Manchester Memoirs, Vol. xlviii. (1904), No. 7- 



VII. On Phenomena due to Repetitions of Stress, 

 and on a New Testing Machine. 



By Frank Foster, B.Sc. 



(Communicated by Dr. G. Wilson.) 



deceived and Head January igth, igo4. 



In this paper I wish to review some of the more 

 important phenomena due to repetitions of stress on 

 metals, to attempt to explain them and also to describe a 

 new machine for their study. 



The theory here sketched is mainly that presented by 

 the author more than a year ago in a paper read before 

 the Owens College Engineering Society*, but recent 

 experiments by Professor Ewing whilst not affecting, 

 indeed strengthening, the fundamental idea on which the 

 theory rests have yet pointed out the existence of an 

 important and at the time unforeseen development in the 

 metal during alternations of stress. 



About 40 years ago Wohler showed that a bar of 

 metal would ultimately break under a load less than its 

 static breaking load as determined in the ordinary testing 

 machine, provided that the load was removed and re- 

 applied continuously. The number of these repetitions 

 required to produce fracture was greater the less the 

 stress, but fracture would ultimately result with loads 

 which never by a large margin reached the elastic limit 

 of the material. 



Quite recently Professor Reynolds and Mr. Smith 

 have shown also that the number of repetitions necessary 

 for fracture is less the greater the rapidity with which 

 they take place. 



*" A possible explanation of the phenomena caused by repetitions of 

 stress." Mechanical Engineer, Nov; 22nd and 29th, 1902. 



March nth, igo4. 



