The temperature‐dependence of some mechanical properties of a cured epoxy resin system
TL;DR: In this paper, 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.
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.
Citations
More filters
TL;DR: In this article, different synthetic strategies for the preparation of benzoxazine monomers and blends, their polymerization reaction mechanisms, and the structure-property relationships of the cured materials have been discussed.
1,022 citations
Cites background from "The temperature‐dependence of some ..."
...According to many authors for epoxy resins, the crosslink density has little or no influence on stiffness or rigidity in the glassy state [156–158]....
[...]
TL;DR: A new class of epoxy nanocomposites with completely defined organic/inorganic phases was prepared by reacting octakis(glycidyldimethylsiloxy)octasilsesquioxane with diaminodiphenylmethane (DDM) at various compositional ratios and the effects of reaction curing conditions on nanostructural organization and mechanical properties were explored.
Abstract: A new class of epoxy nanocomposites with completely defined organic/inorganic phases was prepared by reacting octakis(glycidyldimethylsiloxy)octasilsesquioxane [(glydicylMe2SiOSiO1.5)8] (OG) with diaminodiphenylmethane (DDM) at various compositional ratios. The effects of reaction curing conditions on nanostructural organization and mechanical properties were explored. A commercial epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) was used as a reference material throughout these studies. FTIR was used to follow the curing process and to demonstrate that the silsesquioxane structure is preserved during processing. OG/DDM composites possess comparable tensile moduli (E) and fracture toughness (KIC) to, and better thermal stabilities than, DGEBA/DDM cured under similar conditions. Dynamic mechanical analysis and model reaction studies suggest that the maximum cross-link density is obtained at N = 0.5 (NH2:epoxy groups = 0.5) whereas the mechanical properties are maximized at N = 1.0. Digestio...
479 citations
TL;DR: In this paper, a new class of phenolic-like thermosetting resins was developed that is based on the ring opening polymerization of a benzoxazine precursor, which is copolymerized with an epoxy resin in order to modify their performance.
425 citations
TL;DR: In this article, molecular dynamics and molecular mechanics simulations are used to establish well-equilibrated, validated molecular models of the EPON 862-DETDA epoxy system with a range of crosslink densities using a united atom force field.
268 citations
TL;DR: In this article, a sonication technique was used to disperse fluorinated single-wall carbon nanotubes (FSWCNT) in the glassy epoxy network resulting in nanocomposites having large improvement in modulus with extremely small amount of FSWCNT.
259 citations
References
More filters
01 Jan 1969
TL;DR: In this article, a review of the properties of cross-linked polymers is presented from the practical viewpoint of an experimental scientist who is using cross-link polymers but who is not an expert on the theory of crosslinking.
Abstract: Many of the polymers used in composite systems and in other applications are cross-linked or thermoset polymers. How do such cross-linked polymers differ in properties from the better-understood linear or thermoplastic polymers? This review paper attempts to answer this question. The paper is written from the practical viewpoint of the experimental scientist who is using cross-linked polymers but who is not an expert on the theory of cross-linking. In spite of their intractable nature once they have been formed, and the difficulty of fabricating highly cross-linked polymers, such materials have some outstanding properties that make them ideal for many applications. The properties include (1) excellent dimensional stability and low creep rates, (2) resistance to solvents, and (3) in many cases, high heat-distortion or softening temperatures.
646 citations
TL;DR: In this article, the authors used a differential scanning calorimeter (DSC) under isothermal conditions in the range 50-150°C to collect and process rate and integral heat of reaction data during cure.
571 citations
TL;DR: The fracture toughness of epoxy used in the bulk and adhesive form was measured by a previously developed technique as mentioned in this paper, where the uniform double cantilever-beam specimen, which was described earlier, was modified to a tapered beam, which simplified the experimental procedure and calculations for obtaining toughness measurements.
Abstract: The fracture toughness of epoxy used in the bulk and adhesive form was measured by a previously developed technique. The uniform double cantilever-beam specimen, which was described earlier, was modified to a tapered beam, which simplified the experimental procedure and calculations for obtaining toughness measurements. by varying the ratio of hardener to resin and post-cure temperature on a single epoxy system (DER 332-TEPA), it was found that the toughness of the epoxy used in either bulk or bond form varied by a factor of approximately five. A particular combination of composition and post-curing temperature generally yielded higher toughness in the bulk than in the bond form. This was not always the case, however. At high post-cure temperatures, where the bonds were very tough, their toughness exceeded that of the bulk material. Hence, it does not appear possible to predict joint toughness from bulk toughness measurements. The toughness of joints was found to be a single-valued function of tensile modulus. For the bulk material, on the other hand, the toughness obtained on the epoxy having a specific modulus depended on the combination of composition and post-cure temperature. Joint toughness for any combination of composition and post-cure temperature depended only on the cracking rate. If the epoxy was the type that caused cracks to jump rapidly, the epoxy was tough and vice versa. For a particular epoxy system, toughness was increased by driving the crack at an increasing rate.
170 citations
TL;DR: In this paper, the free volume interpretation of the dependence of relaxation times and viscosities on temperature can be extended to their dependence on concentration, pressure, and tensile strain, where the treatment is probably limited to conditions where the fractional free volume is not greater than 0.08.
Abstract: The free volume interpretation of the dependence of relaxation times and viscosities on temperature can be extended to their dependence on concentration, pressure, and tensile strain. The coefficient which in theWilliams/Landel/Ferry equation represents the thermal expansion of the relative free volume has the following analogs, respectively: for concentration dependence, a constant closely related to the fractional free volume of the diluent liquid; for pressure dependence, the part of the compressibility attributable to collapse of free volume; for tensile strain, a constant proportional to 1–2μ, whereμ isPoisson's ratio. The treatment is probably limited to conditions where the fractional free volume is not greater than 0.08. In the case of pressure dependence, some viscosity data on hydrocarbon and silicone liquids at high pressures are found to agree closely with the predicted form with reasonable values of the associated parameters.
149 citations
TL;DR: In this paper, the authors proposed a stress-activated devitrification of a small amount of material at the tip of a chance nick or flaw, to a softer rubbery state, and then cavitation of the softened material is then assumed to take place under the same dilatant stress responsible for its formation.
Abstract: Crazing in glassy plastics is attributed to a stress-activated devitrification of a small amount of material at the tip of a chance nick or flaw, to a softer rubbery state. Subsequent cavitation of the softened material is then assumed to take place under the action of the same dilatant stress responsible for its formation. A transition to ductile yielding is proposed to occur when the material in the tip region undergoes large deformations before softening. The proposed mechanism of crazing is shown to provide quantitative predictions for the magnitude of tensile stress at which crazing occurs, the increase in crazing stress with hydrostatic pressure, the transition at high pressures to a yielding process without crazing, the reduction in crazing stress in the presence of certain liquids and vapours and, to some extent, for the effects of temperature and pre-orientation. These theoretical predictions are found to be in reasonably satisfactory agreement with experiment. In view of the limited number of adjustable parameters in the theory (the principal one being the stress-magnification factor associated with a typical nick or flaw), this general agreement over a wide range of experimental conditions and variables suggests that the proposed mechanism of stress-crazing is basically correct.
141 citations