THE PHENOMENA OF RUPTURE AND FLOW IN SOLIDS. 
175 
initial stresses due to cracking as much as possible, while at the same time keeping the 
temperature so low that appreciable deformation of the crack did not occur. It was 
found that the bursting strength increased with the annealing temperature up to about 
400° C., while between 400° C. and 500° C. very little further change was perceptible. 
From this it was inferred that relief of the initial stresses was sufficient for the purpose 
in view at a temperature of 450° C. 
The principal stresses at rupture, Q and R, were calculated from the observed 
bursting pressure by means of the usual expressions for the stresses in thin hollow 
spheres and circular cylinders, the thickness of the glass near the crack being measured 
after bursting. In the case of the tubes the cracks were parallel to the generators, 
and provision was made for varying Q by the application of end loads. 
In dealing with the longer cracks, leakage was prevented by covering the crack on 
the inside with celluloid jelly, the tube being burst before the jelly hardened. In the 
case of the smaller cracks leakage was imperceptible and this precaution was unnecessary. 
The time of loading to rupture varied from 30 seconds to five minutes. No evidence 
was observed of any variation of bursting pressure with time of loading. 
The results of the bursting tests are set down in Tables II. and III. below. 2c is 
the length of the crack, Q and R are the calculated principal stresses respectively 
Table II.—Bursting Strength of Cracked Spherical Bulbs. 
2c 
D 
Q 
R 
R Jc. 
inch. 
inch. 
lbs. per sq. inch. 
lbs. per sq. inch. 
0-15 
1*49 
864 
864 
237 
0-27 
1-53 
623 
623 • 
228 
0-54 
1-60 
482 
482 
251 
0-89 
2-00 
366 
366 
244 
Table III.—Bursting Strength of Cracked Circular Tubes. 
2c 
D 
Q 
R 
R Jr.. 
inch. 
inch. 
lbs. per sq. inch. 
lbs. per sq. inch. 
0-25 
0-59 
-621 
678 
240 
0-32 
0-71 
-176 
590 
232 
0-38 
0-74 
- 31 
526 
229 
0-28 
0-61 
55 
655 
245 
0-26 
0-62 
202 
674 
243 
0-30 
0-61 
308 
616 
238 
parallel and perpendicular to the crack, and D is the diameter of the bulb or tube. 
The thickness of the bulbs was about 0-01 inch and the tubes 0-02 inch. 
