The impact resistance of composite materials — a review

Proprietes mecaniques de melange resines epoxyde-caoutchoucs liquides (copolymeres d'acrylonitrile et de carboxybutadiene). Mecanisme etudie par dilatometrie en etirage uniaxial

/pdf/toughening-mechanisms-in-elastomer-modified-epoxies-part-1-2cagbbaheh.pdf

Toughening mechanisms in elastomer-modified epoxies Part 1 Mechanical studies

Deformation and fracture behaviour of a rubber-toughened epoxy: 1. Microstructure and fracture studies

Ice formation and accretion may hinder the operation of many systems critical to national infrastructure, including airplanes, power lines, windmills, ships, and telecommunications equipment. Yet despite the pervasiveness of the icing problem, the fundamentals of ice adhesion have received relatively little attention in the scientific literature and it is not widely understood which attributes must be tuned to systematically design “icephobic” surfaces that are resistant to icing. Here we probe the relationships between advancing/receding water contact angles and the strength of ice adhesion to bare steel and twenty-one different test coatings (∼200−300 nm thick) applied to the nominally smooth steel discs. Contact angles are measured using a commercially available goniometer, whereas the average strengths of ice adhesion are evaluated with a custom-built laboratory-scale adhesion apparatus. The coatings investigated comprise commercially available polymers and fluorinated polyhedral oligomeric silsesquio...

/pdf/relationships-between-water-wettability-and-ice-adhesion-3zdb7rkfa7.pdf

Relationships between Water Wettability and Ice Adhesion

The role Of matrix ductility on the toughenability and toughening mechanism of elastomer-modified, diglycidyl ether of bisphenol A (DGEBA)-based epoxies is investigated Matrix ductility is varied by using epoxide resins of varying epoxide monomer molecular weights These epoxide resins are cured using 4,4′ diaminodiphenyl sulphone (DDS) and, in some cases, modified with 10 vol% carboxyl-terminated copolymer of butadiene and acrylonitrile (CTBN) Fracture toughness values for the neat epoxies are found to be almost independent of the monomer molecular weight of the epoxide resin used However, the fracture toughness of the elastomer-modified epoxies is found to be very dependent upon the epoxide monomer molecular weight Tensile dilatometry indicates that the toughening mechanism, when present, is similar to the mechanism found for piperidine cured, elastomer-modified epoxies studied previously Scanning electron microscopy and optical microscopy techniques corroborate this finding

/pdf/toughening-mechanisms-in-elastomer-modified-epoxies-5775eqdi9l.pdf

Toughening mechanisms in elastomer-modified epoxies

The fracture behavior of a piperidine/bisphenol A diglycidyl ether (A) resin has been determined in bulk and as an adhesive using the linear elastic fracture methods developed by Mostovoy1. The effect of adding carboxy-terminated butadiene–acrylonitrile (CTBN) elastomer to resin A was investigated. The opening-mode fracture energy () of resin A was 120 to 150 J/m2, and largely attributable to plastic deformation. Fractographic evidence was obtained for plastic flow at the crack tip during crack initiation. Propagation was unstable due to the rate dependence of the plasticity. There were no significant differences in the bulk and adhesive fracture behavior. Addition of 5–15% CTBN to resin A produced minute elastomer particles which increased to ∼4000J/m2 (at 15%). Further CTBN addition resulted in an elastomer–epoxy blend and a decrease in fracture energy. Fractography again indicated that crack initiation involved plastic deformation but that the elastomer had greatly increased the volume in which the deformation occurred. The adhesive fracture of the elastomer–epoxy was found to be strongly dependent on the crack-tip deformation zone size (ryc) in that was a maximum when bond thickness was equal to 2 ryc. At bond thicknesses less than 2 ryc, there was a restraint on the development of the plastic zone resulting in lower values.

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

The bulk and adhesive fracture behavior of a diglycidyl ether bisphenol-A epoxy modified with 15% carboxy-terminated butadiene acrylonitrile was determined as a function of temperature. The bulk fracture toughness increased sharply near the resin Tg in a manner similar to unmodified epoxy resins. The adhesive fracture energy exhibited a maximum with respect to bond thickness and this maximum broadened and shifted to larger bond thicknesses with increasing temperature. These results are discussed in terms of the size and stress condition of the crack tip deformation zone.

Effect of Temperature on the Adhesive Fracture Behavior of an Elastomer-Epoxy Resin

The fracture energies of elastomer-modified epoxy polymers have been determined over a range of strain rates from 10−2 to 103 sec−1. The modifiers included a liquid carboxyterminated butadiene acrylonitrile and a solid rubber. They were used alone and also in combination. In all cases, the modifiers increased the toughness of the base resin by orders of magnitude and one combination of liquid and solid rubber increased toughness by 60 times. There was a general decrease in fracture energy with increasing strain rate but even during impact testing the modified epoxys were 10 to 20 times tougher than the base polymer. Scanning electron microscopy revealed that, when combined with the liquid rubber, the solid rubber induced a localized shear yielding.

The fracture of an epoxy polymer containing elastomeric modifiers

The adhesional shear strength has been determined for ice formed against polished steel, monolayers adsorbed on steel and thin plastic coatings painted on metal surfaces The adsorbed monolayers reduced the shear strength to about one-third of that for ice on clean steel The monolayers also had the effect of changing the character of the breaks from clearly cohesional to apparently adhesional failure The shear strength from the plastic coatings ranged from values equal to that of ice against clean steel to values 70 to 80% lower The reduction in shear strength did not correlate with the water contact angle on the coatings but was usually found to be due either to air entrapment at the ice/coating interface or to cohesive failure of the coating itself The ice separated from the various substrates was examined microscopically by forming plastic replicas of the ice surface These studies helped determine the mechanism of failure and, since one of the replicating solutions was also an ice etchant

Ice Adhesion to Hydrophilic and Hydrophobic Surfaces

The kinetic parameters of the polymerization of diglycidyl ether of bisphenol A with hexahydrophthalic anhydride and benzyldimethylamine as catalyst were determined using differential scanning calorimetry. The reaction was found to be first order with some variation with temperature, and the activation energy and natural log of the frequency factor were 25 kcal/mole and ∼25 sec−1, respectively. These results are discussed with respect to a steady-state mechanism of the polymerization and compared with results reported for other epoxide–anhydride reactions.

Willard D. Bascom

Papers

The fracture of epoxy- and elastomer-modified epoxy polymers in bulk and as adhesives

Effect of Temperature on the Adhesive Fracture Behavior of an Elastomer-Epoxy Resin

The fracture of an epoxy polymer containing elastomeric modifiers

Ice Adhesion to Hydrophilic and Hydrophobic Surfaces

Kinetics of epoxy resin polymerization using differential scanning calorimetry