Fatigue Studies of Non-Ferrous Sheet Metals^ 



By JOHN R. TOWNSEND and CHARLES H. GREENALL 



The paper describes the development of a fatigue test machine for 

 sheet metals and gives results of fatigue tests on five alloys of alpha brass, 

 one alloy of nickel silver, one alloy of phosphor bronze and Everdur. 



The results indicate that cold work raises the endurance limit but not 

 proportionally to the increase in tensile strength produced by the same 

 cause. 



Micrographs are shown indicating that fatigue failure of the metals 

 investigated is transcrystalline. 



Dispersion hardening of alpha brass by nickel silicide increases the 

 endurance limit. 



The ratio of endurance limit to ultimate tensile strength of these alloys 

 varies from .12 to .36 depending on composition, heat treatment, and cold 

 work. These ratios are much lower than similar ratios for steel. 



THE materials referred to in this paper are those non-ferrous sheet 

 metals that are employed in electromechanical devices such as 

 telephone apparatus and includes a wide variety of equipment, such as 

 switches, relays, jacks, contact springs,^ etc. These metals are em- 

 ployed principally in springs used for electrical contacting purposes. 

 In many cases these springs have precious metal contacts welded to 

 them and in other cases the metal itself is used for the contact. Many 

 of these springs are subjected to millions of cycles of stress and it is 

 important, therefore, that the endurance limit of these materials be 

 known in order that apparatus may be designed which will endure for 

 its required service life. Very little precedent has been established in 

 the design of fatigue machines for the testing of sheet metals and it 

 was necessary, therefore, to develop a form of fatigue machine 

 especially suitable for these materials. 



Another joint paper by one of the authors describes these non-ferrous 

 metals and explains various methods of test and the commercial limits 

 developed for specification purposes.'' 



Sheet Metal Fatigue Specimen 



The specimen shown by Fig. 1 was designed to simulate in its 

 major dimensions the normal size of the springs used in telephone 

 apparatus. It will be noted that the design of the specimen provides 

 a section of uniform stress for ^ inch at approximately }4 inch 

 from the clamped end of the specimen. This is accomplished by 



1 Presented before A. S. T. M. Convention, June 24-28, 1929. 



^ "Telephone Apparatus Springs," by John R. Townsend: Proceedings A. S. M. E., 

 1928; Bell System Technical Journal, April, 1929. 



^"Mechanical Properties and Methods of Test for Sheet Non-Ferrous Metals," 

 by J. R. Townsend, W. A. Straw and C. H. Davis, presented before A. S. T. M. 

 Convention, June 24-28, 1929. 



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