifiers have significantly improved the fracture toughness of highly crosslinked networks.

The temperature‐dependence of some mechanical properties of a cured epoxy resin system

Abstract: The tensile mechanical properties and fracture toughness of a Bisphenol-A type difunctional epoxy resin, cured with different amounts of metaphenylene diamine, using two cure cycles, were determined over a range of temperature. The tensile modulus in the glassy state was seen to be predominantly related to intermolecular packing, while in the rubbery state crosslink density was the important factor. Yielding appeared to be due to an increase in free volume as a result of dilatation during the tensile test and was related to a critical shear stress. The large strain properties like tensile strength, elongation-to-break, and toughness showed a more complex dependence on chemical structure, molecular architecture, intermolecular packing, and crosslink density. The roles played by the relaxation processes in determining mechanical properties are highlighted.

Epoxy resin composition

Abstract: An epoxy resin composition comprising (a) an epoxy resin, (b) a lactone obtained by decarboxylation condensation reaction of a saturated alicyclic 1,2-dicarboxylic acid anhydride, and if necessary (c) a curing agent for the epoxy resin and (d) a curing accelerator gives a cured article showing almost no or very slight curing shrinkage

Matrix solidification and the resulting residual thermal stresses in composites

Abstract: The disparate thermal expansion properties of the fibres and matrices in high-performance composites lead to an inevitable build up of residual thermal stresses during fabrication. We first discuss the thermal expansion behaviour of thermoplastic and thermoset polymers that may be used as high-performance composite matrices. The three classes of polymers considered are epoxies, amorphous thermoplastics, and semicrystalline thermoplastics. The relevant thermal expansion data for prediction of the magnitude of the residual stresses in composites is the zero (atmospheric)-pressure thermal expansion data; these data are plotted for a range of thermoplastics and a typical epoxy. Using the technique of photoelasticity, we have measured the magnitude of the residual stresses in unidirectional graphite composites with an amorphous thermoplastic matrix (polysulfone) and with an epoxy matrix (BP907). The temperature dependence of the residual stress build up and the resulting magnitude of the residual stresses correlate well with the thermal and physical properties of the matrix resin.

Selective transformation of 2,3-epoxy alcohols and related derivatives. Strategies for nucleophilic attack at carbon-1

Abstract: Obtention dans les conditions de la transposition de Paynes de t-butylthio-1 alcanediols-2,3

Semiconductor memory device

Abstract: PURPOSE:To enable to erase according to light stored informations even for a resin sealed semiconductor memory device by a method wherein the upper surface of a semiconductor element is covered with ultraviolet transmitting resin, and moreover the part not provided with the resin thereof is sealed with another resin CONSTITUTION:A tab 2 mounting a semiconductor element 3 and a part of connector wires 4 are covered with ultraviolet transmittable resin 7, and after the resin is hardened, the whole is resin-molded using resin being different from the above-mentioned resin 7 and to be used for usual resin sealing, epoxy resin for example, leaving a part of leads 6 After then, the resin sealing body 8 on the upper surface of the semiconductor element 3 is cut to be removed up to expose the transparent resin 7 in a rectangular shape, for example, and an opening part 80 is formed to enable to project ultraviolet rays to the semiconductor element (semiconductor memory) 3 through the opening part 80 and the transparent resin 7 Informations are stored to a circuit element in the semiconductor element 3 from the outside leads 60, and the stored informations thereof can be erased by the irradiation of ultraviolet rays permeating the transparent resin 7

The physical basis of moisture transport in a cured epoxy resin system

Abstract: The moisture transport characteristics of a difunctional epoxy resin cured with different amounts of metaphenylene diamine, using two cure cycles, are reported. Besides studying the kinetics of moisture sorption at 20, 50, 75, and 100°C, the investigations also included measurement of thermal expansion coefficients and dynamic mechanical transition of the dry and wet samples. The moisture sorption of the sample is shown to be related to its specific volume and hence to its fractional free volume. In the glassy state, the free volume is apparently in the form of frozen voids, and moisture sorption/desorption at this temperature is of the Langmuir type with little or no bond formation. At higher temperatures the free volume is generated predominantly through segmental motion of the α transition. The Henry's Law mode becomes operative, and the moisture can now form bonds. The possible effect of nonuniform crosslink density on moisture sorption is also considered.

Thermally transferable layers of radiation sensitive epoxy resins used to prepare protective coatings and relief images

Abstract: A process for the production of a protective layer or a relief image on a substrate, wherein a radiation-sensitive layer, consisting of a solid film-forming epoxy resin containing a photoinitiator, which can be activated by radiation, for the polyaddition reaction, is transferred from a support to a substrate, then exposed directly or under a photomask and hardened by the action of heat, after which, if appropriate, the unexposed parts are developed with a solvent. The process is suitable, for example, for the production of printed circuits, solder resist masks and offset printing plates.

Chemical epoxidation of a natural unsaturated epoxy seed oil fromVernonia galamensis and a look at epoxy oil markets

Abstract: Since 1963, production of all epoxy esters has ranged from 60 to 150 million lb annually, a steady 7% of the 1 to 2 billion lb of annual plasticizer production. Growth rates in production averaged 4.3% for all plasticizers, 3.8% for all epoxy esters and 5.0% for epoxidized soybean oil (ESBO). ESBO accounted for 70–76% of total epoxy ester production (1963–1982). The natural liquid epoxy oil fromVernonia galamensis seed, with oxirane value (4.1%) and viscosity (100 cps) similar to some commercial epoxy fatty esters but with molecular weight similar to epoxidized vegetable oils, combines some of the properties of both commercial types. Chemical epoxidation ofVernonia oil raises the oxirane content to 8.2, intermediate between ESBO and epoxidized linseed oil (ELSO), while consuming less of the costly epoxidizing reagents. Epoxidation proceeds in stepwise fashion through partially epoxidized products, which are converted to final product. Since the major fatty components ofVernonia oil arecis-12,13-epoxy-9-octadecenoic (75%) and linoleic (13%) acids, further epoxidation produces fatty acids that are specifically epoxidized at the 9,10- and 12,13-positions, and the major product has 6 epoxy units per triglyceride molecule. The resulting mixture of products has compositional and physical properties distinctly different from commercial samples of ESBO and ELSO.

An Assessment of the Impact Performance of Bonded Joints for Use in High Energy Absorbing Structures

Abstract: Using an instrumented impact test, the strength and energy absorption of bonded single lap joints have been measured for single lap joints with four epoxy adhesives and three aluminium alloy adhere...

Oxidative skeleton breaking in epoxy–amine networks

Abstract: Etude par spectrometrie IR et DSC des oxydations photo et thermique de divers polycondensats tridimensionnels epoxyde-amine

Failure analysis of a graphite/epoxy laminate subjected to combined thermal and mechanical loading

Abstract: Quasi-static thermal stress response and failure behavior of graphite/epoxy lam inated plates under combined intense thermal and mechanical loadings are investigated. The temperature field is obtai...

Micromechanisms of crack propagation in hybrid-particulate composites

Abstract: Etude sur des melanges resine epoxyde-CTBN (copolymere de carboxybutadiene et d'acrylonitrile) et de verre

Sized glass fibers and reinforced polymers containing same

Abstract: Strands of chemically treated glass fibers of the present invention result in fiber reinforced polar thermosetting and thermoplastic polymers having good strength properties. The chemically treated glass fibers are treated with the an aqueous chemical treating composition having an epoxy polyurethane copolymer or a polyepoxide resin with blocked polyisocyanate functionality, and at least one or more organo coupling agents. The epoxy polyurethane copolymer or epoxy with polyisocyanate functionality can be chain extended with organic polyols. The blocked polyisocyanates can be either partially or fully blocked. Also the aqueous chemical treating composition can have one or more cationic and/or nonionic fiber lubricants, epoxy polyvinly acetate copolymer in conjunction with an ethylene vinyl acetate copolymer or an epoxy polymer and mixtures of the fiber lubricant with the polymeric materials.

High impact strength fiber resin matrix composites

Abstract: Improved fiber resin matrix prepreg fabrics are disclosed which are comprised of a first layer of reinforcing fabric coated with an epoxy resin composition and a discrete second layer of an epoxy resin modified with an elastomeric polymer. The discrete second layer is provided with a support comprising a gauze-like, lightweight fibrous mat or carrier of lightweight fibers that preserves the second "interleaf" layer during cure. Cured composites having the continuous interleaf layer intact exhibit high impact strength and resistance to impact damage. 6

Adhesion of Graphite Fibers to Epoxy Matrices. III. The Effect of Hygrothermal Exposure

Abstract: Surface treatments have been used to promote shear strength between graphite fibers and epoxy matrices by adding polar surface groups to increase the attraction between the fiber surface and the polar epoxy matrix. Because of the polar interactions between fiber and matrix, interfacial bonding may be susceptable to moisture attack resulting in permanent loss of fiber matrix bonding with a resultant loss in composite shear strength. Fiber “finishes” are also used to improve the processability of surface treated graphite fibers. These “finish” layers may not respond to hygrothermal exposure in the same manner as the matrix. Type AS1 surface treated graphite fibers and surface treated and “finished” (ASIC) for improved adhesion to epoxy matrices were used in this study. Single fibers were encapsulated in an epoxy-mPDA matrix so that interfacial shear strength and matrix response to shear loading could be quantified and observed microscopically with polarized light as a function of moisture exposure ...

Water in epoxy resins Part II. Diffusion mechanism

Abstract: A model is proposed for the diffusion mechanism of water in glassy epoxy resins. The polymer network is assumed to consist of two regions in which water molecules possess different mobilities. By considering the distribution of water molecules among these regions it is possible to describe the concentration dependency of the diffusion coefficient in the sorption and resorption processes. The diffusion coefficient becomes constant when the sorption temperature is close to the effective glass transition temperature of the epoxy-water binary mixture. An explanation of this effect is also provided by the model.

Mechanics and mechanisms of fracture of thermosetting epoxy polymers

Abstract: Thermosetting epoxy polymers are widely employed in structural engineering applications and thus a knowledge of the mechanics and mechanisms of the fracture of such materials is of vital importance. The present Chapter discusses the fracture of epoxy polymers, concentrating on the use of a continuum fracture mechanics approach for elucidating the micromechanisms of crack growth and identifying pertinent failure criteria.

A fracture mechanics approach for designing adhesively bonded joints

Abstract: An analytical and experimental investigation was undertaken to determine if the adhesive debond initiation stress could be predicted for arbitrary joint geometries. The analysis was based upon a threshold total strain-energy-release rate (Gth) concept. Two bonded systems were tested: T300/5208 graphite/epoxy adherends bonded with either EC-3445 or FM-300 adhesive. The Gth for each adhesive was determined from cracked-lap-shear (CLS) specimens by initiation tests. Finite-element analyses of various tapered CLS specimen geometries predicted the specimen stress at which the total strain-energy-release rate (GT) equaled Gth at the joint tip. Experiments verified the predictions. The approach described herein predicts the maximum stress at which an adhesive joint can be cycled yet not debond. Furthermore, total strain-energy-release rate appeared to be the driving parameter for cyclic debonding and debond initiation in structural adhesives. In addition, debond initiation and growth were found to occur with virtually no peel stress present.

The Effect of Hygrothermal Fatigue on Physical/ Mechanical Properties and Morphology of Neat Epoxy Resin and Graphite/Epoxy Composite

Abstract: The effect of moisture absorption, desorption, and thermal spiking on the physical/mechanical properties of TGDDM/DDS epoxy resin was investigated and compared to the Gr/Ep composite The mechanism of moisture diffusion in the neat resin was described on the morphological level The diffusion rate of moisture in epoxy resin was found to depend on the mobility of molecular chains within an inhomogeneous epoxy network Two well-known concepts of plasticization of amorphous polymers, the lubricity theory and the gel theory, were invoked to describe the interactions between the absorbed moisture and the resin network Slight permanent changes in properties of the neat resin were observed after one absorption-desorption cycle In the thermal spiking experiment, only the spiking temperature above the glass transition of the moisture saturated epoxy resins changed their internal structure and produced very small (thin) microcracks By comparison with the neat epoxy resin, the Gr/Ep composites contain the reinforcement-matrix boundary region, characterized by the highest restrictions to molecular mobility The absorbed moisture during the static hygrothermal fatigue cannot effectively plasticize this region But during thermal spiking, the formation of microcracks is observed within the reinforcement-matrix boundary region as well as an increase in the moisture content

Effect of water on the properties of epoxy matrix and composite

Abstract: The complex sorption behavior of the water in amine-epoxy thermosets is discussed and related to depression of the mechanical properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis. In particular, two different types of epoxy materials have been chosen: low-performance systems of diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, and high-performance formulations based on aromatic amine-cured tetraglycidyldiamino diphenylmethane (TGDDM) which are commonly used as matrices for carbon fiber composites.