Lower Ultimate Strength Research Articles

A Study of Mechanical and Optical Properties of an Alternating NBR and an Emulsion NBR

Abstract At low elongation, over the range of temperatures and frequencies studied, the dynamic properties (elastic modulus and loss factor) and activation energy for the glass-rubber transition are the same for highly alternating and emulsion copolymers of acrylonitrile and butadiene. At higher elongation the stress-birefringence and x-ray data on cured (1.7 phr dicumyl peroxide) highly alternating copolymer show the occurrence of strain-induced crystallization, whereas the emulsion copolymer does not crystallize under strain. The stress-strain data for the highly alternating copolymer cured at 1.7 phr dicumyl peroxide and for the emulsion copolymer cured at 1.7 phr and 0.8 phr show that at 1.7 phr dicumyl peroxide the highly alternating copolymer has higher ultimate strength. However, the emulsion copolymer cured by 0.8 phr dicumyl peroxide shows tensile properties similar to those of the highly alternating copolymer cured by 1.7 phr dicumyl peroxide. Therefore, it may be concluded that the increased strength and ultimate elongation of highly alternating copolymer, as reported by Furukawa, are due to the fact that at the same curative level the emulsion copolymer gets over-cured resulting in lower ultimate strength and elongation. This present study indicates that it is not appropriate to compare the ultimate properties of the emulsion and highly alternating copolymers cured at the same level of dicumyl peroxide. Slight adjustment in curing condition brings highly alternating and emulsion copolymers closer in tensile strength and ultimate elongation. In conclusion, it may be said that this study indicates that highly alternating NBR shows tensile properties similar to those obtained for emulsion NBR already produced commercially.

Plastic Softening of Magnesium Oxide at High Temperatures by Nickel Oxide Addition

Magnesium oxide single crystals containing 0.3% nickel oxide were tested in tension at high temperatures. The stress‐strain relationship and deformation modes were similar to those identified for pure magnesium oxide. Alloy specimens had lower yield and ultimate strengths than pure magnesia at all temperatures above 1200° C and showed a greater tendency for kinking, polygonization, and recrystallization. It is proposed that the reducing atmosphere in the furnace causes the alloy crystals to decompose by the removal of oxygen and internal precipitation of nickel. The excess vacancies so produced enhance the nonconservative mobility of dislocations.

Tensile properties of pyrolytic tungsten from 1370° to 2980°C in vacuum

The tensile properties of annealed pyrolytic tungsten were measured at a strain rate of 0.02/min from 1370° to 2980°C in vacuum. Data for powder metallurgy and plasma-flame single-crystal tungsten are shown for comparison. A few engineering stress-strain curves are given for pyrolytic and powder metallurgy tungsten. Although voids are present in the pyrolytic material after annealing, the voids which form and grow during testing have a more important detrimental effect on ductility. The “as deposited” anisotropy of the microstructure is maintained after recrystallization and enhances the tendency to void formation and growth. With the exception of one specimen which contained no voids, as the result of a lower annealing temperature, pyrolytic tungsten has a lower ultimate strength than powder metallurgy tungsten in the temperature range studied.