THE RELEASE OF STRAIN IN GLASS*

Abstract

Measurements of strain release1 showed that check results were obtained only when the previous history of the samples was the same. Moreover, it was found that the release of strain was more rapid at first than could be accounted for by the equation of Adams and Williamson. This paper discusscs the effect of previous history on the measurements, describes an improved device for loading the specimens, and suggests a logarithmic equation which, in general, fits the observations better than that of Adams and Williamson. Tests of the equation are made both on data obtained from the modified apparatus described and on the data of Adams and Williamson. It is indicated that the Adams and Williamson equation gives too long an annealing time at higher temperatures and too short an annealing time at lower temperatures. It appears that the rate of release of strain depends on some power of the strain which varies from unity at high temperatures where the glass is a viscous fluid to a higher power at low temperatures where the release of strain is elastico-viscous in character. With a siugle specimen at any fixed temperature in the annealing range, however, it appears that the release of strain in various parts of the specimen takes place at a rate which is proportional to the strain, but that the rate undergoes continual change with time.