Showing papers on "Epoxy published in 1993"

Application of dynamic mechanical analysis for the study of the interfacial region in carbon fiber/epoxy composite materials

Abstract: The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.

History and bibliography of polymeric insulators for outdoor applications

Abstract: A history of polymeric insulators is given, beginning in the 1940s when organic insulating materials were used to manufacture high-voltage indoor electrical insulators from epoxy resins Their advantages and early experiences with them are given A bibliography covering mainly 1970 to the present is given >

An Edge Crack Torsion Method for Mode III Delamination Fracture Testing

Abstract: A new fracture toughness test, the edge crack torsion method, has been developed for characterizing the mode III delamination behavior of composites. The test is based on a laminate specimen subjected to torsion to propagate an edge delamination crack in its midplane. The crack growth mode of the specimen has been deduced to be mode III from fracture mechanics principles. The torsional behavior and the corresponding fracture parameter GIIIC have been analyzed on the basis of plate torsion and laminate theory. Edge crack torsion tests were performed to measure GIIIC of several carbon fiber/epoxy composite systems. Laminate layups were optimized to yield linear elastic fracture behavior of the specimens. The specimens were also sufficiently compliant to allow GIIIC to be readily obtained by using the compliance calibration method. The deformation characteristics of the specimens were found to follow the laminate torsion description. SEM observations showed fracture surface morphology varying with resin microstructures and, for the case of an untoughened matrix, were consistent with what was reported in the literature for other proposed mode III fracture tests.

Light-induced optical waveguide uptapers.

Abstract: Permanent uptapers have been produced in a UV-cured epoxy by a self-induced waveguide, created by exposure to cw 532-nm light. The photorefractive effect in this material produces high-quality, low-loss waveguides, which adiabatically taper to give spot sizes of as much as 50 μm diameter. The waveguides can be used at 1550 nm to form low-cost beam expanders with separations of a few millimeters.

Thermoplastic resin composition.

Abstract: A thermoplastic resin composition prepared by blending (a) 0.1-99 wt.% of a fluoropolymer containing a hydroxyl or epoxy group at least at one terminal of the main and side chains thereof and having a number-average molecular weight of 2,000 to 1,000,000 and (b) 1-99.9 wt.% of a heat-resistant thermoplastic resin having a crystal melting point or a glass transition point of 150 °C or above. This composition is one comprising various heat-resistant thermoplastic resins and a functional fluoropolymer that is well compatible with the resin and is capable of forming a homogeneous dispersion.

Epoxy resin composition and well treatment method

Abstract: In one embodiment, an epoxy resin composition is provided comprising: an epoxy resin and a partially reduced aromatic amine hardening agent. In another embodiment, a well treating composition is provided comprising: an epoxy resin; a partially reduced aromatic amine hardening agent; a solid particulate material; and a carrier fluid. In yet another embodiment, a method of treating a subterranean formation is provided. The inventive method comprises the step of placing the inventive well treating composition into the formation.

Curing agents for epoxy resins

Abstract: In order to convert epoxy resins to hard, infusible thermoset networks it is necessary to use crosslinking agents. These crosslinkers , hardeners or curing agents as they are widely known, promote cross-linking or curing of epoxy resins. Curing can occur by either homopolymerisation initiated by a catalytic curing agent or a polyaddition/copolymerisation reaction with a multifunctional curing agent. Specific curing mechanisms will be detailed within the ensuing sections.

Toughened plastics I : science and engineering

Abstract: Mechanisms of Toughening Thermoset Resins Fracture-Toughness Testing of Toughened Polymers Multiple-Phase Toughening-Particle Morphology: Effects on the Properties of Rubber-Toughened Poly(methyl methacrylate) Toughened Semicrystalline Engineering Polymers: Morphology, Impact Resistance, and Fracture Mechanisms Deformation and Fracture Toughness in High-Performance Polymers: Comparative Study of Crystallinity and Cross-Linking Effects The Damage Zone in Some Ductile Polymers Under a Triaxial Tensile Stress State Additive Effects on the Toughening of Unsaturated Polyester Resins Particle-Matrix Interfacial Bonding: Effect on the Fracture Properties of Rubber-Modified Epoxy Polymers Macroscopic Fracture Behavior: Correlation with Microscopic Aspects of Deformation in Toughened Epoxies Optimization of Mode-I Fracture Toughness of High-Performance Epoxies Using Designed Core-Shell Rubber Particles Toughening of Epoxy Resin Networks with Functionalized Engineering Thermoplastics Epoxy-Rubber Interactions The Synergistic Effect of Cross-Link Density and Rubber Additions on the Fracture Toughness of Polymers Rubber-Modified Epoxies: Analysis of the Phase Separation Process Thermal Shock Resistance of Toughened Epoxy Resins Toughening Epoxy Resin with Poly(methyl methacrylate)-Grafted Natural Rubber Toughening Epoxies Using Rigid Thermoplastic Particles: A Review Preparation of Poly(butylene terephthalate)-Toughened Epoxies Toughening of Epoxy Resins by Epoxidized Soybean Oil Structure-Property Relations of High-Temperature Composite Polymer Matrices Model Multilayer Toughened Thermosetting Advanced Composites Multiphase Matrix Polymers for Carbon Fiber Composites Thermal Characterization of the Cure Kinetics of Advanced Matrices for High-Performance Composites

Comparison of microwave and thermal cure of epoxy resins

Abstract: Stoichiometric mixtures of DGEBA (diglycidyl ether of bisphenol A)/DDS (diaminodiphenyl sulfone) and DGEBA/mPDA (meta phenylene diamine) have been isothermally cured by electromagnetic radiation and conventional heating using thin film sample configurations. Fourier transform infrared spectroscopy (FTIR) was used to measure the extent of cure. Thermal mechanical analysis (TMA) was used to determine the glass transition temperatures directly from the cured thin film samples. Well-defined glass transitions were observed in the TMA thermograph for both thermal and microwave cured samples. Significant increases in the reaction rates have been observed in the microwave cured DGEBA/DDS samples. Only slight increases in the reaction rates have been observed in the microwave cured DGEBA/mPDA samples. Higher glass transition temperatures were obtained in microwave cured samples compared to those of thermally cured ones after gelation. The magnitude of increases of glass transition temperature is much larger for the DGEBA/DDS system than DGEBA/mPDA system. The microwave radiation effect was much more significant in DGEBA/DDS system than in DGEBA/mPDA system. DiBenedetto's model was used to fit the experimental Tg data of both thermal and microwave cured epoxy resins.

Chip carrier with protective coating for circuitized surface

Abstract: A chip carrier is disclosed which includes a chip carrier substrate and at least one semiconductor chip mounted in a flip chip configuration, via solder balls, on a circuitized surface of the chip carrier substrate. The solder balls are encapsulated in a first encapsulant having a composition which includes an epoxy. In addition, at least a portion of the circuitry on the circuitized surface is encapsulated in a second encapsulant having a composition which includes a urethane, and which composition is chosen so that the second encapsulant exhibits a modulus of elasticity which is equal to or less than about 10,000 psi. As a consequence, the second encapsulant exhibits neither internal cracks, nor interfacial cracks at the interface with the first encapsulant, nor does the second encapsulant delaminate from the circuitized surface, when the chip carrier is thermally cycled.

Synthesis and characterization of novel epoxy monomers and liquid crystal thermosets

Abstract: Four new epoxy monomers have been synthesized and characterized as part of a program to prepare novel liquid crystal thermoset (LCT) materials. Three of the new epoxy monomers contained a biphenyl mesogen and were not liquid crystalline (LC). The remaining epoxy monomer, which contained a 1,4-dibenzoyloxybenzene mesogen, was synthesized in an overall yield of 30% and displayed a broad (83°C) nematic liquid crystalline phase. The new liquid crystalline epoxy monomer was cured at 120°C and postcured at 175°C with a stoichiometric amount of 1,4-phenylenediamine. The thermal transitions of the resulting LCT were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM), thermomechanical analysis (TMA), and wide angle x-ray diffraction (WAXD) as a function of cure time and temperature. A process characterization diagram was constructed which shows that LCTs based on this new LC monomer can be processed in the liquid crystalline phase over a broad range of times and temperatures. Qualitative agreement with previous epoxy LCT results was found, as LCT's with smectic phases and without clearing temperatures were observed at long cure times (high crosslink densities), whereas nematic phases with clearing temperatures predominated in networks at short cure times (low crosslink densities). © 1993 John Wiley & Sons, Inc.

Repair efficiency in fatigue‐cracked aluminium components reinforced with boron/epoxy patches

Abstract: This paper describes studies on fatigue crack propagation in cracked aluminium alloy (2024 T3) panels repaired with boron/epoxy patches, adhesively bonded with either an epoxy-nitrile film adhesive or an acrylic adhesive. Studies were undertaken to assess the effect on patching efficiency of (a) disbonding of the patch system and (b) test temperature. A simple model is proposed for estimating the reduction of patching efficiency due to cyclic disbonding of the reinforcement. In the elevated-temperature tests it was found, unexpectedly, that patching efficiency in panels patched using the film adhesive was unaffected by temperatures up to 100°C.

Micromechanical Modeling of Composite Compressive Strength

Abstract: Composite compressive failure is studied using a micromechanical (beam-on-elastic foundation) model, and the stiffness of the foundation is determined through an elasticity solution of the foundation model problem. An explicit expression has been derived for evaluation of composite longitudinal compressive strengths (CLCS). It is found that this expression predicts relatively lower CLCS compared to classical models, and closely matches some experimental data for carbon fiber/epoxy composites. It is found that a complete matrix slippage will reduce the CLCS by over 50%.

Curing in Thick Composite Laminates: Experiment and Simulation

Abstract: Thick part ( > 5 cm) temperature profiles were obtained from a one- dimensional experiment. These results are compared with the predictions of a computer simulation containing improved and existing models for extent of reaction, viscosity and other composite properties of the same resin/fiber system. In particular the simulation recovers the thermal behavior of a 5 cm thick, unidirectional Hercules AS-4/3501-6 graphite/epoxy composite laminate. Application of consolidation pressures based on pre dicted viscosities led to dramatic improvement in void content of a real laminate. The sim ulation is used to investigate important processing variables and changes in chemo rheology and temperature in a thick section laminate during cure. The following results are found: imtial extent of reaction is relatively unimportant; consolidation is important; the peak temperature originates near the surface of the laminate and propagates to the center; asymmetric temperature application changes the viscosity and cure prof...

Reaction mechanisms, microstructure, and fracture properties of thermoplastic polysulfone‐modified epoxy resin

Abstract: The microstructure and fracture properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resins modified with phenolic hydroxyl-terminated polysulfone (PSF) and cured with diaminodiphenyl sulfone (DDS) hardener have been investigated as a function of the molecular weight and concentration of PSF. The microstructure changed from a typical particulate structure to a phase-inverted structure as the molecular weight and/or the concentration of the modifier increased. The fracture toughness, measured by compact tension tests, increased with the microstructural changes toward the phase-inverted structure. The level of minor reactions such as etherification and homopolymerization reactions increased with increasing molecular weight and/or concentration of the modifier, in line with the tendencies observed in microstructure and fracture toughness. In the system containing 20 wt% of M[sub n] 10,000 PSF, about 30% of the epoxy groups were consumed by etherification and homopolymerization reactions, whereas none of these reactions occurred in the unmodified system. The increase in minor reactions in the modified systems may be to be due to the restricted molecular mobility, resulting from the increase of system viscosity caused by the modification.

Synergistic Thermal-Moisture Damage Mechanisms of Epoxies and Their Carbon Fiber Composites

Abstract: Experiments were conducted measuring the changes in weight of neat epoxy resins and carbon fiber reinforced epoxy composites during immersion in distilled water in temperature range from 0.5°C to 80°C. From the weight change data, the values of maximum moisture contents and diffusion coefficients were determined. Systematic studies were carried out on the "reverse thermal effect" for both neat resin and composite. A critical temperature was observed below which the materials exhibit normal behavior (the rate of absorption of water into epoxy resin increases with increasing temperature) and once the materials saturated with water at temperatures above it, the reversibility of reverse thermal effect was observed. A possible mechanism involving moisture-induced elastic cavities is suggested to explain the effect. The effects of water on Tg, thermal expan sion and yield stress of neat epoxy resin were studied.