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VI. The Phenomena of Rupture and Flow in Solids. 
By A. A. Griffith, M. Eng. [of the Royal Aircraft Establishment). 
Communicated by G. I. Taylor, F.R.S. 
Received February 11,—Read February 26, 1920. 
Contents. 
Page 
1. Introduction.163 
2. A Theoretical Criterion of Rupture.165 
3. Application of the Theory to a Cracked Plate.167 
4. Experimental Verification of the Theory.172 
5. Deductions from the Foregoing Results ..177 
6. The Strength of Thin Fibres.180 
7. Molecular Theory of Strength Phenomena.183 
8. Extended Application of the Molecular Orientation Theory.186 
9. Practical Limitations of the Elastic Theory.192 
10. Methods of Increasing the Strength of Materials.194 
11. Application of the Theory to Liquids .... 195 
12. Summary of Conclusions.197 
1 . Introduction. 
In the course of an investigation of the effect of surface scratches on {he mechanical 
strength of solids, some general conclusions were reached which appear to have a direct 
bearing on the problem of rupture, from an engineering standpoint, and also on the 
larger question of the nature of intermolecular cohesion. 
The original object of the work, which was carried out at the Royal Aircraft Estab¬ 
lishment, was the discovery of the effect of surface treatment—such as, for instance, 
filing, grinding or polishing—on the strength of metallic machine parts subjected to 
alternating or repeated loads. In the case of steel, and some other metals in common 
use, the results of fatigue tests indicated that the range of alternating stress which 
could be permanently sustained by the material was smaller than the range within 
which it was sensibly elastic, after being subjected to a great number of reversals. 
Hence it was inferred that the safe range of loading of a part, having a scratched or 
VOL. CCXXI.-A 587. 2 A [Published October 21, 1920. 
