An epoxy system consisting of diglycidyl ether ofbutanediol, DGEB, cured with 4-4' diaminodiphenyl sulfone, DDS, has been used for a study of the effect of crosslinking density on the properties of the epoxy resin. Because of the low curing rate at room temperature and the low glass-transition temperature, this system was amenable to a wide range of controlled crosslinking density. The crosslinking density was monitored by FTIR (Fourier transform infrared spectroscopy), which followed the change in concentration of the epoxy groups during the curing reaction. The bulk density was found to increase linearly with the crosslinking density. The modulus, the upper yield point, the lower yield point, and the degree of retraction of a deformed sample all increased with the degree of crosslinking. The thermally stimulated depolarization (TSD) @peak was found to vary with crosslinking density, but the y-peak was not changed. The TSD a-peak was found to decrease in strength, but increased in temperature as the crosslinking density increased. This observation suggests that TSD measurements are a good monitor of crosslinking density of epoxy resins, particularly near the final stage of the crosslinking reaction.
The fracture toughness of an epoxy resin system, diglycidyl ether of butanediol, DGEB, cured with 4-4' diaminodiphenyl sulphone, DDS, has been studied by varying the crosslinking density and state of aging. A stahle, but rough, crack propagation was observed with specimens that were 99 percent cured and quenched. When the extent of curing was less than 99 percent or the material was aged for more than 20 min at 62"C, crack propagation was of the unstable stick-slip nature. Aging was found to decrease the initiation fracture toughness dramatically, but the arrest fracture toughness was almost unchanged. This result was associated with a change of relaxation strength of the primary, a, transition with aging. An increase of crosslinking density was found initially to reduce the fracture toughness of this epoxy resin, but the fracture toughness increased after 87 percent of curing. The initial decrease of the fracture toughness was attributcd to a decrease of relaxation strength of the primary transition (i.c., the area under the a-relaxation peak), while the increase of the fracture toughness after87 percent curing was explained by the onset ofthe stablerough crack propagation. Micrographs taken by scanning electron microscopy showed possible existence of blunting during crack propagation and a decrease of blunting with the extent of aging.higher testing speed. The initiation fracture toughness, Gi, approached the value of the arrest fracture toughness, G,, as the testing speed increased. At an even higher speed, G, equaled G,, and the crack propagation became continuous.
Potassium hydroxide and sodium hydroxide were found to be satisfactory for polishing various surfaces of rutile. Dislocation etch pits could be produced by alkali fusions, SS% orthophosphoric acid, and concentrated sulfuric acid. The { llO}-, near { 11 1 ) -, (001)-, and { 100) -type surfaces were etched and the etch pits were analyzed in terms of their relation to the deformation systems and crystal symmetry. The correlation between etch pits and dislocations was substantiated by means of matched cleavage surfaces, existence of substructures, generation of dislocations, dislocation densities, and polygonization phenomena. Dislocations were introduced by impacting and macroscopic plastic deformation. Generation of dislocations was observed from 1050°C to as low as room temperature. The slip planes confirmed by means of dislocation traces and slip lines were { 110 ) -and { 101 ]-type planes. The slip direction corresponding to the { 110) -type plane was [OOl 1, the close-packed direction. The Burgers vector, structure, and motion of dislocations in the edge orientation on the { 110) [OOl] system were determined by analyzing the crystal structure. The Burgers vector was c [OOl 1, the lattice translation vector, and the dislocations did not dissociate into partial dislocations. Another possible slip system was the (100) [OlO] system.
An x-ray diffraction investigation of the structure of β′-NiAl alloys was conducted to define the state of order, identify the lattice sites occupied by compositional vacancies, and measure both static and vibrational components of atomic displacements, all as functions of temperature and composition. Long-range order was found to be virtually complete up to 1000 °C and remained substantial up to the melting points of the alloys. Compositional vacancies present in Al-rich β′ alloys were found to occupy Ni lattice sites only, at least to 1000 °C. Static atomic displacements were minimal at stoichiometry, increased with initial Ni or Al additions, and then decreased with further Ni or Al additions, with the maximum displacement about midway between stoichiometry and the β′ phase boundaries. Vibrational atomic displacements were also minimal at stoichiometry, but in contrast to static displacements, increased continually as either Ni or Al was added. Atomic displacements were correlated with known mechanical properties of β′-NiAl alloys.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.