586 



BELL SYSTEM TECHNICAL JOURNAL 



brasses hardened by nickel and silicon otherwise mentioned as alloys 



Nos. 3Z, 34 and 35 respectively. 



MiCROSTRUCTURE 



Fig. 10 shows a photograph of a number of broken specimens. 

 The regularity of the break is shown and in every case occurs 

 within the uniformly stressed area. Photomicrographs shown by 

 Fig. 11 are typical of the various alloys. In these cases incipient 

 cracks are revealed within the uniformly stressed area. It is seen 

 that these cracks are, without exception, transcrystalline and there 



EVERDUR ALLOY 

 SPRING TEMPER 



PHOSPHOR BRONZE 

 ALLOY "C"— 4 NOS. HARD 



NO. 33 ALLOY 



NO. 34 ALLOY 

 ALPHA BRASSES — HEAT TREATED 



NO. 35 ALLOY 



ALLOY "G" BRASS 

 ANNEALED 



ALLOY "B" nickel SILVER 

 ANNEALED 



ALLOY "A BRASS 

 ANNEALED 



Fig. 10 — ^Typical Broken Fatigue Specimens. 



appears to be no distortion of the metal adjacent to the fractures. 

 With regard to the typical structure of the hardened brass alloys 

 reference is made to the previous paper. ^ 



Discussion 



Examination of the results shown by Table II reveals that the ratio 

 of endurance limit to tensile strength for sheet non-ferrous metals is 

 much lower than that reported for steel rod.^ These ratios reported 

 for plain carbon and alloy steels in all heat treatments vary from .35 

 to .67 averaging about .40 whereas for these sheet non-ferrous metals 

 these ratios vary from .14 to .36. 



^ " Heat Treatment and Mechanical Properties of some Copper-Zinc and Copper- 

 Tin Alloys containing Nickel and Silicon," by W. C. Ellis and Earle E. Schumacher. 

 Proc. A. I. M. M. £., 1929. 



^"The Fatigue of Metals," by H. J. Gough, Scott Greenwood & Sons. Also 

 "The Fatigue of Metals," by H. F. Moore and J. B. Kommers, McGraw Hill & Co. 



