Showing papers on "Epoxy published in 1987"

The Role of the Interface in Carbon Fibre-Epoxy Composites

Abstract: The final performance of a composite material depends strongly on the quality of the fibre-matrix interface. The interactions developed at the interface were studied using the acid-base or acceptor-donor concept. The surface characteristics of the carbon fibres and the epoxy matrix were studied using a tensiometric method and the inverse gas chromatography technique. Acid-base surface characters could be determined allowing the interactions at the interface to be described by a specific interaction parameter. It was shown that the shear strength of the interface, as measured by a fragmentation test, is strongly correlated to this specific interaction parameter, demonstrating the importance of acid-base interactions in the fibre-matrix adhesion.

Parameters determining the strength and toughness of particulate filled epoxide resins

Abstract: The effects of such parameters as the filler volume fraction, particle size, aspect ratio, modulus and strength of filler, resin-filler adhesion and toughness of the matrix on the stiffness, strength and toughness of particulate filled epoxide resins have been evaluated. The mechanisms of deformation and rupture in these multiphase materials are discussed, illustrated byin situ mechanical tests in the scanning electron microscope.

Curable compositions containing n-sulfonylaminosulfonium salts as cationically active catalysts

Abstract: Mixtures which are curable by heating or irradiation with actinic light contain one or more cationically curable compounds, such as an epoxy, an olefinically unsaturated monomer, amino resin or phenolic resin, and as a cationically active curing catalyst one or more N-sulfonylamino-sulfonium salts of the formula ##STR1## such as N-p-toluenesulfonyl-N-methylaminodiphenylsulfonium hexafluorophosphate with or without quinones or peroxides are suitable, inter alia, for producing moldings, coatings, relief images and resist patterns.

The abrasive wear behaviour of continuous fibre polymer composites

Abstract: The dry abrasive-dominant wear behaviour of several composite materials consisting of uni-directional continuous fibres and polymer matrices was investigated. Seven materials were examined: neat epoxy (3501-6), carbon fibre epoxy (AS4/3501-6), glass fibre/epoxy (E-glass/ 3501-6), aramid fibre/epoxy (K49/3501-6), neat polyetheretherketone (PEEK), carbon fibre/PEEK (APC2) and aramid fibre/PEEK (K49/PEEK). The wear behaviour of the materials was characterized by experimentally determining the friction coefficients and wear rates with a pin on-flat test apparatus. First, the effects of the operation variables apparent normal pressure, sliding velocity and apparent contact area were observed. The dimensionless wear rate increased linearly as the apparent normal pressure increased and decreased as the apparent contact area increased. Second, through microscopic observations of the worn surfaces and subsurface regions, basic wear mechanisms were identified as a function of fibre orientation. Observations of fibre-abrasive particle interactions allowed for the differentiation of the dominating wear mechanisms. Finally, a network of data was compiled on the wear behaviour in terms of the three material parameters: fibre orientation, fibre material and matrix material. This enabled the systematic selection of an ideal low wear composite material which would consist of a PEEK matrix reinforced with aramid fibres oriented normal to the contacting surface and carbon fibres oriented parallel to the contacting surface.

Low thermal expansion,heat conducting laminates having layersof metal and reinforced polymer matrix composite

Abstract: Heat conducting laminates and laminated heat conducting devices having at least one layer of metal (80) and at least one layer of polymer matrix composite material (82, 84) having low-thermal-expansion reinforcing material (90) distributed throughout and embedded therein. The coefficient of thermal expansion and the thermal conductivity of the laminated heat conducting devices are defined by the metal in combination with the polymer matrix material and the low-thermal-expansion reinforcing material in the laminate. The coefficient of thermal expansion and thermal conductivity of a heat conducting device can be controlled by bonding at least one layer of metal to at least one layer of polymer matrix composite material having low-thermal-expansion reinforcing material distributed throughout and embedded therein. In one embodiment, the laminated heat conducting device comprises a plurality of alternating layers of aluminum and epoxy resin having graphite fibers distributed throughout the epoxy resin.

High solids sag resistant cycloaliphatic epoxy coatings containing low molecular weight high tg organic polymeric sag resisting additives

Abstract: Sprayable, thermosetting, sag-resistant coating composition comprising at least 50 weight percent nonvolatiles comprising: (a) 100 weight parts of a crosslinkable cycloaliphatic epoxy containing at least one cycloaliphatic ring, (b) 0 to 100 weight parts of a crosslinking/chain-extending agent compatible with and capable of crosslinking and/or chain-extending said epoxy, and (c) a sag control system comprising 5 to 40 weight parts of an organic polymer having a glass transition temperature of at least 25°C and a number average molecular weight of not more than 12,000.

Role of matrix‐particle interface adhesion on fracture toughness of dual phase epoxy‐polyethersulfone blend

Abstract: Compatibility or miscibility of a polyethersulfone (ICI: Victrex 100P) and a tetrafunctional epoxy (Ciba-Geigy: MY-720), cured with an aromatic anhydride, has been studied using scanning electron microscopy, x-ray microanalysis, and dynamic mechanical spectroscopy. Fracture toughness of epoxy and a blend of epoxy and polyethersulfone has been measured using three point bend tests (ASTM: E-399-81). Fracture surfaces were examined by x-ray microanalysis for detecting concentration of sulfur, present in polyethersulfone, in the matrix and precipitated phase. The influence of the morphology of the epoxy/polyethersulfone blend on its fracture toughness and toughening mechanism has been studied. Fracture toughness values of unmodified and modified cured epoxy resin were evaluated as a function of test temperature.

X-ray photoelectron spectroscopic studies of carbon fibre surfaces

Abstract: Carbon fibres were anodically surface treated by passing them continuously through an electrochemical bath, thus simulating a possible industrial surface-treatment process. Composites were made from these fibres with an epoxy resin and their interlaminar shear strength (ILSS) tested. The surfaces of the fibres were examined by X-ray photoelectron spectroscopy after treatment. Both golvanostatic and potentiostatic cell control led to treated fibres that produced composites with high interlaminar shear strengths (80 to 90 MPa). The effect of potential, reaction time, electrolyte and subsequent heating of the fibres in a vacuum on the ILSS of the composites is reported. The rise in ILSS with surface treatment is not dependent upon the O-1 s: C-1 s ratios or the amount of carboxyl functionality present on the surface. This suppors the view that mechanical keying of the resin to the fibre surface plays an important role in forming the fibre-resin bond.

Modeling Stiffness Reduction of Graphite/Epoxy Composite Laminates:

Abstract: An investigation has been conducted into the effects of fatigue loading on the stiffness and strength degradation of composite laminates. An experimental test program using graphite/epoxy [±35]2s laminates has been conducted to generate meaningful data for this evaluation. Based on this investigation, a model is proposed to relate the stiffness degrada tion to the fractional life expended at a given stress level and also to the residual strength degradation. These models are restricted to specimens subjected to constant amplitude fatigue loadings.

A model for resin flow during composite processing part 2: Numerical analysis for unidirectional graphite/epoxy laminates

Abstract: In this paper numerical results are presented for resin flow during processing of unidirectional graphite/epoxy laminates. Resin pressure and velocity profiles, as well as resin loss, specific permeability, and resulting thickness changes, were computed to examine the effects of one and two-dimensional flow, initial laminate thickness, and various cure cycles. Input data to the model are also discussed in detail. Analysis of the input data on the stress-strain behavior of graphite fiber beds showed that the bed consolidation behavior can be divided into three regions. “Free-bleeding” (O psig and negligible bleeder resistance to flow at the boundaries) during two-dimensional resin flow leads to rapid decay in resin pressure. Comparison of the predicted results for the resin mass loss and the average final thickness per ply with experimentally determined values shows good agreement.

Interlaminar shear fracture toughness and fatigue thresholds for composite materials

Abstract: Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.

High strength, light weight structural composite and method of preparing same

Abstract: A light weight structural composite comprised of a cellular core having high dynamic load-bearing properties and a fiber reinforced resinous skin on all edges of the core and on the top and bottom surfaces thereof. The cellular core may comprise an array of balsa wood blocks, the skin may comprise a fiberglass reinforced epoxy or polyester resin, and the core and skin may be formed into a monolithic composite which is particularly suitable for use as a high strength to weight ratio ground opening cover.

Study of matrix cracking and delamination in glass/epoxy laminates

Abstract: This study focused on characterizing matrix cracking and delamination behavior in multidirectional laminates. Static tension and tension-tension fatigue tests were conducted on two different layups. Damage onset, accumulation, and residual properties were measured. Matrix cracking was shown to have a considerable influence on residual stiffness of glass epoxy laminates, and could be predicted reasonably well for cracks in 90 deg piles using a simple shear lag analysis. A fracture mechanics analysis for the strain energy release rate associated with 90 deg ply-matrix crack formation was developed and was shown to correlate the onset of 90 deg ply cracks in different laminates. The linear degradation of laminate modulus with delamination area, previously observed for graphite epoxy laminates, was predicted for glass epoxy laminates using a simple rule of mixtures analysis. The strain energy release rate associated with edge delamination formation under static and cyclic loading was difficult to analyze because of the presence of several contemporary damage phenomena.

Epoxy resin composition.

Abstract: An epoxy resin composition suitable for use as a casting resin for the potting of an ignition coil is disclosed which comprises: (A) a mixture containing (a1) a liquid, Bisphenol-type epoxy resin, and (a2) an inorganic filler, (a3) a polyether polyol; and (B) a liquid curing agent including (b1) an acid anhydride, and (b2) an imidazole compound. f

Damage tolerant composites containing infusible particles

Abstract: Damage tolerant composites comprising high strength filaments in the form of bundles or tows of continuous fiber and a tough phase separated, crosslinked epoxy resin matrix are disclosed. The crosslinked epoxy resin matrix comprises infusible particles made from a rubber polymer that reside primarily between plies of the composite and critically have a median particle size between 10-75 microns. Prepregs for making the damage tolerant composites and methods of making such prepregs and the epoxy resin compositions thereof are also disclosed The epoxy resin compositions comprise the infusible particles which become segregated as to size on a surface layer of the prepreg during the process of combining the high strength filaments of the prepreg and the resin containing the epoxy resin composition.

Interphase Composition in Aluminum/Epoxy Adhesive Joints

Abstract: Model epoxy/aluminum adhesive joints were constructed with a geometry that allowed cracks to be propagated extremely close to the adhesive/adherend interface. The joints were fractured in air and the fracture surfaces analyzed using angle resolved X-ray photoelectron spectroscopy. Fracture occurred in a manner that left a significant amount of aluminum oxide on the epoxy side of the fracture surface and very little epoxy on the aluminum side. Aliphatic amine curing agent found associated with the aluminum oxide on both the adhesive and the adherend sides of the fracture surface was protonated by the acidic hydroxyls present in the aluminum hydroxide. Moreover, catalysis of the curing reaction by these hydroxyls resulted in an increased degree of crosslinking in the regions of the adhesive very close to the oxide surface. Thus, the aluminum oxide surface modified the structure of the adhesive in the near surface regions and resulted in the formation of a distinct interphase region with a compositi...

Study of model polydiacetylene/epoxy composites: Part 2 Effect of resin shrinkage

Abstract: On prepare un composite modele constitue d'une monofibre cristalline de polydiacetylene dans une resine epoxyde. Mesure de la deformation le long de la fibre en fonction de la deformation de la matrice et de la temperature de post-durcissement

Characterization of epoxy-bismaleimide network matrices

Abstract: This study investigated intercrosslinked networks formed by co-curing two thermosets: a tetrafunctional epoxy/amine and a bismaleimide formulation. The mechanical properties and phase behaviour of the intercrosslinked networks were compared with the corresponding neat epoxy and bismaleimide systems. In addition, the reaction scheme of the epoxy-bismaleimide resin mixtures was investigated using differential scanning calorimetry. A homogeneous structure for the networks was suggested by the results of both dynamic mechanical analysis and scanning electron microscopy. In contrast to most epoxy systems modified with rubbers or thermoplastics, phase separation was not observed in these intercrosslinked epoxy-bismaleimide networks.

Printed wire circuit board and its method of manufacture

Abstract: Thermal shock tolerance is achieved in conductive core printed wire circuit boards, especially those having graphite or copper-Invar-copper cores for heat removal and expansion control, by filling the oversized through-holes with glass-filled, m-diallyl phthalate resin and plating on the inner surface of a bore drilled through the resin. Meta-diallyl phthalate has a coefficient of thermal expansion that is lower than epoxy and that is closer to that of the core. It creates a substantially void free, dielectric collar between the plating and the core to insulate the two electrically. Its use temperature is higher than epoxy while its curing temperature is lower than polyimide. The boards can be made by molding of the thermosetting resin in a peel ply process that avoids milling of the board and reduces waste.

Parameters determining the strength and toughness of particulate-filled epoxy resins

Abstract: The effects of such parameters as the filler volume fraction, particle size, aspect ratio, modulus and strength of filler, resin-filler adhesion, and toughness of the matrix on the stiffness, strength, and toughness of particulate-filled epoxy resins were evaluated. The mechanisms of crack initiation and subsequent crack propagation in these multiphase materials are discussed and illustrated by scanning electron microscopy of fracture surfaces.