The Influence of Temperature on the Mechanical Strength of Glass
JSGT 1942 V26 T035-T061
Measurements of the strength of glass laths under bending have been made on more than 2000 specimens of drawn sheet glass approximately 0.25-0.29cm thick at temperatures ranging from 20° to some 20° below the softening point (Mg). The test-pieces were 0.5cm wide and of effective length, 5cm, with ground and polished sides and fire-finished edges, and they were loaded at the uniform rate of 150g per second to cause fracture in about one minute. Under these conditions the strength remained unaffected by temperature until about 30-40° below the transformation point, 534°. Above this point the strength began to fall off, being reduced by about one-third at the highest temperature at which experiments were practicable, namely, about 20°below Mg. At still higher temperatures, the viscous deflection of the glass strip prevented satisfactory measurement being made. A striking fact was that the fractured surfaces exhibited the same characteristics at 580° as at 20°. In another section of the investigation, specimens were loaded with fractions of the mean breaking load, when it was found that at the higher temperatures the test-pieces sustained the load for longer periods before breaking. In each of the many series of experiments, at least 100 specimens were tested at each temperature considered. The erroneous conclusion to which investigators may be led when depending on much smaller numbers of tests was demonstrated by the variation found to occur in the present investigation in the mean strength values when based on smaller samples. The wisdom of basing the tests on fire-finished specimens was also indicated. The experimental results differ fundamentally from those for metals.
G. O. Jones, B.A., B.Sc., Ph.D., and Professor W. E. S. Turner
