Showing papers on "Epoxy published in 1984"

Constitutive Theory for Strongly Anisotropic Solids

Abstract: We shall discuss a number of problems concerned with stress and deformation analysis of fibre-reinforced composite, and other strongly anisotropic, materials. The kind of composite material in mind is one in which a matrix material is reinforced by strong stiff fibres which are systematically arranged in the matrix. The fibres are considered to be long compared to their diameters and the fibre spacings, and to be quite densely distributed, so that the fibres form a substantial proportion (typically about 50% by volume) of the composite. There are many such composite materials now in use or under development; examples are carbon fibre reinforced epoxy resins, boron fibre reinforced aluminium, and nylon or steel reinforced rubber which is used in tyres, hosepipes and belts.

Crack propagation in a glass particle-filled epoxy resin

Abstract: The investigation outlined in the preceding paper has been extended to cover the effect of particle/matrix adhesion upon crack propagation in an epoxy resin reinforced with spherical glass particles. The behaviour has again been interpreted in terms of crack pinning and blunting. It has again been shown that in the absence of blunting a critical crack opening displacement criterion can be applied. The strength of the particle/matrix interface is found to affect both the crack propagation behaviour and the appearance of the fracture surface. It is also found to have a profound effect upon the fracture strength of the composites. The best overall mechanical properties are obtained for composites containing particles treated with coupling agent.

Crack propagation in a glass particle-filled epoxy resin: Part 1 Effect of particle volume fraction and size

Abstract: Crack propagation in an epoxy resin reinforced with spherical glass particles has been followed using a double-torsion test. In particular the effect of strain rate, volume fraction and particle size upon the stability of propagation, the Young's modulus, the critical stress intensity factor,KIc and the fracture energy,GIc has been studied. It has been shown that the crack propagation behaviour can be explained principally in terms of crack pinning, although it has been found that propagation is also affected by blunting the breakdown of the particle—matrix interface. It has been demonstrated that crack-front pinning is consistent with a critical crack opening displacement criterion.

Compression Failure Mechanisms in Unidirectional Composites

Abstract: Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model.

Curing reaction of epoxy resins with diamines

Abstract: The curing reaction of a commercial bisphenol A diglycidyl ether (BADGE) with ethylenediamine (EDA) was studied by differential scanning calorimetry. Different kinetic expressions were found with isothermal (low temperature range) and dynamic (high temperature range) runs. Two competitive mechanisms are shown to be present: an autocatalytic one (activation energy E = 14 kcal/mol) and a noncatalytic path characterized by a second-order reaction with E = 24.5 kcal/mol. At low temperatures both mechanisms took place simultaneously, showing a significant decrease in the reaction rate after the gel point. At high temperatures only the noncatalytic reaction was present, without showing a noticeable rate decrease in the rubber region. Also, a third-order dependence of the glass transition temperature on reaction extent is shown.

Mixed-mode strain-energy-release rate effects on edge delamination of composites

Abstract: Unnotched graphite/epoxy laminates, designed to delaminate at the edges under static and cyclic tensile loads, were tested and analyzed. The specimen stacking sequences were chosen so that the total strain-energy-release rate, G, for edge delamination was identical for all three layups. However, each layup had different percentages of crack-opening and shear-mode strain-energy-release rates, G sub 1 and G sub 2, respectively. Results with composites made from T300 graphite fibers and 5208 epoxy, a brittle resin, indicated that only G sub 1 contributed to delamination onset under static loading. However, results with composites made from C6000 fibers and H205 epoxy, a tougher resin, indicated that the total F governed the onset of edge delaminations under cyclic loads. In addition, for both materials, the threshold level of G for delamination onset in fatigue was significantly less than the critical G sub c measured in static tests. Futhermore, although the C6000/H205 material had a much higher static G sub c than T300/5208, its fatigue resistance was only slightly better. A series of mixed-mode tests, like the ones in this study, may be needed to evaluate toughened-resin composites developed for highly strained composite structures subjected to cyclic loads.

Probabilistic Failure Strength Analyses of Graphite/Epoxy Cross-Ply Laminates:

Abstract: This paper treats the failure characteristics of [0/90/0] and [90/0/90] cross-ply laminates based upon the statistical strength analysis. The stress redistributions at the failure of the 90 ° ply are analyzed using a shear-lag model, taking the thermal residual stresses and Poisson effect into consideration. The formulae for determining first cracking, subsequent multiple cracking and ultimate fracture are derived. The present analysis is compared with the existing experimental results for graphite/epoxy cross-ply laminates, and reasonable agreements have been obtained.

Effects of phase separation in crosslinked resins containing polymeric modifiers

Abstract: The study reported in this thesis concerns the relationship between morphology and the properties of multicomponent epoxy and methacrylate resins. The thermodynamic and kinetic aspects of phase separation in reactive, thermosetting, systems are explored and applied to the investigation of blends of 'high performance' epoxy resins with polyethersulphone. The mechanical properties of the same cured blends are shown to be insensitive to considerable variations in composition, cure and the resulting morphology, both in the bulk-resin and in carbon fibre-epoxy laminate forms. Room temperature fracture and yield behaviour of highly cross linked and rubber modified methacrylates, of rubber modified dysfunctional epoxies, as well as of the above mentioned epoxy/polyether sulphone blends, is investigated. Special emphasis is placed on a comparison of the kinetics of tensile creep between the different systems. Loss of ductility in the highly cross linked resins is shown to result in a very limited scope for toughness enhancement by the usual rubber toughening methods.

The fracture of particulate-filled epoxide resins

Abstract: The double torsion test technique was used to investigate the fracture properties of two commercial epoxide resins filled with glass beads. The influence of varying the volume fraction of glass, the mean particle size and the pre-treatment of the glass surface on the stress intensity factor have been determined. A correlation has been found between the compressive yield strength and the stability of fracture in these composites, similar to that found for unfilled epoxide resins.

The study of model polydiacetylene/epoxy composites: Part 1 The axial strain in the fibre

Abstract: Le compose modele est soumis a une deformation d'etirage dans une direction parallele a la fibre. On determine la deformation tout au long de la fibre par spectroscopie Raman et de la matrice par les techniques classiques

Crack propagation in a glass particle-filled epoxy resin Part 2 Effect of particle-matrix adhesion

Abstract: The investigation outlined in the preceding paper has been extended to cover the effect of particle/matrix adhesion upon crack propagation in an epoxy resin reinforced with spherical glass particles. The behaviour has again been interpreted in terms of crack pinning and blunting. It has again been shown that in the absence of blunting a critical crack opening displacement criterion can be applied. The strength of the particle/matrix interface is found to affect both the crack propagation behaviour and the appearance of the fracture surface. It is also found to have a profound effect upon the fracture strength of the composites. The best overall mechanical properties are obtained for composites containing particles treated with coupling agent.

Hybrid particulate-filled epoxy-polymers

Abstract: Relations structure-proprietes mecaniques de melanges resine epoxyde-copolymere de carboxybutadiene et d'acrylonitrile contenant des billes de verre

Moisture solubility and diffusion in epoxy and epoxy-glass composites

Abstract: The solubility and kinetics of moisture transport mechanisms in epoxy-type resin and resin-glass composites have been investigated over a range of partial pressure and temperature. Moisture absorption-desorption in these systems is a quasi-reversible process, the kinetics of which are non-Fickian (Type II) and dependent on prior history. The multistaged sorption and transport behavior are interpreted in terms of multiphase models.

The application of X-ray photoelectron spectroscopy to the study of polymer-to-metal adhesion: Part 2 The cathodic disbondment of epoxy coated mild steel

Abstract: The delamination of a commercial epoxy coating applied to cathodically protected mild steel has been investigated from both a mechanistic and a kinetic standpoint. X-ray photoelectron spectroscopy shows the locus of failure to be invariant with surface profile, and essentially adhesive in nature. The substrate pretreatment does, however, determine the kinetics of disbondment. A three-stage process for such failure is identified, the rate-controlling step passing from oxide reduction at a defect to the cathodic area exposed, and finally to interfacial path length. A simple relationship is presented to describe the disbondment rate in terms of this interfacial path length. The concept of a critical disbondment velocity for the epoxy mild steel system is proposed. It is shown that oxide reduction is an important precursor to cathodic disbondment for this system.

Impact resistant matrix resins for advanced composites

Abstract: Described herein is a composition which contains a specific group of hardeners, an epoxy resin and a thermoplastic polymer When combined with a structural fiber the composition produces composites which have improved impact resistance, improved tensile properties and high compressive properties

Thermokinetics and chemorheology of the cure reactions of the tetraglycidyl diamino diphenyl methane–diamino diphenyl sulfone epoxy systems

Abstract: The cure behavior of commercial grade TGDDM–DDS mixtures of compositions ranging from 10 to 100 phr of hardener and the thermal polymerization of the epoxy component are analyzed by means of differential scanning calorimetry. The kinetic parameters and heats of reaction determined in isothermal and dynamic scans suggest that DDS primary amine addition and epoxide etherification dominate the cure reactions. The primary amine epoxide addition is characterized by overall heat of reaction (referred to the weight of the epoxy component) of 255 cal/g and by an activation energy of 16.6 kcal/mol. The corresponding values for the etherification reaction are, respectively, 170 cal/g and 41 kcal/mol. A method of derivation of the epoxide conversion from the heat evolved in DSC thermal scans of these systems is presented. The results are in good agreement with independent IR determinations. The steady shear and oscillatory viscosity measurements and the calorimetric analysis of the isothermal cure at 140°C, 160°C, and 180°C of a TGDDM–DDS mixture containing 35 phr of hardener indicate that gelation is principally governed by the primary amine addition. The gelation limits calculated in isothermal tests by combining the calorimetric analysis and the theory describing the nonlinear copolymerization of the tetrafunctional TGDDM with an essentially difunctional DDS were in good agreement with the values experimentally determined through rheological measurements.

Epoxy resin cure. II. FTIR analysis

Abstract: Fourier transform infrared (FTIR) spectroscopy is used to determine the cure rate of an epoxy resin consisting of Tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) and diaminodiphenylsulfone (DDS). Cure rates at 120 and 160°C are shown to increase noticeably when 1% BF3–MEA is added to either TGDDM to TGDDM plus DDS. Fluoroboric acid is shown to increase the cure rates even more than the BF3–MEA. These Results combined with the NMR results in the accompanying article indicate that BF3–MEA is not a catalyst for epoxy resin cure. Instead it is rapidly hydrolyzed to fluoroboric acid which acts as the catalyst.

An additive for increasing the strength and modulus of amine‐cured epoxy resins

Abstract: The reaction product of 4-hydroxyacetanilide and 1,2-epoxy-3-phenoxypropane, when added at 19 wt% to a conventional epoxy-resin-curing agent mixture, increases the tensile strength of the cured system from 82 MPa to 123 MPa and increases the shear modulus (20°C, 1 Hz) from 970 MPa to 1560 MPa. As well as showing increased strength, the tensile-test specimens also fail in a ductile fashion, i.e., the slope of the stress–strain curve is negative at failure, with appreciable localized deformation occurring during fracture. For notched samples (compact tension specimens), the fracture properties are strongly strain-rate-dependent. At low strain rates the additive-containing sample has a fracture energy (, critical strain energy release rate) about twice that of the additive-free control, but at higher strain rates falls to about 65° of the control value. The critical stress for crack propagation is also strain-rate-dependent and is about 50% higher than the control at low strain rates and about 10% less than the control at higher strain rates. Dynamic mechanical analysis and dielectric loss measurements indicate that the additive causes a decrease in the Tg and a suppression of the β-relaxation. Chemically, the additive accelerates the cure process but does not significantly alter the final extent of reaction of the epoxy resin. After curing, the additive is almost totally extractable by solvent indicating that it is not chemicaly bound to the polymer. These observations are discussed in terms of the concept of antiplasticization.

Epoxy resin composition

Abstract: PURPOSE:An epoxy resin composition of a low dielectric constant and excellent chemical resistance, containing an epoxy resin, a curing agent, a specified potassium titanate powder or whiskers CONSTITUTION:A resin composition containing 100ptswt epoxy resin containing at least two epoxy groups in the molecule, 1-200ptswt curing agent, and 5- 500ptswt potassium titanate powder (particle diameter of 01-100mu) or whiskers surface-treated with a silane or titanate coupling agent The curing agents include acid anhydride or amine types, and are selected according to the purpose of use When the above potassium titanate is in the form of whiskers, it can be added in only a small amount, because of its marked thickening effect Therefore, it is suitable for use as a reinforcement used in combination with a different filler Potassium titanate powder is usually preferred

Hydrogen bonding in epoxy resin/poly(ε-caprolactone) blends

Abstract: Poly(ϵ-caprolactone) (PCL) of ca. 20,000 molecular weight is shown to be partially miscible with three aromatic-amine-cured epoxy resins. This conclusion is based on the depression of the epoxy Tg, the effect on physical and mechanical properties, and the observation that a large proportion (40-55%) of the PCL ester groups are involved in hydrogen bonding. This miscibility behavior is compared to PCL blends with anhydride-cured epoxy resins, which appear to have a two-phase morphology. The different miscibilities are rationalized on the basis of the existence of functional groups (e. g., hydroxyl) in amine-cured epoxies which are capable of hydrogen bonding to the PCL ester groups. Anhydride-cured epoxy resins contain fewer potential hydrogen bonding sites.

Epoxy resin composition

Abstract: Epoxy resin compositions including an epoxy resin, a hardener and an additive containing a rust preventing film forming component are provided. The additive is lanolin and/or a lanolin derivative. Optionally, the composition also includes a secondary additive selected from organosilicon compounds, organoaluminum compounds, organotitantium compounds, organotin compounds, liquid rubber having functional groups at both ends of the molecule, petroleum lubricating oils or Japan wax. These epoxy resin compositions, when used as encapsulating materials, prevent moisture and impurities from invading the surface of the device.

Fiber Stresses in a Cracked Monolayer: Comparison of Shear-Lag and 3-D Finite Element Predictions*:

Abstract: Shear-lag and 3-D finite element predictions for the fiber stresses in a cracked monolayer are compared. Results are given for 5-fiber wide boron/aluminum and Kevlar 49/epoxy monolayers containing a single broken fiber. Both methods of analysis are found to predict nearly the same fiber stress distribution along the crack- tip fiber when the monolayer is fully elastic. Results for highly loaded monolayers with extensive matrix yielding are not in quite as good agreement, but even then the predicted stress distributions are within 5%. These calculations show that a shear-lag analysis is accurate even when 1) the matrix is relatively stiff and can carry substantial loads (e.g., boron/aluminum), and 2) the fiber is highly anisotropic, (e.g., Kevlar 49/epoxy).

The Silane Interphase of Composites: Effects of Process Conditions on Gamma-Aminopropyltriethoxysilane

Abstract: FT-IR spectroscopy was used to collect spectra of γ-aminopropyltriethoxy silane (γ-APS) coupling agent deposited on KBr plates, modeling the silane interphase of composites, to study the effects of heating the γ-APS film under various environmental conditions. This coupling agent is used in fiber-reinforced epoxy composites. An aminebicarbonate salt forms when the sample is dried in a moist carbon dioxide environment giving rise to a series of bands from 2800 to 2000 centimeter−1 (cm−1) and bands at 1637 cm−1, 1330 cm−1, 696 cm−1, and 663 cm−1. The primary amine group is split into two bands at 1572 cm−1 and 1486 cm−1 in the NH3+ form. Heating removes the aminebicarbonate salt at temperatures above 95°C and condenses the γ-APS polymer to a polysilsesquioxane film. The aminebicarbonate salt partially reforms if the γ-APS film is stored in a moist CO2 environment. At temperatures above 120°C the primary amine of γ-APS is oxidized in air to imine groups. In the process of evolving the CO2 the polymer is further condensed and the amine groups can be converted to imines if the temperatures exceeds 120°C. Both processes reduce the reactivity of the coupling agent with the epoxy resin. The structure of the silane interphase must be controlled during the processing of the composite to yield materials with maximum properties.

Method of removing flow-restricting materials from wells

Abstract: Flow-restricting materials containing epoxy resins present in a well treated with an epoxy resin, for the purpose of coating and consolidating unconsolidated sand adjacent the well and/or gravel packing in the well, or of coating metallic equipment in the well, to prevent corrosion or the deposition of organic or inorganic solids on the equipment, by contacting the flow-restricting material with a solvent composition, comprising, N-methyl-2-pyrrolidone and a diluent in an amount of 0 to 80% by wt., for a time sufficient to form a flowable fluid and removing the flowable fluid from the well. Combination well treatments include consolidating sand and/or gravel in a well or coating metallic equipment in the well with an epoxy resin and, thereafter, subjecting the treated well to the above solvent treatment to remove flow-restricting materials from the well.

Curing of epoxy resins with 1-[di(2-chloroethoxyphosphinyl) methyl]-2,4-and -2,6-diaminobenzene

Abstract: Fire resistant compositions were prepared using 1-di(2-chloroethoxy-phosphinyl)methyl-2,4- and -2,6-diaminobenzene (DCEPD) as a curing agent for typical epoxy resins such as EPON 828 (Shell), XD 7342 (Dow), and My 720 (Ciba Geigy). In addition, compositions of these three epoxy resins with common curing agents such as m-phenylenediamine (MPD) or 4,4'-diaminodiphenylsulphone (DDS) were studied to compare their reactions with those of DCEPD. The reactivity of the three curing agents toward the epoxy resins, measured by differential calorimetry (DSC), was of the order MPD DCEPD DDS. The relatively lower reactivity of DCEPD toward epoxy resins was attributed to electronic effects.