Robert L. Cottington

Effect of temperature on the adhesive fracture behavior of an elastomer-epoxy resin

Abstract 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.

Ice Adhesion to Hydrophilic and Hydrophobic Surfaces

Abstract 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...

Air Entrapment in the Use of Structural Adhesive Films

Abstract Air entrapment during the preparation of bonds with structural adhesive films was examined by a microscopy study of glass/adhesive/glass specimens. It was observed that initially a thin film of air is trapped between the adhesive and adherend and covers over 50 % of the interfacial area. As the specimen is heat cured this air draws up into bubbles that are eventually displaced into the adhesive layer. Incomplete displacement occurs if the resin does not fully wet the adherend surface (contact angle greater than zero) or the resin does not become sufficiently fluid during the heat cure. The trapped air, whether displaced into the resin or held at the interface, could be eliminated from the bond by starting the cure in vacuum (5 mm Hg) and subsequently releasing the vacuum at the temperature at which the resin is in its most fluid condition. Specimens of bonded aluminum panels were tested in a T-peel configuration. An increase in bond strength of as much as 30% could be realized by complete void re...

Interactions in Neopentyl Polyol Ester—Tricresyl Phosphate—Iron Systems at 500 F

Neopentyl polyol esters, typical of turbine engine lubricant base stocks, are thermally stable at 500 F, unless, as reported by others, ferrous metals are present; in the latter case oil degradation and metal corrosion are severe. Tricresyl phosphate (TCP) stabilizes the metal-ester system by generating a passive oxide film on the active metal surface. In the presence of water, TCP accelerates ester hydrolysis, resulting in acids corrosive to lead. Aliphatic amines which react with TCP acidic impurities or breakdown products reduce the catalyzed hydrolysis of the esters. TCP reacts with free carboxylic acids to generate corrosive phosphoric-type acids. Reaction mechanisms are postulated. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference held in Houston, Texas, October 14–16, 1969

Inhibition of Iron-Catalyzed Neopentyl Polyol Ester Thermal Degradation Through Passivation of the Active Metal Surface by Tricresyl Phosphate

To investigate the role of tricresyl phosphate (TCP) in inhibiting the iron-catalyzed thermal degradation of a neopentyl polyol ester gas turbine lubricant base stock, various TCP/ester combinations were encapsulated in mild steel tubing and heated at 500 F up to 96 hours. The relative degradation rates of the individual mixtures were measured by monitoring the effusion site of hydrogen (a degradation byproduct) through the capsule all. The capsule interiors were then examined by electron microscopy and diffraction to determine whether correlation assisted between the features of the surface films formed and the reserved degradation rates. Distinctive films were produced in each test mixture. When ester degradation was inhibited by the addition of 2–10% TCP, characteristic iron oxide layer was always found at the ester/steel interface. It was postulated that TCP induces the formation of this film, that the film is the agency of inhibition, and that it is similar in action and genesis to the iron oxide pas...

Adhesive Fracture Energies of Some High Performance Polymers

Abstract A fracture mechanics approach was applied to determine the adhesive fracture energy of various high performance polymers. These polymers, including both thermosetting and thermoplastic materials, generally offer higher temperature capability than conventional epoxies. Double tapered cantilever beam specimens were used for fracture tests at both room temperatures and 225°C. The adhesive fracture energies of a tetrafunctional epoxy and a phthalocyanine resin were also determined at low temperatures. Adhesive fracture behavior of polymers at high temperatures was found to depend on polymer glass transition temperature, whereas at low temperatures it was related to secondary relaxation processes in the glassy state.

The dynamic mechanical properties and fracture behaviour of phthalocyanine polymers

The dynamic mechanical properties of a series of phthalocyanine polymers with varying aliphatic chain length linking stable phthalocyanine nuclei have been studied. Dynamic shear modulus and polymer loss factor were determined using a torsion pendulum. Polymer fracture energies were also determined using both the standard compact tension specimens and double-tapered cantilever beam specimens. The results showed that both the dynamic shear modulus and the glass transition temperature increased with decreasing molecular flexibility and increasing extent of cure. The fracture energies increased with increasing molecular flexibility. It was also shown that extended thermal treatment could greatly embrittle the thermosetting polymers and hence reduce the fracture toughness, even though such treatments usually promoted crosslinking leading to higher moduli and glass transition temperatures for these polymers.

The loading-rate dependent fracture property of a toughened epoxy polymer

SummaryThe fracture energy of an elastomer-modified epoxy polymer was determined as a function of loading rate. Fracture tests were carried out by using compact tension specimens and standard Izod impact specimens. The fracture energy of the base epoxy was increased by the elastomeric additives. The extent of increase, however, was found to decrease with increasing loading rate.

Lubricants from Mixed Pentaerythritol Esters of 2-Ethylhexanoic and Isostearic Acids

A mixed pentaerythritol ester composed of 25 mole percent 2-ethylhexanoic and 75 mole percent of isostearic acid substituents was synthesized and characterized. By means of the synthetic and analytical procedures developed, this mixed ester can be prepared in a highly reproducible manner. Oxidation and thermal stabilities, corrosivity, and wetting characteristics are reported. The ester is of interest in instrument and bearing applications where a viscous lubricant having excellent low-temperature properties is required. Presented at the 26th ASLE Annual Meeting in Boston, Massachusetts, May 3—6, 1971